Patients with acute coronary syndromes who underwent an early invasive strategy had a lower risk of cardiac death and hospitalization for MI compared with those who received a conservative approach, according to a retrospective cohort study.

The trial, which included national healthcare data from Denmark, found that cardiac death occurred in 5.9 percent of patients in the early invasive group compared with 7.6 percent of patients in the conservative group.

Further, the rates of hospitalization for MI were 3.4 percent and 5 percent in the invasive and conservative groups, respectively, while the rates for all-cause death were 7.3 percent and 10.6 percent, respectively.

Patients were followed for 60 days after hospitalization or until they died.

Lead researcher Kim Wadt Hansen, MD, of Bispebjerg University Hospital in Copenhagen, and colleagues published their results online in the Annals of Internal Medicine on Oct. 26.

“Our findings confirm those of several randomized clinical trials,” the researchers wrote. “Thus, health care providers are encouraged to adhere to the time frames stated in international guidelines and fast-track protocols.”

They collected data from five national registries and included patients with acute MI or unstable angina who were hospitalized for a first acute coronary syndrome from Jan. 1, 2005, through Dec. 31, 2011, in Denmark.

They defined early invasive treatment as “diagnostic coronary angiography within 72 hours of the index hospitalization, assuming cardiac catheterization with intent to perform revascularization if appropriate on the basis of coronary anatomy.” With the conservative approach, patients received an angiographic assessment at least 72 hours after the index hospitalization or no cardiac catheterization.

In Denmark, all citizens are covered by a national healthcare system and receive care for acute coronary syndrome at five invasive heart centers or eight smaller hospitals that perform cardiac procedures.

This study included 54,694 patients, of which 44 percent received an early invasive treatment strategy. The mean follow-up among surviving patients was 60 days.

Of the patients in the conservative group, 56.3 percent had cardiac catheterization between days 3 and 30, 1.3 percent had the procedure between days 31 and 60 and 42.2 percent did not receive an invasive examination within 60 days.

Subgroup analyses found an early invasive strategy in patients with MI was associated with a lower risk for cardiac death; patients who were 75 and older seemed to benefit the most from an early invasive approach; and patients admitted directly to an invasive heart center seemed to benefit the most from an early invasive strategy.

The researchers mentioned a few limitations of the study, including that they did not have information on electrocardiographic findings, cardiac troponin measurements, types of MI and other clinical variables. They also noted one registry did not distinguish between STEMI and non-STEMI.

Jeptha Curtis, MD, and Harlan Krumholz, MD, of the Yale School of Medicine, wrote in an accompanying editorial that the study design precluded the researchers from drawing causal inferences.

“The predicament is that this study— comparative effectiveness research that used national observational data, applied strong analytic methods, and was published in a leading journal—cannot strongly support causal inference,” they wrote. “The quality of the data remains a critical issue, as do the questions about whether the methods can overcome concerns about residual confounding. Almost every comparative effectiveness article using observational data, however well-done, must be circumspect in asserting causal inference.”