The magnitude of sinus cycle length change during ventricular tachycardia is predictive of successful antitachycardia pacing.

Background: Despite the wide use of antitachycardia pacing (ATP) in patients with implantable cardioverter defibrillators (ICDs), predictors of ATP success remain poorly understood. We hypothesize that the degree of sympathoexcitation, as measured by the sinus cycle length (SCL) shortening during ventricular tachycardia (VT), is a predictor of ATP success.
Methods and Results: The charts of 462 patients with dual-chamber ICDs were reviewed. A total of 88 events in 26 patients met the inclusion criteria and were analyzed. The mean SCL during the 4 seconds preceding the VT onset (SCL-baseline), and during the 4 seconds prior to ATP delivery (SCL-VT) was measured. The percent shortening in SCL was calculated as ((SCL-baseline) - (SCL-VT))/(SCL-baseline) x 100. Patients were classified into the ATP-success and ATP-failure groups depending on the VT(s) response to ATP. Using a t-test analogue for clustered data, patients in the ATP-success group exhibited a greater shortening in SCL when compared with the ATP-Failure group (5.8% compared to 4.7%, P = 0.007). The successful ATP events displayed an average SCL shortening of 6.0% compared to 1.8% in the unsuccessful ATP events (P = 0.029). When the events were analyzed, the sensitivity and specificity of a shortening in SCL of >10% in predicting ATP success were 0.29 and 1.
Conclusion: We have shown that the SCL change during VT, a marker of the autonomic changes that accompany a tachycardia, is useful in predicting ATP success. Our findings suggest that analysis of the SCL during VT might play a role in future programming of ATP in patients with ICDs.