Atrioventricular block and pause-dependent torsade de pointes

Figures

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  Figure 1. Electrocardiograms (ECGs). A: ECG from October 2015 with 3:2 AV block. Initially, conducted QRS complexes are narrow with relatively short PR intervals. With subsequent conducted beats, there is slight PR prolongation and a change of QRS morphology to right bundle branch block. B: ECG from January 2016 with initial 2:1 AV block followed by 1:1 AV conduction. The first 3 QRS complexes are narrow. During 1:1 AV conduction, the first QRS complex is narrow and subsequent QRS complexes widen. PR slightly prolongs between the first and second conducted QRS complex and then remains constant.

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  Figure 2. Telemetry results in January 2016 are representative of episodes of polymorphic ventricular tachycardia in a setting of short–long–short sequences. A: The pause leading to the run of nonsustained ventricular tachycardia is preceded by a premature ventricular contraction and a nonconducted P wave. B: The pause is preceded only by a nonconducted P wave.

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  Figure 3. Ladder diagrams to explain most likely explanation of block in the electrocardiograms (ECGs) presented in Figure 1. A: Referring to the first ECG (Figure 1A), the atrioventricular (AV) prolongation and incomplete left and right bundle branch block are explained by a diseased His-Purkinje system. B: The second ECG (Figure 3B) shows a narrow QRS complex when there is 2:1 AV block (both left and right bundles have opportunity to recover at slower cycle length) but transitions to incomplete left bundle branch block with a faster rate (acceleration-dependent block). A = atrium; AVN = atrioventricular node; HPS = His-Purkinje system; ILBB = incomplete left bundle branch block; IRBB = incomplete right bundle branch block; V = ventricle.