The Great Escape: Junctional Escape—Capture Bigeminy

Abstract

Escape-capture bigeminy is a bigeminal rhythm in which each escape beat is followed by a captured beat. This dysrhythmia is very rare, because its manifestation requires the sinus interval to be longer than the escape interval. This is possible only with severe sinus nodal disease, where the intrinsic sinus rate is extremely low, or with a sinus rhythm associated with an accelerated junctional rhythm. The authors review the case of a 75-year-old man who presented with occasional dizziness and near-syncopal episodes. He was diagnosed with escape-capture bigeminy and subsequently underwent pacemaker placement.

ECG of the Month

“…1 Requirements for escape-capture bigeminy to endure are that the effective intersinus interval must exceed the sum of the escape interval and the refractory period following the escape complex and that the escape complex cannot alter the sinus node' s cycle duration (eg, through retrograde AV nodal conduction). 2,4 For the cat of the present report, the effective intersinus interval (920 milliseconds) was longer than the escape interval (520 milliseconds) and the refractory period as a result of the second-degree AV block, and the ventricular escape complexes did not alter the sinus cycle duration because of the lack of ventricular-to-atrial conduction secondary to interference dissociation. As a result of this physiologic collision, there was mutual extinction of the opposing electrical wavefronts, which occurred within the AV conduction system in this case ( Figure 2).…”

ECG of the Month

“…Several forms of escape-capture bigeminy are possible, but the most common forms in humans are associated with sinus node dysfunction or second-degree AV block. 4 It was our hypothesis that the anaphylactic response secondary to the bee venom contributed to the underlying bradycardia and J-point depression in the dog of the present report. [7][8][9] The case described in the present report is an example of escape-capture bigeminy secondary to transient sinus node dysfunction in a dog; the features of the case resemble those of junctional escape-capture bigeminy in a human in which sinus node dysfunction was diagnosed via electrophysiologic testing.…”

“…This bigeminal rhythm disturbance is considered exceedingly rare because unique conditions are necessary for this rhythm to persist. 1,4 Although these proposed explanations can be considered plausible, neither can be proven without results of an intracardiac electrophysiological assessment. For persistence of escape-capture bigeminy, the effective intersinus interval (ie, the time between conducted sinus impulses [approx 1,800 milliseconds in this dog]) has to exceed the sum of the escape interval (approx 1,000 milliseconds in this dog) and its refractory period, and the escape complex cannot alter the sinus node's cycle duration (eg, because of retrograde AV conduc- Figure 1 and ladder diagrams of the 2 proposed mechanisms for the dog's underlying bradyarrhythmia.…”