Considerations about the polemic J point location
V) The J-point of the electrocardiogram
Approximate point of convergence between the end of QRS complex and the onset of ST segment.
It is considered the point at which the QRS complex finishes and the ST segment begins..
The J-point is an essential landmark for measuring QRS duration and ST segment elevation and/or
depression. J-point represents approximate the end of depolarization and the beginning of repolarization as
determined by the surface ECG. There is an overlap of ≈10 milliseconds. (1)
The J point is used to measure the degree of ST elevation or depression present. It is very important in ACSST segment elevation myocardial infarction (STEMI).
The TP segment of precedent beat and the PRs or PQs segment (PRs), are used as reference as the isoelectric
line.
The J-point
TPs
PRs
1.
ST
Mirvis DM. Evaluation of normal variations in S-T segment pattern by body surface
mapping: S-T segment elevation in absence of heart disease. Am J Cardiol 1982;50:122
TP-s
PRs
Answer: using the PRs and TPs of precedent beat as isoelectric line. ST
elevation must be measured at the beginning on J-point.
The "tangent"
This complex is commonly called a "fireman's cap" because it resembles the profile of a firefighter's
helmet. Seasoned medics will recognize this as trouble because of the elevated S-T segment. STsegment elevation = 4mm. Look at the tracing. Remember the J point is where the S wave makes a
right turn toward the T wave.
The J-point is easy to identify when the ST segment is horizontal and forms a sharp angle with the last
part of the QRS complex. However, when the ST segment is sloped or the QRS complex is wide, the two
features do not form a sharp angle and the location of the J-point is less clear. There is no consensus on
the precise location of the J-point in these circumstances. Two possible definitions are:
I) The point at which the ECG trace becomes more horizontal than vertical. In these cases “The
tangent” line method is appropiate
“The tangent” line
IV) When the upstroke of the S wave has not a clear J-point of inflection, the tangent line method is
ideal
70%
A
>29%
B
rS
<1%
C
QS
qrS
70%
A
>29%
B
rS
<1%
C
QS
qrS
Tangent lines
The three possible QRS patterns in V1-V2 in uncomplicated Complete LBBB: rS (70%), QS
(>29%) and qrS (<1%).
PROPER MEASUREMENT OF QRS DURATION
Real end of QRS
Incorrect end of QRS
False end of QRS
Correct end of QRS
The first change in the slope
Is the end of QRS
Outline that shows the proper measurement of QRS complex duration.
A
B
J-point
J-wave
ST elevation
V2
J-point
V4
D
C
J-wave
New J-wave
Terminal QRS slurring
aVF
V4
A and B classic definition of ERP always with ST segment elevation
A) ERP with only ST segment elevation
B) ERP with ST segment elevation and J-point at the end of J wave.
C and D New concept of ERP without ST segment elevation
C) J-point elevation and terminal QRS slurring without ST segment elevation. ) The first point of
inflection of R wave descendent ramp is considered the real J-point. In these cases “The tangent
line” method is ideal.
D) J-wave without ST segment elevation
1.
Pérez MV, Friday K, Froelicher V. Semantic confusion: the case of early repolarization and the J point.
Am J Med. 2012 Sep;125:843-844.
The figure shows in lead V4 the "upwardly concave" the classic "hooked J-point" in lead V4
typical of benign early repolarization pattern. ST-elevation looks like a "smiley face."
Brugada Type 1 ECG pattern
High take-off of does not coincide with J-point. Absence of clear r´ wave
At 40ms of high tale-off the decrease in amplitude of ST segment is ≤ 40mm or 0.4mV
J-point
“The tangent line”
“Upwardly Convex” ST-segment elevation upwardly convex
Typical electrocardiographic pattern, Brugada Type 1: ST segment elevation ≥ 2 mm, upwardly convex and
followed by inverted symmetric T wave in the right precordial leads (V1, V2 or V3). The QRS duration is
longer than RBBB and there is a mismatch between V1 and V6.
1.
Nishizaki M, Sugui K, Izumida N et al. Classification and assessment of computerized diagnostic
criteria for Brugada-type electrocardiograms. Heart Rhythm. 2010 Nov;7:1660-1666.
Type 1:
Brugada pattern
Type 2:
Saddle-back pattern
High
take-off
40 ms
80 ms
β
80 ms
Type 2: The r´ wave is rounded, wide and usually of relatively low voltage The angle between the upslope of
the S-wave and the downs lope of the r'-wave. (β angle) > 58°. Descending arm of r´ coincides with
beginning of ST segment (J-point) Duration of the base of the triangle of r´ at 5mm from high take-off
>3.5mm The QRS duration is longer in Brugada pattern type 2 than in other cases with r´ in V1 and there is a
mismatch between V1 and V6. In Brugada pattern the QRS complex end is earlier in V6 than in V1-V2.
1.
2.
Bayés de Luna A, Brugada J, Baranchuk A, Borggrefe M, Breithardt G, Goldwasser D, Lambiase P,
Pérez-Riera AR, Garcia Niebla J, Pastore CA, Oreto Guiuseppe, McKenna William. Zareba W,
Brugada R, Brugada P. Current electrocardiographic criteria for diagnosis of Brugada pattern: a
consensus report. Journal of Electrocardiol. 2012; 45:433Chevallier S, Forclaz A, Tenkorang J, et al. New electrocardiographic criteria for discriminating
between Brugada types 2 and 3 patterns and incomplete right bundle branch block. J Am Coll
Cardiol.2011 Nov 22;58: 2290-2298.
Type-1 ECG Brugada pattern: J point and ST segment elevation ≥2 mm, with upper convexity(1A)
or descending oblique rectilinear(1B) and negative symmetrical T wave on right precordial leads
(V1-V2 or V1-V3) and/or high right precordial leads V1H, V2H and V3H.
Sub- Types-1 ECG Brugada pattern
Subtype 1A
Subtype 1B
J-point
Upwardly convex ST segment
ST-segment rectilinear oblique descendent
with “the tangent line” method is not possible
to know J-point localization
J-point
J-point
J-point
The patient was a young symptomatic (repetitive syncope episodes) Thai man, with positive familial
background of SCD in young first degree relatives. He died 24h after performing this ECG. The ECG
shows persistent ST segment elevation in the inferior and low lateral precordial apical leads (V5-V6),
associated with concomitant reciprocal or mirror image in the anteroseptal wall that was not modified
with the use of sublingual nitrate in absence of hypothermia, electrolyte imbalance or ischemia.
Sub type IC was denominated “LAMBDA”

wave by Ihor Gussak et al(1)
“The tangent line” is very appropiate for this subtype
J-point
J-point
J-point
Sub-type IC: ST-segment elevation is triangular or coved to the top (“coved type”) ≥ 2mm
(0.2mV), and followed by negative T wave located in inferior or inferoapical leads.
1.
Gussak I, Bjerregaard P, Kostis J. Electrocardiographic "lambda" wave and primary idiopathic
cardiac asystole: a new clinical syndrome?J Electrocardiol 2004;37:105-107.
A
B
C
J point
PR
interval
J point
J point
TP
Segment
A) A normal ECG complex shows TP segment and PR segment, which may be used as reference
points to the isoelectric line.
B) The ST-segment is measured the J point. This ST-segment shows ST-segment depression of
almost 5 mm.
C) ST-segment elevation of approximately 45 mm is depicted.
This 12-lead ECG shows acute anterior STEMI in the presence of right bundle branch block, but you
really need a trained eye to see it.
We talk a lot about the “rule of appropriate T-wave discordance” with bundle branch blocks. What
makes this case difficult is the fact that the T-waves are appropriately discordant.
However, the J-points are concordant in leads V1-V4!
In leads V1-V3 the Twaves are appropriately
discordant.
J point
However, the
J-points are
inappropriately
concordant.
This is normal and
suggestive of acute
STEMI.
If you look carefully you will see that the point at which the QRS complex turns into the ST-segment (the Jpoint or “junction” point) is elevated above the isoelectric line.
That’s abnormal for right bundle branch block. In fact, if the J-point isn’t isoelectric in the right precordial
leads it should be slightly depressed (in the same direction as the T-waves).
Lead V4 looks the most abnormal.
J point
The tangent line
In lead V4, once again the trick is to accurately locate the J-point. Once that is
accomplished it becomes obvious that ST-elevation is present.
The T-waves are appropriately discordant.
If you’re still having doubts, consider that Q-waves are present in leads V1-V4.
to “consider the company” that any ECG abnormality keeps.
Finally, let’s look at leads III and aVF.
In the context of J-point elevation in the anterior leads, the ST-depression in leads III and aVF must be
presumed to be reciprocal changes. We are forced to assume that these are reciprocal changes. Once again,
it’s the sum of all these abnormalities that is significant. They are more than the sum of their parts.
This patient was in fact diagnosed with an acute anteroseptal ST-elevation myocardial infarction.
Man who had coronary revascularization a time ago.
Continuous Holter monitoring during an episode of angina and
concomitant ST segment elevation and ischemic giant J-wave
"lambda-like type” associated with Premature Ventricular
Contractions with Bigeminy sequence and very short coupling. The
PVCs disappear immediately after cessation of vasospastic
ischemia with administration of sublingual nitrate