ECG Challenge: No Ma'am, It's Not Indigestion

Philip J. Podrid, MD

Disclosures

May 01, 2018

Discussion

The diagnosis is atrial tachycardia, ST elevation myocardial infarction (STEMI) of the anterior wall, QRS (electrical) alternans, and T-wave alternans.

Figure 2. Courtesy of Dr Podrid.

The rhythm is regular at a rate of 150 beats/min. The QRS complex duration is normal (0.08 sec) and there is a normal axis between 0° and +90° (positive QRS complex in leads I and aVF). The QT/QTc intervals are normal (240/380 msec). ST segment elevation is seen in leads V3-V5 (↓), consistent with an acute anterior wall STEMI. There is also beat-to-beat variation in the QRS complex amplitude (+,*), known as "QRS" or "electrical alternans", as well a T-wave alternans, especially prominent in lead V2. Before each QRS complex, P waves are seen (^) with stable RP (0.24 sec) and PR (0.18 sec) intervals. The P waves are negative in leads II and aVF and positive in lead aVR. Etiologies for a long RP tachycardia include sinus tachycardia (not likely given the negative P waves in lead II and aVF), ectopic junctional tachycardia, atrial tachycardia, atrial flutter (with 2:1 AV block, not likely because no second atrial waveform is seen), atrioventricular reentrant tachycardia (AVRT), and an atypical atrioventricular nodal reentrant tachycardia (AVNRT) (fast-slow). Although it cannot be definitively established whether this is an atrial tachycardia, AVNRT, or AVRT, the most common arrhythmia associated with a long RP interval is atrial tachycardia. QRS alternans is most commonly associated with a large pericardial effusion or tamponade due to swinging of the heart in the fluid-filled sac (a "pendulum effect"). However, QRS alternans may be seen in other situations, including any rapid supraventricular tachycardia, acute MI, dilated cardiomyopathy, or decompensated heart failure. In these situations, the alternans is the result of beat-to-beat changes in calcium fluxes into the myocardium. In this case, the QRS alternans may be the result of either the atrial tachycardia or the STEMI.

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