Importance of compensatory heart rate increase during myocardial ischemia to preserve appropriate oxygen kinetics.

J Cardiol. 2017 Mar 7. pii: S0914-5087(16)30308-2. [Epub ahead of print]

Yoshida S, Adachi H, Murata M, Tomono J, Oshima S, Kurabayashi

BACKGROUND: Myocardial ischemia induces cardiac dysfunction, resulting in
insufficient oxygen supply to peripheral tissues and mismatched energy production
during exercise. To relieve the insufficient oxygen supply, heart rate (HR)
response is augmented; however, beta-adrenergic receptor blockers (BB) restrict
HR response. Although BB are essential drugs for angina pectoris, the effect of
BB on exercise tolerance in patients with angina has not been studied. The aim of
this study was to clarify the importance of HR augmentation to preserve exercise
tolerance in patients with angina pectoris.
METHODS: Forty-two subjects who underwent cardiopulmonary exercise testing (CPX)
to detect myocardial ischemia were enrolled. CPX was performed until exhaustion
or onset of significant myocardial ischemia using a ramp protocol. Subjects were
assigned to three groups (Group A: with ST depression during CPX with significant
coronary stenosis and taking BB; Group B: with ST depression and not taking BB;
Group C: without ST depression and not taking BB). HR response to exercise was
evaluated during the following two periods: below and above ischemic threshold
(IT). In Group C, it was evaluated during the first 2min and the last 2min of a
ramp exercise.
RESULTS: No significant differences were observed among the three groups with
regard to patients’ basic characteristics. Below IT, there were no differences in
oxygen pulse/watt (O2 pulse increasing rate), HR/watt (ΔHR/ΔWR), and ΔV˙O2/ΔWR.
Above IT, O2 pulse increasing rate was greater in Group A than in Group B.
ΔHR/ΔWR was smaller in Group A than in Group B. ΔV˙O2/ΔWR became smaller in Group
A than in Group B. There was no difference in anaerobic threshold, and peak V˙O2
was smaller in Group A than in Group B.
CONCLUSIONS: Restriction of HR response by a BB is shown to be one of the
important factors in diminished exercise tolerance.