Relaxin is a naturally occurring hormone thought to be responsible for maternal haemodynamic adjustments to the metabolic demands of pregnancy, including increased vasodilation and renal function. Current ESC guidelines recommend vasodilators for patients admitted with acute heart failure and SBP greater than 110 mmHg. Limited information, however, has been available on the interaction between symptom relief and initial blood pressure.
In the preliminary study of RELAX in Acute Heart Failure (Pre-RELAX-AHF), John R. Teerlink, from University of California San Francisco/Veteran Affairs Medical Centre and colleagues set out to compare the effect of intravenous relaxin with placebo on symptom relief in 234 patients with symptomatic acute heart failure (moderate/severe dyspnea), SBP greater than 125 mmHg, and mild to moderate renal impairment. They were enrolled within the first 16 hours of admission and randomised to four doses of IV relaxin or placebo for 48 hours.
The study (Lancet 2009; 373: 1429-39) showed that in AHF patients a relaxin dose of 30 mcg/kg/day improved dyspnea, signs of congestion, in-hospital worsening of heart failure and the combined endpoint of heart failure re-hospitalisation and death compared to patients treated with standard care plus placebo.
In the current abstract Teerlink and colleagues went on to further investigate whether there might be an interaction between baseline blood pressure and the treatment effects of relaxin on dyspnea. Patients from the Pre-RELAX-AHF study were selected who received relaxin 30 mcg/kg/day (n = 42) and compared to patients given standard of care plus placebo (n = 61), with changes in dyspnea modelled over five days with respect to baseline blood pressures.
Results show a significant interaction effect between baseline blood pressure and improvements in dyspnea (p<0.009). Relaxin was much more effective than standard of care in patients with baseline blood pressures of 135 mmHg or greater. Most patients in the study had SBP greater than 135 mmHg, says Teerlink, adding there were relatively few patients with SBP <135mmHg, limiting reliability of findings below this level.