EP ROUNDS An Unusual Cause of Tachycardia-Induced Myopathy FREDERIC ANSELME; JOOST FREDERIKS, NOEL G. BOYLE, PANOS PAPAGEORGIOU, and MARK E. JOSEPHSON From the Harvard Tborndike Electrophysiologic Institute, Beth Israel Hospital, Boston, Massachusetts Introduction A 31-year-old female was admitted for the management of congestive heart failure, which was believed to be due to a peripartum cardiomyopathy. She also acknowledged a long history of palpita- tions. An echocardiogram demonstrated a dilated hypokinetic left ventricle with an ejection fraction of approximately 30%. In the hospital, two types of incessant supraventricular tachycardia were ob- served (Figs. 1 and 2). In order to more accurately define her arrhythmias. and because of the possibil- ity of tachycardia-mediated cardiomyopathy, she underwent an electrophysiological study. Her ar- rhythmias were identified and cured by radiofre- quency catheter ablation. Follow-up over the course of the next 6 months the patient's cardiomy- opathy dramaticaly improved. Her last ejection fraction was nearly 50%. She no longer requires di- uretics, and is functional Class I-II. Based upon Fig- ure 1, panels A-C, what is the likelihood for this pa- tient to develop supraventricular tachycardia and why?Comparing panels A andC, how to explain the slower ventricular response at a faster atriai rate? Interpretation 1:2 Tachycardia During Sinus Rhythm (Fig. 1, panels A-C) The initially observed spontaneous rhythm was a regularly irregular narrow QRS tachycardia 'Supported by a grant from La Federation Francaise de Car- dinlogie. Address for reprint.s: Mark E. Joseplison, M,D., Harvard Thorn- dike Electrophysiologic Institute, Beth Israel Hospital, 330 Brookline Ave., Boston, MA 02215. Fax: (fil7) 667-4833. Received October 2. 1995: accepted October 2, 1995. with a cycle length (CL) of approximately 315 ms. The atriai rate was 95 beats/min (CL of 630 ms) with a P wave duration of 120 ms. TheP wave was upright in leads I, II, and III. Two QRS complexes followed each P wave (Fig. 1, panel A). Intracar- diac recordings revealed a His potential before each QRS complex with a constant H-V interval of 36 ms. These findings indicated the presence of a sustained simultaneous conduction through the fast atrioventricular (AV) nodal pathway (leading to a first A-H interval [A-Hf] of 128 ms) and the slow AV nodal pathway (leading to a second A-H interval [A-Hs] of 458 ms). Several other surface ECG patterns observed during the study were re- lated to this mechanism. Runs of right bundle branch block QRS tachy- cardia were the consequence of 1:2 AV conduc- tion with aberrancy during sinus rhythm. This phenomenon was initiated and terminated be- cause of isolated block in the slow pathway. The first block led to a short-long-short sequence in the His-Purkinje system and initiated right bundle branch block as shown in Figure 1, panel B. The intermittent block in the slow pathway, which oc- curred at sinus cycle lengths < 540 ms, was most likely due to Wenckebach periodicity since the A- Hs intervals lengthened slightly before block. What seemed to be a sinus bradycardia with ventricular higeminy on surface EGG. was also due to 1:2 AV nodal conduction (Fig. 1. panel G). Intra- cardiac recordings revealed a sinus cycle length at 560 ms with 2:1 AV conduction. The first sinus complex was conducted by both AV nodal path- ways, whereas the second sinus beat blocked in both AV nodal pathways. This occurred because at this particular sinus rate, which is faster than in Figure 1, panel A, conduction delay in the slow pathway led to a short interval (100 ms) between PACE, Vol. 19 January 1996 115