The Significance of ATP Therapy Failure During Appropriate ICD-Delivered Therapy in Patients With Ventricular Tachycardia

Prospective clinical trials have demonstrated that ICD-delivered therapy reduces mortality in patients at risk for sudden cardiac arrest due to ventricular tachycardia (VT). ICDs through anti-tachycardia pacing (ATP) modalities are able to terminate spontaneous VT. Although ATP is highly effective in terminating VT in ICD patients, 5 - 30% of these events ultimately need shocks. Unsuccessful ATP attempts, as well as shocks, prolong the duration of the episode and are associated with poor clinical outcomes. Methods: Our study focused on 1873 ICD-delivered therapies in pts who received ICD implants from 2008 to 2012 and completed one year follow up. Only patients who received ATP therapy for the first time for a ventricular tachycardia (VT) event were included. All therapy zones contained ATP therapy followed by shock therapy. Results: 806 pts with ICD implants for primary or secondary prevention were analyzed. Study population consisted of 636 (78.9%) males and 170 (21.1%) females with average age of 72.8±29.8y (range: 29 - 98y). 622 (77.2%) of these patients had successful termination of VT with ICD-delivered ATP therapy. In 184 (22.8%) patients with unsuccessful ATP, appropriate ICD shocks were delivered. Only 66.8% of patients with failed ATP had successful VT termination after 1st ICD shock. More than 33% of patients required 2 or more ICD-delivered shocks, of which 13% required four or more. No gender based difference was found regarding success for VT termination after first, second or multiple ICD delivered shocks. Conclusions: 1) ATP therapy is successful in the majority of patients. 2) After ATP failure only 66.8% of pts respond to first ICD shock. 33.2% require multiple ICD shocks that delay VT termination and may lead to worse clinical outcomes. 3) ATP failure for VT termination may identify patients who are at increased risk for failure to respond to ICD shocks. A careful observation and further clinical correlation is warranted in this group.