Whether lower heart rate thresholds (defined as the percentage of age-predicted maximal heart rate achieved, or ppMHR) should be used to determine chronotropic incompetence in patients on beta-blocker therapy (BBT) remains unclear. In this retrospective cohort study, we analyzed 64,549 adults without congestive heart failure or atrial fibrillation (54 ± 13 years old, 46% women, 29% black) who underwent clinician-referred exercise stress testing at a single health care system in Detroit, Michigan from 1991 to 2009, with median follow-up of 10.6 years for all-cause mortality (interquartile range 7.7 to 14.7 years). Using Cox regression models, we assessed the effect of BBT, ppMHR, and estimated exercise capacity on mortality, with adjustment for demographic data, medical history, pertinent medications, and propensity to be on BBT. There were 9,259 deaths during follow-up. BBT was associated with an 8% lower adjusted achieved ppMHR (91% in no BBT vs 83% in BBT). ppMHR was inversely associated with all-cause mortality but with significant attenuation by BBT (per 10% ppMHR HR: no BBT: 0.80 [0.78 to 0.82] vs BBT: 0.89 [0.87 to 0.92]). Patients on BBT who achieved 65% ppMHR had a similar adjusted mortality rate as those not on BBT who achieved 85% ppMHR (p >0.05). Estimated exercise capacity further attenuated the prognostic value of ppMHR (per-10%-ppMHR HR: no BBT: 0.88 [0.86 to 0.90] vs BBT: 0.95 [0.93 to 0.98]). In conclusion, the prognostic value of ppMHR was significantly attenuated by BBT. For patients on BBT, a lower threshold of 65% ppMHR may be considered for determining worsened prognosis. Estimated exercise capacity further diminished the prognostic value of ppMHR particularly in patients on BBT.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine