Influence of renal dysfunction on therapy and prognosis in patients with myocardial infarction

Abstract

The aim of this thesis is to evaluate the influence of renal dysfunction on the presentation for myocardial infarction (MI), its treatment and outcome. Patients between 2003 and 2006 were selected from the nationwide Swedish coronary care unit (SWEDEHEART) registry. The renal function was estimated with the Modification of Diet in Renal Disease (MDRD) study formula.

In article I the characteristics of an unselected MI population (n=57 477) is presented. The mean (SD) renal function was 72 (28) ml/min/1.73 m2 and 33% had at least moderate renal dysfunction. Patients with lower renal function differed by being older and having more co-morbidities. They presented less often with chest pain and ST-elevation MI. After adjustments, lower renal function was independently associated with a less frequent use of in-hospital therapies. In-hospital mortality increased exponentially from 2.5% in those with normal renal function to 24.2% in those with renal failure.

In article II the Cockcroft-Gault (CG) and the MDRD formula were compared in 36 137 patients. The largest difference between the formulas was seen in females, the elderly and in those with low body weight, where renal function was estimated lower with the CG formula. The CG formula classified more patients as having at least moderate renal dysfunction, who after multivariable adjustment had higher one year mortality.

In article III medical and invasive therapy in 23 262 patients with non-ST-elevation MI were compared at different renal function stages. Invasive therapy was used less frequently in those with lower renal function (36% in those with moderate renal dysfunction compared to 62% in normal renal function). After multivariable adjustment, invasive therapy in patients with mild-to-moderate renal dysfunction was associated with lower one year mortality. The advantage with invasive therapy decreased in those with severe renal dysfunction with no benefit in those with renal failure. In article IV in-hospital survivors of MI (n=42 814) were analyzed to assess the association of statin therapy at discharge with one year survival. After multivariable adjustment, statin at discharge was associated with a 37% reduction in one year mortality (HR 0.63, 95% CI 0.58-0.68, p<0.001). With lower renal function statin therapy was associated with an improved survival, although the effect declined and was less certain in those with renal failure.

In conclusion, renal dysfunction is present in about a third of patients admitted with a MI. It identifies patients with a worse prognosis who are treated less often both medically and invasively. A less frequent use of available treatments may partially explain their worse prognosis.