Between January 2006 and December 2009, 180,734 patients received an ICD that could be matched to CMS claims. Patients were excluded if they had a previous ICD (n=55,822), previous pacemaker (n=19,214), EF >35% (12,000) or unknown EF (n=1,362), receipt of an ICD for secondary prevention (n=11,412), receipt of a bi-ventricular (n=36,007) or unknown device type (n=107), or a documented pacing indication (n=12,767), resulting in a study cohort of 32,034 patients from 1270 hospitals. () In this cohort, 62% (n=19,788) received a dual chamber device and 38% (n=12,246) received a single chamber device. Patients who received a dual chamber device were more likely to be male, have a history of syncope, a history of sustained or non-sustained ventricular tachycardia, ischemic heart disease, an EF ≥ 30%, first degree heart block, right or left bundle branch block and a wider QRS duration. ( and )
Baseline characteristics of patients receiving single or dual chamber implantable cardioverter defibrillators (ICDs) in overall cohort.
Baseline physician and hospital characteristics among patients receiving single or dual chamber implantable cardioverter defibrillators (ICDs) in overall cohort.
Unadjusted rates of any complication were higher for dual chamber ICDs, with the largest absolute difference in mechanical complications requiring repeat operation for system revision. () The unadjusted rate of HF hospitalization within one year of implantation was modestly lower for single chamber devices (14.72 vs. 15.54% ; p=0.047; risk difference −0.82; 95% CI −1.63, −0.02). Unadjusted rates of all-cause hospitalization and mortality within one year of implantation did not differ by device type (43.79% vs, 44.87%; p=0.058; risk difference −1.08; 95% CI −2.20, 0.03) and 9.85% vs. 10.12%; p=0.436; risk difference 0.27; 95% CI −0.41, 0.94) respectively).
Unadjusted rates of outcomes among patients receiving single vs. dual chamber ICD.
The propensity model included 41 variables (all variables in and except discharge medications) and had an area under the receiver operating characteristic curve (AUC) of 0.66; 95% CI 0.65–0.67. This low AUC suggests that the choice of a dual chamber device is relatively random with respect to patient characteristics, which itself does not indicate a diminished capacity to reduce confounding. Sufficient overlap between the two groups existed to compare treatment effects. () In total, 11,619 (95%) single chamber patients were matched to 11,619 dual chamber patients. After propensity score matching, standardized differences were less than 10% for all variables, indicating the two treatment groups were similar with respect to observed characteristics. ( and )
Distribution of propensity scores for receipt of dual chamber device among single and dual chamber groups.
Characteristics of propensity score-matched patients receiving single vs. dual chamber ICD.
Physician and hospital characteristics among propensity score-matched patients receiving single vs. dual chamber ICD.
In the propensity-matched cohort, rates of any of the assessed complications were significantly lower for single chamber ICDs (3.51% vs. 4.72% p<0.001; risk difference −1.20; 95% CI −1.72, −0.69), with the largest absolute difference in mechanical complications requiring re-operation for system revision (1.43% vs. 1.98%; p=0.001; risk difference −0.55; 95% CI −0.88, −0.22). () Rates of all-cause hospitalization, HF hospitalization and mortality at one year did not differ between device types. () After further adjustment for discharge medications and accounting for matching, device type was still not significantly associated with mortality and hospitalization outcomes (9.85% vs. 9.77%; HR 0.99, 95% CI 0.91–1.07; p=0.792 for 1-year mortality; 43.86 vs. 44.83%; HR 1.00, 95% CI 0.97–1.04; p=0.821 for 1-year all-cause hospitalization; and 14.73% vs. 15.38%; HR 1.05, 95% CI 0.98–1.12; p=0.189 for 1-year HF hospitalization). Results were similar in models also accounting for clustering among hospitals.
Rates of outcomes in propensity score-matched patients receiving single vs. dual chamber ICD.
Rates of any complication were higher among patients receiving dual chamber devices for all subgroups (age, gender and presence of renal dysfunction). Women receiving dual chamber devices had a particularly high rate of complications (6.43%). () However, no statistically significant interactions between these subgroup characteristics and device type were identified (all p-values for interaction >0.05). Furthermore, no significant differences in the association between device type and mortality, all-cause hospitalization or HF-hospitalization were observed for any of the subgroups evaluated (p-values >0.05 for interaction between stratification variable and device type for all outcomes).
Rates of any complication among subgroups in the matched cohort.