Usually in hypertension, both systolic and diastolic blood pressures are raised. However, there can be conditions in which only either of the two is raised above normal. Isolated systolic hypertension is a clearly defined separate entity in JNC 7 classification. In isolated systolic hypertension, only the systolic blood pressure is above normal. Both hypertension and isolated systolic hypertension (ISH) can cause target-organ damage in hypertension.
However, in JNC 7, no separate classification of hypertension is mentioned with high diastolic blood pressure and normal systolic blood pressure (Isolated diastolic hypertension or IDH). This condition is included in the hypertension/prehypertension category and treated along similar lines as other forms of hypertension. Earlier diastolic blood pressure was considered the most important predictor of future cardiovascular system risk. However, the current weight of evidence from numerous studies suggests otherwise.
In comparison to hypertension with systolic elevation of blood pressure (isolated systolic hypertension or systolic-diastolic hypertension), isolated diastolic hypertension confers a much lower risk of future complications due to target-organ damage. IDH with systolic blood pressure lower than 140 mm Hg is considered to be equivalent to normal blood pressure in terms of risk for cardiovascular complications and is not associated with any adverse outcome. Only ISH and systolic-diastolic hypertension increases the risk for future complications.
There are also speculations regarding the possibility that the elevated diastolic pressure in IDH might be artifactual due to an error in the measurement of blood pressure by routine auscultatory method. Studies using more accurate techniques for blood pressure measurement showed that diastolic blood pressure can be overestimated sometimes. This combined with the possibility that the IDH carries a much lower risk for target-organ damage raises serious question marks on the currently recommended pharmacological therapy for IDH.
However, despite numerous studies, the significance of IDH is not yet fully known and recently there have been some mixed reports on the future outlook of isolated diastolic hypertension. One recent trial found like isolated systolic hypertension and systolic-diastolic hypertension, IDH also is associated with increased risk of cardiovascular diseases. It was found in the PROGRESS (Perindopril Protection Against Recurrent Stroke Study) trial that lowering blood pressure in isolated diastolic hypertension is beneficial in reducing the risks of major vascular events (stroke, etc.). However, it might be too early to change the views based on finding of just one trial, and more research is needed in this area. It might be possible that there may be only slight benefit from anti-hypertensive drugs in IDH, and the big question still remains unanswered that whether exposing a person with IDH to lifelong medications, and their adverse effects is worth the slight reduction in risk?