Defibrillators are appropriate for only a minority of patients with HCM who have important risk for sudden death. The criteria for placement of ICDs in patients with HCM are and involve, in every case, individual judgement.
The most serious arrhythmias that HCM patients can experience are rapid and prolonged venticular arrhythmias. During these sustained, ventricular arrhythmias, there is frequently a fall in blood pressure and even unconsciousness. Unless terminated, some can lead to fatal consequences. These arrhythmias require prompt termination which can be most readily accomplished by the administration of an electrical shock passed across the chest. Outside the hospital, this might be accomplished by an ambulance team who place external paddles on the chest and deliver a shock. Electrical defibrillation is also applied with an implantable device. This device, permanently available to monitor a patient's rhythm, can automatically and in a short period of time, deliver lifesaving electrical energy directly to the heart muscle. Patients who are deemed high risk for the development of these dangerous arrhythmias will thus often be treated with an implanted device so that they are permanently protected without need for intervention by bystanders or emergency personnel.
These devices are called implantable cardioverter defibrillators (ICD). These are implanted much the way permanents pacemakers are. Using a large vein that passes underneath the collar bone, a wire or lead passed intravenously into the right side of the heart.This lead is connected to the device which is then buried under the skin beneath the collar bone. This device monitors and records the electrical signals from within the heart and tells the device when the heart has gone into a rapid, dangerous arrhythmias. When this device detects a dangerous arrhythmia, it delivers enough electrical energy through the lead into the heart that it resumes its normal electrical activity. The entire process of detection and termination of this potentially fatal arrhythmia can last only a few seconds. Because this period of time is so brief, the patient usually comes to no harm. The ICD can be highly effective and often life saving in patients who may otherwise succumb to dangerous electrical conditions.
Because the decision to implant an ICD has life-long implications, detailed discussion its benefits and risks are essential before the procedure is scheduled.