Supine Systolic Blood Pressure and 1-Year Mortality in Patients With Acute Chest Pain

Abstract

To the Editor: Dr Stenestrand and colleagues analyzed data from 119 151 participants in the Registry of Information and Knowledge About Swedish Heart Intensive Care Admissions (RIKS-HIA) who were treated for chest pain in the intensive care unit from 1997 to 2007. The study reported that absolute 1-year mortality was 40.3% higher in quartile 1 (Q1, supine systolic blood pressure 128 mm Hg) compared with quartile 2 (Q2, supine systolic blood pressure 128-144 mm Hg), adjusted for age; sex; smoking status; diastolic blood pressure; use of antihypertensive medication and nitroglycerin at admission; and use at discharge of antihypertensive, statin, antiplatelet, and anticoagulant drugs and other lipid-lowering medication. As a study limitation, the authors said that “it is possible that factors not present in the RIKS-HIA database, such as malnutrition or anemia, might explain part of the relatively poor prognosis associated with low admission systolic BP.” However, another possible confounder is sleep apnea, an important pathophysiological and prognostic factor in cardiovascular disease. Sleep apnea may have been more prevalent in Q1 than in Q2: individuals in Q1 were older and had higher heart rate than those in Q2, and sleep apnea is generally more prevalent among older individuals and is associated with higher heart rate. Despite a greater prevalence of -blocker use in Q1 than in Q2, Q1 participants had higher heart rate, possibly due to a more intense sympathetic activation in Q1, consistent with associated sleep apnea. Relative to Q2, Q1 participants had greater prevalence of aspirin and statin use and lower total cholesterol levels and diastolic blood pressure, traditionally associated with better prognosis in chest pain. Consequently, it is possible that a negative prognostic factor in chest pain such as sleep apnea was not evaluated. In previous studies, sleep apnea was present in up to 57% of patients with acute coronary syndrome, being associated with increased coronary restenosis, major adverse cardiac events, and cardiac death. Based on these data, undiagnosed or untreated sleep apnea might explain, at least in part, the poor prognosis associated with low admission supine systolic blood pressure in acute chest pain in the study by Stenestrand et al. However, this hypothesis would have to be addressed by a prospective clinical study.