A new, stripped-down model of the implantable cardioverter-defibrillator seems safe and effective in this relatively small study, but its lean features menu will send large, long-term data collection back in time, Dr. Leslie A. Saxon said in an accompanying editorial (Circulation 2013;128:938-940).
The subcutaneous implantable device harkens back to the first generation of such equipment, and it lacks the hardware and software upgrades that enabled their rapid evolution to multifunctional devices with performance data that can be instantaneously acquired.
"Without the ability to remotely collect episodes in all subcutaneous device recipients, it is difficult to know how the learning around spontaneous VT/VF episodes and treatment will occur, other than the old-fashioned way, through case reports and post-approval registries," she wrote. "This is a significant limitation from a clinical learning and safety advisory perspective."
The study involved 314 patients, 21 of whom received a total of 119 shocks for spontaneous arrhythmias. The success rates were high – 92% for ventricular tachycardia and 97% for ventricular fibrillation. "Although these data are reassuring and comparable to transvenous ICD success rates, the overall number of treated episodes is incredibly small in comparison with the data on transvenous defibrillator therapies delivered outside the hospital, over the life of the device, that are available for analysis in tens of thousands of patients," Dr. Saxon noted.
Patient selection will be key in appropriately deploying the device, she said.
"Selecting the appropriate candidate for the subcutaneous rather than transvenous ICD requires an acknowledgment of the strengths and limitation of each device and an educated guess, as well, regarding the clinical course of the patient, over the battery life of the ICD," she said. "Patients with advanced symptom class heart failure or very depressed ventricular function may face additional risk at implant because of the need for at least two ventricular fibrillation inductions and the longer times to defibrillation associated with the subcutaneous device. There remain a significant percentage of patients with clinical profiles favorable for a subcutaneous device. These predominately include those with prohibitive vascular access issues and those at heightened risk for major systemic infection with an indwelling chronic vascular lead."
Dr. Saxon is chief of the division of cardiovascular medicine at the University of Southern California. She is on the medical advisory boards of Boston Scientific and Medtronic and was a principal investigator on the device study.
