Cardiac Resynchronization Therapy In Heart Failure: Recent Advances And New Insights Bhatia V, MD*, Bhatia R, MD?, Dhindsa S, MD?, Virk A, MD, MPH? * Department of Medicine,?Mercy Hospital of Buffalo, Buffalo, NY, 14220,USA. ? State University of New York, Buffalo, NY, 14220,USA.

摘要

Newer non-pharmacological therapies for heart failure are being evaluated for patients of congestive heart failure (CHF). Mechanical support with left ventricular assist devices and heart transplantation are reserved for the minority of patients who have severely decompensated heart failure . Despite these therapeutic advances, it is generally accepted that current therapies do not adequately address the clinical need of patients with heart failure, and additional strategies are being developed. Cardiac resynchronization therapy (CRT) is a new modality that involves synchronization of ventricular contraction and has shown a lot of promise in managing symptomatic patients of CHF who are on optimal medical therapy and have interventricular conduction delay (IVCD). It has improved exercise tolerance and NYHA functional class in such patients in sinus rhythm and a recent meta-analysis has also shown mortality benefits in CHF. Recently benefits of CRT have also been observed in CHF patients who do not have wide QRS complexes on electrocardiogram (EKG). It has also been shown to benefit drug refractory angina in CHF. Recent studies have also focused on the combined use of CRT and implantable cardioverter defibrillator (ICD) and it has shown encouraging results. Our aim in this descriptive review is to define practice guidelines and to improve clinicians' knowledge of the available published clinical evidence, concentrating on few randomized controlled trials. Introduction Approximately 30 percent of patients with cardiomyopathy have IVCD such as left or right bundle-branch block, leading to loss of coordination of ventricular contraction 1 , 2 . This dyssynchronous pattern of ventricular contraction is believed to contribute to the pathophysiology of heart failure, reducing the already diminished contractile reserve of the heart 3 . Specifically, dyssynchronous contraction exacerbates inefficient use of energy by the heart (a process termed mechanoenergetic-uncoupling 4 ). The finding of IVCD has been associated with clinical instability and an increased risk of death in patients with heart failure 5 , 6 , 7 , 8 . Accordingly, the idea that cardiac-pacing technology might be used to restore the synchrony of ventricular contraction has been of theoretical interest for over a decade. Pacing modalities that utilize biventricular (BiV) or left ventricular (LV) stimulation to optimize cardiac pump function through synchronization of ventricular contraction are referred to as resynchronization or ventricular resynchronization therapies 2 . Resynchronization therapies can be present in a single device, in a device equipped with bradycardia pacing support, or incorporated into an ICD 9 . CHF and IVCD The most common causes for an IVCD in patients with heart failure are delayed left ventricular activation and left bundle branch block (LBBB). Impaired left ventricular function is also seen in otherwise normal subjects with isolated LBBB 10 . Approximately 20 to 30 percent of patients with symptomatic heart failure have an IVCD. 2 In a study done by Farewell et al 11 patients with a hospital diagnosis of "heart failure" were investigated. These patients did not undergo cardiac catherterization. The criteria for inclusion were severe heart failure (NYHA Class III or IV), heart failure due to dilated cardiomyopathy, QRS duration > 120 ms, or the presence of LBBB or RBBB. Using these criteria, approximately 10 percent of an unselected group of heart failure patients who are admitted to a typical district general hospital in United Kingdom during a calendar year would be candidates for biventricular pacing. A recent study done by Erdogan et al 12 estimated that biventricular pacing might be considered as an adjunct to standard heart failure therapy in 5-10 patients per year per 100,000 residents in industrial countries. In Europe Resynchronization therapy is approved for symptomatic heart failure that occurs in the setting of IVCD or BBB. This approval was granted on the basis of several studies of acute resynchronization therapy and data compiled in approximately 150 patients receiving BiV or LV stimulation for three months as part of two controlled studies (InSync 13 , 14 and PATH-CHF 15 ). In the United States, resynchronization therapy with or without an ICD is approved for patients with NYHA class III-IV heart failure on the basis of the chronic studies described below, which were all performed with a control group randomly assigned to no resynchronization therapy 16 , 17 , 18 , 19 , 20 , 21 , 22 . There is another setting in which resynchronization might be important. It is estimated that approximately 8 to 15 percent of patients with advanced heart failure have pacemakers implanted for symptomatic bradycardia. Such patients have an increased risk