Resting bradycardia not associated with worse outcomes in middle-aged and older adults

1. Based on data from the Multi-Ethnic Study of Atherosclerosis (MESA) cohort, resting heart rate (HR) lower than 50 beats per minute was only associated with worse outcomes if patients were taking HR-lowering medications. In contrast, HR greater than 80 beats per minute (bpm), regardless of HR-lowering medications, was associated with poorer outcomes.

2. While patients taking HR-lowering medications had significant medical comorbidities compared to those not taking such medications, HR seemed to be an independent risk factor, with lower HR conferring a benefit. There was, however, a ‘J-curve’ observed amongst those taking HR-lowering medications, and a very low HR (<50 bpm) was associated with worse outcomes.

Evidence Rating Level: 2 (Good)

Study Rundown: Bradycardia, defined as a resting heart rate (HR) under 60 beats per minute, is often seen in asymptomatic young-adults with strong cardiovascular fitness. However, this can be a sign of conduction disease in the elderly, and can be associated with symptoms. Whether bradycardia, either in the setting of medications or not, confers a higher, independent risk for cardiovascular events is unknown. This study, which used data from the Multi-Ethnic Study of Atherosclerosis (MESA) cohort, sought to evaluate this relationship. The results of the study showed that a resting heart rate (HR) lower than 50 beats per minute was only associated with worse outcomes if patients were taking HR-lowering medications. In contrast, HR greater than 80 beats per minute (bpm), regardless of HR-lowering medications, was associated with poorer outcomes. While patients taking HR-lowering medications had significant medical comorbidities compared to those not taking such medications, HR seemed to be an independent risk factor, with lower HR conferring a benefit. There was, however, a ‘J-curve’ observed amongst those taking HR-lowering medications, and a very low HR (<50 bpm) was associated with worse outcomes.

The strength of the study was the diversity of the cohort studied and the long-term follow up, which was needed to study CVD events and mortality. The weakness of the study was the major differences between groups taking HR-lowering medications versus those who were not, so the two sub-groups could not be compared to one another. Although comorbidities within the two subgroups were controlled, there was still risk for bias.

Click to read the study, published today in JAMA Internal Medicine

Relevant Reading: Relation of heart rate at rest and long-term (>20 years) death rate in initially healthy middle-aged men.

In-Depth [retrospective cohort]: The purpose of this study was to evaluate the relationship between bradycardia and incident cardiovascular disease (CVD) and mortality. The study population was the Multi-Ethnic Study of Atherosclerosis (MESA) cohort, which was a population based cohort of over 6,000 people consisting of four ethnic groups (38% white, 28% African American, 22% Hispanic, and 12% Chinese). The age groups represented were 45-84 year olds. The group was recruited between 2000 – 2002 and followed for about 10 years. The major outcomes evaluated were cardiovascular events and mortality. Just under 15% percent of the study population was taking medications to decrease heart rate.

Among patients not taking HR-lowering medications, the mean (SD) HR was 63 (9.5) bpm. Among patients taking HR-lowering medications, the mean (SD) HR was 60 (9.7) bpm. There was higher mortality associated with HR <50 bpm amongst patients taking HR-lowering medications (HR 2.42; 95%CI 1.39–4.20), but outcomes were not worse amongst those not taking any such medications. Amongst both subgroups, incident CVD and mortality were lowest in HR 50-59 bpm range, and highest in the HR >80 bpm range. For patients not taking HR-lowering medications, the increased risk in those with HR >80 bpm was as follows: for incident CVD, hazard ratio 1.55 (95%CI 1.08–2.22); for mortality, hazard ratio 1.49 (95%CI 1.08–2.05). For patients taking HR-lowering medications, the increased risk in those with HR >80bpm was as follows: for CVD events, no statistically significant; for mortality, hazard ratio 3.55 (95%CI 1.65–7.65).

Image: PD

©2016 2 Minute Medicine, Inc. All rights reserved. No works may be reproduced without expressed written consent from 2 Minute Medicine, Inc. Inquire about licensing here. No article should be construed as medical advice and is not intended as such by the authors or by 2 Minute Medicine, Inc.