Mortality among high-risk patients with acute myocardial infarction admitted to U.S. teaching-intensive hospitals in July: a retrospective observational study

Abstract

Background: Studies of whether inpatient mortality in US teaching hospitals rises in July as a result of organizational disruption and relative inexperience of new physicians (July effect) find small and mixed results, perhaps because study populations primarily include low-risk inpatients whose mortality outcomes are unlikely to exhibit a July effect.

Methods and results: Using the US Nationwide Inpatient sample, we estimated difference-in-difference models of mortality, percutaneous coronary intervention rates, and bleeding complication rates, for high- and low-risk patients with acute myocardial infarction admitted to 98 teaching-intensive and 1353 non-teaching-intensive hospitals during May and July 2002 to 2008. Among patients in the top quartile of predicted acute myocardial infarction mortality (high risk), adjusted mortality was lower in May than July in teaching-intensive hospitals (18.8% in May, 22.7% in July, P<0.01), but similar in non-teaching-intensive hospitals (22.5% in May, 22.8% in July, P=0.70). Among patients in the lowest three quartiles of predicted acute myocardial infarction mortality (low risk), adjusted mortality was similar in May and July in both teaching-intensive hospitals (2.1% in May, 1.9% in July, P=0.45) and non-teaching-intensive hospitals (2.7% in May, 2.8% in July, P=0.21). Differences in percutaneous coronary intervention and bleeding complication rates could not explain the observed July mortality effect among high risk patients.

Conclusions: High-risk acute myocardial infarction patients experience similar mortality in teaching- and non-teaching-intensive hospitals in July, but lower mortality in teaching-intensive hospitals in May. Low-risk patients experience no such July effect in teaching-intensive hospitals.

Keywords: mortality; myocardial infarction.

Figure 1

Adjusted inpatient mortality among patients admitted with AMI during May and July, according to teaching-intensive hospital status and predicted inpatient mortality risk. Adjusted inpatient mortality for teaching-intensive and non-teaching-intensive hospitals during May and July was estimated from a difference-in-difference logistic regression model which adjusted for patient age, sex, race, AHRQ predicted mortality, and year. The July mortality effect among high risk patients is (22.7 – 18.8) – (22.8 – 22.5) = 3.6 percentage points, p-value = 0.02. The July mortality effect among low risk patients is (1.9 – 2.1) – (2.8 – 2.7) = -0.3 percentage points, p-value = 0.24.

Figure 2

Adjusted rates of percutaneous coronary intervention among patients admitted with AMI during May and July, according to teaching-intensive hospital status and predicted inpatient mortality risk. Adjusted rates of PCI for teaching-intensive and non-teaching-intensive hospitals during May and July was estimated from a difference-in-difference logistic regression model which adjusted for patient age, sex, race, AHRQ predicted mortality, and year. The July PCI effect among high risk patients is (19.4 – 19.4) – (13.5 – 13.2) = -0.3 percentage points, p-value = 0.80. The July PCI effect among low risk patients is (52.8 – 52.9) – (49.0 – 48.8) = -0.3 percentage points, p-value = 0.71.

Figure 3

Adjusted rates of complications from bleeding among patients admitted with AMI during May and July, according to teaching-intensive hospital status and predicted inpatient mortality risk. Adjusted rates of bleeding complications for teaching-intensive and non-teaching-intensive hospitals during May and July was estimated from a difference-in-difference logistic regression model which adjusted for patient age, sex, race, AHRQ predicted mortality, and year. The July bleeding effect among high risk patients is (11.9 – 11.0) – (7.1 – 7.2) = -1.0 percentage points, p-value = 0.53. The July bleeding effect among low risk patients is (10.8 – 10.6) – (6.9 – 6.9) = 0.2 percentage points, p-value = 0.94.