J-Curve Phenomenon: Does It Exist?
Numerous studies over the past few years have documented an non-linear relationship between blood pressure and cardiovascular events (i.e., a J-shaped curve), especially in patients with known coronary artery disease. In most of these studies though a J-c
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Introduction
Increased blood pressure (BP) is the most common modifiable risk factor for cardiovascular disease, accounting for an estimated 17 million deaths worldwide each year. This number is projected to increase to 23 million or 24 % of total deaths worldwide by 2030 [1]. Clinical trials have shown that reduction in BP is associated with up to 40–45 % reduction in the incidence of stroke, 20–25 % reduction in the risk of myocardial infarction and up to 50 % reduction in the risk of heart failure [2, 3]. Though the prognostic importance of blood pressure [4–9] is now well established, the school of thought, over the past 100 years, has largely switched from the initial essential hypertension leaving it alone principle to the current aggressive control, the lower the better principle. The seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7) states that ‘‘the relationship between blood pressure and risk of cardiovascular events is continuous, consistent, and independent of other risk factors [10].’’ Though this linear theory and the lower the better hypothesis has been challenged for three decades with reports of a J curve relationship showing higher event rates at both high and low BP [11–18], it has been brought into the limelight recently with the publication of the Action to Control Cardiovascular
S. Bangalore Leon H. Charney, Division of Cardiology, New York University School of Medicine, New York, USA e-mail: [email protected] F. H. Messerli (&) Division of Cardiology, Columbia University College of Physicians and Surgeons, St. Luke’s-Roosevelt Hospital Center, New York, USA e-mail: [email protected] A. E. Berbari and G. Mancia (eds.), Special Issues in Hypertension, DOI: 10.1007/978-88-470-2601-8_23, Ó Springer-Verlag Italia 2012
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Risk in Diabetes Blood Pressure (ACCORD BP) trial. ACCORD BP is one of the few large randomized trials designed to evaluate a BP-lowering strategy (intensive vs. standard), rather than two different treatments. At the end of 4.7 years of follow-up, targeting a systolic pressure of \120 mmHg, when compared with \140 mmHg in patients with diabetes, did not reduce the rate of fatal and nonfatal major cardiovascular events except for stroke [19]. The observation of a J curve in observational studies has led to hotly debated issues and has proved controversial. The JNC 7 thus states ‘‘there is no definitive evidence of an increase in risk of aggressive treatment (a J-curve) unless DBP is lowered to \55 or 60 mmHg by treatment [10].’’ This chapter discusses the findings of recent studies and critically reviews the effect of excessive BP lowering on adverse cardiovascular events.
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The J-Curve Phenomenon
The J-curve phenomenon, wherein the risk of cardiovascular events follows a bimodal distribution with an increase in risk at both high and very low BP, was reported first in the literature approximately three decades ago, when Stewart demo
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