A:V = 1:1 cardiac arrhythmia detection by VA interval analysis.

Dual-chamber-sensing implantable-cardioverter defibrillators are soon expected to replace ventricular sensing devices. The addition of an atrial sensing lead will dramatically improve the specificity of arrhythmia detection. Even when using combined ventricular and atrial rate criteria, ambiguity in the case of atrial tachycardia with: anterograde conduction versus ventricular tachycardia with: retrograde conduction still remains. The introduction of dual-chamber sensing in antitachycardia devices allows for additional features, such as the measurement of atrioventricular (AV) and ventriculoatrial (VA) intervals. This study investigated relationships between AV and VA intervals to address problems arising in tachycardias with confounding 1:1 relationships. Thirty-one passages of 1:1 anterograde conduction from nine patients during atrial pacing at cycle lengths of 600-300 ms and 24 passages of 1:1 retrograde conduction from eight patients during ventricular pacing at cycle lengths of 600-300 ms were analyzed. Moving averages of three successive VA interval measurements were used to develop a criterion to be implemented into an algorithm to reduce ambiguity. Five randomly selected ventricular pacing passages were used as a training set. Upper and lower VA interval boundaries (234 ms and 132 ms) determined from the training set were used to classify 1:1 retrograde activation. To account for premature beats and outliers, the boundary criterion required 9 of 12 of the most recent moving averages to fall within the upper and lower limits. Of the 19 analyzed passages of ventricular pacing, 18 (95%) were correctly classified using the VA interval as an added feature. Of the 31 atrial pacing passages, 24 (77%) were correctly classified. Using only atrial or ventricular rates, all 1:1 tachycardias in this patient sample would be classified as ventricular tachycardia, resulting in false shocks. Specificity of diagnosis in ambiguous 1:1 tachycardias can be increased using VA interval measurements at the cost of minimum loss in sensitivity for ventricular tachycardia detection. This algorithm imposes little in additional computation for dual-chamber-sensing implantable-cardioverter defibrillators and greatly reduces the possibility of false shocks in 1:1 supraventricular tachycardias.