Long-Term Clinical Outcomes and Predictors of Mortality in Implantable Cardioverter-Defibrillator Recipients in New Zealand (ANZACS-QI 83)

Background

The long-term clinical outcomes of implantable cardioverter-defibrillator (ICD) recipients across New Zealand are unknown. This study aims to compare the all-cause mortality of primary and secondary prevention ICD recipients in New Zealand and identify predictors of mortality.

Method

Patients who received a primary or secondary prevention ICD in New Zealand between 2016 and 2020 were identified using the Aotearoa NZ All Cardiology Services Quality Improvement Cardiac Implanted Device Registry [ANZACS-QI DEVICE], a national registry for cardiac implantable electronic devices. Patients with infiltrative cardiomyopathies, congenital heart disease, and channelopathies were excluded. The primary outcome was all-cause mortality. Secondary outcomes were cardiovascular (CVD) mortality, non-CVD mortality, heart failure hospitalisation, and ventricular arrhythmia hospitalisation. Log-rank tests on Kaplan–Meier curves and 4-year Kaplan–Meier event rates were reported. Cox regression multivariate analysis was performed to identify predictors of all-cause mortality.

Results

There were 1,990 patients, including 1,067 (53.6%) primary prevention and 923 (46.4%) secondary prevention ICD recipients, with a mean follow-up of 4.0±1.5 years. The median age was 62 years, 29.6% were Māori or Pacific Islanders.

At 4 years, the all-cause mortality was higher in the primary prevention group than in the secondary prevention group (17.1% vs 11.8%; p=0.002). This was due to a higher rate of CVD mortality (11.9% vs 7.3%; p=0.008), with no significant difference in non-CVD mortality (5.9% vs 4.8%; p=0.093). Compared with the secondary prevention group, the primary prevention group had more heart failure hospitalisations (30.2% vs 17.9%; p<0.001) but fewer ventricular arrhythmia hospitalisations (14.8% vs 29.0%; p<0.001).

Significant predictors of mortality in multivariate regression analyses were Māori or Pacific Islander ethnicity (primary prevention hazard ratio [HR] 2.12; p<0.001; secondary prevention HR 1.71; p=0.018); older age (per 10-year increase in age: primary prevention HR 1.33; p=0.003; secondary prevention HR 1.72; p<0.001), and poorer renal function (per 10 mL/min/1.73m² decrease: primary prevention HR 1.21; p<0.001; secondary prevention HR 1.25; p<0.001). Previous myocardial infarction was not a significant predictor of mortality in either cohort.

Conclusions

In New Zealand ICD recipients, long-term all-cause mortality and CVD mortality rates were higher in primary prevention than secondary prevention ICD implants. Non-CVD mortality was low and similar in both cohorts, consistent with appropriate patient selection. The higher mortality observed for Māori and Pacific Islander patients require further investigation.