Is lower diastolic blood pressure always better?

Dr Fagard from Belgium addresses an interesting conundrum in the treatment of high blood pressure: can there be too much of a good thing? In other words, does dramatically lowering diastolic blood pressure lead to an adverse prognosis, especially in older patients? The background for this question can be found in the debate over the existence of the so-called “J-curve” relationship between cardiovascular morbidity and mortality on the one hand and diastolic blood pressure on the other in hypertensive patients who are undergoing aggressive antihypertensive treatment. For example, an adverse effect was suggested by a 2002 meta-analysis of seven hypertensive treatment trials,¹ but these findings were not demonstrated in a meta-analysis from 2005, which showed that aggressive lowering of diastolic blood pressure did not cause harm.² Neither report differentiated between patients who had both systolic and diastolic hypertension and those who had isolated systolic hypertension.

To help resolve the latter issue, Dr Fagard conducted a retrospective review of the Systolic Hypertension in Europe (Syst-Eur) trial. He randomized 4,583 patients who were at least 60 years old and had a systolic blood pressure between 160 and 219 mm Hg and a diastolic blood pressure below 95 mm Hg to either a placebo or active-treatment arm. Among the 2,358 patients in the active-treatment arm, the 336 with coronary artery disease were found to have a higher risk of developing cardiovascular complications than the 2,022 patients without coronary artery disease. Dr Fagard concludes that the former patients are the ones who may need the most care in not allowing diastolic blood pressure to get too low.

How do these results compare with those of another large trial—the Systolic Hypertension in the Elderly Program (SHEP)?³ SHEP patients had only isolated systolic hypertension, and a J-curve relationship was found during the active-treatment phase of the trial. Unlike the present report, SHEP did not risk stratify for coronary artery disease prevalence. The latter feature is one of the strengths of Dr Fagard’s report because it allows the clinician to appreciate that lowering diastolic blood pressure too much (to 55 mm Hg or below) in patients with coronary artery disease may cause untoward complications. One of the unanswered questions from Dr Fagard’s study is why non-cardiovascular mortality increased as diastolic blood pressure decreased in both patients with and without coronary artery disease, leaving one to wonder what caused the difference in total mortality compared with cardiovascular mortality.