Reestratificación en el momento del recambio del desfibrilador automático implantable

Abstract

Based on the results of several large, randomized, clinical trials, implantable cardioverter defibrillators (ICDs) have become a ‘‘gold standard’’ therapy in prevention of sudden cardiac death. Under current guidelines, ICDs are implanted in patients who survived cardiac arrest or hemodynamically unstable ventricular tachycardia, as well as in primary prevention, mainly for those with ischemic or nonischemic cardiomyopathy with left ventricular ejection fraction (LVEF) 35%, New York Heart Association functional class II/III, optimal pharmacotherapy, good life expectancy, and no identifiable reversible causes of low LVEF. 1 Current guidelines do not distinguish between patients implanted de novo and those undergoing elective battery replacement. No doubts exist about the need to replace ICD in secondary prevention patients; however, a debate continues on how to approach subjects implanted in primary prevention referred for elective replacement due to battery depletion. Despite decades of clinical experience, no consensus exists on how to stratify the risk of sudden cardiac death. The current approach, in which low LVEF is considered the only risk stratifier, is far from optimal. A substantial number of ICD recipients who are eligible for a device replacement have never developed arrhythmia requiring ICD therapy. As evidenced by randomized trials and ICD registries, only 20% to 30% of patients implanted for primary prevention receive appropriate ICD shocks. Therefore, at the time of generator replacement physicians have to face 2 problematic groups of patients: a) those who have never had appropriate therapy but still present low LVEF qualifying them for an ICD, and b) those who have never had ICD shocks and at the time of replacement present with improved LVEF falling beyond ICD indications criteria. Patients who have not received any antiarrhythmic therapy most probably constitute a group of subjects who were ‘‘too healthy’’ or ‘‘too sick’’ for ICD implantation. There is an ongoing debate on how to stratify the risk of sudden cardiac death and better identify patients with low LVEF who develop ICD-treatable arrhythmia. Even though a plethora of noninvasive risk markers such as electrocardiogram and imaging techniques, laboratory tests, and simple bedside tests has been investigated, no consensus has been achieved so far. The rate of death without appropriate ICD therapy is substantial. Patients with multiple comorbidities and those with advanced heart failure are prone to die from noncardiac or nonarrhythmic causes that could not be prevented by ICD therapy. The study by Goldenberg et al 2 showed that a bedside clinical risk score composed of 5 variables (New York Heart Association functional class > II, age > 70 years, blood urea nitrogen > 26 mg/dL, QRS duration > 120 ms, and atrial fibrillation) was able to identify patients who did not benefit from ICD implantation. A group from Leiden 3 proposed the FADES (Functional class, Age, Diabetes, Ejection fraction, Smoking) score to identify patients who would die without appropriate therapy. In patients with a FADES score of 3.0-5.5 points, the cumulative incidence of death without appropriate ICD therapy was 41%. In patients who at the time of generator replacement present with LVEF above ICD indications limits, 3 potential clinical situations should be considered: a) there was an unrecognized reversible cause of left ventricular dysfunction at the time of implantation; b) spontaneous positive remodeling occurred, and c) a patient might have had inappropriately assessed LVEF at the time of implantation and in fact has never fulfilled the implantation criteria. Recent data from the MADIT-CRT 4 trial showed that 38% of patients enrolled in a trial based on the criterion of LVEF < 30% had significantly higher ejection fraction values (in the range of 30.1%-45.3%) when echocardiographic data was analyzed centrally by echo experts. The subjective nature of LVEF estimation and poor reproducibility of the results have always been criticized in the context of using LVEF as a sole risk marker for sudden cardiac death. To avoid the risk of inappropriate qualification for ICD therapy related to spontaneous positive remodeling, a limit of at least 40 days after myocardial infarction and 9 months after a new onset of nonischemic cardiomyopathy is required. However, it seems there is a substantial proportion of patients who will recover left ventricular function over a longer period of time, especially among those with nonischemic cardiomyopathy. Attempts are always being made to exclude reversible causes such as tachycardiomyopathy, myocarditis, excessive alcohol consumption, nonadherence to drug therapy, or suboptimal treatment. In patients with atrial fibrillation, it should also be emphasized that a restoration of a sinus rhythm by cardioversion or ablation may significantly improve left ventricular function.