| Abstract: | ![]()
Since February, 1980 nearly 200 automatic cardioverter - defibrillators have been implanted in patients with malignant ventricular arrhythmias. The currently-employed device weighs 298 grams and occupies a volume of 162 cm3. There are two defibrillation electrodes which also serve as sensors: one, an intravascular catheter placed in the superior vena cava at the level of the right atrium; the other, a flexible rectangular patch placed extrapericardially over the apex of the heart. Additionally, there is a bipolar right ventricular electrode for rate counting and R-wave synchronization which will eventually be used for pacing as well. The unit is powered by lithium batteries with a projected monitoring life of three years, or the capability of discharging approximately 100 times. The arrhythmia detector activates the cardioverter -defibrillator about 15 to 20 seconds after diagnosing a "treatable" arrhythmia, identified on the basis of a striking absence of isoelectric potential segments characteristic of ventricular fibrillation and many ventricular tachycardias. The diagnosis also requires fulfillment of individually-programmed heart rate criteria. If the initial discharge of 25 joules is ineffective, the device will recycle as many as three times with a final pulse of up to 42 joules. Of the twelve nonsurvivors among the initial 52 implantees who underwent implantation through September, 1982, only four deaths were unwitnessed and considered to be sudden and arrhythmic; the other eight deaths were due to heart failure or unrelated causes. Thus, from a predicted mortality of 48% in the same group of patients if the automatic defibrillator had not been implanted, the "sudden death" mortality was reduced to 8.5%. |
