Low diastolic blood pressure (DBP) is frequently found in patients with isolated systolic hypertension and represents a major therapeutic dilemma because initiation of antihypertensive drug therapy to reduce systolic blood pressure (BP) risks a further decrease in DBP levels. Instigating incremental DBP reductions are of concern because in cohort studies and post hoc analyses of randomized controlled trials on subjects with or at risk for coronary disease, low DBP has consistently been associated with an increased risk of cardiac events, which results in a J-shaped mortality curve. 1 Coronary perfusion occurs during diastole and compromised coronary flow precipitated by reduced DBP has been proposed as a potential mechanism for this increased risk. 1,2 Although it is difficult to pinpoint an exact threshold of DBP at which further BP reduction is potentially harmful, contemporary guidelines indicate that providers should exercise caution when reducing DBP < 60 mmHg in patients with established coronary artery disease. 3,4 This threshold is somewhat arbitrarily defined. In some studies, the association with increased risk occurred at higher DBP levels. 1,5 Notably, in patients who were referred for coronary angiography, the probability of reduced coronary blood flow distal to coronary stenosis was substantially increased when central DBP was 60 mm Hg. 2 It is important to note that the Canadian Hypertension Education Program (CHEP) Recommendations Task Force do not consider a DBP 60 mmHg to be an absolute contraindication to further systolic BP reduction. However, CHEP advises watching carefully for symptoms or signs of myocardial ischemia if further BP-lowering is attempted in such patients. 6In this issue of the Canadian Journal of Cardiology, Mace-Brickman and colleagues report the results of an observational analysis of 466 patients seen in a Canadian tertiary care hypertension program. 7 The premise for the study is based on the thesis that vigorous hypertension treatment to reach recommended BP targets might lead to diastolic hypotension and its potentially deleterious consequences on coronary artery disease complications. The prevalence of low BP, defined as 60 mmHg was 10.5% at baseline; an additional 16% had diastolic hypotension at least once during the follow-up period. In patients with low DBP at baseline, the mean number of prescribed antihypertensive drugs did not change over the follow-up period (3.6 medications at baseline vs 3.7 at follow-up). Despite the lack of apparent up-titration of antihypertensive drugs, systolic BP decreased from 133 to 126 mm Hg (P ¼ 0.04), which perhaps reflected greater medication adherence or use of more synergistic combinations. However, for unclear reasons, DBP slightly increased from 53 to 55 mm Hg (P ¼ 0.07) in these patients. Notably, although the authors commented that patients with low DBP 'did not have. any tapering of their antihypertensive medications,' most hypertension specialists would not reduce antihypertensive drug doses on the basis of low DBP alone un...
