[The metabolic-chronotropic relation in patients with heart failure--a correlation with functional capacity]

Previous studies on chronotropic incompetence (CI) in patients with congestive heart failure (CHF) have defined it as the inability to achieve > 80% of age predicted maximum heart rate (HR) (adequacy of HR response to submaximal exercise levels not being considered). The metabolic chronotropic relation (MCR) concept proposed by Wilkoff allows the assessment of the entire chronotropic function. The value of such an approach for the evaluation of CI in patients with CHF, and its relation to exercise capacity, is unclear at present.

We imposed maximal symptom-limited treadmill exercise testing while measuring breath-by-breath oxygen consumption, using CAEP protocol, in 25 patients (19 men), 49 +/- 10 years, all in sinus rhythm, with CHF secondary to dilated cardiomyopathy (17) or ischemic heart disease (8), NYHA class II-III. Anaerobic threshold (AT) was attained by all. No exercise was terminated due to arrhythmia or ischemia. MCR was calculated as the slope of the relation between the percentages of HR and metabolic reserves achieved at the end of each exercise stage. Using 2.0 standard deviations below the mean level of MCR in healthy controls, we defined an MCR value < 0.84 as abnormal. The parameters analysed were: age, drug therapy, fractional shortening (FS-%), resting HR (RHR-bpm), exercise duration (DUR-min), peak HR (HRp), peak oxygen consumption (VO2p-ml/kg/min), percentages of predicted maximal HR (% PMHR) and VO2 (% PMVO2), peak ventilatory equivalent for CO2 (VE/VCO2-L/min), time to AT (T-AT), and VO2 at AT (VO2-AT).

MCR was normal (1.01 +/- 0.18-0.86 to 1.19) in 10 patients--Group I, and abnormal (0.66 +/- 0.13-0.42 to 0.81) in 15 (60%) patients--Group II. A similar proportion of patients in both groups were taking ACE inhibitors, digoxin and amiodarone. [table: see text] CI defined as an inability to achieve a % PMHR > 80% occurred only in 6 (24%) patients, all in Group 2 (p = 0.022 versus abnormal MCR).

In CHF patients, CI assessed as an abnormal MCR is frequent, and relates to an impaired exercise capacity.