"Double Capture" - a technique to differentiate narrow complex Supraventricular Tachycardias.

Background: There are various diagnostic manoeuvres to distinguish between atrial tachycardia (AT), atrio-ventricular nodal re-entrant tachycardia (AVNRT) and orthodromic re-entrant tachycardia (ORT) when assessing a narrow complex supraventricular tachycardia (SVT) in the electrophysiology (EP) laboratory. These manoeuvres are commonly used in combination to come to a diagnosis due to the inability of a single test to be able to reliably differentiate between the arrhythmias.

Objective: To determine whether a single captured His-synchronous simultaneous extra-stimulus in the atrium and ventricle ("Double Capture") can reliably distinguish the mechanism of a narrow complex SVT.

Methods: At a single institution, we reviewed the data on patients in whom this maneuver was performed as part of their routine electrophysiology study and analyzed the intracardiac recordings. There were 44 patients who underwent routine electrophysiology studies for narrow complex SVTs and the maneuver was attempted. If the simultaneous extra-stimuli was delivered when the His was refractory and captured both the atrium (A) and ventricle (V), the earliest signal was assessed to attempt to differentiate the mechanism.

Results: Double Capture was attempted in 44 patients of which six were excluded due to incorrect timing or inadequate electrogram recordings. Of the 38 remaining patients who either had AVNRT or ORT (no atrial tachycardias were included), "Double Capture" was achieved in 29 patients (76%). In patients in whom "Double Capture" occurred, reproducible termination of the tachyarrhythmia with "Double Capture" corresponded with ORT (n = 7). In patients with "Double Capture" with a His signal as the first signal post, and ongoing tachycardia, this typically corresponded with a diagnosis of AVNRT (n = 20), though there were two exceptions with ORT (n = 2).

Conclusion: In this small study, "Double Capture" of the A and V during a sustained narrow complex SVT without change to the tachycardia or His interval timings was able to confirm AVNRT with a specificity of 78% and ORT with a specificity of 100%. This maneuver may be especially helpful to confirm bystander pathways or assess septal pathways.