EKG of the Week

A 34 y/o female presents c/o palpitations x 1 hour.

Q1. What does the EKG demonstrate?

Q2. What is the significance of this finding?

A1. Ventricular bigeminy

A2. It represents a regular pattern of PVCs which is unlikely to degenerate into V-tach.

Premature ventricular contractions (PVCs) occur in wide a variety of pathologic and nonpathologic states. Occasional PVCs are com­monly seen in healthy adults, more so under conditions associated with catecholamine excess, such as pain, anxiety, and use of stimu­lants (e.g., caffeine, nicotine, cocaine, amphetamines). Pathologic conditions associated with frequent PVCs include myocardial infarction, electrolyte disturbances, and medication toxicity. Although usually not requiring any intervention, frequent PVCs may occasionally herald the onset of VT—for example, in the setting of ST elevation myocardial infarction or in patients with a prolonged QT interval.

A PVC appears as a wide–QRS complex extrasystole without a preceding P wave. Most PVCs capture the AV node, making it refractory to the next arriving atrial impulse. Because retrograde conduction of a PVC rarely extends far enough to capture and reset the SA node, however, atrial impulses continue to arrive at the AV node at the intrinsic sinus rate. As a result, the R-R interval surrounding a PVC ends up being equal to twice the intrinsic R-R interval length, a phenomenon known as a compensatory pause. Rarely, a PVC will capture the SA node, resulting in a noncompensatory pause, or will fail to capture the AV node, leaving the underlying rhythm completely unaffected (a so-called interpolated PVC).

Bigeminy occurs when there is an extrasystole after every native beat, so that every other impulse is extrasystolic; trigeminy (every third beat) and quadrigeminy (every fourth beat) are similar. Therapy for PVCs is directed toward correcting any precipitat­ing condition, be it a catecholamine excess, a drug effect, an elec­trolyte imbalance, or cardiac ischemia. When occurring in isolation, symptomatic PVCs can be treated with low-dose beta-blocker therapy, but this is rarely an emergency need. Although lidocaine will suppress PVCs, it is not recommended in the absence of VT owing to limited clinical benefit and the risk of systole.

(Yealy, Kosowsky. Dysrrhythmias. In Rosen’s Emergency Medicine, 8th ed. Ch. 79)