Our data indicate that the single largest cause of death among dialysis patients after surgical coronary revascularization is attributable to arrhythmic mechanisms. In this population of patients with ischaemic heart disease, treated with optimal surgical coronary revascularization (CAB including the use of internal mammary grafts), the probability of arrhythmically mediated death was not lower than that reported for the entire US dialysis population. In 2002, the 2-year probability of all-cause death was 40% and sudden cardiac death 14% in the prevalent US dialysis population [1
]. In the present study, for dialysis patients receiving CAB surgery with internal mammary artery graft use, 2-year all-cause mortality was 43% and mortality attributed to arrhythmic mechanisms was 14%. Our data suggest that the persistent risk of arrhythmically mediated death is a major contributor to poor long-term outcomes after surgical coronary revascularization in dialysis patients.
Prior studies of coronary revascularization have suggested a reduction in sudden death after surgical coronary revascularization, but studies attempting to further analyze the potential additional benefit of defibrillators have yielded mixed results. Prior clinical trials [the Coronary Artery Surgery Study (CASS) and the European Coronary Surgery Study] [16,17
] indicate that the risk of sudden death is reduced after surgical coronary revascularization compared with medical therapy. In the Coronary Artery Bypass Graft Patch trial [18
], prophylactic defibrillator therapy in patients with impaired left ventricular systolic function did not further improve the outcome for patients receiving surgical coronary revascularization. This lack of detectible additional benefit with defibrillators is attributable to the significant reduction of sudden death after surgical coronary revascularization [19
]. Makikallio et al
] reported in an observational study that myocardial revascularization is the treatment strategy associated with the greatest reduction in the risk of sudden cardiac death (compared with medical treatment with beta-blockers, aspirin, statins and angiotensin-converting enzyme inhibitor agents). In contrast, in the Antiarrhythmics versus Implantable Defibrillators registry [20
], the survival benefit of defibrillators was not attenuated by surgical coronary revascularization. In a retrospective analysis of patients receiving implantable cardioverter defibrillators, Brockes et al
] reported similar rates of delivered shocks and mortality in patients with and without coronary revascularization, implying that the risk of sudden death is not always nullified by coronary revascularization.
Prior publications on percutaneous and surgical coronary artery revascularization in the general population provide a frame of reference for the long-term risk of sudden cardiac death after coronary revascularization. Holmes et al
], using the 1985 to 1986 National Heart, Lung, and Blood Institute Percutaneous Transluminal Coronary Angioplasty (NHLBI PTCA) Registry of 2127 patients, reported an overall 5-year cardiac mortality of 5.3%, noncardiac mortality of 4.8% and 5-year sudden death incidence of 2.0%. In the higher risk subset of patients with a history of congestive heart failure, 5-year cardiac mortality was 27.2%, noncardiac mortality 15.7% and the 5-year sudden death incidence 10.5%. In patients with severe concomitant noncardiac disease, 5-year cardiac mortality was 14.7%, noncardiac mortality 12.9% and 5-year sudden death incidence 3.2%. Finally, in a subset analysis of 951 patients receiving coronary revascularization (CAB surgery or percutaneous coronary intervention) before being enrolled in the Multicenter Automatic Defibrillator Implantation Trial II (MADIT-II), Goldenberg et al
] reported a significant time-dependent relationship of prior coronary revascularization and implantable cardioverter defibrillator benefit: 36% reduction in the all-cause mortality risk and 68% reduction in the sudden cardiac death risk in patients undergoing coronary revascularization more than 6 months before MADIT-II enrollment, but no benefit in patients enrolled within 6 months of coronary revascularization.
The magnitude of the sudden death risk in the CASS study is considerably lower than in our study. For the highest risk quartile in the CASS study, the 5-
year incidence of sudden cardiac death was 16% for medically treated and 5% for surgically treated patients. In the entire study, there was nearly a threefold relative risk of sudden death in the medical group compared with the CAB surgery group [16
]. In contrast, we report a 14% 2-
year incidence of arrhythmically mediated death in dialysis patients after CAB surgery.
Our study is limited in several ways. The USRDS database consists of predominantly administrative data. Clinical data including coronary anatomy, left ventricular ejection fraction and anatomic adequacy of coronary revascularization cannot be determined from this source. Cause-specific mortality is not based on adjudication, as would occur in a clinical trial, but from information obtained from the Centers for Medicare & Medicaid Services ESRD Death Notification form. Our definition of ‘arrhythmically mediated death’, obtained from the USRDS database, may not be identical to ‘sudden death’ or ‘sudden cardiac death’ reported in clinical trials. Our estimate of the frequency of arrhythmically mediated death (as an equivalent to sudden death), however, is likely to be accurate, as the proportion of mortality attributed to arrhythmic mechanisms in the USRDS database (about 27%) is similar to the 25–26% sudden death (as a percentage of all-cause mortality) reported in the 4D [24
] and HEMO [9
Our study does not provide any information on the potential benefits of surgical coronary revascularization in improving survival. It is plausible (but not studied) that our study patients who received coronary revascularization for the treatment of obstructive coronary artery disease could have had worse outcomes with a more conservative approach. We do not suggest that coronary revascularization in dialysis patients is not efficacious. Rather, a significant residual hazard of arrhythmically mediated death remains that is not nullified by coronary revascularization. Sudden cardiac death is a major manifestation of ischaemic heart disease [3
]. Although myocardial ischaemia is likely a trigger for sudden cardiac death in dialysis patients, our data suggest that other mechanisms (such as left ventricular hypertrophy and myocardial fibrosis) may be paramount in the ESRD population [25
Coronary revascularization may be a particularly incomplete therapy for cardiac disease in ESRD patients, as a large untreated hazard of arrhythmic death may remain. In this special population, additional treatment strategies targeting the ‘non-ischaemic’ contributors to sudden cardiac death may be necessary.