A 47-year-old woman with scleroderma, pulmonary hypertension, and a history of mitral valvular replacement for mitral regurgitation had an asymptomatic bout of tachycardia while in the hospital because of infection of a Hickman catheter. She was not taking digitalis. Her electrocardiogram (Figure) shows a rapid ventricular rate and bigeminal rhythm. The V1 rhythm strip reveals an atrial rate of 177 beats per minute. A P wave, seen in the middle of each of the longer R-R intervals, is conducted with a P-R interval of 0.20 seconds. The next P wave occurs just after the QRS and is conducted with a P-R interval of 0.33 seconds. A third P wave can be seen at the beginning of each QRS ending the shorter R-R intervals and is not conducted. The series of events then repeats itself. Thus, the rhythm is atrial tachycardia with 3:2 atrioventricular block of the Wenckebach type. The RS in leads I and V6 and the rsR′ in V1indicate incomplete right bundle branch block.
Figure.
Electrocardiogram during tachycardia shows a bigeminal rhythm. See text for description.
Bigeminal rhythms have many causes (Table) (1). High among them is 3:2 atrioventricular block that usually is of the Wencke-bach type. Any form of group beating suggests the possibility of atrioventricular Wenckebach, and finding P waves and progressive lengthening of the P-R interval before the nonconducted P confirms that diagnosis. Atrial tachycardia with block may result from digitalis excess, in which case the P-wave axis usually is more vertical than in the electrocardiogram shown here (2), but it also may occur whenever there is atrial disease and physiologic and/or pathologic failure of atrioventricular conduction.
Table.
Some causes of bigeminal rhythm
| • Alternate beats are premature: atrial, ventricular, junctional |
| • Nonconducted atrial premature beats after every second QRS |
| • Sinus rhythm with 3:2 atrioventricular block: Wenckebach, Mobitz II |
| • Other supraventricular rhythms with 3:2 atrioventricular block |
| • Atrial flutter with alternating 2:1 and 4:1 block |
| • 3:2 exit block: sinoatrial; escape rhythms—atrial, junctional, ventricular; accelerated rhythms-atrial, junctional, ventricular |
| • Escape-capture bigeminy with escape focus: atrial, junctional, ventricular, electronic pacemaker |
| • Atrial tachyarrhythmias with 3:2 atrioventricular response of an electronic pacemaker |
References
- 1.Bayes de Luna A. Clinical Electrocardiography: A Textbook. Mount Kisco, NY: Futura Publishing Co; 1993. pp. 341–342. [Google Scholar]
- 2.Wellens HJJ, Conover MB. The ECG in Emergency Decision Making. Philadelphia: WB Saunders Co; 1992. pp. 143–144. [Google Scholar]