title: [Chronotropic-metabolic index in Chagas' disease].
abstract: Chronotropic incompetence is a common feature in Chagas' disease patients. New methodologies are now available to evaluate the chronotropic response in different subsets. The chronotropic-metabolic index (CMI) is one of these new indexes and quantifies the relationship between the increment of heart rate and the maximal oxygen consumption (VO2 max) during exercise testing. In normal subjects there is linear response and the index is round 1.0. The aim of the study was to evaluate the chronotropic response in healthy controls and Chagas' disease patients with and without left ventricular dysfunction, using CMI. Twenty-four controls and 171 Chagas' disease patients underwent a clinical protocol and maximal exercise testing. Chagas' disease patients were divided into two groups: Ch1= patients with ejection fraction (EF) > 39% and Ch2 = EF < 40%. CMI was analyzed and calculated according to the Wilkoff method. Chagas' disease patients were older than controls and showed higher prevalence of right bundle branch block, as well as lower VO2 max during exercise. Both groups of Chagas' disease patients showed a less steep curve in the chronotropic-metabolic index (Ch1: 0.91+/-0.10, Ch2: 0.89+/-0.08) than controls (1.0+/-0.12, p < 0.001). Chagas' disease patients with and without left ventricular dysfunction chronotropic incompetence may exhibit reduced chronotropic response to exercise, expressed by a less steep chronotropic-metabolic index.
authors.affiliation: Faculdade de Medicina, Universidade de Minas Gerais, Belo Horizonte, MG, Brazil.
authors.forename: Ana Luiza Lunardi
authors.initials: AL
authors.lastname: Rocha
authors.forename: Manoel Otávio da Costa
authors.initials: MO
authors.lastname: Rocha
authors.forename: Bruno Otávio Soares
authors.initials: BO
authors.lastname: Teixeira
authors.forename: Federico
authors.initials: F
authors.lastname: Lombardi
authors.forename: Cláudia Drumond Guimarães
authors.initials: CD
authors.lastname: Abreu
authors.forename: Roberto José
authors.initials: RJ
authors.lastname: Bittencourt
authors.forename: Márcio Vinícius Lins
authors.initials: MV
authors.lastname: Barros
authors.forename: Antonio Luiz Pinho
authors.initials: AL
authors.lastname: Ribeiro
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D002598:Chagas Cardiomyopathy / Q000503:physiopathology; D014355:Chagas Disease / Q000503:physiopathology*; D003430:Cross-Sectional Studies; D005080:Exercise Test; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology*; D011446:Prospective Studies; D018487:Ventricular Dysfunction, Left / Q000503:physiopathology*