Background:
Previous literature on percutaneous coronary intervention (PCI) indicated that hospital volume is inversely related to in-hospital mortality but its impact on other characteristics such as likelihood of stent implantation and number of stents remains unclear.

Methods:
Using German national health records, all patients undergoing coronary angiography with a documented coronary artery disease were identified by ICD and OPS codes. Risk-adjustment was applied to account for differences in the examined patient population.

Results:
In 2017, 528,188 patients with coronary artery disease underwent coronary angiography in Germany. Mean age was 69.8 years and 29.3% were female. 55% of all patients received PCI, with 1.01 stents implanted per patient. In-hospital mortality was 2.9%, length of hospital stay was 6.5 days and mean reimbursement was €5,531. Low volume centers treated more acute coronary syndromes and emergency admissions, high volume centers more complex cases with 3-vessel coronary artery disease, left main stenosis, and in-stent stenosis. Multivariable regression analyses showed a positive linear correlation between hospital volume and likelihood of stent implantation (p=0.003) as well as number of implanted stents (p=0.020). No association was found between hospital volume and in-hospital mortality (p=0.105), length of hospital stay (p=0.201) or reimbursement (p=0.108). Examination of the non-linear impact of procedure volumes on stent implantation indicates a ceiling effect in the volume-outcome relationship: implantation likelihood and number of stents per patient are lowest in centers with less than 100 procedures per year (about 34% and 0.6). Then, implantation likelihood and number of stents constantly increase until the volume category of 500 procedures per year and center. For centers with >500 procedures per year, likelihood of stent implantation and number of implanted stents remained relatively stable (about 60% and 1.1).

Conclusion:
Findings suggest that low volume centers provide emergency care regarding PCI. More complex cases are treated in high volume centers, with a higher likelihood and number of stent implantations, while ensuring consistent mortality rates and safety.


Figure: Non-linear impact of procedure volumes