The implantable cardiac defibrillator: is the glass half empty or half full?

implantable cardioverter-defibrillator (ICD) is one of the great engineering achievements of the twentieth century.1 This electronic device detects potentially lethal cardiac arrhythmia (ventricular fibrillation [VF] or ventricular tachycardia [VT]) and shocks or overdrives the heart to restore normal sinus rhythm. Smaller than the tiniest cell phone, the ICD system consists of a battery, leads to sense rhythm and to deliver the shock, a computer that analyzes cardiac waveforms and initiates a counter-pulsation algorithm, charging circuitry that converts battery power to the voltage and current needed to overcome the arrhythmia, and memory to document cardiac and device activity. Additional components of the system include an external programmer to interrogate the ICD memory and to tailor sensing and firing algorithms to optimize care for a particular patient. Initially approved by the Food and Drug Administration in 1985, the first-generation ICD was bulky, weighing more than 9 ounces. Implantation was a complex open-heart surgical procedure (thoracotomy) with the attendant risks of general anesthesia and surgical site infection. Rudimentary sensing algorithms resulted in occasional false firings, which some patients equated to "being kicked by a mule." Battery life was at best 2-3 years and necessitated additional surgery to replace the pulse generator. While Medicare coverage soon became available, eligibility criteria were highly restrictive, framing the device as: "... a treatment of last resort for patients who have documented episodes of life-threatening tachyarrhythmia or cardiac arrest not associated with myocardial infarction. Patients must also be found by electrophysiologic testing to have an inducible tachyarrhythmia that proves unresponsive to medication or surgical therapy . . ."2 Over the ensuing 20 years, the technology has steadily evolved.3 The device has shrunk to less than one-fifth the original size, the number of leads has been reduced, and sensing algorithms refined. Battery life has improved to the point where 5-10 years may elapse before pulse generator replacement is required. Most importantly, the smaller and more elegant design facilitated a much simpler implantation procedure that does not require opening the chest, and can be performed in an ambulatory surgery center under local anesthesia. Technological evolution combined with growing evidence for survival benefit has resulted in progressive relaxation of Medicare coverage criteria. From the beginning, controversy has surrounded the ICD because of debate over whether or not the technology is "cost-effective." Determinants of ICD cost-effectiveness relative to standard care include the cost of the procedure, the survival benefit of the device, and the risk of cardiac arrhythmic death in the target patient population. Over time, the annualized cost of the ICD has decreased due to less invasive surgery and longer battery life. Lower costs make the device more cost-effective. Conversely, broadening of selection criteria has reduced the relative risk of patients receiving the therapy, which tends to reduce cost-effectiveness. The Multicenter Automatic Defibrillator Implantation Trial II (MADIT II) trial evaluated ICD benefit and cost relative to conventional pharmacologic therapy among myocardial infarction survivors with impaired cardiac pumping ability as evidenced by an