In a large observational study of US veterans with chronic kidney disease, the combination of low systolic BP and low diastolic BP was associated with high mortality rates. Further, diastolic BP <70 mm Hg was linked to higher mortality in this patient population, regardless of systolic BP level.
The lowest mortality rates for this group of patients with chronic kidney disease (CKD) were reported in those with stage I hypertension (systolic BP 140 mm Hg-159 mm Hg or diastolic BP 90 mm Hg-99 mm Hg), according to the report.
“The optimal BP in patients with CKD seems to be 130-159/70-89 mm Hg,” Csaba P. Kovesdy, MD, of the division of nephrology at the Memphis Veterans Affairs Medical Center, and colleagues wrote.
Association of BP and death
The researchers reviewed all serum creatinine measurements obtained in US Department of Veterans Affairs hospitals between October 2004 and September 2006. They studied veterans who had non-dialysis–dependent CKD, BP measurements available between October 2004 and April 2012, and could be sufficiently followed for survival analysis (n=651,749; mean age, 73.8 years; 87.8% white). Participants were grouped in categories of systolic BP and diastolic BP in 10-mm Hg increments to assess the association of BP with mortality rates. Median follow-up was 5.8 years.
In the entire study population, 238,640 participants died during the follow-up period (mortality rate, 73.5 deaths per 1,000 patient years; 95% CI, 73.2 deaths per 1,000 patient years to 73.8 deaths per 1,000 patient years). The greatest risk for mortality was in patients with systolic BP <120 mm Hg and diastolic BP <80 mm Hg (adjusted HR=1.42; 95% CI, 1.41-1.43). The lowest mortality risk was in patients with systolic BP 140 mm Hg to 159 mm Hg or diastolic BP 90 mm Hg to 99 mm Hg (adjusted HR=0.95; 95% CI, 0.94-0.96).
When the researchers calculated mortality HRs associated with mutually exclusive categories of systolic BP and diastolic BP combinations, they found the HRs within a category of systolic BP were more likely to be higher the lower the diastolic BP. The highest risk occurred when diastolic BP decreased to less than approximately 70 mm Hg.
The findings “could be due to compromised blood flow to vital organs (especially low [diastolic] BP compromising coronary perfusion) or the high burden of comorbid conditions (for example, CHF) that is characteristic of populations with this association pattern,” Kovesdy and colleagues wrote. They recommended that “further analyses be done in BP treatment trials to determine whether active intervention improves survival in persons with low [diastolic] BP.”
Until there are results from clinical trials to determine “the ideal BP target for antihypertensive therapy in patients with CKD … low BP should be regarded as potentially deleterious in this patient population, and we suggest caution in lowering BP to less than what has been demonstrated as beneficial in randomized, controlled trials,” the researchers wrote.
A cause for concern
In a related editorial, Dena E. Rifkin, MD, MS, of the University of California, San Diego, and Veterans Affairs Healthcare System, San Diego, and Mark J. Sarnak, MD, MS, of Tufts Medical Center, said the study showed that “a seemingly acceptable [systolic] BP combined with a low [diastolic] BP may be a cause for concern, especially in older patients with CKD and comorbid conditions.”
However, they wrote, “It may not be the BP combination per se but the characteristics of the persons with that combination that lead to greater mortality rates. … Low [diastolic] BP may be a marker of the severity of vascular disease or vascular stiffness rather than a modifiable risk factor.”
For more information:
Kovesdy CP. Ann Intern Med. 2013;159:233-242.
Rifkin DE. Ann Intern Med. 2013;159:302-303.
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