Introduction to Pacemakers and Implantable Defibrillators

The Normal Heart Beat

The heart’s electrical system controls the rhythmic contractions that keep the heart pumping and circulating blood throughout your body. These electrical impulses start at the sinus node, a group of specialized heart cells that are the heart’s natural pacemaker. The impulse then travels to the atrioventricular node, where it is then distributed to the main pumping chambers of the heart over a network of specialized nerve-like fibers.

The Slow Heart Beat

If the natural pacemaker or any part of the electrical network fails, even briefly, this could cause the heart to go too slowly or stop. This may be called Bradycardia, Sick Sinus Syndrome or Heart Block. The treatment of slow heart beating is to implant an artificial pacemaker.

The Fast Heart Beat

If your heart goes inappropriately too fast, it is called tachycardia. There are many types of tachycardia, some of which are relatively benign and others that have more serious implications. The Cardiac Electrophysiologist is responsible for evaluating these patients to assess their risk of major complications from tachycardia and to formulate a treatment plan. While some tachycardias are treated with medicines, many are now treated with a catheter procedure, also known as a catheter ablation. Catheter ablation is particularly attractive as it represents curative therapy, replacing the need for long term pill therapy for fast heart rhythms.

The more dangerous types of arrhythmia frequently require implantation of a cardioverter defibrillator (ICD). ICD devices treat potentially life threatening heart rhythm disturbances, providing the patient with full time coverage if a dangerous arrhythmia occurs.

Fainting

Fainting is a symptom where the patient has a brief loss of consciousness and falls due to a lack of muscular tone. There are many synonyms for fainting: falling out, blackout, pass-out, and collapse to mention a few. The medical term for a faint is syncope (also known as neuro-cardiogenic or neurally-mediated syncope). Fainting can be due to many different causes, from slow heart beating to fast heart beating, or even low blood pressure. Although less common, fainting could be due to problems unrelated to the heart. The Cardiac EP is specialized in performing this evaluation and determining the best treatment for recurrent fainting spells.

Sudden Cardiac Arrest

A sudden cardiac arrest most commonly occurs in patients with known heart disease, particularly those patients with weakened hearts. Heart pumping function is commonly assessed by determining the patients Ejection Fraction (EF). A patient’s EF is commonly determined by a heart ultrasound (echocardiogram), or by cardiac catheterization or nuclear heart imaging. Those patients with an EF less than or equal to 35% are particularly prone to Sudden Cardiac Arrest. The EP physician is frequently called upon to assist the primary care physician or general cardiologist to perform a risk assessment for patients with known heart disease to determine a patient’s risk for a sudden cardiac arrest. Once this risk assessment is complete, the EP’s job is to find the best type of preventive treatment, usually implantation of a cardioverter defibrillator. It is alarming to know that 90-95% of cardiac arrest victims do not survive these events unless they have an implantable defibrillator.

Implantable Heart Rhythm Devices

EP physicians are experts in the implantation and follow-up of pacemakers and implantable defibrillators.

St. Jude Medical Pacemaker Information

Boston Scientific Device Information

Medtronic Device Information

Pacemakers

A pacemaker is a device about the size of two stacked half dollars. Within the pacer is a computer and battery. The pacemaker is surgically implanted under the skin, with one or two wires (or leads), threaded through veins and into the heart. The job of the pacemaker is to prevent the heart from going too slowly. The pacer can detect your normal rhythm and works “on demand”, that is, only as much as needed. The EP doctor’s clinic has a small computer that communicates with the pacemaker through the skin and allows your device to be adjusted and personalized for an individual patient’s needs. The pacemaker battery has a 7-10 year life span.

Implantable Defibrillators

An implantable defibrillator (ICD) is a device that is similar to a pacemaker, but in addition to treating slow heart rhythms, it is designed to treat life-threatening fast heart rhythms by overdrive suppression of the tachycardia, or delivering a life saving shock to the heart. The ICD is implanted in a manner similar to a pacemaker. Because of the higher energy needed to shock the heart, the device is about the size of a small pager (2" x 2"” x ½") and its battery life is about 5-7 years.

Cardiac Resynchronization Therapy

More recent developments in implanted device technology have given devices specifically aimed to help people with congestive heart failure (CHF). This therapy is known as Cardiac Resynchronization Therapy (CRT).

CRT is designed for those patients who in addition to the having a high risk for a cardiac arrest also have severe symptoms of congestive heart failure (a weak heart).

A CRT device is implanted much like a pacemaker or ICD, except there is an additional pacing wire placed into a vein on the backside of the heart. This extra wire allows your EP physician to adjust the timing sequence of the contraction of the heart to optimize the heart function, similar to what a mechanic does to adjust the timing of the spark plugs in a car to improve the horsepower. The CRT devices are implanted in addition to the usual heart medicines your doctors use to treat CHF. CRT devices are very successful in helping heart failure patient’s breathe easier, have more energy, and live longer. Cardiac EP’s are also experts in the programming and management of CRT devices. Often, we perform optimization of these devices to offer patients even better results from their CRT devices. This is often performed by using echocardiography (cardiac ultrasound) to guide your EP in special programming of your CRT device.