Isolated Clinic Hypertension and Target Organ Pathology
Although there exists some disagreement regarding the relative cardiac risk and subsequent treatment recommendations for individuals with confirmed isolated clinic hypertension, it has been suggested that this frequent condition may be partially responsible for the weak relation commonly observed between office blood pressure determinations and hypertensive target organ damage (Perloff et al., 1983).
In other words, the reason that clinic-derived measures of blood pressure correlate poorly with indicators of target organ pathology is that samples of persons with elevated clinic blood pressures contain numerous individuals with isolated clinic hypertension, a condition thought to be relatively benign with regard to target organ pathology.
Although it seems obvious that persons with isolated clinic hypertension would exhibit less target organ pathology than persons with diagnosed essential hypertension, let’s examine the evidence that has addressed this hypothesis. Over a dozen studies have assessed target organ pathology among isolated clinic hypertensive patients and compared these values with both sustained hypertensive patients and normotensive controls (see Pickering, Coats, et al., 1999).
From their review of this body of literature, Pickering et al. concluded that target organ pathology of isolated clinic hypertensive patients is invariably less than patients with established hypertension. However, the relation between target organ pathology of isolated clinic hypertensive patients when compared to normotensive controls is less clear. In about half the studies that have been conducted, target organ parameters from isolated clinic hypertensives closely resembled those of normotensive controls (for example, Cavallini et al., 1995; Pierdomenico et al., 1995); however, the remaining studies showed that target organ pathology among isolated clinic hypertension exceeded that of normotensive controls (for example, Kuwajima et al., 1994; Palantini et al., 1998).
Findings from this latter group of studies were somewhat difficult to interpret because ambulatory blood pressures of the isolated clinic hypertensive patients were significantly higher than the normotensive controls, albeit in the normal range of blood pressure.
Mallion et al. (1999) also conducted a review of this body of literature and came to a similar conclusion; studies that found significant differences between isolated clinic hypertensive patients and normotensives tended to employ more liberal ambulatory blood pressure classification criteria for isolated clinic hypertensive patients. For example, in such studies, a patient with a mean clinic blood pressure of 140 / 90 mm Hg and a mean ambulatory blood pressure of 138/88 mm Hg could be classified as having isolated clinic hypertension.
Given that the mean difference between these two assessments was only 2 mm Hg, it hardly seems to represent the type of discrepant blood pressure information typically seen in isolated clinic hypertension. Interestingly, in Mallion et al.’s review, studies adopting the recommended lower cutoffs for ambulatory blood pressures failed to show any difference between isolated clinic hypertension and normotension on a number of measures of target organ pathology.
In an effort to control for group blood pressure differences observed in previous studies, Muldoon et al. (2000) compared the degree of carotid artery atherosclerosis in isolated clinic hypertensives with both hypertensive patients matched on clinic blood pressures and normotensive patients matched on ambulatory blood pressures. In contrast to the suggestions of Mallion et al. (1999), the same blood pressure criteria (140 / 90 mm Hg) was used for both clinic and ambulatory blood pressure measures in categorizing individuals into groups.
After controlling for blood pressure, results revealed that the degree of carotid artery atherosclerosis was equivalent between isolated clinic hypertensive and essential hypertensive patients, and that both hypertensive groups exhibited greater pathology than normotensive controls. Therefore, these findings supported the hypothesis that isolated clinic hypertension was nota benign condition, at least as it pertained to carotid artery pathology.
Finally, Pickering et al. (1999) also examined studies that contrasted cardiovascular morbidity and mortality between isolated clinic hypertensive patients and patients with sustained hypertension. Although not a large number of studies have examined this relation, isolated clinic hypertension was associated with lesser risk for cardiovascular morbidity and mortality than essential hypertension.
In sum, isolated clinic hypertension appears to be associated with less risk for cardiovascular disease and hypertensive target organ pathology than essential hypertension. Among studies adopting the recommended lower cutoff criteria for home or ambulatory blood pressures (135 / 85 mm Hg), there are typically few differences observed between isolated clinic hypertensives and normotensives. In fact, Mallion et al. (1999) stated that as a result of adopting these lower reference values, isolated clinic hypertension became less prevalent and may no longer be considered a significant diagnostic problem.
Nevertheless, there continue to be many patients who exhibit classic isolated blood pressure profiles, and they continue to create difficulties for establishing accurate diagnoses and making appropriate treatment decisions. Additionally, most of the studies that have explored the relation between isolated clinic hypertension and target organ pathology have focused upon measures of left ventricular functioning or kidney pathology. It is possible that isolated clinic hypertension may be associated with a specific type of target organ pathology, perhaps with the carotid artery as suggested by Muldoon et al. (2000).
Although it is premature to derive this type of conclusion from the evidence of a single study, it is important to acknowledge that a variety of types of target organ pathology should be considered and examined before drawing any definitive conclusions regarding the pathological risks associated with isolated clinic hypertension.