Implantable defibrillators are small devices placed under the skin of the chest. Using high-energy shock therapy called antitachycardia pacing (ATP), they detect and stop possible cardiac arrhythmias such as ventricular tachycardia and thereby reduce the risk of sudden death. ATP delivers a sequence of small impulses to the heart to restore its normal rhythm and stop arrhythmia painlessly. Traditional systems require the implantation of leads that pass through the veins to the heart. Subcutaneous implantable defibrillators have recently been developed, which do not require leads, but they cannot perform antitachycardia pacing, which limits their usefulness.
Now, a study published in the journal JAMA that involved Lluís Mont, the head of the Atrial Fibrillation Unit, the leader of the IDIBAPS research group Biopathology and treatment of cardiac arrhythmias and Steering Comittee member of the study, compared the effectiveness of ATP with the effectiveness of direct current shock therapy in a double-blind randomised trial. This project, named APPRAISE-ATP, is the largest randomized study with defibrillators. The findings indicate that the benefits of ATP are limited in patients who have received an implanted defibrillator as a primary means to prevent sudden death. Thought ATP was observed to extend the time until the first direct current shock, it did not decrease the total number of shocks needed or mortality. Patients undergoing ATP were also found to have a higher incidence of ‘arrhythmic storms’. These findings could expand the indications for subcutaneous defibrillators, which use systems without intracardiac leads to deliver direct current shocks to the heart when they detect arrhythmias, but cannot administer ATP.
As Lluís Mont explains, ‘The results of this study may help us to decide on the best defibrillator for each patient, especially if we consider that leadless pacing systems combined with subcutaneous defibrillators could potentially be just as effective, but with fewer serious complications’.
Led by the University of Rochester Medical Center, this study, the largest to date, included 2,595 patients who had been implanted with a defibrillator for ventricular tachycardia. The patients were randomly assigned to two groups: one received antitachycardia pacing before shock therapy and the other received direct shock therapy.
The results show that antitachycardia pacing delayed the need for the first shock by 28%, yet the total number of shocks and mortality remain unchanged, regardless of whether ATP was administered beforehand.
