DESCRIPTION

This is a wide complex rhythm which has no preceding P waves, originating from the ventricles, with a rate under 100 but over 60. Why isn’t it ventricular tachycardia (VT)? Because we defined VT as a wide complex rhythm originating in the ventricles with a rate over 100, silly! You might see P waves wandering before or even after the QRS complexes (see arrows), as this rhythm might compete with the sinus node for dominance, or send P waves retrograde into the atrium just like a junctional rhythm.

What if the idioventricular rhythm has a rate less than 60? Then it’s not accelerated: it’s just plain old idioventricular rhythm. Physiologists from the Olden Days saw if ventricular muscle was isolated and allowed to function on its own, it would spontaneously depolarize at rates in the 40–60 range.

HABITAT

This is most commonly found in the coronary unit or the Emergency Department in patients who have had myocardial infarctions, especially if they’ve been recently reperfused.

CALL

“This person is in VT and I want to shock him, but he’s eating breakfast!”

RESEMBLANCE TO OTHER ARRHYTHMIAS

A paced rhythm with very small pacemaker spikes might look like an idioventricular rhythm, so look carefully at all the leads before you commit yourself … or check to see if there’s a pacemaker bulging in your patient’s chest. Ventricular tachycardia can be mistaken for accelerated idioventricular rhythm if you can’t count. And for heaven’s sake, don’t overlook P waves: sinus rhythm with a bundle branch block looks like an idioventricular rhythm if the P waves are small!

CARE AND FEEDING

This rhythm thrives on neglect: don’t do anything! It terrifies the nursing staff, however; they usually want to either shock the patient or pump him or her full of some toxic antiarrhythmic agent like lidocaine or amiodarone. Make sure the chemistries are all right, and remind them (and yourself, if you’re also getting antsy) to resist the temptation to do anything else; this rhythm is almost always hemodynamically very stable and usually goes away by itself.

If the idioventricular rhythm isn’t accelerated (i.e., slower than 60) it might start to get too slow; if this starts to cause hypotension or related symptoms the benign neglect we accord to an accelerated idioventricular rhythm may not be appropriate. Here we might start to consider maneuvers to speed things up, such as a pacemaker.

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