RIGA STRADINS UNIVERSITY
Eva Strīķe
Evaluation of hemodynamic fluctuations by
invasive and semi- invasive monitoring during
off-pump myocardial revascularization surgery
Summary of Thesis
Anesthesiology and Intensive care
Riga 2007
Introduction
While being free of some adverse effects of cardiopulmonary bypass, the off-pump
coronary artery bypass grafting (OPCAB) surgery still requests a thorough monitoring
of a range of cardiac function and circulation parameters.
Data collecting systems, both invasive and semi-invasive, allow for obtaining
circulation-specific information. A 1996 Connors A.F. study demonstrated that
Pulmonary Artery catheter (РАС) extends patient stay in ICU and hospital and even
contrabutes to mortality increase for 39% for those patients whose treatment was
guided by РАС readings. Another 5 year randomized study of Richard C., et al. 2003,
denied mortality increase, though confirmed the same recovery percentage as for
patients without РАС. The above, as well as РАС-induced complications, its costs
and long learning curve drew our attention to minimally invasive methods.
Invasive and semi-invasive methods, whose theoretical concept should be evaluated
by clinical practice, could be an alternative to РАС. Each of the methods has its
advantages and drawbacks, the rendered information and application techniques may
vary as well.
To make our judgement evidence-based, we are to answer four major questions when
implementing the new method /125/:
1. Whether the new method is as good as „golden standard" (thermodilution as a
replacement for Fick method /107/).
2. Whether the new method allows for gaining new information.
3. Whether the understanding of new information changes the patient
management tactics.
4. Whether the above changes, if any, influence patient recovery.
The methods were assessed in their interrelation, keeping in mind the goal of the
study - to develop efficacious method for intraoperative assessment of hemodynamic
fluctuations.
We hope that the results we obtained could be helpful for ICU and Anesthesia
professionals. By analyzing published data and summarizing them with our own
findings I intend to develop an optimal method for monitoring cardiac function during
off-pump myocardial revascularization surgery. Early diagnostics and management of
circulatory system disfunction in these patients can prevent development of such lifethreatening complications as hypoperfusion-induced multiorgan failure and severe
ischaemic heart failure, while stable hemodynamics during surgery improves recovery
prognosis and reduces treatment duration both in ICU and hospital.
Aim of the Study
To develop clinically safe, meaningful and scientifically validated method for
monitoring patient cardiac function during off-pump myocardial revascularization
surgery.
Objectives
1. To measure fluctuations of specific hemodynamic pressures, as well as
alterations of myocardial circulation during revascularization of relevant
cardiac muscle zones (segments).
2. To evaluate and compare continuous cardiac output alterations during
revascularization of different myocardial zones, by both invasive and semiinvasive monitoring of cardiac function.
3. To study fluctuations of specific hemodynamic pressures, myocardial
circulation and cardiac output, as well as interrelation of those during
revascularization surgery.
Thesis to defend
1. Surgical manipulations during off-pump coronary artery bypass grafting
(OPCAB), regardless of the revascularization zone, result in hemodynamic
fluctuations, manifested mostly as right vetricle disfunction.
2. Monitoring of cardiac circulation by ECG while heart is verticalized and
stabilized is not unbiassed.
3. Ischaemia-induced left ventricle systolic disfunction may be readily revealed
rather by oesophageal echo-doppler than by thermodilution.
4. Monitoring of cardiac output with oesophageal echo-doppler is necessary to
detect myocardial systolic disfunction during left ventricle lateral and
posterior wall revascularization.
Structure of the work
Research work has been written in Latvian. It consist of 12 chapters (introduction,
literature review, aim and objectives, contribution and impact, material and methods,
statistical analysis of results, results, discussion, conclusions, practical
recommendation and list with references consisting of 146 titles). Total volume of the
research work covers 94 pages including 15 tables and 44 figures.
Study Design
The study was being performed at VAS Paula Stradina University Hospital within
Latvian Cardiac surgery center (LCSC) from year 2001 till 2005. The study was
approved by Paula Stradina University Ethics Committee.
Involved patients, demography, anaesthesia, extent of surgery
158 patients undergoing sternotomy OPCAB in LCSC from 2002 till 2004 were
involved in the evaluative study of monitoring of cardiac function and circulatory
alterations with invasive and semi-invasive methods during off-pump CABG. 36
patients were withdrawn from protocol due to the adverse effects listed in exclusion
criteria, or due to swithching to other type of surgery during the intervention.
Exclusion criteria included conditions, able to interfere with linear blood flow in
descending aorta or right heart and/or prevented establishing selected hemodynamic
monitoring systems.
Exclusion criteria were the following: aortic valve disfunction, history of aortic valve
implantation, subvalvular stenosis, dilation of descending thoracic aorta, cardiac
arrhythmias (non-sinus), postoperative mechanical circulatory support with
intraaortic balloon pumping (IABP), oesophagus diseases, preoperative history of
tricuspid valve insufficiency more than degree II.
Hemodynamic monitoring was performed with units and devices, available at LCSC:
HP, Edvards Lifescience, HemoSoniclOO.
Patients demographics
122 patients were involved in the study, thereof 94 (77%) male and 28 (23%) female
patients of 34 to 83 years of age. Average analyzed patient age was 61.8±9,7 years.
The dominating CHF class preoperatively was CCVS class II and IV, average
myocardial functional index LVEF of 54,48 % ±8,5%, with minimum LVEF of 26%
and maximum LVEF of 73% (Table 1). 55% of all of the involved patiens had a
history of myocardial infarction (MI).
TABLE 1
Patients breakdown
N of patients
Percentage (%)
94
28
61,8 ±9,7
77%
23%
120
2
98,6%
1,6%
109
9
68
92,4%
7,6%
55,7%
Sex:
male
female
Age (yearas ±SD)
CCVS class:
I-III
IV
LVEF:
>40%
20-40%
History of MI
All of the patients were intubated for surgery, had a 20F arterial cannula (B Braun
Medic system Arteriofix art. cat. Set. 20G/ 80mm) inserted via a. radialis or a.
femoralis and central venous cannula inserted via v. jugularis int. dx. The cannulatubing lines were used to connect cannulas to monitor (Philips M3000A/M3046A),
displaying both pressure curves and readings.
Involved patients got combined intravenous/inhalation anaesthesia
Measuring CO fluctuations during OPCAB
7,5(F) size floating balloon catheter (177F75- CCO/Sv02) was introduced via 8(F)
size port, placed in v.jugularis interna preoperatively after the patient was intubated.
Transoesophageal echodoppler probe (HaemoSonic 100) was inserted to Th5-6 level,
then position was checked and the probe was fixed (depth of probe taken at teehline)
to avoid dislocation.
Measurements of relevant hemodynamic pressures, cardiac function and myocardial
circulation were taken at the following time points of surgery:
1. t1 - after pericardiotomy;
2. t2 (LAD) - during LV anterior wall revascularization (1 min after heart was
positioned and stabilized);
3. t3 (Cx) - during LV lateral and inferior wall revascularization (1 min after heart
was positioned and stabilized);
4. t4 (RCA) - during LV posterior wall revascularization (1 min after heart was
positioned and stabilized);
5. t5 - after grafting, before the chest is closed, with stabilized hemodynamics.
At the same surgery timepoints (t1, t2, t3, t4, t5) the relevant hemodynamics data were
analyzed, which were supposed to influence CI values, obtained by TD and ED.
Arterial blood sampling for blood gas testing was done. Core temperature of the
patient was continuously measured with Foley thermosensor and recorded at the
beginning of the surgery, at the end of the surgery and at 6h, 12h and 24h
postoperatively.
Statistical methods
Hemodynamic data are presented as mean plus or minus the standard deviation. The
data completely registered for all events were analyzed by group mean comparison for
repeated measurement differences compared with baseline and for difference
compared with the previous value.
Differences between CI monitoring methods were plotted as suggested by Bland and
Altaian (the difference between the two measures (TD CI- ED CI) is plotted against
their mean [½( TD CI + ED CI)]). The mean difference is a measure of how well the
two techniques agree on average. A measure of precision or range of agreement for a
given individual is expressed as the 95% limits of agreement (if 95% limits of
agreement are within clinically acceptable limits the two techniques may be used
interchangeably).
All statistical calculations were performed with SPSS software (version 12.0).
Two - sided p value < 0,05 was regarded as statistically significant result.
Measurement of relevant general parameters of hemodynamics and blood
chemistry sampling in ICU.
At the next stage - at 1h, 6h and 12 h postoperatively (ta - 1 h, tb - 6 h, tc - 12 h)- we
measured hemodynamic parameters of the patients, as well as postoperative bleeding,
and made blood count and blood chemistry sampling. Also, intubation time and
duration of patient stay in ICU and the hospital were recorded.
Results
Medical history of the 122 involved patients is shown in Table 1. For all of the
patients it was the first surgery. Duration of it was 75 to 310 minutes (M = 178.5 min,
SD - 53.8 min).Duration of surgery and patients' stay in OR depended on the extent
of the surgery, determined by the number of grafts (r = 0,69 with p < 0,001).
Patients breakdown by the number of grafts was as follows: 32,8% (40 patients) had 2
artery grafting, 32,8% (40 patients) had 3 artery grafting, 18,9% (23 patients) had 1
artery grafting, 13,9% (17 patients) had 4 artery grafting, and just 1.6% (2 patients)
had five artery grafting.
Average N of grafts in one patient was 2,5 ±1,0. Overall N of grafts in LV anterior
wall was 107, with 48 and 68 grafts in inferior and lateral walls respectively (Table
2).
TABLE 2
N of grafts depending on revascularization area
Revascularization area
LAD
Cx
RCA
N of grafts
107
48
68
The extent of circulatory fluctuations during surgery was measured by systemic
pressure, heart rate (HR) and pulmonary artery pressure alterations. Myocardial
circulation was evaluated by ST segment deviation in ECG II (ST1) and V5 (ST2)
leads. Descriptive statistics of vital signs depending on revascularization area is
displayed in Table 3.
TABLE 3
Recorded relevant circulatory values (N = 122): HR- heart rate, SAP- systolic arterial
pressure, DAP - diastolic arterial pressure, PAmP - pulmonary artery mean pressure,
PAdP - pulmonary artery diastolic pressure, ST - ST segmentdeviation in leads II abd V5
of ECG, mm, standard deviation of it (±).
Values
HR
ST1(I)
ST2(II)
Units
T1(baseline) t2 (LAD)
Beats per
64±11
min (BPM)
-0,04
-0,18
t3(Cx)
U (RCA)
t5 (end)
70±11,3
72±14,7 74±11
72±10
0,1
-0,15
-0,09
-0,05
0,01
-0,05
0,04
-0,07
SAP
mmHg
123±18
98±14
87±12
96 ±13
114±16
DAP
mmHg
73±14
58±14
53±14
57±12
67±11
PAmP
mmHg
19±4
20±5
21±6
20±9
18±3
PAdP
mmHg
11±3
11±4
12±5
12±3
10±3
The most distinct changes from baseline were found during LV posterior/inferior wall
revascularization (t3), with such most variable parameters as systemic pressure (SAP =
87 ± 12,0 mmHg; DAP = 53 ± 14,0 mmHg), myocardial circulation alterations (ST/ = 0,09; ST2 = -0,05) and mild mean HR increase (HR t3=72± 14,7 and HR t4 = 74±
11).
During revascularization of other coronary arteries basins SAP and DAP decreased by
21,8% (SAP) and 27,7% (DAP) from baseline. (Charts 1, 2). We are to note that
bringing the heart back to its atatomical position we observed stabilization of
hemodynamics, and by the end of surgery (t4) systemic pressures were decreased by
just 7,2% (SAP) and 7,4% (DAP) from baseline.
Chart 1. SAP mean relative value changes (%) from baseline depending on
revascularization area.
Chart 2. DAP mean relative value changes (%) from baseline depending on
revascularization area.
Two different methods were used to measure systemic vascular resistance
(SVR) along with SAP and DAP measurements. Both methods' SVR curves
have no significant difference. The most distinct SVR increase was seen during
left circumflex
coronary artery (LCX) remodelling (t3), associated with the lowest SAP and DAP values,
which can be explained by the therapy of hemodynamic alterations during surgery (Chart 3).
Chart 3 Systemic vascular resistance (SVR) mean value changes from basleine and standard
deviations, depending on revascularization area
Alterations of pulmonary artery mean and diastolic pressures were observed during
the whole surgery, especially during revascularization of LV inferior (t3) and posterior
walls (t4) (PAdP by +3,6% and by +6,3%; PAmP by +3,9 % and by +1% from
baseline) (Charts 4 and 5). By the end of intervention relevant preload parameters
were decreased by up to 8,1% (PAdP) and 7,6% (PAmP) from baseline.
Chart 4. Pulmonary artery diastolic pressure mean relative value changes (%) from
baseline depending on revascularization area.
Chart 5. Pulmonary artery mean pressure mean relative value changes (%) from baseline
depending on revascularization area.
During OPCAB for LCX and RCA grafting {t3) heart is being displaced out of its
anatomical position in thorax. Loss of cardiac muscle contact with pericardium and
changes in heart electrical axis result in ECG voltage decrease. In 12 patients
undergoing LV inferior and lateral wall revascularization we failed to register ST
segments in lead II or observed R-wave voltage decrease. The above means that in
these patients myocardial circulation cannot be monitored by ECG. We found no ST
segment deviations exceeding ±1,0 mm (Chart 6) for all patients.
Chart 6. ST segment deviations, mm, from baseline, depending on revascularization area.
13 patients developed heart rate and rhythm alterations during surgery, thereof four
had impaired atrioventricular conduction and six had sinus bradycardia (below 40
bpm). The above arhythmias were controlled by temporary atrial pacing. In two
patients cardioversion was necessary due to tahysystolic atrial fibrillation, while one
patient underwent defibrillation due to ventricular fibrillation. The rest of the patients
had no significant HR changes whatever the revascularization area was. The changes
were controllable without switching to another type of surgery (Chart 7).
Chart 7. Heart rate changes, depending on revascularization area.
Cardiac function changes during surgery were monitored in all of 122 patients: by
ED alone in 28 patients, simultaneous CO measurement by both thermodilution and
ED in 88 patients, total of 326 pair measurements (Chart 8). Six patients were
withdrawn from protocol, as getting stable and full ED signal failed. In these patients
CO changes were measured with TD alone.
Chart 8. Patient distribution by CO measurement methods.
A parameter to compare under this protocol was CI, which is indexed CO value,
divided by patients body surface area (BSA) in m2 (CI = CO/BSA).
When testing a hypothesis of mean CI value equality for both methods we found
statistically reliable difference only during LV lateral/inferior wall revascularization:
t3 r = 0,34; p = 0,032 and t4 r = 0,185; p = 0,477. Lowest CI values were shown by
ED method, demonstrating even dangerously low values (Chart 9) - ED CI = 1,73
1/min/m
Chart 9. Descriprive statistics of ED (HemoSonic100) and TD (РАС) measured cardiac
index (1/min/m2) alterations, depending on revascularization area.
At the beginning and at the end of surgery for other LV walls revascularization both
methods demonstrated close correlation (Table 4) between CI mean values with high
reliability.
TABLE 4
Descriptive statistics of cardiac index (1/min/m2) alterations and correlation, depending on
revascularization area
Timepoints and
areas
РАС CI
ED CI
M
N
SD SEM
M
N
SD
SEM
r
P
Baseline
2,46 88 0,51 0,05 2,45 88 0,55
0,06 0,698 0,001
LAD
2,25 76 0,52 0,06 2,28 76 0,52
0,06 0,629 0,001
Dl
2,16 17 0,67 0,16 2,71 17 0,81
0,20 0,185 0,477
Cx
1,62 40 0,39 0,06 1,89 40 0,43
0,07 0,340 0,032
RCA
2,51 54 0,15 0,43 2,06 54 0,50
0,07 0,426 0,001
Endpoint
2,56 85 0,53 0,06 2,60 85 0,55
0,06 0,824 0,001
According to Bland and Altman method mean, difference and shift are the tools to
find correlation between mean values /9/, obtained by the two methods. Separate
fluctuations of accuracy of measurements or coincidence are supposed to lie within
95% confidence interval, which is at two standard deviation levels.
Difference between baseline values, measured by ED and TD methods in involved
patients is displayed in Chart 10 by linear regression line (straight), considering
confidence interval to be 95%.
Chart 10. Difference between ED-derived and TD-derived CI baseline values in involved
patients. Chart displays linear regression line (straight) and its 95% confidence interval.
Chart shows that in three patients biggest CI values were measured by ED and in five
patients the ED value exceeded the TD value. Data for 8 patients are beyond the 95%
confidence interval, which means that 6.6% of patients had deviation more than 2
SDs.
Chart 11. Difference between ED-derived and TD-derived CI LAD values in involved
patients. Chart displays linear regression line (straight) and its 95% confidence interval.
Only one patient had higher ED-derived CI value during LV anterior wall
revascularization (Chart 11), but in three patients this value exceeded the TD-derived
one. Data for total of 4 patients were beyond the 95% confidence interval, which
means that 3.3% of patients had deviation more than 2 SDs.
Similar CI mean value percentage was observed during RCA revascularization,
however, during revascularization of LCX we found a difference in CI values (Table
5). Dispersion analysis showed statistycally reliable dispersion (F =18,331; p =
0,001).
TABLE 5.
Cardiac index (I/min/m2) alterations / test results, depending on revascularization area
ΔM
t
P
Baseline
0,011
0,248
0,804
LAD
-0.029
-0.557
0.579
Dl
-0,554
-2,411
0,028
Cx
-0,271
-3,594
0,001
RCA
0,450
1,112
0,271
Endpoint
-0,038
-1,090
0,279
Timepoints and areas
There is moderate correlation (r = 0,570; r2 = 0,325; p = 0,001) between ED-derived
and TD-derived CI values during revascularization of LV posterior and inferior walls.
Difference between ED-derived and TD-derived CI values measured when
performing distal anastomosis for LCX was beyond the 95% confidence interval in 23
patients (26%) (Chart 12).
Chart 12. Correlation between ED-derived and TD-derived CI values in involved patients
when performing distal anastomosis. Chart displays linear regression line (straight) and its
95% confidence interval.
After performing distal anastomoses the heart was brought to its anatomical position.
At this stage of surgery no major alterations of hemodynamics, myocardial circulation
or cardiac function were observed. The last comparative measurement of ED-C/ and
TD-C/ was done at the end of surgery. Two patients had ED-derived CI value higher
than TD-derived one, however, one patient had TD-derived CI value higher than EDderived. Data for 3 patients were beyond the 95% confidence interval, which means
that 2.5% of patients had deviation more than 2 SDs (Chart 13).
Chart 13. Difference between ED-derived and TD-derived CI t5 values in involved patients.
Chart displays linear regression line (straight) and its 95% confidence interval.
When comparing values of systemic pressures to ED-derived and TD-derived CI
values we found no reliable correlation between SAP and DAP and CI values, though
PAdP and PamP demonstrated negative linear trend. Chart 14 presents fluctuations of
systemic pressure relative values compared to baseline and depending on
revascularization area and interrelation thereof with ED-derived and TD-derived CI
values.
Chart 14. ED CI; TD CI relative mean values and SAP relative mean values compared to
baseline and depending on revascularization area.
When any of the patients developed hemodynamics impairments of different extent
(MAP < 60 mm/Hg; CI < 2,0 1/min/m2) during surgery, we performed Trendelenburg
maneuvre to redistribute the circulating blood volume, which resulted in increased
preload, as well as in right heart flow and pressures increase.
24% of patients required circulation stabilization therapy perioperatively:
• rhytm control: 8% of patients had atrial pacing (ICU 1.6%), 1.64% had
cardioversion due to atrial fibrillation and 0.8% had defibrillation due to
ventricular fibrillation;
• 23.8% of patients were administered inotropic support with catecholamines
during surgery and in ICU
Minutes descriptive analysis of postoperative period
Duration of patient stay in OR, thoracotomy, artificial ventilation and exposed body
surface (ca. 30 - 40%) resulted in hypothermia in these patients. Despite using patient
warming devices, OR temperature and warming of infusion solutions 53% of the
patients undergoing surgery had core temperature decrease below 36° С Patient
average core temperature at the beginning of the surgery was 36.5° С with SD = 0,48
°C, but at the end of surgery - 35.8° С with higher SD = 0.78 ° С It order to prevent
hemodynamics alterations, cardiac arhythmias, excessive bleeding and blood
viscosity impairments it is necessary to maintain the body temperature during the
surgery close to normal. Moreover, perioperative body temperature alterations
interfere with TD CO measurements.
Patients with lowest recorded core temperature during surgery developed shivering
followed by fever of 38.3° С in ICU (14 patients). Postoperative bleeding volume
(blood volume in mL in drainage system postoperatively) was compared to patient
core temperature at the end of surgery; we found reliable negative correlation. One
patient had to undergo resternotomy due to excessive bleeding. After the surgery
all of the patients were referred to ICU with ET tube in place. 23.8% of patients
required inotropic myocardial support using catecholamines (24h in ICU), 51 patient
(41.8%) developed atrial fibrillation during postoperative period. Duration of ICU
stay after OPCAB was within 13 to 120 hours (M = 27,9 ± 16,2 h). 25% of 122
patients stayed in ICU for over 40 hours.
Duration of intubation during ICU stay was within 90 to 910 minutes (M = 315,5 min,
SD = 147,6 min). Two patients had mechanical ventilation for 1050 and 2390
minutes.
Patients with prolonged ICU stay demonstrated elevated creatine kinase level but had
the same systemic pressures, ventilation figures, troponine, BUN and creatinine
levels, as well as diuresis and postoperative blood loss figures. Duration of stay in the
ICU did not correlate with method of CO monitoring during surgery
Postoperative creatine kinase (CK) alterations
After 1 hr postop the CK level was 187,4 ± 80,1 U/mL on average. Maximum CK
elevation was observed 12 hr after the surgery, in ICU, M = 796,9 ± 916,6 U/mL.
Standard deviation of the value confirms considerable data dispersion and urges to
find out the reasons for CK elevation.
Chart 15. Postoperative creatine kinase (CK) and troponine I (TI) alterations (6 h, 12 h, 24 h).
When analyzing CK-MB and T I elevation, we found weak but reliable positive
correlation (r = 0,219; p = 0,031) between troponine and CK values with reliable
difference (p = 0,001 [t = 6,652]) in t-test mean value (Chart 15).
Reliable CK elevation (p<0,05) is found in patients with prolonged surgery time,
bigger N of grafts, postoperative CK elevation and ED-derived CI value changes
during revascularization of LV inferior and posterior walls.
Patients were divided into two groups by preoperative CK level. First group had CK
of up to 900 U/mL, while the second had CK of over 900 U/mL.
Chart 16. Descriptive statistics of ED-derived cardiac index (L/min/m2) depending on
revascularization area and postop CK level.
Further analysis of correlation between CK elevation and its possible causes revealed
that the second group had bigger number of grafts, more distinct ED-derived CI
alterations compared to the first group. Also, the second group had lower CI values
during operation (Chart 16). However, we found a correlation with ED-derived CI (r
= -0,37, p < 0,05). Right heart monitoring system (TD РАС) presened lower systolic
function impairments at the moment (Chart 17).
Chart 17. Descriptive statistics of РАС TD-derived cardiac index (1/min/m2) depending on
revascularization area and postop CK level 12 hr after the surgery.
No intrahospital mortality was observed in studied patient group. Duration of stay in
the hospital was distributed evenly, mostly within 6 t ol4 days (M = 10.2 days, SD =
2.9 days).
Discussion
Altered circilation during off-pump myocardial revascularization surgery is
secondary to myocardial ischaemia, reduced preload, heart compression, myocardial
dysfunction, increased mitral regurgitation to the combination of the above factors.
Our study demonstrated that altered circulation dirung such kind of surgery is
observed at any myocardial wall revascularization (SAP -20,8% to -9,2%, DAP 20,2% to -29,2%, PAdP +1,4% to +6,3%; PAmP -0,6% to +3,9%). Moreover,
changes in right ventricle function and filling (increase of PAdP) was seen more often
during revascularization of front and inferior walls, as right ventricle has thinner wall
and lower circulation pressure than left one. That is why the right ventricular effect is
higher even when the left ventricular wall is stabilized. This can explain our finding:
an increase in pulmonary artery diastolic pressure and pulmonary artery mean
pressure (+6,3% PAdP t4), which was proportionally higher than CI changes.
Our findings supplement and confirm published data about increased right heart
filling and left ventricular diastolic dysfunction during Dx, LAD and RCA
reconstruction to be found both in humans (Do Q.B., Cartier R., 1999) and animals
(Grundeman P.F., Borst C, 1999).
However, results of Do Q.B. study (2002) of hemodynamic changes during
OPCAB differ from our ones. Do observed more pronounced hemodynamic changes
(PAmP increase for 30% and reduced CI) only during revascularization of heart front
wall. We are to note that in 55 patients, involved into Do study, another
(compression) type of heart stabilizer was used.
We found that the major heart function and myocardial circulation alterations
were observed during lateral and posterior walls revascularization (t3), associated
with the most marked systemic pressure changes (SAP = 87,2 ± 12,0 mmHg; DAP =
52,9 ± 14,0 mmHg), myocardial circulation alterations (ST1 = -0,09; ST2 = -0,05)
and mild mean heart rate increase (HR t3 = 71,9 x min-1 ± 14,7 min-1 and HR t4 =
73,6 min-1 ±11 min-1). At this stage of the surgery anatomical position of the heart is
changed - the heart is "verticalized" and stabilized. Nierich A.P., 2000, et al., when
studying heart response to verticalization, found in TEE that atrial septum is shifted
left and right ventricular geometry is changed. However, he noticed that the adequate
evaluation of heart filling and contractility by TEE is difficult in these circumstances,
as the echo-signal is poor. Royse C.F., 2003 explains this by the changed heart
position against oesophagus.
The same limitations for heart verticalization apply to ST segment analysis of
ECG (Nierich A.P.; Diephuis J., 2000). The phenomenon could be explained by heart
electric axis shift against ECG electrodes. Moises V.A. et al., 1998, and Kotoh K.
1999, independently of one another, studied ischaemia-induced left ventricular
systolic dysfunction by comparative analysis of segmental myocardial wall motion,
detected by TEE, and changes of ST-segment of ECG during OPCAB
revascularization. In 64% of cases TEE registered segmental wall motion
abnormalities, although altered myocardial circulation was found by ECG only in
19% of the cases.
We saw reduced and irregular ECG voltage mostly during posterior wall
revascularization. When evaluating myocardial circulation by ST-segment alterations
in ECG leads II and V5 and comparing the results to postoperative elevation of
markers of myocardial damage (troponine I), we concluded that postoperative
elevation of troponine is not associated with detected ST-segment changes in ECG
(the same as in Moises V.A. study), but corresponds more to CI changes, detected by
ED. We explain decrease of CI at this stage of the surgery by isolated segmental left
ventricular systolic dysfunction, possibly caused either by heart fixation or by
decreased myocardial circulation. Segmental myocardial alterations and decreased
end-diastolic filling of left ventricle (diastolic dysfunction) is the cause of global
alterations in cardiac output, which we saw in our study during revascularization of
posterior wall with marked decrease of ED CI (CI = 1,73 1/min/m2) and mild and
delayed TD CI (CI = 1,97 1/min/m2).
According to published recommendations (The Annals of Thoracic Surgery,
1997; 63: S90), we used Trendeleburg maneuver to stabilize circulation during distal
anastomoses visualization (after the heart was verticalized and stabilized). The "headdown" position considerably enhanced blood flow to the heart, respectively increased
heart preload, thus providing for better end-diastolic LV filling and SV (Boulain T.
2002). In majority of the patients this maneuver caused no alterations of heart
contractility, but in those having preoperative history of severe cardiac systolic and
diastolic failure (CHF NYHA III-IV) Trendeleburg maneuver caused decreased CI,
followed by necessity to administrate inotropic stimulation (in 20 patients).
Nevertheless, the increase of cardiac preload is not always possible without
causing global decrease of cardiac function. In patients with considerably decreased
preoperative cardiac output {EF <40%) increased preload may cause severe left heart
failure. We made a comparative analysis of our results. In a patient with EF of 35%
the PAmP during LAD and Dx grafting was 28 mm Hg, PAdP was 19 mm Hg, SAP 75
mm to 90 mm Hg; also both CO monitoring methods showed decreased global
function of both ventricles: ED CI t2 1,9 1/min/m2; TD CI t2 2,0 1/min/m2 with
prolonged postoperative ventilation (780 minutes), stay in ICU (39 hours) and hospital
stay (22 days). Dagenais F. and Cartier R., 1999, presented the same results in patients
having severe cardiac failure. Based on their own results they proposed for difficult
situations to use
invasive strategy to control pulmonary artery hypertension and right ventricle failure,
namely to partially occlude v.cava inferior by applying a ligature, thus decreasing the
preload.
Lundell D.C. and Crouch J. D., 1998, studied use of miniature right heart
support mechanical system during creation of distal anastomoses in off-pump surgery
and found that right heart mechanical support is enough to provide left ventricle
preload and stable circulation. Several authors confirm in their studies that OPCAB is
a method of choice in patients with severe heart failure (Zaugg M., 2002; Sergeant P.,
de Worm E., 2001; Jagaden О., 2001; Al-Ruz:eh S., 2003). Still the risk of multiorgan
hypocirculatory dysfunction is present, unless sufficient circulatory stability is
provided during the procedure (unless early detection of the cause of impaired
circulatory equilibrium and its prevention is possible). The following ischaemia,
oxidative stress and increased calcium concentration in the cell changes its energy
status, i. e. elevates the level of energy enzyme creatine kinase, CK (Shlattner U.,
2005, 2002).
In our patients, who had decreased blood circulation volume during surgery (ED CI)
saglabājās samazināts asins cirkulāciju apjoms, involving creation of several
anastomoses, we saw increased concentration of both creatine kinase (CK > 900 U/l)
and troponine (r = 0,32, p = 0,004).
To provide for optimal myocardial oxygen supply and circulatory equilibrium
Bernard F. and Denault A., 2001, after analyzed their results, proposed the following
algorithm: to decrease myocardial oxygen consumption and to provide for relatively
high coronary perfusion pressure (MAP > 70 mmHg) by intensive volume
replacement and vasopressors, while avoiding administration of ß-agonists even at
low CI values (compared to preoperative data). Administering catecholamines in
patients with limited coronary circulation may increase myocardial oxygen
consumption, while the delivery is impaired, and may interfere with the course of
surgery (stabilization of cardiac wall).
Increased heart rate and contractility makes it difficult to model distal
anastomosis, thus compromising its quality. That's why the first and the most
effective step during the procedure is to communicate to a surgeon and to return the
stabilized heart to its anatomical position or, when changing heart position, to
stabilize circulation before creating anastomosis, as in this case its quality is not
influenced by a hurry, caused by unstable circulation of the patient. Recovery of MAP
when the heart is in its anatomical positions allows for improved coronary circulation
and prevents from acute heart failure. This is confirmed by our results - at the end of
the procedure patients' CI values recovered to baseline level. Still it is to be kept in
mind that decreased CI should be above the level of undisturbed tissue perfusuion
(Sv02 stays above 60%) and there are no metabolic acidosis signs in blood gas test,
because early diagnosis and treatment of the shock considerably improve patient
recovery prognosis (Rhodes A., 2004).
Global perfusion pressure MAP is the most used and the most misinterpreted
value in association with CO (Hoffman G.M., 2005). MAP depends on kinetic energy
of the heart as well as on interaction of blood flow, viscosity, systemic vascular tone
and backflow pressure (CVP). Concerning interaction of MAP and CO there exist two
wrong conclusions: good blood pressure means good cardiac output, so, increase in
MAP means increases in CO. SVR trend regarding the CO is opposite - decreased
MAP is followed by activation of the sympathetic nervous system, while increased
MAP is followed by decrease in sympathetic activity and increase in parasympathetic
activity. This physiological response equalizes MAP fluctuations, which evidences
that MAP is a late indicator of insufficient circulation till the moment of global
vascular spasm.
Just like Colan S.D., 1998, and Hoffman G.M., 2005, we did not notice reliable
correlation between systemic pressure and CO. Actually, administration of
vasopressors increases just systemic resistance by increasing the tone of capacitance
vessels, but does not influence the CO. It can be clearly demonstrated by blood flow
velocity in descending aorta (ED), when administration of vasopressors decreased the
blood flow velocity. Decreasing vascular resistance is one of the ways to improve
cardiac function in patients with signs of cardiac failure (CI < 2,2). However, changes
in SVR cause systemic pressure alterations, and keeping these two parameters
balanced during OPCAB requires use of more sensitive systems for monitoring of
tissue perfusion and cardiac functions (CI).
Our study of the efficacy of less invasive CI monitoring during off-pump
myocardial revascularization was associated with repeated publications, denying
significance of РАС. In their multicenter study of 1996 Connors A.F., Speroff Т.,
Dawson N.V. found that invasive monitoring, involving РАС, extends patient stay in
ICU and the hospital and even increases mortality for up to 39% in patients, whose
management was guided by РАС. In 2005 JAMA published a review by Shah M.R. ,
dealing with the results of ESCAPE (The Evaluation Study of Congestive Heart
Failure and Pulmonary Artery Catheterization Effectiveness) study, as well as of 13
other randomized clinical trials regarding use of РАС as a management guide in 5051
patients from year 1085 till 2005.
Eligible studies involved those with summarized data on patients, who
underwent surgery or ICU patients with progressive cardiac failure, diagnosed ARDS,
sepsis; studies involved analysis of mortality, duration of stay in the hospital, use of
inotropes and vasodilators. It was found that РАС does not impact patient recovery
time and does not increase mortality. Neutral effect of РАС with regards to
improvement of clinical situation can be explained by the absence of evidence-based
effective management strategy, guided by PAC-derived data.
The use of РАС itself decreases the incidence of critical situations, but has no
impact on mortality and recovery time. However, РАС is an indispensable tool when
it is necessary to evaluate oxygen delivery and consumption. This means that the
information on cardiac output and its components is necessary in intensive care and
critical condition settings. This makes it necessary to carry out extended studies on the
efficacy of patient management strategy, based on noninvasive evaluation of
hemodynamics. In the same ESCAPE study it was concluded that reduced volume
therapy regardless of the preload monitoring type (with or without РАС) considerably
improved condition of the patients with cardiac failure.
The main discussion in the above studies was about the evaluation of heart
filling. According to Frank-Starling law of the heart, the end-diastolic length of
muscle fibers defines the force of cardiac muscle contraction. The increase in cardiac
output volume induced by increased transmural filling pressure is an important
adaptive mechanism of normal heart function, providing adaptation to changed
venous backflow. In cardiac failure the Starling curve becomes more flat, because the
ventricle becomes less sensitive to preload, i. e. equivalent cardiac output can be
achieved with higher filling pressures. However, higher heart filling pressure results
in altered myocardial perfusion or congestion in pulmonary circulation loop, up to
pulmonary eodema in the most severe cases. The results we obtained demonstrate that
the use of the most frequent indicator for preload evaluation - the CVP - is
disputable; also the preload cannot be unambiguously evaluated by PAmP or PAWP,
because right heart and left heart preloads are not the same. According to Harris L.M.,
1997, and Maynar J., 2005, these pressures have limited clinical relevance, affected
by a range of such factors, as heart and patient positioning, venous capacity, heart
ventricle compliance, heart valves function, pulmonary pressure, as well as lung
ventilation volume and mode. Moreover, evaluation of circulating volume should be
done before administering vasopressors.
Another way to evaluate heart filling is to measure the duration of systolic blood
flow in descending thoracic aorta (Singer M., 1989; Vallee F., 2005; Monnet X,
2005). Randomized study of McKendry M., 2004, demonstrated that patients, in
whom postoperative volume substitution was carried out according to ED-method
guided protocol, had considerably shorter duration of stay in a hospital. It is difficult
to prove whether static (absolute) duration of systolic blood flow in descending aorta
is dependent or independent part of the volume as per Frank-Starling law of the heart.
Recent Monett X., 2005, report proved the opposite, i. e. adjusted duration of flow is a
poor indicator of volume deficite. In similar studies, but in different physiological
settings, Leather H.A. and Wouters F.F., 2001, clearly demonstrated that epidural
anesthesia-induced redistribution of circulation increased the difference between ED
and TD values.
Based on these studies, the authors concluded that the ED method is possibly
not the right one to analyze absolute values of heart filling and cardiac function. After
having reviewed the results of the aforementioned studies and compared those to our
own results we concluded that contradictory results of different studies could be
associated with detecting the diameter of the aorta by nomograms, not by actual
measurements. In our study we used ED method with M-mode signal in addition to
Doppler signal, Which allowed us to detect diameter of aorta in every systole. A range
of other studies (Wakeling H.G., 2005; Tan H.L., 2005), as well as our one, proved
that dynamic monitoring of heart rate adjusted duration of Doppler-flow is a good
preload indicator.
The other most frequently evaluated worldwide indicator in patients having
unstable hemodynamics is cardiac output, which is measured in different ways (pulse
contour analysis, transpulmonary, lithium dilution, thermodilution, echodoppler,
transthoracic electrical bioimpedance, etc.). Each of the methods have its own
advantages in different clinical situations. In order to develop clinically safe and
relevant method of patient cardiac function monitoring during off-pump myocardial
revascularization surgery, we used both TD and ED to measure and compare changes
in cardiac function during revascularization of different myocardial zones. We found
that cardiac output values were virtually the same in stable hemodynamic conditions
(t1 r = 0,7; p = 0,001; t5 r = 0,82; p = 0,001), but reliably different in altered
hemodynamics (r = 0,34; p = 0,032), which can be explained by peculiarities of each
of the methods - different location of measurement, time to obtaining the value and
concomitant factors. The same results were demonstrated in Valtier В., 1998, Singer
M, 1989, and Bein В. studies in ICU patients, as well as in Hullett В., 2003, study in
OPCAB patients.
TD CI value is being measured automatically every 2 minutes by thermodilution
catheter, placed in right ventricle. The proximal part of the thermodilution circuit
imitates heat signal at a constant rate, while the distal part senses the temperature
difference, influenced by right ventricular blood flow velocity and direction, as well
as by blood temperature. That is why CI evaluation by TD method requires
consideration of temperature of injecte dvolume, injection velocity and patient own
temperature fluctuations. The above factors may influence the thermodilution curve
(Lichtenthal P.R., 1983) and, correspondingly, the CI absolute value (Section 3.2.3.,
Table 3.3.)- Despite the use of heating devices and warming of infusions 53% of the
patients, involved in our study, had bode temperature decreased below 36,0°C (mean
temperature at the beginning of the surgery was 36,5 °C ± 0,48 °C, but at the end of
the surgery it was 35,8 °C with SD = 0,78 °C). Decreased tissue temperature during
surgery may cause hemodynamic alterations, heart arrhytmias, changed blood
viscosity and excessive bleeding (Fig. 8.16). Patients with lower tissue temperature
during surgery had postoperative shivering in ICU, followed (in 1.5 hours) by
hyperthermia over 38,3 °C (14 patients), which causes higher oxygen demand while
oxygen supply is limited.
ED CO is less influenced by external factors (temperature, ventilation volume),
but more influenced by cardiac function and precise location of the probe (Monnet X.,
2006). ED-derived direct measurement is aortic blood flow (ABF) in descending
thoracic aorta, which means that ED probe measures ABF, not the CO. ABF is always
less than CO, because part of the stroke volume gets to the vessels of the aortic arch.
Although this volume varies and depends on the circulatory status and concomitant
diseases of the patient, ABF mostly is 70% of CO (Boulnois J.G., 2000). Blood flow
velocity, acceleration and duration is being measured by ED every systole (while by
TD method - every two minutes), so measurement trends (Royse A.G., 2003) may
early reveal systolic dysfunction of left ventricle. Still some factors may influence the
CO measurements:
• It is assumed that descending aorta is a cylinder, although its actual anatomy
may be different depending on the pulse pressure and aortic compliance;
• Aortic blood flow is assumed to be laminar, although tachycardia, anaemia and
aortic valve lesions may cause turbulent flow (Chaney J.C, 2002);
• For precise measurement the Doppler ray shoud be directed transversely to
blood flow or with the deviation of less than 20° (Oh J.K., 1999);
• Red blood cells velocity is higher in the centre of aortic lumen than at the
aortic wall;
• CI deriving from aortic blood flow is done with an assumption that 30% of
stroke volume is distributed to brachiocephalic and coronary arteries.
However, this figure depends on patient circulation and concomitant diseases
(Boulnois J.L., 2000);
• It is assumed that diastolic blood flow in descending aorta is negligible.
Unstable hemodynamics is associated with redistribution of circulation,
primarily with decreased blood flow in abdominal organs, which blood supply is
determined by blood flow in descending aorta, that is why flowmetry in decscending
aorta is helpful in understanding physiological alterations of circulation.
Published reports on ED and TD comparative analysis have considerably
discrepant results. Correlation coefficient value varies from r - 0,52 (Schmid E. R.,
1993) to r = 0,98 (Lavandier В., 1988; MarkJ.B., 1986; Perrino A.C., 1990). Schmid
E.R., et al. 2003, consider the reason of the discrepant results to be non-uniform and
small involved patient populations, different statistical analyses, different protocols of
the studies, as well as different requirements for accuracy of both studied and
reference methods, or even commercial interest. In his studies, comparing different
methods, Critchley L.A.H..1999, calculated combined measurement error (20% in
each of the methods) and concluded that it shoud not exceed 30%. Sure, comparative
analysis of the two methods should take into account also standard deviation, which in
"ideal" case is to be 0 L/min (Bland M.J., Altman D.G., 1986). In his study Dummler
R. et al, 2000, found conformity of the obtained values, but calculated combined
measurement error happened to be 44%. In out study this value was 36%.
Several studies mark out clinical relevancy of ED method, noting improved
patient recovery in case the therapy was guided according to results, derived byED
method. Although the ED method cannot completely replace the TD method, it can
offer instant, accurate enough and noninvasive CO evaluation during OPCAB.
Conclusions
1. Revascularization of any of myocardial zones by off-pump CABG is followed
by hemodynamic alterations.
2. Right ventricle disfunction prevails during revascularization of left ventricle
anterior, lateral and inferior walls.
3. Cardiac output values, monitored by invasive and semi-invasive methods, do
not considerably differ in stable hemodynamic status (r = 0,9; p < 0,001), but
are reliably different (p < 0,005) in altered hemodynamic (LV posterior and
lateral wall revascularization).
4. Our study evidences that semi-invasive cardiac output monitoring by echodoppler during off-pump myocardial revascularization surgery is alternative,
safe and informative method of detection of ischaemia-induced left ventricle
systolic disfunction during left coronary artery grafting.
Practical recommendations
1. Due to heart transposition and heart electrical axis displacement it is impossible
to detect decrease in myocardial circulation with following systolic dysfunction
neother by ECG nor by TEE and TD РАС. We may recommend in this instance
to use ED method to evaluate preload and systolic function of the heart.
2. After summarizing the information on evaluation of cardiac function and
circulatory alterations using invasive and semi-invasive methods during
OPCAB myocardial revascularization surgery we may recommend eosophageal
echo-doppler for semi-invasive cardiac output monitoring as alternative, safe
and informative method of evaluation of left ventricle systolic dysfunction
during left coronary artery grafting.
3. We recommend to use ED method during OPCAB revascularization surgery:
•
•
•
•
•
As separate method or combined with TD РАС;
To measure CO in all of the patients with left coronary artery lesion;
To measure preload;
To detect circulatory alterations;
To help select patients for invasive cardiac monitoring using РАС.
4. ED method is not applicable during OPCAB surgery in the event that oxygen
supply and consumption is to be assessed.