By definition, ventricular tachycardia (VT) is a tachydysrhythmia originating from a ventricular focus with a rate > 120 beats/minute. If a rhythm on first glance appears to be suggestive of ventricular tachycardia in appearance, but the rate is < 120 bpm, then consider the possibility of one of three VT mimics:
* Hyperkalemia
* Type IA medication toxicity (e.g. Tricyclic Antidepressant)
* Accelerated idioventricular rhythm (AIVR)
Each of these mimics can give the appearance of a wide-complex rhythm suggestive of a "slow" ventricular tachycardia. AIVR is present in up to 20% of patients after an acute MI (1). AIVR is also common after successful reperfusion with thrombolytics, but it is not considered a reliable indicator of reperfusion. Most episodes are self-limited and do not require treatment.
It is important to recognize that treatment of one of these mimics with an antiarrhythmic typically used for VT can have catastrophic consequences. Administration of lidocaine for a wide complex tachycardia due to hyperkalemia misdiagnosed as VT has resulted in asystole (2). Similarly, lidocaine for AIVR has resulted in asystole, as has amiodarone.
So, beware of “slow VT”; when the diagnosis is in doubt, it may be worthwhile to administer intravenous sodium bicarbonate which will treat 2 of the three mimics noted above (hyperkalemia and type Ia antidysrhythmic overdose).
References:
(1) Ryan TJ, et al. AHA/ACC guidelines for the management of patients with acute myocardial infarction: executive summary. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Management of Acute Myocardial Infarction) Circulation 1996;94: 2341-50.
(2) McLean SA, et al. Lidocaine-induced conduction disturbance in patients with systemic hyperkalemia Ann Emerg Med 2000;36(6):615-8.
A great clinical pearl from emedhome.com: Ventricular Tachycardia Mimics
Reproduced in its entirety from emedhome.com:
