The problem it aimed to solve
Sudden cardiac death is often caused by ventricular fibrillation, a chaotic electrical state in which the heart quivers instead of pumping. Hospitals could treat it with a shock from an external machine if it was given within minutes, but a patient at home had no such help. The idea behind the implantable cardioverter-defibrillator, usually called an ICD, was to put a monitor and shock generator inside the patient so that it could detect the rhythm and treat it automatically. In effect it was a tiny ECG machine joined to a treatment unit, an early example of closed-loop systems in medicine.
Mirowski’s idea
Michel Mirowski, a cardiologist born in Poland who worked in Israel and then at Sinai Hospital in Baltimore, is the person most closely associated with the ICD. According to the usual account, the project began after the death of a colleague from a heart rhythm disorder in the late 1960s. Mirowski began to ask whether a device could watch for the dangerous rhythm and shock it automatically. He worked with Morton Mower, and with the engineer Stephen Heilman and others, in Baltimore.
Many cardiologists at the time were skeptical. A prominent objection was that an implanted device would fire at the wrong moment, or fail to fire at the right one, and that the population likely to benefit was too small and unpredictable to justify the risk. Some experts argued that sudden death could not be prevented in any practical way. The team continued anyway, and credit for the early work is shared between several researchers.
From laboratory to animal tests
The early work consisted of building a sensing circuit that could recognize ventricular fibrillation, a power source able to deliver a strong shock and a way to store energy between uses. The first devices were not tiny. They were built in the 1970s with components of the period, relied on large batteries and capacitors (storing enough energy for a shock was a hard energy storage problem in miniature), and were too big to place in the chest. Trials in dogs in the early 1970s showed that the principle worked: a device could detect fibrillation and shock the heart back to normal rhythm.
Industrial partnership was needed to produce hardware suitable for people. A medical device company took on development, and the first versions were designed for the abdomen, with the generator implanted below the ribs and connected to the heart by wires.
The first human implants
The first human implant in the United States is usually dated to 1980. It was performed at Johns Hopkins Hospital in Baltimore, with the cardiac surgeon Levi Watkins Jr. credited for the operation, in a patient who had survived repeated episodes of cardiac arrest. Accounts give February 1980 for this operation, though they differ in some of the smaller details. Early devices used implanted electrodes in the form of patches or coils sewn on the surface of the heart, which meant opening the chest and made the surgery heavier than a pacemaker implant. Those first units could shock a dangerous rhythm but offered few of the programmable features seen later.
After initial clinical trials, the US Food and Drug Administration approved the device in 1985. That approval is often treated as the date when the ICD became a standard product, though uptake was gradual and use was initially limited to patients who had survived cardiac arrest.
What the first devices could and could not do
The earliest ICD was largely a one-answer device: when it detected fibrillation, it delivered a shock. Later models added the ability to treat a dangerous but organized fast rhythm with lower-energy pulses, known as cardioversion, and some could pace the heart if it slowed after a shock. The word “cardioverter” in the name refers to this wider range of therapies, though the first model was mainly about defibrillation.
The early generation also had problems. The shock is painful, accidental shocks occurred, batteries drained faster than expected and the surgery had its own risks. Over time, programmable settings, better detection and smaller sizes addressed many of these concerns. How the units shrank and gained transvenous wires is a separate chapter, as is the longer history of external defibrillation that came first.
Recognition and legacy
Mirowski received professional honors in the 1980s, though he died in 1990, when ICD use was still growing. The device he championed went on to be implanted in very large numbers worldwide. Because its path involved many people, simple statements such as “Mirowski invented the ICD” are best read as shorthand for his leading role.
What to remember
The ICD is an example of a device whose idea was widely doubted until persistent evidence changed minds. Its history shows how a clinical problem, engineering effort and patient trials combined. Modern devices rely on integrated circuits and improved battery chemistry that were not available to the first team, and much of the progress consisted of making each part smaller and more reliable. This article is history only and is not medical advice; decisions about any heart device belong to patients and their physicians.