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Sinus Bradycardia and the Appearance of a Ventricular Escape Rhythm

Image 2 of 4 in Series "Slowing of the Sinus Rate and the Emergence of a Ventricular Escape Rhythm"

Description

The initial rhythm is sinus bradycardia at a rate of 47/min. The first four complexes originate from the SA node. The sinus rate then slows slightly and a fifth P wave occurs. However, this slight decrease in the sinus rate to 45/min results in a delay in the appearance of the next QRS complex, allowing the emergence of a ventricular escape rhythm. This rhythm is accelerated idioventricular rhythm (AIVR) at a rate of 47/min. AIVR begins with the fifth QRS complex. Note that these complexes are wider due to their ventricular origin. The right bundle branch block-like morphology of these QRS complexes is consistent with an origin in the left ventricle.

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This image is part of the series "Slowing of the Sinus Rate and the Emergence of a Ventricular Escape Rhythm"

Other images in this series

Normal Sinus Rhythm at Baseline

by: Joe B. Calkins, Jr., M.D.

The ECG is normal. The rhythm is normal sinus rhythm. Rate is 74/min.

Sinus Bradycardia and the Appearance of a Ventricular Escape Rhythm: Illustration of the Underlying Timing and Intervals

by: Joe B. Calkins, Jr., M.D.

The intervals underlying the occurrence of the ventricular escape rhythm in the previous ECG are illustrated. The interval between the first and second P waves is 1,270 msec, corresponding to a rate of 47/min. An increase in the interval between the fourth and fifth P waves to 1,327 msec, or a decrease in the sinus rate to 45/min, allows a ventricular focus to escape overdrive suppression by the SA node, resulting in accelerated idioventricular rhythm (AIVR) at a rate of 47/min.

Accelerated Idioventricular Rhythm

by: Joe B. Calkins, Jr., M.D.

The final ECG in this series shows accelerated idioventricular rhythm (AIVR) at a rate of 43/min. QRS complexes are wide due to their ventricular origin. P waves are superimposed on the initial portion of the first and sixth QRS complexes, consistent with an underlying marked sinus bradycardia. A narrower QRS complex follows the seventh P wave and represents a fusion complex that results from simultaneous depolarization of the ventricles from electrical impulses arising from two sites, in this case, from the SA node and the left ventricle.