Use of impedance cardiography in evaluating the exercise response of patients with left venticular dysfunction
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Invasive studies in patients with left ventricular dysfunction show that data at rest (e.g. ejection fraction-EF) are poor predictors of the changes in cardiac output (CO) which occur with exercise. This investigation was undertaken to determine whether impedance cardiography could be used in such patients to assess CO response to exercise. The method was compared with the direct Fick method. Over a range of COs between 4 and 18 min-1 there was no systematic error. Reproducibility for CO over one week was highly significant (r = 0.94; P less than 0.001). Impedance cardiography was incorporated into routine exercise testing on a bicycle ergometer for a group of 15 patients (mean age 53.2 +/- 3.0 yrs, SEM) who had sustained a major myocardial infarct 6 to 12 months previously, (EF 38.1 +/- 3.5%, SEM). CO was measured at the end of each 3-min stage. In eight patients (EF 40.0 +/- 3.4%, SEM) CO response was abnormal with either a decrease or a failure to increase with increasing workloads. Conventional end-points i.e. angina, attainment of 85% of predicted maximum heart rate, abnormal blood pressure response or excessive dyspnoea did not indicate consistently a need to terminate the test. It is suggested that impedance cardiography is a useful non-invasive method of evaluating patients with left ventricular dysfunction.
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