The Brain and Heart Want Different Blood Pressure Goals

The optimal systolic and diastolic blood pressure (BP) target for each person may depend on his or her individual risk profile, an observational study suggested.

Based on the 33,357-patient ALLHAT trial, there appeared to be a U- or J-shaped association between risk of several cardiovascular events and BP, such that going too low in systolic or diastolic BP was not good for the patient. The nadir of risk was observed at different BP combinations depending on the outcome of interest:

• All-cause mortality: 140-155/70-80 mm Hg
• Congestive heart failure (CHF): 125-135/70-75 mm Hg
• Myocardial infarction (MI): 110-120/85-90 mm Hg

In contrast, the association of systolic BP and stroke was linear: the lower the better in this regard, noted Tara Chang, MD, MS, of Stanford University School of Medicine in California, and colleagues in the Journal of the American College of Cardiology.

"For stroke prevention, therefore, the old BP adage 'the lower the better' holds true. This is a pivotal take home message for practicing cardiologists -- were it not risky for the heart, the brain would prefer an optimally cerebroprotective systolic BP of 110-120 mm Hg," wrote a trio led by Franz Messerli, MD, of the Swiss Cardiovascular Center and University of Bern in Switzerland, in an accompanying editorial.

"This should not surprise those among us who remember that because of autoregulation, the brain is able to maintain a relatively constant blood flow despite large fluctuations in perfusion pressure," Messerli and colleagues added. "In contrast to the brain, perfusion of the heart predominantly occurs during diastole. Consequently, an inappropriately low diastolic BP is prone to compromise myocardial perfusion."

Based on ALLHAT, BP targets may need to be tailored to the cardiovascular event for which the patient is most at risk, Chang's group said.

"For example, for a given person with history of a previous stroke, more aggressive BP lowering may be warranted given the linear association seen, whereas for the person with a history of previous MI, care would need to be taken to avoid excessive diastolic BP lowering," they suggested.

Current U.S. guidelines target a BP <130/80 mm Hg in nearly all patient populations.

"The BP management of stable CAD [coronary artery disease] patients with cerebrovascular disease remains challenging and needs careful shared decision-making. Questions remain as to if we should continue with medical therapy aimed at lowering BP, or should we consider further options for increasing diastolic pressure leeway, to the point of prophylactic coronary artery revascularization," the editorialists wrote.

Such prophylactic revascularization, to improve the tolerability of a lower diastolic BP, would need to be reconciled with the ISCHEMIA trial's finding that revascularizing asymptomatic patients with stable CAD did not improve outcomes, Messerli's team acknowledged.

ALLHAT was an older trial that had randomized adults to chlorthalidone, amlodipine, or lisinopril for a target BP of <140/90 mm Hg. Investigators took a median 14 BP measurements per person.

The trial included 33,357 patients ages 55 and older with at least one other cardiovascular risk factor. Mean age at baseline was 67.4 years, 53.1% of the cohort were men, and 47.3% were white. Average BP was 145.6/83.7 mm Hg.

Nearly a quarter of patients had at least one primary composite outcome event (all-cause mortality, MI, CHF, or stroke) over a median 4.4 years.

Chang and colleagues acknowledged that their report alone "cannot determine the optimal BP targets for patients at this time given that it is a retrospective observational analysis" subject to potential residual confounding.

Additionally, the study is not generalizable to lower-risk or normotensive populations. The investigators also did not use models that adjusted for time-varying variables such as change in comorbidities.

Nevertheless, their findings align with the INVEST study, which had showed a greater risk of MI instead of stroke with lower diastolic BP in patients with hypertension and CAD, Messerli's group said.

Comment