Monday, September 2, 2019

What is the differential of this very unusual ECG?


Take a look at this ECG first without clinical context:
What do you think?








There is sinus bradycardia with very unusual shortened QT interval (approximately 400 ms), for a QTc (Bazett) 358 ms. The T-waves have high amplitude and narrow bases, reminiscent of hyperkalemia, maybe also with hypercalcemia. The T-waves are not bulky or fat, and are therefore not hyperacute regardless of their amplitude.

Short QTc is rare, but has been described as less than 360 ms for males and less than 370 ms for females. Furthermore, less than 330 ms (males) or less than 340 ms (females) can be termed "very short QTc" and, in the absence of reversible causes, is considered by some to be diagnostic of Short QT Syndrome (SQTS) in an appropriate setting.



Now for the clinical context:

This was a young man with a gunshot wound to the head, who arrived comatose and critically ill. CT scan showed severe brain injury and cerebral edema.

As we have shown on this blog, intracranial hemorrhage can cause various ECG findings, sometimes imitating ischemia, often with bizarre long QT syndromes reminiscent of takotsubo / stress cardiomyopathy. However this is the first time I have seen dramatically shortened QT in this setting. There was no prior for comparison, but this finding would be extremely unlikely to be present on baseline, in the absence of congenital short QT syndrome.

The potassium and calcium levels were within normal limits.



Learning Points:
This ECG in another clinical context should make you consider hyperkalemia and/or hypercalcemia, but would not be consistent with hyperacute T-waves.

ICH / Brain injury can manifest in many bizarre ways on the ECG, usually with long QT with bizarre morphology, but many other findings may be possible. These ECG findings typically correlate with worse outcomes, however most practitioners would say that ECG findings rarely, if ever, add prognostic information beyond standard clinical evaluation in this setting.


Reference:

Viskin S. The QT interval: too long, too short or just right. Heart Rhythm 2009 May;6(5):711-5.


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Comment by KEN GRAUER, MD (9/2/2019):
===================================
Great case by Dr. Meyers about an important ECG entity that is not commonly seen. As I suspect many of those reading this column did — I initially put hyperkalemia at the top of my differential diagnosis list.
  • That said — these T waves would be among the tallest and “skinniest” I’ve ever seen, if the etiology of this T wave appearance turned out to be hyperkalemia ...
Dr. Meyers highlights that an equally impressive finding as T wave appearance in this tracing is the shortened QTc interval. And, there’s another finding ...
  • For clarity — I’ve numbered the beats in the long lead V1 rhythm in Figure-1.

QUESTION #1: What is the rhythm in Figure-1?

Figure-1: The ECG shown in this case. What is the rhythm?


ANSWER: The QRS complex is narrow. Although easy to overlook if not carefully measured — the R-R interval in the long lead V1 rhythm strip is not regular. Figure-2 shows the variation in R-R intervals (BLUE numbers indicating R-R interval duration in milliseconds).
  • Upright P waves with a fixed PR interval precede beats #3,4,5 and 6 (RED arrows in the long lead V1 rhythm strip). Presumably, these are sinus P waves — albeit the P wave is extremely small in amplitude, and the PR interval looks to be relatively short.
  • We only see 1 QRS complex for lead II. This is beat #1 — which is not preceded by any P wave at all.
  • I believe the small-amplitude negative “dip” preceding beat #2 in the long lead V1 is artifact. I don’t believe any P wave precedes beat #2.
  • Beat #7 is cut off — and, the RED question mark, followed by a drop in the PR interval indicates there is artifact. I don’t believe any conclusion can be made about atrial activity for beat #7.
  • BOTTOM LINE: The longest R-R interval in the long lead V1 is between beats #1 and 2 (Figure-2) — and neither of these 2 beats is preceded by any P wave. Therefore, beats #1 and 2 are junctional escape beats. The underlying rhythm in Figure-1 is marked sinus bradycardia with sinus arrhythmia — and when the sinus rate slows enough, junctional escape beats arise.
Figure-2: I’ve numbered and labeled key parts of Figure-1 (See text).


QUESTION #2: How short is the QTc?



ANSWER: The QTc is determined by taking the longest QT interval that you can confidently measure on the 12-lead ECG — and then correcting this QT interval for heart rate.
  • With heart rates over 60/minute (if using the Bazett formula) — the QTc will be more than the QT interval that you measure.
  • With slower heart rates (under 60/minute, if using the Bazett formula) — the QTc will be less than the QT interval that you measure.
Looking at the 12-lead tracing in Figure-2 — I thought the longest QT interval that I could clearly measure was in either lead V2 or V3. I measured 360 ms (thin vertical BLUE lines in V3 showing from where I measured). The R-R intervals both preceding and including this longest measured QT interval correspond to a heart rate of ~43/minute.
  • MD CALC is a handy link that provides near instant correction of the measured QT according to heart rate — allowing you to calculate the QTc by any of the 4 most commonly used corrective formulas ( = Bazett — Fridericia — Framingham — Hodges).
A measured QT interval of 360 ms = small boxes on ECG grid paper. Plugging in this number into MD CALC for a heart rate of 43/minute yields the following results for the QTc:
  • Bazett formula QTc = 305 ms.
  • Fridericia formula QTc = 322 ms.
  • Framingham formula QTc = 299 ms.
  • Hodges formula QTc = 330 ms.
Conclusions:
  • None of the formulas are perfect. Each has its advocates. There is some variation in QTc value determinations — but it’s clear in Figure-2 that the QTc is very short.
  • Because the heart rate is so slow — the QTc turns out to be significantly less than the longest measured QT interval (which was 360 ms).


QUESTION #3: What is the “Short QT Syndrome” ?



ANSWER: A nice review of Short QSyndrome (SQTSappears in Arrhythm Electrophysiol Rev (2014 — by Rudic et al) — CLICK HERE.
  • As emphasized in this article — SQTS is an inherited cardiac channelopathy determined by the presence of symptoms (syncope, cardiac arrest), positive family history, and the ECG finding of an abnormally short QTc interval.
  • SQTS is a relatively new diagnosis that has only been recognized as a distinct clinical entity since 2000. The disorder is rare — but its importance is as a potential cause of atrial and ventricular arrhythmias, including cardiac arrest. Treatment is by ICD (implantable cardioverter defibrillator).
  • Males with a QTc ≤330 ms — and females with a QTc ≤340 ms are defined as having SQTS, even if they are asymptomatic.
  • Males with a QTc ≤360 ms — and females with a QTc ≤370 ms are said to have a short” QTc. Such patients may have SQTS if, in addition to the "short" QTc there is a history of cardiac arrest, unexplained syncope or atrial fibrillation at an early age.


QUESTION #4: What are the ECG features of “Short QT Syndrome” ?



ANSWER: A series of gene mutations have been described in association with SQTS (See link to the Rudic article above). By definition — these gene mutations are all associated with a short QTc interval, as defined above in answer to Question #3.
  • Sometimes, the only ECG abnormality is an overly short QTc interval.
  • BUT — some patients with SQTS manifest specific ECG patterns. One of these patterns consists of T waves that are tall, peaked, symmetrical and narrow-based with a morphology that is completely consistent with the T waves in Figure-2 (especially the T waves in leads V2, V3 and V4).
  • U waves are often prominent with SQTS (This is best seen in lead V2 of Figure-2).
  • Sometimes the ST segment is absent (ie, the QRS complex may seem to immediately follow the T wave). This was not the case in Figure-2 — as a short ST segment is present here.
BOTTOM LINE: This tragic case of a young man critically ill with a gunshot wound to the head provides us with the fascinating ECG shown in Figure-1.
  • The principal findings of exceedingly tall, peaked and pointed T waves with narrow base an exceedingly short QTc were not explained by either hyperkalemia or hypercalcemia — as both electrolytes were within the normal range.
  • CNS catastrophes (as in the case of this comatose patient) — typically present with marked QTc prolongation — and morphologically, with broad T waves that fan out to a broad base. If anything — bradycardia should further prolong the QT. Other than this bradycardia, one would not expect the ECG findings seen here with coma from CNS trauma.
  • I learned from this case that the T wave morphology seen in Figure-1 is perfectly consistent with one of the ECG patterns of SQTS, in this patient with a markedly shortened QTc (See Figure-1 in the above referenced review by Rudic et al).
  • As per Dr. Meyers (and in the absence of a prior ECG for comparison) — we can strongly suspect that the ECG of this patient incidentally revealed a previously undetected congenital SQTS.
  • P.S.  It is easy to overlook a short QTc. Don't forget to look for this in patients with syncope, cardiac arrest and/or unexplained arrhythmias.


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