Cardiac resynchronization therapy

Cardiac resynchronisation therapy (CRT or CRT-P) is the insertion of electrodes in the left and right ventricles of the heart, as well as on occasion the right atrium, to treat heart failure by coordinating the function of the left and right ventricles via a pacemaker, a small device inserted into the anterior chest wall. CRT is indicated in patients with a low ejection fraction (typically 120 ms. The insertion of electrodes into the ventricles is done under local anesthetic, with access to the ventricles most commonly via the subclavian vein, although access may be conferred from the axillary or cephalic veins. Right ventricular access is direct, while left ventricular access is conferred via the coronary sinus (CS). CRT defibrillators (CRT-D) also incorporate the additional function of an implantable cardioverter-defibrillator (ICD), to quickly terminate an abnormally fast, life-threatening heart rhythm. CRT and CRT-D have become increasingly important therapeutic options for patients with moderate and severe heart failure. CRT with pacemaker only is often termed "CRT-P" to help distinguish it from CRT with defibrillator (CRT-D). The key indication for CRT is left bundle branch block (LBBB) of the heart, a cardiac abnormality leading to delayed left ventricular contraction. LBBB causes a QRS prolongation of ≥120 ms on the electrocardiogram, contributing to poor left ventricular coordination and reduced systolic function, thereby reduced ejection fraction (