J-shaped curve defines heart rate association with outcomes in NSTE-ACS

8 March 2010

MedWire News: Patients with non-ST-segment elevation acute coronary syndrome (NSTE-ACS) are at increased risk for cardiovascular events if their heart rate (HR) on presentation is very low or high, report researchers.

This J-shaped relationship between HR and outcomes contrasts with the direct linear relationship seen in stable coronary artery disease (CAD), where the lower the heart rate is the better the prognosis, and should be considered in ACS prognostic models, say Franz Messerli (Columbia University, New York, USA) and team.

The researchers studied 139,164 patients with NSTE-ACS enrolled in the CRUSADE (Can Rapid risk stratification of Unstable angina patients Suppress Adverse outcomes with Early implementation of the American College of Cardiology/American Heart Association Guidelines) quality improvement initiative.

As reported in the European Heart Journal, 10,391 (8%) of the patients presented with bradycardia (<60 beats per minute [bpm]) and 31,405 (23%) with tachycardia (≥100 bpm).

Overall, 8819 (6.5%) patients suffered a primary outcome event (death/nonfatal re-infarction, or stroke) during hospitalization, of whom 5271 (3.90%) died, 3578 (2.65%) had re-infarction, and 1038 (0.77%) had a stroke.

“The relationship between presenting HR and the primary outcome followed a J-shaped curve with increased event rates above and below a nadir of 60–69 bpm (p<0.001),” Messerli and colleagues write.

Compared with the referent group with a HR of 60–69 bpm, patients with a presenting HR <50 bpm had a 1.31-fold higher risk for the primary outcome, and those with a presenting HR of >130 bpm a 1.43-fold higher risk, after adjusting for baseline variables.

Even among patients presenting with “normal” HR of 60–100 bpm the risk for the primary outcome was higher in those with a presenting HR of 90–99 bpm, at an odds ratio of 1.21 compared with the referent group.

Further analysis indicated that the same pattern was seen for the relationship between HR and total mortality, regardless of baseline use of beta-blocker therapy.

Nevertheless, Stéphane Cook and Otto Hess, from the Swiss Cardiovascular Center in Bern, Switzerland, highlight in a related editorial that mortality rates were lowest when a HR of 50–60 bpm was observed without beta blockers – and twice as high in patients in this HR range on beta-blocker therapy.

“This is an important point, which probably reflects a triviality: A ‘natural’ low HR signals a ‘healthier’ heart while a similar low HR achieved with a HR-reducing drug indicates a more ‘damaged’ heart,” they write.

Although unfortunately CRUSADE has no information concerning the underlying cardiac rhythm (mainly the presence of atrioventricular block or atrial fibrillation), they say, the findings “point towards ‘good clinical sense’ showing that HRs at the extremes (<50 bpm and >100 bpm) are associated with a poor in-hospital outcome and that drug-lowering therapy to attain a resting HR of <70 bpm but >50 bpm will reduce patient mortality.”

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

Eur Heart J 2010; 31: 552–560