Mild pulses of electrical energy just as effective as more powerful and painful shocks to interrupt life-threatening rapid heartbeats

Oct 22 2004

Mild pulses of electrical energy can be just as effective as more powerful and painful shocks to interrupt life-threatening rapid heartbeats, according to a report in Circulation: Journal of the American Heart Association.

Ventricular tachycardia (VT) is a fast heartbeat originating in the heart’s ventricle chamber and can be life-threatening. VT is often treated with an implantable cardioverter-defibrillator (ICD), a device that delivers an electrical shock to restore an irregular heart rhythm. But these shocks are painful and some ICD patients report a decline in their quality of life. ICDs can also provide overdrive pacing to electrically convert a sustained rapid heartbeat.

In this study, researchers found that the pacing function of ICDs alone could end an irregular heartbeat without the need for painful shocks. Antitachycardiac pacing (ATP) successfully terminated 81 percent of rapid heartbeats when used as initial therapy in patients with ICDs.

Quality of life improved whether patients were treated with ATP or shocks, but the improvement was greater with the ATP, researchers said.

“ATP is highly effective in treating ventricular tachycardia and prevents painful shocks without any clinical difference from shock therapy,” said Mark S. Wathen, M.D., associate professor of medicine, arrhythmia services at Vanderbilt University Medical Center in Nashville, Tenn. Wathen was lead author of this study by the multi-center trial known as Pacing Fast Ventricular Tachycardia Reduces Shock Therapies (PainFREE Rx II).

Traditionally, ATP has been applied only to slower forms of VT (below 190 beats per minute) that presumably have less risk of acceleration in response to pacing or easing fainting. In this trial, ATP was used for all VT less than 188 bpm with a 90 percent success rate. The trial randomized only the faster VTs (188-250 bpm).

The study involved 634 patients with ICDs, who were randomly assigned to initial treatment with ATP or to shocks and followed for 11 months. The ICDs were programmed to detect fast ventricular tachycardia (FVT) – rapid heartbeats of 188 to 250 bpm.

In the ATP-treated group, pacing was the initial therapy. The device advanced to shock treatment if ATP failed to terminate the rapid heartbeat within a specified period of time. In the second treatment group, shocks were the initial form of treatment. If the rhythm was faster than 250 bpm, then the first therapy was shock in all patients.

In the shock-treated group, 147 episodes of FVT were detected, and 99 were treated by a total of 110 shocks. In the remaining cases, the shocks terminated spontaneously in 44 instances, and four episodes involved patients who had been crossed over to the ATP group at patient or physician request.

In the ATP treatment group, the first ATP attempt terminated 229 of the 284 episodes. The total included eight episodes in which FVT re-initiated so quickly that the ICD recognized the repeat FVT as ATP failure and delivered a shock. In the 54 cases of true ATP failure, the FVT episodes were treated by shock in 49 cases and by additional pacing in the remaining cases.

The two treatments had similar safety. The median duration of FVT episodes was 10 seconds in the ATP group and 9.7 seconds in shock treatment arm. Acceleration of FVT occurred in 2 percent of episodes in the ATP patients and 1 percent of the shock patients. A total of three patients developed syncope (loss of consciousness) during FVT, two in the ATP group and one in the shock group.

A total of 56 patients died during the study, and the estimated one-year survival was 91 percent. The investigators reported that 32 patients in the ATP group died (10 percent) and 24 (7 percent) died in the shock group. Sudden cardiac death occurred in one patient in the ATP group and two in the shock group.

Among patients who had at least one episode of FVT, 98 completed a quality-of-life questionnaire before the study began and after 12 months. The shock group had improvement in the bodily pain domain of the survey but not in the other domains that were included in the questionnaire. In contrast, the ATP group had significant improvement in seven different areas, including physical functioning, bodily pain, social function, and overall mental and physical status. None of the average domain scores decreased in either group from baseline to 12 months.

“This is the first prospective randomized trial to demonstrate that empirical ATP is safe and effective compared with shocks for FVT. ...These observations, combined with the established efficacy of ATP for slower VT, reposition the ICD as primarily an ATP device with only occasional backup defibrillation [shock],” the investigators stated.

Researchers said ATP should be the preferred therapy for VT in most ICD patients.