A new method using pulmonary gas-exchange kinetics to evaluate efficacy of beta-blocking agents in patients with dilated cardiomyopathy.
OBJECTIVE
The effects of beta-blocking agents on exercise tolerance in cardiopulmonary exercise testing (CPX) have not been fully identified. Because the negative chronotropic effects of these agents produce a sluggish increase in heart rate (HR) during CPX, exercise capacity is actually underestimated by methods that depend on HR-related variables such as peak oxygen uptake (O(2)) and anaerobic threshold (AT). The aim of this study was to clarify the efficacy of beta-blocking agents by means of O(2) kinetics, a parameter independent of HR, in patients with dilated cardiomyopathy (DCM).


METHODS
The exercise capacity of 12 patients (9 men and 3 women; mean +/- SD age, 54 +/- 12 years; New York Heart Association class I [n = 1], NYHA class 2 [n = 4], and NYHA class III [n = 6]) with DCM, who were treated with beta-blocking agents, was evaluated by CPX. O(2) was calculated from respiratory gas analysis on a breath-by-breath basis. Nine patients were treated with metoprolol (30 mg or 60 mg), two with carteolol (10 mg or 20 mg), and one patient with atenolol (25 mg).


RESULTS
All patients showed a significantly favorable results (ie, improvement in symptoms of congestive heart failure). Peak O(2) (20.4 +/- 5.1 to 18.8 +/- 5.8 mL/min/kg), AT (12.7 +/- 3.5 to 12.1 +/- 2.1 mL/min/kg), and exercise time (4.8 +/- 2.2 to 4.5 +/- 2.1 s) were unchanged. The time constant of O(2) kinetics (tau) on response to constant low-dose work loading (warm up) decreased significantly (64 +/- 30 to 44 +/- 24 s; p < 0.01) and ejection fraction increased (30 +/- 14 to 44 +/- 15%, p < 0.01) significantly following treatment with beta-blocking agents. In spite of excluding two NYHA I patients, these changes were also statistically correlated.


CONCLUSIONS
In the low level of exercise, tau was prolonged in patients with DCM. Although indexes of total exercise time and AT were not useful markers for clinical improvement in cardiac performance as assessed by echocardiography, measuring can validly assess the beneficial effects in heart failure treated with beta-blocking agents.
Taniguchi
Yasuyo
Y
Second Department of Internal Medicine, Iwate Medical University, Uchimaru 19-1, Morioka City, Iwate, Japan. y_taniguchi@imu.ncvc.go.jp
Ueshima
Kenji
K
Chiba
Ikuo
I
Segawa
Ikuo
I
Kobayashi
Noboru
N
Saito
Masahiko
M
Hiramori
Katsuhiko
K
D000319:Adrenergic beta-Antagonists / Q000009:adverse effects / Q000627:therapeutic use*; D000328:Adult; D000368:Aged; D001262:Atenolol / Q000009:adverse effects / Q000627:therapeutic use; D001794:Blood Pressure / Q000187:drug effects; D002311:Cardiomyopathy, Dilated / Q000188:drug therapy*; D002354:Carteolol / Q000009:adverse effects / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D004359:Drug Therapy, Combination; D004452:Echocardiography / Q000187:drug effects; D005080:Exercise Test / Q000187:drug effects*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D008790:Metoprolol / Q000009:adverse effects / Q000627:therapeutic use; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D011659:Pulmonary Gas Exchange / Q000187:drug effects*; D016896:Treatment Outcome; D018487:Ventricular Dysfunction, Left / Q000188:drug therapy*; D016277:Ventricular Function, Left / Q000187:drug effects
D000319:Adrenergic beta-Antagonists; D001262:Atenolol; D002354:Carteolol; D008790:Metoprolol; D010100:Oxygen