ECG Challenge: An 84-year-old man with known hypertension and coronary artery disease and previous coronary artery bypass graft surgery presents to his cardiologist for a routine visit. His medications include a β-blocker, angiotensin-converting enzyme inhibitor, hydrochlorothiazide, and isosorbide mononitrate. He is feeling well. Physical examination is unremarkable, but his pulse is noted to be irregular. An ECG is obtained.
The rhythm is irregular, but many of the RR intervals are the same; hence, the rhythm is regularly irregular. The rate is 75 bpm. All of the QRS complexes are the same in morphology except for complexes 6 and 10 (↑), which are also premature. The QRS complex duration is normal (0.10 second), and there is a normal axis between 0° and +90° (positive QRS complex in leads I and aVF). The QRS complexes have a normal morphology, but there is low voltage in the limb leads, defined as a QRS complex amplitude <5 mm in each limb lead. In addition, there is increased amplitude of the QRS complexes in leads some of the precordial leads, with an S wave of 25 mm in lead V2 (]) and an R wave of 15 mm in lead V5 ([). This meets one of the criteria for left ventricular hypertrophy (ie, SV2+RV5≥35 mm). There are also ST-T–wave abnormalities in leads I and V4 through V6 (^) that are repolarization abnormalities associated with hypertrophy. They represent subendocardial ischemia. The last part of the myocardium to receive blood and oxygen supply is the subendocardial layer (blood flow is from epicardium to endocardium); hence, with hypertrophy, there may be chronic subendocardial ischemia. The QT/QTc intervals are normal (400/445 milliseconds). Although P waves are not apparent, P waves can be seen (*, v) after each longer RR interval, for example, after the fourth QRS complex (*) and after the 2 premature complexes (v), complexes 6 and 10 (↑). The PR intervals after the 2 premature complexes are the same (0.52 second; ↔). In addition, notches are seen in the T waves of many of the other QRS complexes (+). Importantly, the interval between these notches and the following QRS complex is also 0.52 second (↔), indicating that these notches on the T waves are in fact P waves. Because the P waves are positive in leads I, II, aVF, and V4 through V6, this is a normal sinus rhythm with a first-degree atrioventricular block or prolonged atrioventricular conduction. The 2 early QRS complexes (↑), which are wider than the sinus complexes and have a different morphology, are premature ventricular complexes. Although there is a P wave before these complexes (o), the PR interval (┌┐) is much shorter (0.34 second) than with the sinus complexes; therefore, these complexes are not related to the P waves.
As indicated, a P wave is seen (*) during the long RR interval that follows the fourth QRS complex. Although a QRS complex (↓) follows this P wave, the associated PR interval is shorter (0.36 second; [) than that seen with the sinus complexes. This means that the QRS complex is unrelated to the P wave and that this QRS complex (which has the same morphology as the sinus complexes) is an escape junctional complex. This long RR interval is attributable to a nonconducted premature atrial complex because it can be seen that there is a positive and early waveform (▼) at the end of the fourth QRS complex just before this pause. This waveform is not seen with the other QRS complexes.
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- © 2015 American Heart Association, Inc.