Cutting Inappropriate ICD Shocks: Long Arrhythmia-Detection Time Strategy Confirmed

February 21, 2014

LONDON, UK — Programming implantable cardioverter defibrillators (ICDs) to delay the time they take to treat ventricular arrhythmias—that is, with prolonged detection times—cut mortality by 23% and inappropriate shocks by more than one-half in a meta-analysis encompassing about 4900 patients[1]. The included studies were prospective and multicenter and covered both primary and secondary prevention and patients with either ischemic or nonischemic cardiomyopathy.

The risk of syncope didn't go up significantly with longer detection times, despite traditional concerns that lots of patients wouldn't tolerate prolonged arrhythmia exposure before their ICD is allowed to deliver therapy—either shocks or antitachycardia pacing (ATP). Instead, the extra time frequently gave devices a better chance to exclude non–life-threatening arrhythmias like atrial fibrillation and to let otherwise self-terminating ventricular arrhythmias play out on their own.

"In light of our findings, current 'out-of-the-box' settings used by some ICD manufacturers are likely to be too aggressive, with arrhythmia detection times that in some cases may be as short as one to three seconds," according to the authors, led by Dr Paul A Scott (King's College Hospital NHS Foundation Trust, London, UK). Their results highlight the importance of setting longer default ICD detection times, they add.

The analysis included 4896 patients from the MADIT-RIT , ADVANCE 3 , and PROVIDE randomized trials and the RELEVANT nonrandomized study. Overall, 264 patients received appropriate shocks and 253 experienced inappropriate shocks over follow-ups ranging from 12 to 17 months.

The relative risk (RR) of death from any cause was 0.77 (95% CI 0.62–0.96, p=0.02) in the prolonged-detection-time groups compared with controls; the risks of inappropriate shocks and appropriate and inappropriate ATP also fell significantly.

Relative Risk (95% CI) for ICD Treatment Delivery Using Long Arrhythmia-Detection Time Strategy vs Standard Programming, Meta-Analysisa

Parameter Shocks ATP
Appropriate 0.93 (0.74–1.18) 0.25 (0.15–0.41)
Inappropriate 0.50 (0.39–0.65)b 0.35 (0.19–0.64)

b. p<0.00001
ATP=antitachycardia pacing

Why there were fewer deaths with longer detection times is unclear, the authors note, but it may derive from less exposure to potential hazards of shocks and ATP; inappropriate shocks may up mortality, and ATP poses a small risk of inducing ventricular fibrillation. "Alternatively, it may be due to some other factor, such as the avoidance of the treatment patients get in response to the multiple episodes of ICD therapy (eg, prescription of antiarrhythmic drugs).

Scott reports no conflicts of interest. Disclosures for the coauthors are listed in the paper.


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