Implantable cardioverter-defibrillators can prevent sudden cardiac arrest. Now more people can benefit.
Miniature electronic devices called implantable cardioverter-defibrillators (ICDs) that detect and terminate rapid, irregular beats in the heart’s lower chambers (ventricles)—a problem known as ventricular fibrillation—can be a lifesaver for people susceptible to deadly arrhythmias With recent technological advances, these devices are even safer and more available.
Wireless ICD devices
One breakthrough is an ICD placed under the skin in the chest that can sense and correct abnormal heart rhythms without the use of wires, called leads, implanted into the heart muscle. “There are huge issues with leads,” says Dr. Jagmeet Singh, a cardiologist at Massachusetts General Hospital and associate professor of medicine at Harvard Medical School. “They can fracture, the wires may need to be extracted and replaced over time, and patients can get infections. Now, a patient who might not have been an ICD candidate in the past because of a high risk of lead infections would be a shoo-in for the device.” Wireless devices may also have applications for younger people with congenital heart diseases. These individuals may need several ICD devices over their lifetime, so leadless technology could make ICDs more feasible for this group.
One downside to the design is that, without wires to the heart, the device can’t restore a normal rhythm after it delivers a shock. Therefore, the heart must return to a normal pattern on its own. However, Dr. Singh predicts that this feature will be incorporated as the technology evolves.
Who may need an ICD?
The most common cause of ventricular fibrillation is heart muscle damage from a heart attack or advanced heart failure. Inherited heart defects and other diseases that damage the heart may also lead to ventricular fibrillation.
Other advances in the safety and functionality of ICDs involve refinements in how the devices are programmed. Says Dr. Singh, “Normally we would intervene with a shock within 6 to 7 seconds after the start of an arrhythmia. But some data showed that if you stretch out the interval to 15 or 20 seconds, the arrhythmia often self-terminates so you don’t need to deliver a shock.” Shocks are highly uncomfortable, and people who don’t get the jolts ultimately fared better in the long run, he adds.
For standard ICDs that use leads, a technique called antitachycardia pacing can also help avoid unwanted shocks. (Tachycardia means the heart is beating too fast.) When the mechanism senses the heart rate escalating to about 200 beats per minute (bpm), it sends out a signal to bump the heart rate to 210 bpm. This shortcuts the heart’s electrical circuitry and intercepts the accelerating beat. As a result, the heart is often able reset on its own. If the heart keeps racing after one or two override attempts, the ICD will deliver a shock. However, this technology successfully avoids shocks about 85% of the time.