Cardiovascular Division, Columbia University Medical Center, New York, NY 10032, USA.
Circ Heart Fail. 2012 Sep 1;5(5):560-5. doi: 10.1161/CIRCHEARTFAILURE.112.967695. Epub 2012 Aug 1.
Chronotropic incompetence is defined as the inability to reach 80% of heart rate (HR) reserve or 80% of the maximally predicted HR during exercise. The presence of chronotropic incompetence is associated with reduced peak oxygen consumption, and rate-responsive pacing therapy is under investigation to improve exercise capacity in heart failure (HF). However, uncertainty exists about whether chronotropic incompetence and reduced exercise tolerance in HF are attributable to β-blockade.
Subjects with HF and receiving long-term β-blocker therapy underwent cardiopulmonary exercise tolerance testing under 2 conditions in random sequence: (1) after a 27-hour washout period (Off-BB) and (2) 3 hours after β-blocker ingestion (On-BB). Norepinephrine levels were drawn at rest and at peak exercise. β1-response to norepinephrine was assessed using the chronotropic responsiveness index: ΔHR/Δlog norepinephrine. Nineteen patients with systolic HF (left ventricular ejection fraction, 22.8±7.7%) were enrolled. Mean age was 49.4±12.3 years. Average carvedilol equivalent dose was 29.1±17.0 mg daily. Peak HR off/on β-blockers was 62.7±18.7% and 51.4±18.2% HR reserve (P<0.01) and 79.1±11.0% and 70.3±12.3% maximally predicted HR (P<0.01). For the Off-BB and On-BB conditions, the respiratory exchange ratios were 1.05±0.06 and 1.05±0.10 (P=0.77), respectively, confirming maximal and near identical effort in both conditions. The peak oxygen consumption was 16.6±3.34 and 15.9±3.31 mL/kg/min (P=0.03), and the chronotropic responsiveness index was 19.3±7.2 and 16.2±7.1 (P=0.18).
Acute β-blocker cessation does not normalize the chronotropic response to exercise in patients with advanced HF and chronotropic incompetence.
变时性功能不全定义为运动时无法达到心率（HR）储备的 80%或最大预测 HR 的 80%。变时性功能不全的存在与峰值耗氧量降低有关，正在研究速率响应起搏治疗以改善心力衰竭（HF）患者的运动能力。然而，HF 中变时性功能不全和运动耐量降低是否归因于β受体阻滞剂仍存在不确定性。
接受长期β受体阻滞剂治疗的 HF 患者在随机顺序下进行两种条件下的心肺运动耐力测试：（1）在 27 小时洗脱期（Off-BB）后，和（2）β受体阻滞剂摄入后 3 小时（On-BB）。在休息和峰值运动时抽取去甲肾上腺素水平。使用变时性反应指数评估β1-对去甲肾上腺素的反应：ΔHR/Δlog 去甲肾上腺素。19 名收缩性 HF 患者（左心室射血分数，22.8±7.7%）入选。平均年龄为 49.4±12.3 岁。平均卡维地洛等效剂量为 29.1±17.0mg/天。β受体阻滞剂脱/服后峰值 HR 分别为 62.7±18.7%和 51.4±18.2%的 HR 储备（P<0.01）和 79.1±11.0%和 70.3±12.3%最大预测 HR（P<0.01）。对于 Off-BB 和 On-BB 条件，呼吸交换比分别为 1.05±0.06 和 1.05±0.10（P=0.77），证实两种条件下的努力均达到最大且几乎相同。峰值耗氧量分别为 16.6±3.34 和 15.9±3.31 mL/kg/min（P=0.03），变时性反应指数分别为 19.3±7.2 和 16.2±7.1（P=0.18）。
急性停用β受体阻滞剂并不能使晚期 HF 和变时性功能不全患者的运动时变时反应正常化。
