IMPLANTABLE CARDIAC DEFIBRILLATORS
Interview with Dr. Matthew J. Sandler, MD, FACC, Electrophysiology Department
The implantable cardiac defibrillator (ICD), used to protect patients from ventricular tachycardia, is extremely advanced today, compared to the technology in use just three or four years ago, according to Dr. Matthew J. Sandler of the Electrophysiology Department of Associated Cardiovascular Consultants.
Dr. Sandler said the defibrillators in use now are about the size of a Zippo cigarette lighter. "Defibrillators have dual-chamber pacing for slow heart rhythms and are better designed and equipped to deal with tachycardia and heart failure," he said, adding that indications for the use of the defibrillators have expanded significantly.
"They are indicated now for selected patients who have never had a catastrophic cardiac event such as sustained ventricular tachycardia," Dr. Sandler said. Furthermore, MADIT-II (Multicenter Automatic Defibrillator Implantation Trial), reported in the New England Journal of Medicine in March 2003, shows a benefit in mortality for patients whose ejection fraction is 30 percent or less and who have a history of myocardial infarct.
The study involved 1,232 such patients who were randomly assigned either to receive a defibrillator or to get conventional drug treatment. The results showed a 31-percent reduction in the risk of death in the defibrillator patients compared to the patients who received conventional treatment.
An implantable defibrillator is also indicated for patients with heart failure, a low ejection fraction, and intraventricular conduction delay (i.e., wide QRS on ECG).
"If patients are on optimal medical therapy with persistent heart failure symptoms, they may qualify for a biventricular defibrillator, with a lead going through the coronary sinus to the left ventricle. This resynchronization therapy provides more organized contraction of ventricles, more cardiac output, and improvement of symptoms," Dr. Sandler said. In some cases, he explained, patients' anatomy may not be amenable to the transvenous lead. Therefore, the lead may be placed in an epicardial position by a surgeon.
Dr. Sandler advises that patients who evidence non-sustained ventricular arrhythmia on routine monitoring but whose ejection fraction is abnormally low but greater than 30 percent should most likely undergo electrophysiology studies for risk stratification. Patients who have had inducible sustained ventricular tachycardia should receive a defibrillator.
Dr. Sandler said that current data no longer support serial drug testing with antiarrhythmic drugs for treatment of malignant ventricular arrhythmias, but antiarrhythmics still have a place in patients who refuse or are otherwise unable to undergo a defibrillator implant. He said that not all sustained ventricular arrhythmias are associated with prior myocardial infarction or sudden death. For example, right ventricular outflow tract tachycardia, which can occur in otherwise normal hearts, can be treated with radiofrequency ablation and is curative.
"These patients have excellent prognoses," Dr. Sandler said.
Implantable cardiac defibrillators are warranted in patients with a history of:
- Anterior myocardial infarct and ejection fraction less than 30 percent.
- Spontaneous ventricular tachycardia/ventricular fibrillation not due to reversible causes (i.e. electrolyte abnormalities).
- Inducible ventricular tachycardia during electrophysiology test.
- Congestive heart failure, Class II or III symptoms, ejection fraction less than 30 percent and wide QRS on ECG (biventricular device).