ECG Challenge: Intense Chest Pain and Irregular Pulse

Philip J. Podrid, MD


August 20, 2020

The correct diagnosis is sinus rhythm, premature ventricular complexes, and echo complexes (Figure 2).

Figure 2. Courtesy of Dr Podrid.


The rhythm is irregular but has a repeating pattern of group beating, with three QRS complexes and a pause. This regularly irregular rhythm is 48 beats/min on average.

The first and third QRS complexes are the same and they are wide (0.12 sec) with a morphology typical for a right bundle branch block with an RSR' pattern in V1 (→) and a terminal S wave in leads I and V5-V6 (←). The axis is extremely leftward between -30° and -90° (positive QRS complex in lead I and negative in leads II and aVF). The QRS complex in leads II and aVF is a QS; therefore, the left axis is the result of a chronic inferior wall myocardial infarction. The QT/QTc intervals are normal (480/430 msec and 460/374 msec when the QRS complex duration is considered). The first QRS complex is preceded by a P wave, which is positive in leads I, II, aVF, and V4-V6. The PR interval is constant (0.16 sec). Therefore, this is a sinus complex.

The second QRS complex (^) is wide (0.14 sec) and has an unusual morphology that is not typical for either a left or right bundle branch block. This QRS complex is not preceded by a P wave. The axis is indeterminate between -90° and +/-180° (negative QRS complex in leads I and aVF). An indeterminate axis associated with a QRS complex that is wide and is not supraventricular is the result of direct myocardial activation, including a paced QRS complex (specifically a biventricular paced complex), a ventricular complex, or Wolff-Parkinson-White pattern. Therefore, this is a premature ventricular complex (PVC).

As indicated, the third QRS complex is identical to the first of the three. This QRS complex is preceded by a P wave (*), which is negative in leads II and aVF, so it is not a sinus P wave. Because it is negative in lead aVF, it is coming from either the atrioventricular (AV) node (ie, retrograde) or the low part of the atrium. There is a fixed relationship between the PVC and the negative P wave, and it is likely that the P wave is retrograde, resulting from ventriculoatrial (VA) conduction from the PVC. The supraventricular complex that follows the PVC is called an echo complex.

An echo complex occurs when a QRS complex is not preceded by a P wave (ie, junctional, ventricular, or paced complex) and is associated with intact VA conduction. Intact VA conduction leads to retrograde activation of the atrium (retrograde P wave). With the right timing, this retrograde atrial impulse can enter the AV node and His-Purkinje system to restimulate the ventricles in an antegrade direction (ie, echo back to the ventricles).

Philip Podrid, MD, is an electrophysiologist, a professor of medicine and pharmacology at Boston University School of Medicine, and a lecturer in medicine at Harvard Medical School. Although retired from clinical practice, he continues to teach clinical cardiology, and especially ECGs, to medical students, house staff, and cardiology fellows at many major teaching hospitals in Massachusetts. In his limited free time he enjoys photography, music, and reading.

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