What's This Repeating Pattern?

Philip J. Podrid, MD

Disclosures

November 05, 2018

Figure 2. Courtesy of Dr Podrid

Discussion

The diagnosis is normal sinus rhythm, interpolated premature ventricular complexes (PVCs) in a trigeminal pattern, retrograde concealed conduction, intraventricular conduction delay, and old inferior wall MI.

The rhythm is irregular with a repeating pattern of group beating—ie, three QRS complexes followed by a pause. The rhythm is therefore regularly irregular. The first QRS complex of each group is preceded by a P wave (+) with a constant PR interval (0.18 sec). The P wave is positive in leads I, II, aVF, and V4-V6. Hence this is a sinus complex. The QRS complex is wide (0.14 sec) and it has a morphology that resembles a left bundle-branch block (LBBB) with a broad R wave in leads I and V6 (→) and a deep QS wave in lead V1 (←). However, there are significant Q waves in leads II, III, and aVF (↑) with ST segment elevation consistent with either a recent inferior wall myocardial infarction or an old myocardial infarction with an aneurysm. These abnormalities are not seen with a LBBB as ventricular activation is abnormal. Therefore, this is an intraventricular conduction delay (IVCD).

Another feature consisted with IVCD is the prominent notching of the QRS complex in leads II, III, aVR, and V1. With IVCD, there is conduction through the normal His-Purkinje system, but it is slower. Thus abnormalities of the left ventricle (ie inferior wall myocardial infarction) can be established. With LBBB, left ventricular activation is not via the normal His-Purkinje system but by direct myocardial activation, and abnormalities of the left ventricle cannot be diagnosed reliably. The Q waves in leads II, III, and aVF are indicative of an old inferior wall myocardial infarction and would not be seen with LBBB.

The axis is normal between 0° and +90° (positive QRS complex in leads I and aVF). The second QRS complex (*) is wider (0.18 sec) and has a different morphology. There is no P wave before this complex; therefore, this is a PVC. The third QRS complex has the same duration and morphology as the first QRS complex. There is a P wave before this QRS complex (▲) with the same morphology as the P wave before the first QRS complex. This is a sinus complex. The PVC is not associated with a pause and there is no alteration of the PP interval, which is constant (└┘) with a rate of 54 beats/min. The PVCs are called interpolated—the PVC does not completely depolarize the atrioventricular (AV) node—hence the next on-time sinus impulse is able to conduct through the AV node. However, the PVC does partially depolarize the node due to retrograde concealed conduction. As a result, the sinus impulse conducts through the AV node at a slower rate. The PR interval of the complex following the interpolated PVC is longer (┌┐) (0.26 sec) compared with the PR intervals of the other sinus complexes. Because every third QRS complex is a PVC, this is ventricular trigeminy. The QT/QTc intervals are normal (400/400 msec and 360/360 msec when the prolonged QRS complex duration is considered).

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