Cardiac resynchronization therapy guided by cardiovascular magnetic resonance
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Cardiac resynchronization therapy guided by cardiovascular magnetic resonance Francisco Leyva
Abstract Cardiac resynchronization therapy (CRT) is an established treatment for patients with symptomatic heart failure, severely impaired left ventricular (LV) systolic dysfunction and a wide (> 120 ms) complex. As with any other treatment, the response to CRT is variable. The degree of pre-implant mechanical dyssynchrony, scar burden and scar localization to the vicinity of the LV pacing stimulus are known to influence response and outcome. In addition to its recognized role in the assessment of LV structure and function as well as myocardial scar, cardiovascular magnetic resonance (CMR) can be used to quantify global and regional LV dyssynchrony. This review focuses on the role of CMR in the assessment of patients undergoing CRT, with emphasis on risk stratification and LV lead deployment. Introduction The first demonstration of a beneficial effect from cardiac resynchronization therapy (CRT) was provided by Cazeau et al who, in 1994, treated a 54 year old heart failure patient with four-chamber pacing [1]. Subsequently, acute hemodynamic studies showed that CRT improves cardiac output [2,3]. The Multisite Stimulation in Cardiomyopathies (MUSTIC) study demonstrated that CRT led to an improvement in NYHA class, quality of life, exercise capacity and peak oxygen uptake, as well as to a reduction in heart failure hospitalizations [4]. By 2005, the Cardiac Resynchronization in Heart Failure (CARE-HF) study of patients with moderate-to-severe heart failure showed that CRT-pacing (CRT-P) led to a 36% relative reduction in total mortality [5]. The Comparison of Medical Therapy, Pacing and Defibrillation in Heart Failure (COMPANION) study, which included a similar patient group, had previously shown that addition of a cardioverter defibrillator (CRT-D) led to an additional survival benefit [6]. More recently, the Multicenter Automatic Defibrillator Implantation Trial with Cardiac Resynchronization Therapy (MADIT-CRT) trial has shown that compared with implantable cardioverter defibrillators (ICD) therapy alone, CRT-D therapy is associated with a dramatic reduction in the risk of heart-failure events in relatively asymptomatic (NYHA
class I and II) ICD recipients with a low LVEF and wide QRS complex [7]. The Resynchronization Reverse Remodelling in Systolic Left Ventricular Ventricular dysfunction (REVERSE) study has shown that CRT leads to LV reverse remodelling and an increase in LVEF in the context of milder symptoms (NYHA class I/II) [8]. Studies are already underway to explore the possible benefits of CRT in patients with conventional indications for pacing [9] and patients with a narrow QRS duration [10]. Even if only one of these new indications is added to current guidelines (Tables 1and 2), the demand for CRT is likely to increase exponentially over the current decade. Appropriate diagnosis and management of heart failure not only involves an accurate assessment of myocardial and valvular functio
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