Practice News / Events

Prevention of Sudden Cardiac Death and
Improving Quality of Life with Implantable Defibrillators

By Van H. De Bruyn, M.D.

Sudden cardiac death (SCD) is one of the leading killers in the United States and claims over 340,000 deaths per year. Ventricular arrhythmias cause 75-80% of these deaths and commonly occur in patients who have experienced a previous myocardial infraction. Implantable cardioverter defibrillators (ICDs) are extremely effective at treating such arrhythmias, and recent studies, such as the Sudden Cardiac Death in Heart Failure Trail (SCD-HeFT), clearly demonstrate that ICDs significantly decrease a patient’s risk of sudden death compared to medical therapy alone. Furthermore, additional studies, such as the Comparison of Medical Therapy Pacing, and Defibrillation in Chronic Heart Failure (COMPANION), show that selected patients may actually have significant improvement in their quality of life because of a new generation of ICD that has been developed. It has been known for a number of years that a patient who survives a cardiac arrest is at an increased risk of sudden death and, therefore, benefits from ICD implantation. The ability to predict whether a patient without any prior history of an arrest or any arrhythmia would benefit from ICD therapy was much more difficult until recent trials were reported which resulted in expanded indications. The SDCHeFT trial was a landmark study that sought to determine whether rather simple criteria based on a patient’s ejection fraction (EF) would be sufficient to determine whether patients are at high risk for SCD.

The results were so significant that the study resulted in expanded indications for device therapy. This randomized study was the largest primary prevention ICD trial to date and was reported in the New England Journal of Medicine in January 2005. The study enrolled 2,521 patients with mild to moderate heart failure symptoms (New York Heart Association class II or III), a left ventricular EF of 35% or less, and no history of cardiac arrest; it randomly assigned them to ICD placement versus antiarrhythmic drug treatment with amiodarone versus placebo. Importantly, 48% of SCD-HeFT patients had nonischemic cardiomyopathies, allowing investigators to examine a group of patients not previously shown to benefit from ICD therapy. After a median follow-up of 45 months, patients who received ICDs had a statistically significant 23% relative reduction in all-cause mortality (a roughly 10% absolute reduction) versus placebo. Antiarrhythmic drug therapy showed no survival benefit. SCD-HeFT is remarkable because it clearly demonstrates that primary prevention ICD therapy in a diverse group of heart failure patients saves lives. Furthermore, this was achieved utilizing relatively simple inclusion criteria: EF of 35% or less, and mild to moderate heart failure symptoms. The impact of this study on clinical practice has been dramatic, as the need for risk stratification with an eletrophysiogy (EP) study is now largely gone for this patient population. EP studies are still preformed in certain patients, such as those with nonsustained VT and an ejection fraction from 36 to 40%. Patients may also be an ICD candidate with an EF over 35% if they have conditions such as long QT syndrome, congenital heart disease, hypertrophic cardiomyopahy, syncope, or arrhythmogenic right ventricular dysplasia. Scientific trials such as SCDHeFT provide strong evidence that conventional ICDs reduce mortality; however, these trials generally do not show any improvement in patient quality of life. A new generation of ICDs termed “cardiac resynchronization therapydefibrillators” (CRT-Ds) is aimed at both improving quality of life as well as decreasing mortality. Unlike conventional ICDs that pace only the right side of the heart, CRT-Ds have an additional pacing lead that allows them to pace both ventricles. With this simultaneous ventricular pacing, CRT-Ds correct the underlying dyssynchronous ventricular contraction common in failing hearts. Whether this cardiac resynchronization therapy and the resulting improvement in cardiac pumping ability result in better quality of life was studied in the Comparison of Medical Therapy, Pacing, and Defibrillation in Chronic Heart Failure (COMPANION) trail.

The ground breaking COMPANION study examined 903 patients with advanced heart failure (New York Heart Association class III or IV), a depressed left ventricular EF of 35% or less, and left ventricular dyssynchrony, and randomly assigned them to CRT-D versus medical therapy. After a median follow-up of 16 months, patients receiving CRT-D had a statistically significant 36% relative reduction in all cause mortality versus medial therapy alone. CRT-D patients in COMPANION also had better quality of life and exercise capacity. This translates into decreased frequency and duration of hospitalizations for heart failure exacerbations. COMPANION demonstrated for the first time that ICDs could improve both survival and quality of life in selected patients. Based on data from COMPANION and other trials, CRT-D implants have increased dramatically from less than 5% of ICDs implanted in 2001 to roughly half of all ICDs likely to be implanted in the United States this year. Ongoing research on patient selection and advanced cardiac imaging may extend the use of CRT-Ds even further. Currently, CRT-Ds are generally indicated only for patients who remain symptomatic from heart failure despite optimal pharmacologic management with standard treatment including angiotensin converting enzyme inhibitors and beta blockers. Generally, patient eligibility is less restrictive and implantation is less difficult for conventional ICDs.

CRT-Ds generally require moderate to severe heart failure and a QRS duration greater than 120 ms. Length of hospital stay after the implant is typically one day for patients receiving either conventional ICDs or CRT-Ds. Thirty day mortality (based on recent randomized trials) is about 1% for conventional devices and 1.8% for CRT-Ds. Such mortality figures are not unexpected given the severity of the patients underlying heart disease, and they are less than a nationally representative 5.4%, 30 day mortality for comparable patient undergoing coronary artery bypass graft surgery. Both conventional ICDs and CRT-Ds are capable of defibrillation, bradycardia pacing, and antitachycardia pacing, and provide important information on a patient’s overall arrhythmia burden. Only CRT-Ds increase the pumping ability of the heart via cardiac resynchronization therapy; some CRT-Ds also provide diagnostic information pertaining to the patient’s heart failure status.

Primary prevent ICD implantation is generally deferred in patients who have had an acute myocardial infarction (MI) within the previous 40 days or coronary revascularization within the preceding 3 months. Such delay gives the patient’s EF time to improve and, thereby, obviate the need for an ICD. ICDs are generally not implanted in patients with reversible causes of ventricular arrhythmias, projected survival of less than one year from noncardiac disease, or irreversible brain damage. Additional means of further improving risk stratification, such as T-wave was alternans, are also under investigation. While it is now clear that ICDs can improve survival and quality of life, they are probably underutilized in the United States, and it is thought that less than 25% of eligible patients undergo ICD placement nationally. Conventional ICDs and CRTDs are routinely implanted by the electrophysiologists at Heart Clinic Arkansas.

The Device Clinic at HCA follows all ICD (and pacemaker) patients with its devoted staff that is unique to cardiology clinics in Arkansas and provides a high level of expertise to assist the electrophysiologists with patient focused device management. The clinic has been recognized nationally for the high level of care that it provides. Many ICD patients at HCA are now able to be followed at least in part transtelephonically, which greatly enhanced patient convenience and satisfaction. HCA is also unique in Arkansas by having three Board Certified Electrophysiologists with a devoted EP call schedule that allows for 24 hour, 7 day a week availability for any heart rhythm consultations.

* Bardy,G., M.D. (2005). Sudden Cardiac
Death in Heart Failure Trial, January
2005.
* Bradley,D. J.,MD, PhD (2006).
Expanded indications for implantable
defibrillators. Mayo Clinic, v4(2), p.1-2.
* Bristow, M.R., M.D. (2004) Comparison
of Medical Therapy, Pacing, and
Defibrillation in Heart Failure
(COMPANION Trail). May 2005.
* Shah, B. K., MD (2006). Preventing
sudden cardiac death in patients with
ischemic heart disease. New York –
Presbyterian Heart, v109, p.1,7.