In Reply We appreciate the comments from Dr Littmann regarding our case report on paroxysmal atrioventricular (AV) block.1 His letter highlights heterogeneity in the use of the term paroxysmal AV block.
In this case report, we used the Josephson definition of paroxysmal AV block, a “sudden, pause-dependent phase 4 AV block occurring in diseased conduction system.”2,3 Dr Littmann draws contrast with this definition by highlighting a different form of AV block, “tachycardia-dependent or acceleration-dependent.” This form of conduction abnormality is separate and distinct from phase 4 AV block and is associated with reduced cellular excitability during phase 3 of the actional potential. While phase 3 block can be physiologic and observed in healthy tissue (eg, rate-related bundle-branch block during supraventricular tachycardia), the acceleration-dependent form is pathologic, occurring in diseased conduction systems, which facilitate repetitive subthreshold stimulation. Of note, AV block can occur even in the absence of heart rate changes, when fluctuations in circulating catecholamines, neural input, and coronary blood flow can exacerbate underlying conduction system disease.4 Furthermore, a single patient with a diseased His-Purkinje system may manifest both bradycardia-dependent and tachycardia-dependent AV block.5
Hyman MC, Frankel DS. Tachycardia-Dependent Paroxysmal Atrioventricular Block—Reply. JAMA Intern Med. 2021;181(12):1676–1677. doi:10.1001/jamainternmed.2021.5962
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