What has been the evolution of the implantable cardioverter-defibrillator (ICD) in cardiac medicine?

Updated: Feb 13, 2017
  • Author: Daniel M Beyerbach, MD, PhD; Chief Editor: Jeffrey N Rottman, MD  more...
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Answer

The implantable cardioverter-defibrillator (ICD) has revolutionized the treatment of patients at risk for sudden cardiac death due to ventricular tachyarrhythmias. Initially introduced in humans in 1980 [3] and approved by the US Food and Drug Administration (FDA) in 1985, the ICD has evolved from a treatment of last resort to a first-line treatment and prophylactic therapy for patients at risk for ventricular tachycardia (VT) or ventricular fibrillation (VF). [1] Michel Mirowski conceived of and developed the ICD almost single-handedly. Prompted by the sudden death of a colleague, Mirowski conceived of an automatic, fully implantable defibrillator. Initially, lead systems were epicardial, requiring a thoracotomy for implantation, and pulse generators were large and bulky, requiring abdominal implantation.

Remarkable technologic advances have made ICDs easier and safer to implant and better accepted by patients and physicians. The development of transvenous lead systems, more effective biphasic defibrillation waveforms, and "active can" technology allows implantation in nearly all patients without the need for thoracotomy. [4]

Significant miniaturization of the capacitors and other components has reduced the size of the pulse generator tremendously, permitting subcutaneous pectoral implantation in most patients. [5, 6] A new generation of subcutaneously implanted devices has obviated the need for transvenous leads in a select group of patients. On September 28, 2012, the FDA approved the first subcutaneous ICD (SCD) for ventricular tachyarrhythmias which allows the lead to be placed under the skin rather than through a vein into the heart. [7]  These devices are again larger, as there is a requirement for increased current delivery and, in their present form, have very limited pacing capabilities.

In addition to being considerably smaller than early generations of ICDs, current ICDs have markedly progressed in their therapeutic and diagnostic functions. Early devices were simple “shock boxes,” offering only high-energy shocks when the patient's heart rate exceeded a cut-off point. Diagnostic information was limited to the number of shocks delivered. Current devices offer tiered therapy with programmable antitachycardia pacing schemes, as well as low-energy and high-energy shocks in multiple tachycardia zones.

Dual-chamber, rate-responsive bradycardia pacing is now available in all ICDs, and sophisticated discrimination algorithms minimize shocks for atrial fibrillation, sinus tachycardia, and other non–life-threatening supraventricular tachyarrhythmias. Diagnostic functions, including stored electrograms, allow for verification of shock appropriateness. Device battery longevity has also increased; early devices lasted 2 years or less, while current devices are expected to last 8 years or longer.


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