Cardiac resynchronization therapy (CRT) is an important adjunct to medical therapy of heart failure. Necessary preconditions for a successful application of CRT are mechanical and electrical dyssynchrony of the left ventricle. Small clinical studies with a short follow-up time in patients with advanced systolic heart failure, structural heart disease, low LV ejection fraction (< 35 %) and a wide QRS complex (> 150 ms) demonstrated the beneficial effect of bi-ventricular pacing showing improvement of cardiac function and reduction of heart failure symptoms within a few weeks or months after initiation of CRT.
Large randomized trials (COMPANION and CARE-HF) in patients with advanced heart failure showed a decrease of overall mortality and less heart failure hospitalizations besides improvement of NYHA class. ICD backup in CRT devices proved to be important to reduce sudden arrhythmic death. Since the benefit of decreased overall mortality is limited in severe heart failure, three important trials (REVERSE, MADIT-CRT and RAFT) were launched in order to test the effect of CRT in patients with mild or asymptomatic heart failure (NYHA class I and II). The results of these trials with different study designs, follow-up time and primary endpoints demonstrated that significant „reverse remodeling“, reduction of overall mortality and decrease of heart failure hospitalization can be best achieved in patients with left bundle branch block (LBBB) configuration, a broad QRS complex ≥ 130 ms, sinus rhythm, female gender and non-ischemic cardiomyopathy.
Therefore, prevention of heart failure progression is easier to achieve at an early stage of heart failure by using bi-ventricular pacing with ICD backup. The long-term benefit of CRT in patients that fulfill the effectiveness criteria of CRT is more pronounced in patients with mild- instead of advanced heart failure.
Kernaussagen
Nachdem bei schwerer Herzinsuffizienz (NYHA Klasse III/IV) gezeigt werden konnte, dass eine CRT die Herzinsuffizienzsymptomatik vermindert, die funktionelle Leistung steigern kann und einen günstigen, wenn auch nur mäßigen Effekt auf die Gesamtsterblichkeit, die kardiale Mortalität und die Hospitalisierung wegen Herzinsuffizienz hat, lag es nahe, den Effekt einer biventrikulären Stimulation auch bei einer leichteren Form der Herzinsuffizienz (NYHA Klasse II und I) und damit einer weniger fortgeschrittenen Insuffizienz zu untersuchen.
In 3 großen, randomisierten Studien (REVERSE, MADIT-CRT und RAFT) konnte bewiesen werden, dass eine CRT bei leichter Herzinsuffizienz die Gesamtsterblichkeit senken, die Herzinsuffizienzereignisse vermindern und besonders ein „reverse remodeling“ der Ventrikeldilatation erreichen kann, das mit einer deutlichen Steigerung der linksventrikulären Auswurffraktion einhergeht.
Dieser positive Effekt einer CRT bei leichter Herzinsuffizienz ist auf Patienten mit einer stark eingeschränkten LVEF ( ≤ 30 %) und einen LSB mit einer QRS-Breite im EKG ≥ 130 ms beschränkt – unabhängig vom Vorliegen einer KHK oder einer nicht ischämischen Kardiomyopathie.
Voraussetzung für die günstige Wirkung der CRT auch bei leichter Herzinsuffizienz ist eine optimale medikamentöse Therapie der Insuffizienz.
Selbst wenn eine CRT nur für etwa die Hälfte aller Patienten mit einer systolischen Herzinsuffizienz indiziert sein wird, erscheint sicher, dass die Verhinderung des Fortschreitens der Herzinsuffizienz in einem weniger fortgeschrittenen Stadium der myokardialen Schädigung wichtiger ist als die Implantation eines CRT-Systems in einem weit fortgeschrittenen Stadium mit voraussichtlich nur geringer und kurzzeitiger Milderung der Symptome und bescheidener Verbesserung der Prognose.
Je früher ein unbehandelter, stets progredienter „Remodeling“-Prozess des Herzens durch CRT aufgehalten werden kann, desto größer wird die Möglichkeit sein, eine annähernd normale kardiale Pumpfunktion wiederherzustellen.
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