Implantable Cardiac Devices

PERMANENT PACEMAKER

A PPM may have as few as one lead or as many as three leads. A lead is a specialized wire that conducts electrical impulses. A one-lead device is connected to the right atrium of the heart and provides electrical impulses to pace the heart at a set rate. This device would be used in the subset of patients who have sinus node disease without any other conduction disease from the atria to the ventricles. A two-lead device will have both a right atrial and right ventricular lead, which allows for more complex management. The right atrial lead can sense atrial activity and use that to cause pacing in the ventricles via the right ventricular lead. This would be helpful in a patient with heart block in which the native impulse does not reach the ventricles. In a patient with sinus node dysfunction and lack of intrinsic atrial activity, along with disease in the conduction system, the PPM can send an impulse to the atria via the right atrial lead and then send an impulse to the ventricles via the right ventricular lead. A PPM with three leads is usually referred to as a cardiac resynchronization therapy (CRT) device. It has a right atrial lead, a right ventricular lead, and a coronary sinus lead on the left side. Overall, it functions similarly to a two-lead PPM with the additional benefit being that the coronary sinus lead will send an impulse to the left ventricle, while the right ventricular lead also activates the right ventricle thereby allowing both ventricles to contract simultaneously. A CRT device is typically used in patients with heart failure who also have abnormal conduction to the ventricles. ^,

IMPLANTABLE CARDIOVERTER DEFIBRILLATOR

An ICD may also have one, two, or three leads, which are progressively in the right atrium, right ventricle, and coronary sinus, respectively. The main function of ICD is to detect ventricular tachycardia or ventricular fibrillation and deliver a lifesaving “shock” or “defibrillation” to reset the electrical rhythm of the heart back into normal sinus rhythm. A “shock” is a high-energy electrical impulse generated by the battery and discharged by the capacitor in the device. For ventricular tachycardia, the device may attempt what is referred to as anti-tachycardia pacing in an effort to terminate the arrhythmia without delivering a shock. The anti-tachycardia pacing function delivers a rapid heart rate that can overtake the ventricular arrhythmia. If anti-tachycardia pacing is not effective and the ventricular tachycardia persists, the device will deliver a “shock.” Newer-generation ICD devices with the appropriate leads may also function as a PPM or a CRT device. ^,

Both PPM and ICD can be interrogated by the electrophysiologist to evaluate the device’s health, including its battery life, and to review any abnormal cardiac rhythms that were detected. In the hospital or clinic, the interrogation is done with an external computer that uses a wireless wand peripheral that is placed over the device to obtain information. Newer devices can be remotely interrogated as they first sync to a remote monitor that the patient has in his/her possession, which subsequently transmits data to the physician’s office. A typical battery life for a device is up to 10 years, and when it runs low, the device is replaced entirely with the battery (the leads, which are implanted in the heart, stay in place and are reattached to the new device).