The correct diagnosis is sinus rhythm, Mobitz type II, transient complete atrioventricular (AV) block, and escape ventricular complex (Figure 2).
The rhythm is irregular because of several long RR intervals. All of the long intervals (↔) are the same, the intermediate intervals (⊔) are the same, and the short intervals (⊓) are the same. Therefore, the rhythm is regularly irregular.
The QRS complexes have two different widths and morphologies. The narrow QRS complexes (0.08 sec) have a normal morphology with an axis of about -30° — that is, a physiologic left axis (positive QRS complex in lead I, negative complex in lead aVF, and biphasic in lead II). They are occurring at a regular rate of 72 beats/min.
A very deep S wave (30 mm) occurs in lead V3 ( ] ), which meets one of the criteria for left ventricular hypertrophy (ie, an S wave or R wave in any precordial lead ≥25 mm). The QT/QTc intervals are normal (400 msec/440 msec). A P wave (+) is present before each of these narrow QRS complexes with a stable PR interval (0.36 sec). The P waves are positive in leads I, II, aVF, and V4-V6. Hence, this is a normal sinus rhythm with a first-degree AV block (or conduction delay).
There are two on-time P waves that are not conducted (*), after the second and seventh QRS complexes. The PP intervals are constant (⊓), at a rate of 72 beats/min. The presence of an occasional nonconducted P wave is indicative of second-degree AV block. After these nonconducted P waves, there is a pause (1.4 sec) or long RR interval (↔), which is ended by a QRS complex that is wider (0.12 sec) (↓) and has a morphology and axis different from the sinus complexes. This represents an escape ventricular complex.
A nonconducted P wave followed by an escape ventricular complex indicates a transient complete heart block; the presence of an escape ventricular complex means that the second-degree AV block is a Mobitz type II, with the AV block within the His-Purkinje system. The presence of a second-degree AV block (ie, an occasional nonconducted P wave) with stable PR intervals of the conducted complexes also indicates that this is a Mobitz type II.
Philip J. 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.
You can follow Dr Podrid on Twitter @PPodrid
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Cite this: Philip J. Podrid. ECG Challenge: High Blood Pressure and Asymptomatic - Medscape - Sep 22, 2022.