Country Comparison of Heart Attack Rates Could Improve Care

Acute myocardial infarction (MI) is associated with worse survival in the United Kingdom than in Sweden, highlighting the potential for cross-country comparisons to identify areas for improvement, researchers found.

From 2004 through 2010, the 30-day mortality rate was 10.5 percent in the U.K. and 7.6 percent in Sweden, a difference that was significant even after accounting for differences in patient case mix (mortality ratio 1.37, 95 percent CI 1.30-1.45), according to Harry Hemingway, Ph.D., of University College London, and colleagues.

The gap narrowed over time, but the risk of death remained higher in U.K. patients at the end of the study period, the researchers reported online in The Lancet.

“International comparisons of care and outcome registries might yield important, actionable insights to guide healthcare policy and clinical practice to improve the quality of health systems and prevent avoidable deaths from acute myocardial infarction,” they wrote.

The researchers compared outcomes between Sweden and the U.K. because both countries have universal healthcare systems and national registries for acute coronary syndromes in which all hospitals are required to participate. The analysis included 119,786 patients from Sweden and 391,077 patients from the U.K. who were admitted with an acute MI over the six-year period.

Age and the proportion of females were roughly the same in the two countries, although patients in Sweden were less likely to have ST-segment elevation MI (32 percent versus 40 percent).

All-cause mortality at 30 days was consistently higher in U.K. patients across subgroups defined by troponin concentration, ST-segment elevation, age, sex, heart rate, systolic blood pressure, diabetes status, and smoking status.

The researchers pointed to some differences in care that might explain the disparity, including the much more frequent use of primary percutaneous coronary intervention in Sweden (59 percent versus 22 percent). However, the difference grew smaller over time, particularly after the U.K. implemented a national policy for primary PCI in October 2008.

Swedish patients also were more likely to get a beta-blocker at discharge (89 percent versus 78 percent), although use of evidence-based therapies was not consistently better in Sweden. At discharge, patients in the U.K. were more likely to receive a statin (93 percent versus 80 percent) and an ACE inhibitor or angiotensin receptor blocker (82 percent versus 56 percent).

Mortality remained higher in the U.K., however, even when assuming the equal use of primary PCI, beta-blockers, and other in-hospital treatments, which “suggests that factors outside hospital-based cardiac interventions are also important,” Chris Gale, M.B.B.S., Ph.D., of the University of Leeds in England, and Keith Fox, MBChB, of the University of Edinburgh in Scotland, wrote in an accompanying editorial. 

“Unmeasured factors, such as imbalanced case ascertainment, unmeasured confounders, nonmodeled covariates or missing data, and hospital care systems are probably responsible for the international difference in mortality,” they wrote.

Hemingway and colleagues agreed that the explanation for the mortality difference might involve factors that were not captured in the study, including why certain patients either did or did not receive certain treatments.

But, they wrote, “mortality might be affected by multiple unmeasured features of care, including doses, timing, adherence to drugs, differences in operator experience, shared and specialty care pathways, use of decision-support tools, and organizational culture.”

Although Gale and Fox raised some statistical questions about the study, they wrote, “Nonetheless, through highlighting the prospect of a substantial excess of deaths in the U.K. compared with Sweden, [the researchers] have drawn our attention to the need for further comparative effectiveness research for acute myocardial infarction. Efforts to improve cardiovascular outcomes in the U.K. should, therefore, concentrate on data enhancement through the linkage of electronic healthcare records and the early and systematic implementation of evidence-based therapies across the National Health Service.”