The second analysis involved 15 reports with 5,333 patients, and used multivariate adjustment to find that patients who had received an ICD and also had CKD had a statistically significant, 2.9-fold higher mortality rate than did ICD recipients without CKD, highlighting the high risk for nonarrhythmic death that CKD patients face, said Dr. Makki, a researcher at the University of Iowa in Iowa City. "Despite a paucity of randomized trials in the CKD population, these data support use of ICDs for the prevention of sudden cardiac death in patients at risk," he said. "We believe that ICDs are underused in this population," patients with CKD.
But these analyses are compromised by the data they used, said Dr. Reynolds. The data were "heavily weighted with a couple of large studies that used claims data. My concern is the potential for confounding by indication. Patients who get ICDs are somehow not as sick as those who don’t."
The third study looked at the impact of CKD on the aftermath of ICD replacement among the 1,744 patients enrolled in the REPLACE (Implantable Cardiac Pulse Generator Replacement Registry) trial, which tracked the incidence of complications following replacement of ICD generators and leads. Among the enrolled patients, researchers had renal-function data for 1,662 patients. About 80% had either mild or moderate renal dysfunction, while 6% had an estimated GFR less than 30 mL/min per 1.73 m2, and the remained had normal renal function.
The incidence of complications was 15% overall, and the analysis showed roughly this rate across all strata of CKD severity. Even among patients with severe CKD, the complication rate was about 20%, and not significantly different from patients with even normal renal function, Dr. Suneet Mittal reported at the meeting. The split between major and minor complications also varied little by renal function, and the incidence of infections was 1%-2% across all five levels of renal function examined.
But CKD severity played a big role in 6-month mortality. A multivariate analysis showed that CKD stage played a significant role in survival; for each stage of worsened renal function the risk of death rose by 50%. (Other significant predictors were recent heart-failure hospitalization, severe heart failure, treatment with an antiarrhythmic drug, and history of cerebrovascular disease.) In actual numbers, the 6-month mortality rate was 2% among patients with either none or mild renal dysfunction that jumped to a 9% rate in patients with an estimated GFR of 15-29 mL/min per 1.73 m2, and to 16% in those on dialysis, said Dr. Mittal, a cardiac electrophysiologist at Columbia University in New York. The analyses also showed that the increased mortality risk linked to severe CKD became apparent by a month after ICD replacement, and it was not driven by procedure-related complications.
"Why do these patients [with severe CKD] do so much worse? We thought that if we looked at all their complications we’d pick up the reason, but clearly there are things that we have not yet recognized," Dr. Mittal said. "There are a lot of things that we didn’t capture in the study."
Although the analysis shed little light on what was behind the high mortality risk in severe CKD patients, it effectively highlighted how risky ICD replacements are in any patient.
"The incidence of complications, 15%-23%, was striking. It’s substantially greater than what’s been seen in any registry-based data or administrative-based data," said Dr. Varosy. He cited the unique ability of this registry to capture all the minor complications following ICD replacement.
"These are frightening numbers [because] we tell patients that there is a very small risk" from ICD replacement procedures, commented Dr. Kalyanam Shivkumar, professor and director of the University of California Los Angeles Cardiac Arrhythmia Center.
Dr. Reynolds said that he has been a consultant to Medtronic and Biosense Webster and has received research grants from Edwards Lifesciences. Dr. Varosy had no disclosures. Dr. Adabag said that he had received research grants from Medtronic and Boston Scientific. Dr. Makki had no disclosures. The REPLACE registry was sponsored by Biotronik and Dr. Mittal said that has been a consultant to Biotronik. Dr. Shivkumar had no disclosures.