ECG Challenge: Is This an Effect of AFib Treatment?

Philip J. Podrid, MD

Disclosures

April 02, 2018

Discussion

The diagnosis is atrial tachycardia with variable (2:1 and 3:1) atrioventricular (AV) block and intraventricular conduction delay.

Figure 2. Courtesy of Dr Podrid.

The rhythm is regular at a rate of 72 beats/min, although one longer RR interval is seen (↔). The QRS complex duration is increased (0.16 sec), and there is a morphology of a left bundle branch block (LBBB) with a deep S wave in lead V1 (←) and a broad R wave in lead I (→). However, there is a small septal Q wave in leads I and aVL (*) and a septal R wave in lead V1 (↓). Because septal activation is from a small septal (median) branch from the left bundle branch, when an LBBB is present, septal forces are absent. Moreover, there is a terminal broad S wave in lead V6 (↑). With an LBBB, all forces are directed in a right-to-left direction. There should be no terminal S waves in leads I or V6, which represent left-to-right forces. Indeed, the terminal S wave is more consistent with a right bundle branch block. Therefore, this is an intraventricular conduction delay (IVCD).

Of note, an IVCD represents slow conduction through the normal His-Purkinje system. Therefore, abnormalities affecting the left ventricle can be established. An LBBB represents left ventricular conduction directly through the myocardium and not the normal His-Purkinje system. As a result, abnormalities of the left ventricle cannot be definitively established.

The QRS complex is leftward between 0° and -30° (QRS complex positive in lead I and II—after accounting for the deep S wave—and negative in aVF). The QT/QTc intervals are prolonged (460/500 msec) but are normal when the prolonged QRS complex duration is considered (400/440 msec). Between each QRS complex, there are prominent waveforms (^) that are negative in leads I, II, aVF, and V3-V6. Hence, the underlying rhythm is not sinus.

During the long RR interval (↔), two negative waveforms are seen (+,*) at a rate of about 144 beats/min. Indeed, similar waveforms are seen at the end of some of the QRS complexes (v). When measured, all of the negative waveforms are regular at a rate of 144 beats/min. Therefore, this is atrial tachycardia with 2:1 AV block and one episode of 3:1 AV block. It can be seen that there is slight variability between the atrial waveform and the QRS complex (┌┐). This is due to antegrade concealed conduction. Some of the atrial impulses get through the AV node to stimulate the ventricle. Some impulses are completely blocked, whereas other impulses may partially penetrate the AV node but not get through completely (ie, concealed). However, the AV node becomes partially depolarized; and although the next atrial impulse may get through, it does so at a slower rate, accounting for changes in the "PR" interval.

Sotalol is an antiarrhythmic drug with class II (beta-adrenoreceptor blocking) and class III (cardiac action potential duration prolongation) properties.[1] It is not known whether this patient's ECG findings represent an adverse effect of beta-blocker therapy, but it is certainly possible. Sotalol is contraindicated in the presence of second- and third-degree AV block (unless a functioning pacemaker is present).[1]

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