Cardiac resynchronization therapy (CRT)
CRT & CRTD
Cardiac resynchronization therapy (CRT) is an important new treatment for symptoms associated with congestive heart failure (CHF) caused by weakening of the heart muscle (cardiomyopathy). The idea behind CRT is to restore the pumping action of the ventricles. This can be done by overcoming the delay in electrical conduction (also called resynchronization).
This is accomplished by means of a unique type of cardiac pacemaker. Common pacemakers are typically used to prevent symptoms associated with excessively slow heartbeats. The pacemaker continuously monitors the patient's heartbeat and delivers a tiny, imperceptible electrical charge to stimulate the heartbeat when necessary. Most pacemakers typically have 2 electrodes (or leads), one in the right atrium and one in the right ventricle, which permit the pacemaker to maintain the normal coordinated pumping relationship between top and bottom of the heart. These leads are connected to a battery pack (pulse generator) placed under the skin in the upper chest. In addition to the 2 leads used by a common pacemaker, CRT pacemakers have a third lead that is positioned in a vein on the outer surface of the left ventricle. This allows the CRT pacemaker to simultaneously stimulate the left and right ventricles and restore a coordinated and synchronous pumping action.
Cardiac Resynchronization Therapy Defibrillators (CRT- Ds)
The implant of a CRT-D system typically requires the use of a cardiac resynchronization therapy pulse generator and three electrodes, or leads. The three leads monitor and deliver electrical stimulation to the right atrium, right ventricle, and left ventricle. As in conventional implantable cardioverter -defibrillator (ICD) procedures, a defibrillation lead is inserted into the subclavian vein and positioned in the right ventricle. In some cases, the cephalic or internal jugular vein may be used as an alternative to the subclavian vein.
In addition, a CRT - D system requires the implantation of a third lead into the coronary venous system of the left ventricle to coordinate, or resynchronize, ventricular contractions. This left ventricular lead is inserted into the subclavian vein, introduced into the coronary sinus and advanced into a coronary vein located on the exterior wall of the left ventricle.