We are now in the third generation of these devices. First-generation ICDs merely shocked, and the decision invoked was based on a simple heart-rate threshold. Second-generation ICDs expanded the logical decision and used heart rate derivatives (rate of change, stability of fast rate duration) for improved specificity. Third-generation devices offer tier-therapy (pacing, low energy cardioversion, and defibrillation), as well as ventricular tachycardia (VT) and ventricular fibrillation (VF) zones to further refine therapeutic choice.

Yet ICDs employ ventricular sensors alone for detection strategy, continue to realize false shocks as high as 40% of all delivered, and are experiencing patient dissatisfaction with false shock aggravation and early battery depletion. Microprocessors and analog-to-digital converters are now incorporated into the miniaturized circuitry, giving promise of more sophisticated signal processing techniques to address the arrhythmia detection schemes possible in next-generation ICDs.

This paper describes the historical approach, gives details of ongoing studies in modern research laboratories, and predicts changes in technology which can be expected to dramatically improve the safety and efficacy of ICDs of the future.