How Low Can You Go?

Abstract & Commentary

By Mary Elina Ferris, MD, Clinical Associate Professor, University of Southern California. Dr. Ferris reports no financial relationship to this field of study.

Synopsis: For hypertensives with coronary artery disease, lowering the diastolic pressure below 70-80 mm Hg appears to create increased risk of morbidity and mortality from myocardial infarction and all-cause death.

Source: Messerli FH, et al. Dogma disputed: can aggressively lowering blood pressure in hypertensive patients with coronary artery disease be dangerous? Ann Int Med. 2006;144:884-893.

Using data from the 1997-2003 Invest (International Verapamil-Trandolapril) Study which compared hypertension treatments, a secondary analysis of 22,576 patients with documented coronary artery disease along with hypertension was done to evaluate specific outcomes. Blood pressure (BP) was obtained by averaging 2 readings during visits every 6 weeks for the first six months, then biannually for at least 2 years (median, 2.7 yrs/pt). Follow-up data were available for 97.5% of patients, and individual outcomes were compared to an average BP reading calculated from all readings recorded after the baseline reading. BP averages were grouped in 10 mm strata for the systolic and the diastolic numbers, and compared to death from all causes, fatal/non-fatal myocardial infarction (MI) or stroke.

Hazard ratios were calculated for each outcome and a J-shaped relationship was observed between lowering pressures for MI (both fatal and non-fatal) and all-cause mortality, and for strokes to a lesser extent. Risk of MI and all-cause death were reduced by lowering diastolic pressures to a minimum of 70-80, but any lower was associated with increased risk. This J-shaped curve was also present but more shallow for systolic pressures, and was similar for both treatment strategies in the INVEST trial. The nadir point of declining risk with low pressure was 119/84. When analyzing the effect of multiple variables on this association, most significant was that patients with previous revascularization procedures tolerated lower pressure without less increased risk.

Commentary

It has often been reported that excessive decrease of diastolic pressure can lead to increased risk of coronary heart disease and even death, but this has been disputed, or limited only to increased risk of MI but not stroke. The authors of this article attempt to put the dispute to rest by analyzing data from patients with known coronary artery disease (CAD) who would presumably be most vulnerable to decreased coronary perfusion during diastole.

Their conclusions support the "paradoxical" appearance of a J-curve between rising diastolic pressure and risk of MI or all-cause death, showing that pressures below 119/84 could be harmful for persons with CAD. Only hypertensive patients who have had correction of CAD with revascularization appear to tolerate lower pressures without increased risk, which supports their hypothesis. It could also explain the observed difference between MI over stroke outcomes, since the heart with CAD could be more sensitive than the brain at the lowest pressures.

It's worth noting that patients in this trial were treated with drugs that slow or preserve heart rate; a higher minimum BP might be needed if the heart rate was accelerated and further interfering with perfusion. While the data cannot directly prove that the lowest pressures cause more ischemia, they certainly suggest that we use caution in lowering diastolic pressures below 70-80 mm in our hypertensive patients with CAD.