Isolated Diastolic Hypertension

A not uncommon situation in clinical practice is a young patient who presents with a high diastolic pressure and a normal systolic reading, such as 135/95 mm Hg, or isolated diastolic hypertension. There is a dilemma here: should the patient be treated or not? Traditionally, diastolic pressure has been regarded as the most important of the three measures of pressure (the others being systolic and pulse pressure), but recent attention has been focused on the other two, particularly with the recent trials showing the benefits of treating isolated systolic hypertension, and a flurry of papers suggesting that pulse pressure is the most important risk factor in older patients.

The reasons for the focus on diastolic pressure are largely historical. The first major treatment trial, the Veterans Administration study ¹ conducted by Dr. Ed Fries in the 1960s, used a high diastolic pressure as the main entry criterion; other similar trials have followed suit. One of the largest trials ever conducted, the Hypertension Optimal Treatment (HOT) study, ² attempted to resolve the J‐curve dilemma by titrating patients' diastolic pressures to three levels, 85–90 mm Hg, 80–85 mm Hg, and <80 mm Hg. Even today, a high diastolic pressure is the primary requirement for reimbursement for antihypertensive medications in Finland. ³

An analysis of 1560 participants in a worksite hypertension control program ⁴ categorized them as having either isolated diastolic hypertension (systolic <160 mm Hg and diastolic >90 mm Hg) or combined hypertension (systolic >160 mm Hg and diastolic >90 mm Hg). Over a 4.5 year follow‐up period, there were 24 cases of myocardial infarction, giving a rate of 3.9 per 1000 patient‐years. This was higher in the patients with combined hypertension than in patients with isolated diastolic hypertension (5.2 vs. 2.2 per 1000 patient‐years) but was zero in the subgroup of patients with high diastolic pressures and systolic pressures <140 mm Hg.

One of the most illuminating studies is a prospective analysis of 3267 initially healthy Finnish men who were originally evaluated at age 30–45 and were followed for up to 32 years. ³ They were divided into four groups: normotensives (systolic <160 mm Hg and diastolic <90 mm Hg), combined hypertension (systolic >160 mm Hg and diastolic >90 mm Hg), isolated systolic hypertension (systolic >160 mm Hg and diastolic <90 mm Hg), and isolated diastolic hypertension (systolic <160 mm Hg and diastolic >90 mm Hg). The last group was subdivided according to whether the systolic was <140 mm Hg or between 140 and 160 mm Hg. Not surprisingly, in this relatively young group there were very few with isolated systolic hypertension (17 men), but there was a substantial number (346, or more than 10% of the total) of men with isolated diastolic hypertension, where the systolic pressure was <140 mm Hg. With the normotensives as the reference group, the mortality was increased nearly threefold in the combined hypertensives (relative risk [RR], 2.71) and in the group with diastolic hypertension and systolic pressure between 140 and 160 mm Hg (RR, 1.39) but not in the group with isolated diastolic hypertension defined by a systolic pressure <140 mm Hg.

Another study ⁵ (the Japanese Ohasama study) has reported the same finding using home monitoring. This is of particular interest, since there might be systematic errors in reporting diastolic pressure with home monitors, all of which operate on the oscillometric method. Home readings were obtained in 1913 subjects aged 40 or older (average 61 years) who were followed for 8 years. The cutoff points for the different groups (137 mm Hg for systolic and 84 mm Hg for diastolic pressure) were lower than used in studies based on clinic measurements because these were the numbers above which cardiovascular risk started to increase, and it is well recognized that home readings tend to be lower than clinic readings. The cardiovascular event rate during the follow‐up period was the same in the normotensives (0.33 deaths per 100 person‐years) and those with isolated diastolic hypertension (i.e., systolic pressure <137 mm Hg and diastolic >84 mm Hg), where the event rate was 0.26. Significantly higher rates were recorded in subjects with combined hypertension (1.11) or isolated systolic hypertension (2.04).

A study of the Honolulu Heart Program followed 8006 men for 20 years. ⁶ Isolated diastolic hypertension (IDH) was defined as a systolic pressure <160 mm Hg, and a diastolic pressure >90 mm Hg. For men aged 45–54 years, the relative risks of stroke associated with IDH compared with nonhypertensive subjects was 1.4, whereas for men with isolated systolic hypertension or combined hypertension the relative risks were 4.8 and 4.3.

Thus, the consensus from these four studies that looked at the prognosis of IDH is that if the systolic is <140 mm Hg, a high diastolic pressure is not associated with an adverse prognosis.

In some subjects with IDH, the high diastolic pressure may be artifactual. Some years ago we described a method of measuring blood pressure noninvasively using a high fidelity transducer instead of a stethoscope (wideband external pulse recording), which records the low frequency signals as well as the higher frequency components that are audible as the Korotkoff sounds. ⁷ By visual inspection of the traces recorded during cuff deflation, a very accurate estimation of the true systolic and diastolic pressures can be obtained. We found that this method gave a closer agreement with intra‐arterial pressure than the Korotkoff sound method. When we looked at patients with IDH (systolic <140 and diastolic >90), we found that the diastolic pressure recorded by the conventional auscultatory technique was on average 7 mm Hg higher than the value recorded by the wideband method. ⁸ This difference was only 3 mm Hg in patients with combined hypertension and zero in normotensives. Thus, it appeared that a substantial number of patients with IDH might be misclassified by the conventional method of blood pressure measurement.

How do these findings relate to other epidemiological studies, which have specifically compared the prognostic significance of systolic and diastolic pressures? A recent analysis of the Framingham Heart Study data looked at the ability of systolic and diastolic pressure to predict coronary heart disease as a function of age. ⁹ In subjects younger than 50 years of age, diastolic pressure was significantly better than systolic pressure, whereas systolic pressure was better over the age of 50. However, when the data were analyzed in five age groups, it was only the youngest quintile (younger than 40) where this difference was significant. In addition, the method of analysis may have led to a bias favoring diastolic pressure because the hazard ratios were calculated for a 10 mm Hg change in each blood pressure component. A change of diastolic pressure of 10 mm Hg would in real life be associated with a change of systolic pressure that would be considerably more than 10 mm Hg, so it would be more appropriate to look at percentage changes rather than an absolute value. A very similar analysis was performed in the Physicians' Health Study, ¹⁰ which found that both systolic and diastolic pressure predicted outcomes in the two youngest age groups (under 50 and 50–59), but it too calculated the hazard ratios for a 10 mm Hg change of both systolic and diastolic pressure. Interestingly, the confidence intervals were much wider for diastolic than systolic pressure, suggesting a lack of precision in the measurement. Nevertheless, the authors concluded that systolic pressure should be used to predict risk even in men younger than 60. Another analysis of the Physicians' Health Study and the Women's Health Initiative developed risk equation models for predicting clinical outcomes using both systolic and diastolic pressures. It concluded that in men, both systolic and diastolic pressures predicted risk, but in women only systolic pressure was important. ¹¹

The reconciliation of these analyses with the prospective studies of IDH is more difficult. Unfortunately for the present discussion, none of the studies quoted above looked at the individuals with IDH. The only one to find any superiority for diastolic pressure was the Framingham study, where it applied only to subjects under the age of 40. Therefore, it would seem reasonable not to prescribe antihypertensive treatment for patients who present with a high diastolic pressure and a systolic pressure <140 mm Hg at the present time.

This would be consistent with a set of simple guidelines for primary health care published by Sever ¹² in 1999, which included four rules. Rule One was “abandon diastolic pressure measurement and rely on systolic blood pressure values for decisions on treatment thresholds and goals.” This statement may seem like heresy, but in medicine, as in other fields of human belief and endeavor, today's heresy may be tomorrow's dogma.