What is cardiac resynchronization therapy?
It is a treatment for patients with advanced heart failure. It is indicated in patients with severe systolic dysfunction (the contractile force of the heart is severely impaired), with dyspnea (shortness of breath) for moderate or small efforts and a disorder in the intrinsic conduction system of the heart at the level of the ventricles (manifested by a wide QRS complex, usually left bundle branch block).
These patients have a heart whose contractility is severely impaired and in addition the different segments of their ventricles contract asynchronously, which further decreases the efficiency of cardiac contraction. CRT has been shown to improve cardiac function, quality of life and exercise capacity of patients, reduce hospital admissions and improve survival. Thanks to this treatment, patients can live longer and better.
How does it work?
It is a cardiac stimulation device that has the capacity to send an electrical stimulus to both ventricles, thus improving the lost synchrony in the cardiac contraction of these patients. Resynchronization devices can be pacemakers (they only prevent slow rhythms) or defibrillators (in addition to preventing slow rhythms, they can terminate malignant ventricular arrhythmias, which can lead to sudden death of the patient).
What is the difference with a pacemaker or a conventional defibrillator?
Resynchronizers have the capacity to stimulate the left ventricle. Conventional devices can stimulate and sense in one or two cardiac chambers (the right atrium and right ventricle), but resynchronizers can stimulate in three cardiac chambers (right atrium and both ventricles), hence the name tricameral. The resynchronizer has a third electrode that stimulates directly in the left ventricle. This allows the device to stimulate simultaneously in both ventricles and synchronize the contractility of both. This electrode is usually implanted through the coronary sinus, which is a small vein that surrounds the left ventricle around the mitral annulus. The implantation of this electrode requires special tools and the physician who performs it must know the specific technique.
Which patients can receive this therapy?
Up to 30% of patients with advanced heart failure present intraventricular conduction disturbances, which leads to an asynchrony in normal ventricular contractility and deterioration of cardiac function. CRT is indicated in these patients. CRT is a coadjuvant treatment to pharmacological treatment in patients with advanced heart failure, with systolic dysfunction and electrical asynchrony. Electrical asynchrony is due to a disease of the specific system of the electrical conduction system at ventricular level, manifested by a bundle branch block. Improvement is more evident in patients with left bundle branch block, but CRT may also be indicated in patients with right bundle branch block. A subgroup of patients in whom CRT is indicated is those patients who are pacemaker-dependent and have left ventricular systolic dysfunction.