Population
We carried out a cross-sectional study of the population, including data collected from February 2004 until February 2006, from 81 subjects (46 men and 35 women) aged 41.4 ± 5.6 years (range, 30–50 years), whose ECG, chest X-ray and 2-D echo were normal. Subjects were divided into 2 groups: a Chagas group (54 patients with the indeterminate phase of Chagas' disease) and a control group (27 normal subjects). All patients were referred from the Instituto Nacional de Parasitología "Dr. Mario Fatala Chaben", in Buenos Aires. After patients were explained the goal of this investigation, all of them signed the informed consent.
The study was approved by our Institutional Review Board and the Investigation Health Council of the Secretary of Health of the Government of the City of Buenos Aires.
All patients with Chagas' disease, 25 men and 29 women, aged 41.7 ± 5.7 years (range 30–50 years), had a history of residence in an endemic zone and were asymptomatic.
Exclusion criteria were: coronary artery disease, valvular, myocardial or pericardial disease, congenital heart disease, clinical evidence of heart failure or asymptomatic systolic dysfunction (ejection fraction < 50%), hypertension, diabetes mellitus, anemia, asthma, chronic obstructive pulmonary disease, thyroid dysfunction, renal failure, pregnancy, a history of alcohol intake or other disorders that could potentially cause cardiac disease.
Left ventricular (LV) dilatation was a reason for exclusion of patients when the diastolic diameter of the LV exceeded 3.2 cm/m2, and similarly for systolic dysfunction when shortening fraction was below 28%.
Prior to selection, patients underwent an anamnesis, physical exam, ECG, chest X-ray, cardiac Doppler-echo and laboratory blood tests (complete blood count, sedimentation rate, blood urea nitrogen, creatinine, glycemia, ionogram, T3, T4, TSH and serology for Chagas' disease).
Immunodiagnostic tests were considered reactive for Chagas' disease in the following cases: enzymatic assay > 0.200, quantitative indirect hemagglutination > 1:32, quantitative indirect immunofluorescence > 1:32. Patients in whom 2 of these 3 tests were positive for Trypanosoma cruzi, were considered to have Chagas' disease.
Control group
The control group consisted of 27 healthy volunteers, 21 men and 6 women, with a mean age of 40.5 ± 5.2 years (range 30–48 years), no history of endemic environment for South American trypanosomiasis, negative serology for Chagas' disease, normal physical exam, ECG, chest X-ray and Doppler-echo, and with similar exclusion criteria.
Two-dimensional echocardiography
Doppler-echocardiograms were performed with Philips ultrasound equipment and a 2.5 MHz transducer. Parasternal (long- and short-axis views) and apical views were obtained (four-chamber, two-chamber and apical long-axis views).
All studies were recorded on videotape for their deferred analysis. Echocardiograms were reviewed by 2 experienced readers who were not aware of the serum test results for Chagas' disease.
The M-mode was derived from the short-axis view at the papillary muscle level, and the following parameters were measured according to the American Society of Echocardiography guidelines [6]: LV end diastolic diameter (LVEDd), LV end systolic diameter (LVESd), septal and posterior wall thickness, and antero-posterior diameter of the left atrium, measured from the left parasternal long-axis. The LV shortening fraction was calculated with the following formula: [(LVEDd-LVESd)/LVEDd] × 100.
The LV mass index was calculated according to Devereux's formula [7], and hypertrophy was defined as a value > 134 g/m2 for men and > 110 g/m2 for women.
Transmitral flow velocity
Transmitral flow velocity was used to quantify left ventricular diastolic function (Figure 1). The sample volume was placed at the tip of the mitral valve leaflets in the four-chamber apical view. Peak early diastolic velocity (E-wave), peak late diastolic velocity (A-wave), E/A ratio and early filling deceleration time were measured [8].
All studies were recorded on videotape and later analyzed by two independent investigators who were unaware of the patients' clinical data. For each quantitative parameter, three consecutive beats were averaged.
Statistical analysis
Quantitative data that were normally distributed were expressed as means ± standard deviation, and data with a non-gaussian distribution were expressed as medians (inter-quartile interval).
The comparison of inter-group quantitative variables was performed with a t-test in the case of variables with a normal distribution, and with the Wilcoxon Rank Sum Test in the case of variables with a non-normal distribution.
In 20 subjects, the intraclass correlation coefficient was used [9] to measure the intraobserver agreement between two measurements, and the interobserver agreement between the average of the intraobserver measurements and one interobserver measurement. A p value < 0.05 was considered to be statistically significant.
Statistical analyses were performed with the Statistix 7.0 software for Windows.