External DC defibrillator

The external DC defibrillator emerged from a fundamental insight: alternating current, which Claude Beck had used for the first successful defibrillation in 1947, was unpredictable and often damaged the heart. The adjacent possible for a better approach required understanding cardiac electrophysiology at a level that only became possible in the 1950s, when researchers could systematically study how electrical impulses restored normal rhythm.

Paul Zoll at Harvard demonstrated closed-chest pacing and defibrillation in 1952, proving that patients didn't need open-heart surgery to receive electrical therapy. But AC defibrillation remained problematic—it required high energy, caused burns, and sometimes induced worse arrhythmias than it cured.

The breakthrough came from understanding that ventricular fibrillation could be stopped by a single, precisely timed direct current pulse. Soviet researcher Naum Gurvich had demonstrated DC defibrillation in animals by 1939, but his work remained unknown in the West during the Cold War. Bernard Lown at Harvard independently developed the technique, demonstrating in 1962 that DC shocks were safer, more reliable, and required lower energy than AC.

Lown's DC defibrillator used capacitor discharge—storing electrical energy and releasing it in a controlled pulse—rather than directly applying wall current. This allowed precise control of the waveform, energy level, and timing. The device could be synchronized with the patient's heartbeat to avoid vulnerable periods when shocks might trigger, rather than terminate, fibrillation.

The competitive exclusion of AC by DC defibrillation happened rapidly. By the mid-1960s, DC had become the standard for both cardioversion (restoring normal rhythm from irregular but organized rhythms) and defibrillation (stopping chaotic ventricular fibrillation). The technology enabled coronary care units, where continuous monitoring and rapid defibrillation transformed heart attack survival rates.

The path dependence established by Lown's work persists: modern automated external defibrillators use the same fundamental principle of capacitor-discharged DC pulses, refined but not fundamentally changed from the 1960s breakthrough.