ECG Challenge: A 74-year-old man with a history of hypertension and hypertensive heart disease, taking lisinopril, hydrochlorothiazide, and a β-blocker, presents to his primary care physician for a routine physical examination. He has no symptoms. His blood pressure is 190/100 mm Hg, and the rest of the physical examination is unremarkable. An ECG is obtained (ECG A). The patient is sent to the emergency department where his blood pressure is still elevated. An ECG is repeated (ECG B).
ECG A shows a rhythm that is irregular as a result of several long RR intervals. All 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 2 different widths and morphologies. The narrow QRS complexes (0.08 s) have a normal morphology with an axis of ≈ –30° (ie, a physiological 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 bpm. There is a very deep S wave (30 mm) 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 ms/440 ms). There is a P wave (+) before each of these narrow QRS complexes with a stable PR interval (0.36 s). The P waves are positive in leads I, II, aVF, and V4 through V6. Hence, this is a normal sinus rhythm with a first-degree atrioventricular (AV) block (or conduction delay). There are 2 on-time P waves that are not conducted (*; ie, after the second and seventh QRS complexes). The PP intervals are constant (┌┐) (rate, 72 bpm). The presence of an occasional nonconducted P wave is a second-degree AV block. Following these nonconducted P waves, there is a pause (1.4 s) or long RR interval (↔) that is ended by a QRS complex that is wider (0.12 s) (↓) and has a morphology and axis that is different from the sinus complexes. This represents an escape ventricular complex. The presence of a nonconducted P wave followed by an escape ventricular complex indicates 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.
ECG B shows a rhythm that is slightly irregular because the first 2 complexes (v) are at a slower rate (32 bpm) than the last 4 QRS complexes (44 bpm). The first 2 QRS complexes are wide (0.12 s) and have a morphology that is identical to the 2 escape complexes seen in ECG A. There are no P waves before these QRS complexes, although an occasional P wave (*) that is not associated with the QRS complex is seen. Hence, these are ventricular complexes. Following these 2 complexes, there are 4 narrow QRS complexes (0.08 s) which have a normal morphology that is identical to the narrow QRS complexes seen in ECG A. There is a P wave (+) before these QRS complexes with a stable PR interval (0.36 s), which is the same as the PR interval of the sinus complexes in ECG A. Therefore, these are sinus complexes. Following each of these sinus complexes, there is a second P wave (o) that is nonconducted. The PP interval of the P waves is constant (└┘) at a rate of 72 bpm. This is a second-degree AV block with a pattern of 2:1 conduction or 2:1 AV block. There is a single P wave seen before the second QRS complex (*) with a very long PR interval (0.80 s); thence, this is not conducted and represents AV dissociation. Because the atrial rate is faster than the rate of the QRS complexes, the first 2 QRS complexes represent complete or third-degree AV block with an escape ventricular rhythm. The 2:1 AV block is thus a Mobitz type II. This is the same conduction abnormality as was seen in ECG A.
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- © 2016 American Heart Association, Inc.