Washington, DC - Low-LVEF patients with implantable cardioverter-defibrillators (ICDs) who don't need pacing for bradycardia have about the same quality-of-life outcomes with their devices set to provide atrial-based pacing, activated at a heart rate of 70 bpm (AAI-70), as with devices programmed for only single-chamber backup pacing (VVI-40), according to a randomized trial [1].

The secondary finding from the second Dual Chamber and VVI Implantable Defibrillator (DAVID II) trial, presented here at the Heart Failure Society of America 2007 Scientific Meeting, adds further weight to its previously reported primary results, that neither pacing mode offered a clinical advantage over two years.

The trial's message, according to Dr James R Cook (Baystate Medical Center, Springfield, MA), who is on the DAVID II executive committee, remains that ICDs set to VVI-40 are fine for most eligible low-LVEF patients with healthy sinus nodes. Patients in DAVID II had been randomized to one of the two pacing modes while on, in the overwhelming majority, optimal medical therapy that included beta blockers and either ACE inhibitors or angiotensin receptor blockers; all had LV systolic dysfunction, and most were in heart failure.

Misconceptions about pacing support with ICDs

Dr James R Cook

Cook explained that electrophysiologists, at least, had believed that pacing support was routinely necessary in such patients with ICDs. "One of the things we believed, especially with the prevalent use of amiodarone in the past, was that you couldn't [otherwise] treat the patients optimally with beta blockers, because then you'd be limited by heart rate and blood pressure."

After dual-chamber, rate-responsive pacing (DDDR) apparently worsened outcomes for such patients in the first DAVID trial, "the argument became that maybe it's ventricular pacing that's the issue, and if you atrial pace, you can help people receive the medicine they deserve and improve their quality of life." That trial saw a significantly increased risk of death or heart-failure hospitalization over one year for DDDR compared with VVI-40 pacing. The trial had entered predominantly patients with LV systolic dysfunction secondary to ischemic heart disease.

So the second DAVID was launched to see whether AAI-70 pacing would do at least as well as ventricular backup pacing while allowing optimal medical therapy, Cook observed. Ventricular backup pacing at the time was considered less problematic than DDDR but still thought to entail a potentially detrimental level of right-ventricular stimulation.

The trial randomized 300 patients to AAI-70 and the same number to VVI-40 following successful ICD implantation. All had an LVEF <40%, 87% had a history of MI, and two-thirds had chronic heart failure.

AAI-70 comparable to VVI-40

Among the approximately 90% of patients who received any pacing during the two-year study, surprisingly few heartbeats were actually paced in the VVI-40 group: only 1.2% of beats after three months and 1.0% after 24 months. The corresponding figures for AAI-70 pacing were 47% and 51%, respectively.

The trial's primary outcomes, presented earlier this year at the Heart Rhythm Society 2007 Scientific Sessions and reported by heartwire at the time, included no significant two-year differences between the pacing modes in a composite end point consisting of death or rehospitalization for new or worsened heart failure. The annualized mortality was about 5% in both groups.

Cook told heartwire that all the patients had received dual-chamber pacemakers, but only the atrial wire and only the ventricular wire were activated for AAI-70 and VVI-40 pacing, respectively. Fewer than 8% of the patients had the second wire activated for dual-chamber pacing; such crossovers were at the physicians' discretion.

"There are patients who do have sinus-node dysfunction or AV-conduction disorders, but they are limited and certainly not as prevalent as we thought they were when we had embraced the DDDR pacing mode as necessary to deliver optimal medical therapy and chronotropic support," Cook said.

No effect of pacing mode on quality of life

Patients rated themselves using several quality-of-life instruments, including the SF-36 health survey, which has been validated for rating general functional status and well-being in patients with heart disease, Cook noted; the Minnesota Living with Heart Failure Questionnaire (MLHFQ), also widely used; and the Simple Outcome Screen (SOS) and Global Rating Change (GRC) surveys designed for outcomes assessment in patients with stroke and survivors of cardiac arrest.

The two groups showed statistically similar quality-of-life improvements as measured by the MLHFQ, but there were also suggestions of greater improvement for the VVI-40 group by the SF-36 and for the AAI-70 group according to the SOS/GRC evaluations. With quality-of-life outcomes seemingly all across the board, the investigators interpreted the divergent findings of the SF-36 and SOS/GRC evaluations as "chance variation" and concluded that there was no evidence of better improvement in either group.

"Atrial pacing may be considered a safe alternative, but it offers no clear advantage or disadvantage over ventricular backup pacing, VVI-40," Cook said when presenting the DAVID II quality-of-life results. "If I were to get a defibrillator today and I were a heart-failure patient, I'd get a single-chamber ICD programmed at VVI-40 and maximize medical therapy."

To heartwire, Cook said, pacing the heart at 70 bpm doesn't translate into clinical benefit compared with ventricular backup pacing but in DAVID II "at least it did no harm." If clinicians want to put in a dual-chamber device, he said, it should either be programmed to AAI or use algorithms that minimize ventricular pacing. (A number of manufacturers offer devices with such capability.) But he added, "If there's sinus-node dysfunction or another indication for pacing, atrial pacing can help."

DAVID II was supported by St Jude Medical. Cook reports receiving grants from Boston Scientific, Medtronic, and St Jude Medical.