The weakened heart first attempts to compensate for the increased requirements caused by cardiac disease by pumping more strongly (compensation). This makes the heart muscle not only larger, but also thicker and stronger. These changes in the cardiac structure lead to the left and right halves of the heart no longer being able to contract in coordination.
The muscle cells of the heart slowly shrink and form connective tissue that delays the conduction of electrical excitations. The result is cardiac rhythm disturbances. If the heartbeat becomes too irregular at some point, the pumping power of the heart falls and with it the blood and oxygen supply to the body.
Around one-third of all cardiac failure patients suffer from rapid or slow cardiac rhythm disturbances. Electrocardiogram (ECG) examinations often show a broadened curve complex and an altered curve shape, which are diagnosed by the doctor as left bundle branch block.
The left ventricle does not contract with enough speed or coordination. Several areas of the left ventricle have already completed the contraction, while the other areas have not even started. The uneven contraction of the chambers leads to a swinging motion of blood in the chambers and reduces the pumping output of the heart.
Patients with disturbed stimulus conduction therefore often benefit from implantation of a system for cardiac resynchronization therapy (CRT). This harmonizes the interaction of both chambers by constantly delivering electrical pulses. The heart no longer controls the pumping motion of the chambers. It is now controlled artificially by the CRT device. The controlled interaction of the heart chambers allows the chambers to contract synchronously, which improves the pumping output of the heart.
Cardiac resynchronization therapy (CRT): Devices with an integrated pacemaker or defibrillator
CRT devices are available with defibrillator function (CRT-D) or pacemaker function (CRT-P) depending on whether the patient’s heart beats too rapidly or too slowly. The majority of congestive heart failure patients suffer from excessively fast rhythm disturbances and are therefore at a risk of dying from sudden cardiac death. The damaged heart muscle often triggers misfires that disturb the excitation sequence and, in the worst case, trigger a chain reaction ending in ventricular fibrillation. CRT systems with an integrated defibrillator (CRT-D) not only synchronize the heartbeat, but also treat life-threatening ventricular fibrillation.
Implantation of a CRT system
The implantation of a CRT system is the same as for a pacemaker or defibrillator (ICD). The procedure can be performed under local anesthesia or general anesthesia.
The CRT device is inserted through a small incision on the left side of the body. The physician pushes three thin, insulated cables (leads) from the collarbone (clavicle) to the heart through a punctured vein. The leads are positioned in the heart using an X-ray screen. The physician pushes the leads through a vein and into the right atrium and the right chamber (ventricle). The left chamber must, however, be stimulated by a cardiac vein. For this purpose, the lead is inserted into the coronary artery so that it stimulates the left chamber practically from the outside.
If the leads are correctly placed, the physician connects them to the CRT device and tests them. The settings of the CRT system are then optimized for the patient—including the home monitoring function for remote patient care using telemedicine, if applicable. Once everything has been done and is in order, the physician hides the implanted device in a “pocket” in the pectoral muscle below the collarbone (clavicle) and sutures it with a few stitches.
Components of a CRT system
Systems for cardiac resynchronization therapy (CRT) consist of a pulse generator with a battery and circuitry, as well as three leads. CRT devices with an integrated defibrillator function also contain a capacitor for charging the shock energy. The leads connect the implanted device to the right atrium and both chambers. They record the cardiac rhythm and control the pumping activity.