ECG Challenge: A 76-year-old man with a history of hypertension being treated with a β-blocker and diltiazem, chronic obstructive pulmonary disease, and mild mitral regurgitation presents to his primary care physician with complaints of occasional palpitations that have been present for the past 3 weeks. Physical examination demonstrates a normal blood pressure, an irregular pulse, clear lungs, and a grade 2/6 murmur consistent with mitral regurgitation. As a result of the irregular pulse, an ECG is obtained.
The rhythm is irregularly irregular with an average rate of 42 bpm. The QRS complexes have a normal duration (0.08 second) and a normal morphology. The axis is physiologically leftward between 0° and −30° (positive QRS complexes in leads I and II and negative in lead aVF). The QRS complexes demonstrate low voltage, defined as ≤5 mm in amplitude in each limb lead and ≤10 mm in each precordial lead. It is likely that the low voltage is attributable to chronic obstructive pulmonary disease.
There are only 3 supraventricular rhythms that are irregularly irregular:
Sinus arrhythmia in which there is a P wave before each QRS complex. There is 1 P-wave morphology and a stable PR interval.
Wandering atrial pacemaker or multifocal atrial rhythm with a heart rate <100 bpm or multifocal atrial tachycardia with a heart rate >100 bpm. These arrhythmias have ≥3 different P-wave morphologies without any dominant P wave. There may also be variable PR intervals.
Atrial fibrillation in which there is no organized atrial activity
Atrial flutter or atrial tachycardia may be irregular, but there is a pattern to the irregularity that is based on the presence and extent of AV block. Hence, in this situation these arrhythmias are regularly irregular.
In this case, no organized P waves are seen. There are very prominent atrial waveforms present, especially in lead V1 (^). Although these waveforms resemble atrial flutter waves, they are irregular in amplitude, interval, and morphology. With atrial flutter, all the atrial waveforms are identical in amplitude, interval, and morphology because they are the result of a reentrant mechanism with a fixed circuit and fixed activation sequence. Hence, this is coarse atrial fibrillation. The prominent or coarse atrial waveforms often indicate a more recent onset of atrial fibrillation. With atrial fibrillation the ventricular response rate is dependent entirely upon AV nodal conduction. Because the atrial rate is very rapid and irregularly irregular, the ventricular response rate will also be irregularly irregular. The slow ventricular response rate is likely the result of therapy with a β-blocker and diltiazem, both of which slow conduction through the AV node.
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- © 2014 American Heart Association, Inc.