EMReports | What Was That Wide QRS Tachycardia Rhythm?

What Was That Wide QRS Tachycardia Rhythm?

Larry Mellick, MD, MS, FAAP, FACEP
Professor of Emergency Medicine and Pediatrics
Medical College of Georgia

Pearl: The sudden onset of a wide QRS tachycardia in a young patient brings up several serious diagnostic considerations.

Case: An 18-year-old African-American male with a history of documented supraventricular tachycardia (SVT) treated with sotalol hydrochloride presents to the emergency department with what he thinks is a recurrence of his SVT. His ECG demonstrates an irregular wide QRS tachycardia with a prolonged QT interval. (Figure 1) The nursing staff, assuming this is a reoccurrence of the patient's usual SVT, has the patient Valsalva, and the wide QRS tachycardia returns immediately to a normal sinus rhythm. (Figure 2) This patient eventually is admitted for further evaluation of presumed ventricular tachycardia, which is considered a medication side effect. It is postulated that sotalol with its pro-arrhythmia potentially caused the occurrence of ventricular tachycardia when the patient took a second dose of his sotalol after an SVT episode started that morning.

Discussion: Sotalol hydrochloride is an effective anti-arrhythmic drug with Class II (beta-adrenoreceptor blocking) and Class III (cardiac action potential duration prolongation) properties. It is well known that sotalol can cause a pro-arrhythmia.¹ New or more frequent occurrence of pre-existing arrhythmias paradoxically precipitated by anti-arrhythmic therapy defines pro-arrhythmia. It is a side effect associated with some anti-arrhythmic drugs, as well as with drugs for other indications. A tendency of anti-arrhythmic drugs is to facilitate emergence of new arrhythmias, as demonstrated in the CAST trial.^2,3

Class III drugs primarily block the potassium (K+) channel. Other Class III drugs include amiodarone, dofetilide and ibutilide, somatilide, azimilide, and droneradone.⁴ These drugs act to prolong the action potential duration and refractoriness in slow- and fast-channel tissues. This effect reduces the capacity of all cardiac tissues to transmit impulses at high frequencies, while conduction velocity is not significantly affected. As a consequence of the prolonged action potential, the rate of automaticity is reduced. QT-interval prolongation is the predominant effect on the ECG. These drugs are used to treat supraventricular tachycardias and ventricular tachycardias. Class III drugs are known to have a risk of ventricular pro-arrhythmia such as torsades de pointes ventricular tachycardia. In one early trial of 3,257 patients, pro-arrhythmia was reported in 4.3% of the patients. Of these, 2.4% had torsades de pointes, and 0.8% had sustained VT or VF.⁴

In the case presented, the patient's suspected pro-arrhythmia ventricular tachycardia appeared to respond promptly to a Valsalva maneuver. What about Valsalva and termination of the ventricular tachycardia? It has previously been recognized that some episodes of ventricular tachycardia can be interrupted by the Valsalva maneuver or adenosine.^5,6,7,8 Nevertheless, the routine use of Valsalva in the management of ventricular tachycardia cannot be endorsed as there is also evidence that the Valsalva maneuver may actually increase the QT interval in some patients and conditions.^9,10 This occurrence potentially could accentuate a dangerous rhythm.

However, in this patient, there were some clues that something else might be going on. The wide QRS tachycardia was puzzling. It was extremely irregular and converted with Valsalva maneuver and, as mentioned above, this is unusual for ventricular tachycardia. Also, there were no dissociated p-waves during the putative episode of ventricular tachycardia. After further consideration, the possibility of atrial fibrillation with antidromic (via pathway) conduction (i.e., pre-excited atrial fibrillation) with a rapid ventricular response was postulated. An electrophysiology study of the heart was done and confirmed an accessory pathway, which was subsequently ablated.

This patient case highlights the difficulty of the diagnosis of wide QRS tachycardia in patients with pre-excitation. Atrial fibrillation with aberrant conduction or conduction by an accessory pathway can mimic ventricular tachycardia, and the response to a Valsalva maneuver might also be one of the differentiating features between those two arrhythmias. Even though this patient's wide QRS rhythm was not ventricular tachycardia, clinicians must not forget that rapidly conducted atrial fibrillation in patients with pre-excitation also is considered a relative medical emergency because rapidly conducted atrial fibrillation/flutter also is associated with sudden death.¹¹

References:

Pfammatter JP, Paul T, Lehmann C, et al. Efficacy and proarrhythmia of oral sotalol in pediatric patients. J Am Coll Cardiol1995;26:1002-1007.
Echt DS, Liebson PR, Mitchell LB, et al. Mortality and morbidity in patients receiving encainide, flecainide, or placebo. The Cardiac Arrhythmia Suppression Trial. N Engl J Med 1991;324:781-788.
Anderson JL, Platia EV, Hallstrom A, et al. Interaction of baseline characteristics with the hazard of encainide, flecainide, and moricizine therapy in patients with myocardial infarction. A possible explanation for increased mortality in the Cardiac Arrhythmia Suppression Trial (CAST). Circulation 1994;90:2843-2852.
MacNeil DJ, Davies RO, Deitchman D. Clinical safety profile of sotalol in the treatment of arrhythmias. Am J Cardio. 1993;72:44A-50A.
Waxman MB, Wald RW, Finley JP, et al. Valsalva termination of ventricular tachycardia. Circulation 1980;62:843-851.
Lee YC, Sutton FJ. Valsalva termination of ventricular tachycardia. Circulation 1982;65:1287-1288.
Fu LT, Nozaki M, Iinuma H, et al. Contribution of vagal tone to initiation and termination of ventricular tachycardia: Report of three cases. Clin Cardiol 1980;3:137-142.
Wren C, Rowland E, Burn J, et al. Familial ventricular tachycardia: A report of four Families. Br Heart J 1990;63:169-174.
Mitsutake A, Takeshita A, Kuroiwa A, et al. Usefulness of the Valsalva maneuver in management of the long QT syndrome. Circulation 1981;63:1029-1035.
Haapalahti P, Viitasalo M, Perhonen M, et al. Ventricular repolarization and heart rate responses during cardiovascular autonomic function testing in LQT1 subtype of long QT syndrome. Pacing Clin Electrophysiol2006;29:1122-1129.
Basso C, Corrado D, Rossi L, et al. Ventricular preexcitation in children and young adults: Atrial myocarditis as a possible trigger of sudden death. Circulation 2001;103:269-275.

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