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Cardiac resynchronization therapy
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<p>Cardiac resynchronisation therapy (CRT or CRT-P) is the insertion of <a href="/facts/Electrode/251PaKX8">electrodes</a> in the left and right <a href="/facts/Ventricle_(heart)/FCzV1xm7">ventricles</a> of the heart, as well as on occasion the right <a href="/facts/Atrium_(heart)/eYNg8Vw2">atrium</a>, to treat <a href="/facts/Heart_failure/7fckX3Jm">heart failure</a> by coordinating the function of the left and right ventricles via a <a href="/facts/Pacemaker/b90Qt8ND">pacemaker</a>, a small device inserted into the anterior chest wall. </p><p>CRT is indicated in patients with a low <a href="/facts/Ejection_fraction/uWHyCe9j">ejection fraction</a> (typically <35%) indicating <a href="/facts/Heart_failure/7fckX3Jm">heart failure</a>, where electrical activity has been compromised, with prolonged <a href="/facts/QRS_complex/Pehk2szJ">QRS</a> duration to >120 <a href="/facts/Millisecond/xHCyv235">ms</a>. </p><p>The insertion of electrodes into the ventricles is done under <a href="/facts/Local_anesthetic/5aA2qews">local anesthetic</a>, with access to the ventricles most commonly via the <a href="/facts/Subclavian_vein/SKSKEjRy">subclavian vein</a>, although access may be conferred from the <a href="/facts/Axillary_vein/kjFF8gxj">axillary</a> or <a href="/facts/Cephalic_vein/13dLcyr4">cephalic veins</a>. Right ventricular access is direct, while left ventricular access is conferred via the <a href="/facts/Coronary_sinus/YDLtYx9Q">coronary sinus</a> (CS). </p><p>CRT defibrillators (CRT-D) also incorporate the additional function of an <a href="/facts/Implantable_cardioverter-defibrillator/b5U5lH8K">implantable cardioverter-defibrillator</a> (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). </p>