Isolated systolic hypertension and the J-curve of cardiovascular disease risk

Abstract

Controversy persists regarding the presence and significance of blood pressure ‘‘J-curves’’ of increased cardiovascular disease (CVD) risk as they relate to older people with isolated systolic hypertension (ISH). Age is an important effect modifier favoring diastolic blood pressure (DBP) in young adults, systolic blood pressure (SBP) in middle-aged, and pulse pressure (PP) in the elderly as predictors of CVD events. By contrast, a recent Framingham Heart Study showed that combined blood pressure components increased the prediction of CVD risk over any single blood pressure component. Interestingly, of the 4 blood pressure components [DBP, SBP, PP, and mean arterial pressure (MAP)] only DBP showed non-linear tendencies, which presented as a J-curve of increased CVD risk in this primary prevention study. A low DBP was associated with increased PP, and hence, was a marker for increased arterial stiffness; thus, risk was defined by increased PP that resulted in decreased DBP and increased SBP. On the other hand, when primary CVD events result in poor cardiac function, the presence of combined SBP and DBP J-curves serve as predictors of secondary CVD eventsdso called ‘‘reverse causality’’; thus, risk is associated with decreased rather than by increased SBP. Lastly, treatment-induced cardiac risk is a potential third explanation for J-curves that occur in the presence of hemodynamically significant coronary artery stenosis. The thesis of this presentation is that a treatment-induced cardiac event, as an explanation for the J-curve risk, occurs infrequently as compared to arterial stiffness or reverse causality; furthermore, the exact point at which the J-curve begins, remains in doubt. Nevertheless, only a prospective trial with baseline and pre-event blood pressure determinations can establish the presence and frequency of treatment-induced J-curve risk.