Tachycardia-induced cardiomyopathy is a well known phenomenon in the pediatric population.¹ However, at presentation, the coexistence of an incessantly elevated heart rate and ventricular dysfunction often sparks a “chicken and egg” debate. Determining causality can be even more perplexing if multiple arrhythmias are involved. Since radiofrequency ablation (RFA) is so effective at curing incessant pediatric tachyarrhythmias,^2–4 the best proof of causality may be restoration of acceptable hemodynamics in a compromised patient and eventual complete resolution of cardiomyopathy¹ after a reduction in heart rate is effected by an RFA procedure.

Thus, the potential reward of tachyarrhythmia elimination in this setting may lead to an attempt at RFA in even the sickest children who present with an incessantly elevated heart rate and cardiomyopathy. The following case illustrates the success of this strategy in an extreme circumstance where the patient presented with severe cardiomyopathy requiring support by extracorporeal membrane oxygenation (ECMO), and had both atrial and ventricular tachyarrhythmias.

Case Report
History. The patient was a 14-year-old boy who presented to the Medical University of South Carolina (MUSC) after being transferred from an outlying hospital for incessant polymorphic tachycardia. He had been evaluated for intermittent palpitations about 11 months prior to presentation, but only with an echocardiogram, which was normal, and never with an electrocardiogram (ECG). He was well until one to two months prior to presentation, when he developed gastrointestinal symptoms which never completely resolved. He had progressive fatigue, and eventually, flu-like symptoms over the week prior to presentation. After his family physician noted a rapid pulse, an ECG demonstrated polymorphic tachycardia with what appeared to be features of ventricular tachycardia (VT) and atrial tachycardia (AT) (Figure 1). Although some of the runs of wide complex tachycardia appeared to be ventricular, they virtually always started with atrial ectopy. An echocardiogram prior to transport showed a 24% shortening fraction in sinus rhythm and much less in tachycardia. During transport, the patient deteriorated significantly and experienced at least two seizures, requiring brief CPR, but he had no prolonged hemodynamic compromise. The initial echocardiogram at MUSC showed severe left ventricular dilation to about 7 cm with a barely perceptible shortening fraction of 4% in sinus rhythm. Although tachycardia-induced cardiomyopathy was considered, the initial presumptive diagnosis was myocarditis, and he was placed on ECMO the evening of arrival for deteriorating hemodynamic condition. The initial rhythm at MUSC was sinus rhythm with atrial premature beats that seemed to trigger a right bundle branch block, inferior axis, ventricular tachycardia lasting for two to three seconds and then terminating. The VT was responsive to lidocaine, but he continued to have runs of AT and some wide complex tachycardia for which he was eventually started on IV amiodarone. After a total load of 35 mg/kg and up to 25 mcg/kg/minute, the rhythm became regular with a nearly fixed non-sinus atrial rate of about 120 bpm with occasional exit block and a sinus escape. Given the persistently elevated atrial rate despite hemodynamic support and ventricular arrhythmia control, tachycardia-induced cardiomyopathy from an ectopic atrial tachycardia (EAT) focus was again considered, with presumed triggering of ventricular tachycardia due to severe cardiomyopathy. For EAT resistant to IV amiodarone, catheter ablation was considered the treatment of choice.

Procedure
After informed parental consent, the patient was brought to the electrophysiology (EP) lab on ECMO with the help of the MUSC’s emergency transport team. Virtually no femoral pulse was present during and echocardiography showed no closure of the AV valves during ventricular systole. A duo-decapolar deflectable catheter was looped around the right atrium with its tip in the coronary sinus to use as a reference. A 7 French, 4 mm thermistor tipped catheter (Marinr, Medtronic Inc., Minneapolis, Minnesota) was used for mapping and ablation. Baseline rhythm had a cycle length of about 460–500 msec with an incessant non-sinus atrial rhythm with positive P waves in leads I, AVF, and VI. Every sixth to tenth beat, there was exit block and a “sinus” escape beat with a more positive P wave in lead I. The origin of the dominant rhythm was mapped to the posterior right atrium in a mid position both left to right and infero-superior. The position was very close to the tip of the ECMO cannula (Figure 2), but not quite on the tip. Although atrial activation was early at this point, there was not a big differentiation between proximal and distal electrode pair activation at that location with the distal signal winning out very slightly. The first application of RF energy in this location led to termination of the tachycardia within just a few seconds. However, no ablation parameters could be seen and the application was discontinued. There was initially no recurrence of tachycardia, and a second application was made in this location. Eventually some beats from this area did recur, and the catheter was repositioned to an even better location. Activation in this area preceded the surface P wave by about 44 msec (Figure 3). Application of RF energy in that location led to initial acceleration of the rhythm and then termination at 4.5 seconds (Figure 4). The application was continued for a total of 60 seconds, after which no further activity originated from that location and the atrial cycle length increased to about 700 msec. Further mapping revealed that the new slower rhythm was also non-sinus, appearing to originate from near the base of the right atrial appendage. This rhythm was regular with a rate less than 100 bpm. Limited applications of RF energy in the earliest locations never resulted in a significant change in the rhythm. Consequently, it was eventually considered to be a non-sinus atrial pacemaker of no clinical significance and no further applications of RF energy were made. To rule out any abnormalities of the right atrial appendage, a right atrial angiogram was performed and was normal. Right ventricular biopsies were then performed four times to look for evidence of myocarditis.

Follow Up
Following ablation, the patient was transported back to the ICU, again with the help of the hospital’s emergency transport team. After gradual improvement of ventricular function, he was able to be decannulated from ECMO on post-RFA day 5 and weaned off inotropic support by post-RFA day 9. Lidocaine was continued prophylactically until inotropic support was discontinued. The atrial rhythm became clearly sinus soon after the RFA and gradually slowed to a rate near 60 bpm. Biopsies revealed no evidence of myocarditis. The patient returned to the cardiac EP lab two weeks after his ablation. He was found to have normal coronary arteries, normal cardiac output (4.95 L/kg/minute), and no inducible atrial or ventricular tachyarrhythmias on and off of isoproterenol. Prior to discharge, his shortening fraction was 21% and the patient had no further clinical arrhythmias. LV function had completely normalized by nine months, and LV volume had normalized by seven months post-ablation (Figure 5). He remains tachycardia-free 14 months following his presentation.

Discussion
This case illustrates several interesting and important points: 1) one must have a high index of suspicion for tachycardia-induced cardiomyopathy when patients present with incessant or near incessant arrhythmias and ventricular dysfunction; 2) RFA can be successfully performed even in patients on ECMO; 3) malignant ventricular arrhythmias may be induced by the combination of atrial ectopy and severe cardiomyopathy; and 4) even the most severe cases of tachycardia-induced myopathy are likely to eventually recover normal function when the tachycardia is controlled.

As did arose with this patient, the question of viral myocarditis versus tachycardia-induced myopathy is common in these patients. This patient’s recent symptoms were generalized and could have been secondary to heart failure or a viral illness. Unfortunately, neither viral titers or biopsies can always be used to make a definitive diagnosis of myocarditis. Further, there is no clear effective treatment for myocarditis other than supportive measures.^5,6 Alternatively, treatments for physiological and pathological tachycardias are well established^2–4,7 and generally effective, making it possible to control the ventricular rate in patients with myocardial dysfunction. Rate control may be dually effective, through improved hemodynamics and some likelihood of definitive cure, when the myopathy is secondary to the tachycardia alone.¹

The patient reported here continued to have unrelenting ventricular dysfunction despite some rate control on very high doses of amiodarone, leading to the use of more aggressive therapy. Performance of RFA, as well as other catheter interventions, has been reported in children requiring ECMO.8 Careful planning and cooperation between the ICU, transport, ECMO, and EP lab teams are critical to a successful procedure without complications.

This patient’s acute and chronic recovery of cardiac function, with elimination of all ventricular arrhythmias as well,9 after only atrial RFA essentially proves the etiologic link between his atrial arrhythmia and cardiomyopathy.

Conclusion
A high index of suspicion for tachycardia-induced cardiomyopathy is warranted when patients present with an incessant elevated heart rate and ventricular dysfunction, even in the presence of ventricular arrhythmias. Radiofrequency ablation may be curative and can be successfully performed in patients receiving ECMO support.