ECG Challenge: A 68-year-old man with a history of coronary artery disease and left ventricular dysfunction and with a left ventricular ejection fraction of 35% presents to the emergency department with palpitations, shortness of breath, and lightheadedness. His blood pressure is 90/60 mm Hg, and his pulse is rapid. An ECG is obtained.
There is a regular rhythm at a rate of about 100 bpm. All but 4 of the QRS complexes are wide (0.16 second); the 7th and 11th QRS complexes (+) and the last 2 QRS complexes (▾) are narrow (0.08 second). The wide QRS complexes have an abnormal morphology that does not resemble a typical right or left bundle-branch block. There is an indeterminate axis between −90° and ±180° (negative QRS complex in leads I and aVF). There are no P waves before any of these QRS complexes. However, there are irregularities of the ST-T waves (↓) that likely represent superimposed P waves that are dissociated from the QRS complexes. In addition, a P wave is seen before the 12th QRS complex (↑) with a very short PR interval. This P wave is not conducted; that is, it is dissociated from the QRS complex. An indeterminate axis with a wide QRS complex reflects direct myocardial activation, that is, a ventricular complex, biventricular paced complex, or Wolff-Parkinson-White pattern. This is not a paced rhythm, and the complex is not pre-excited. Therefore, the wide QRS complex is ventricular, and this is an accelerated idioventricular rhythm, often termed slow ventricular tachycardia. Complexes 7 and 11 are narrow (+) and are preceded by a P wave (v). The PR intervals are the same (0.24 second). These QRS complexes are captured, also known as Dressler complexes or beats. This is also consistent with atrioventricular dissociation, further confirming the fact that the rhythm is ventricular. The last 2 QRS complexes are also narrow (▾) and have the same morphology as the 2 Dressler beats. The QT interval is normal (400 milliseconds). The last QRS complex is preceded by a P wave (^) with a PR interval of 0.16 second. This is a conducted sinus complex. The PR intervals of the Dressler beats are longer than the conducted sinus complex as a result of retrograde concealed conduction. The preceding ventricular QRS complex is associated with retrograde impulse conduction into the atrioventricular node that does not completely conduct through (concealed) but results in partial nodal depolarization. Because the atrioventricular node is partially refractory, the next sinus impulse can get through but at a slower rate, accounting for the longer PR interval.
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- © 2015 American Heart Association, Inc.