Background and objective: Evaluation of hemodynamics in patients with acute myocardial infarction is crucial. In clinical practice, the comparison of a new measurement technique with an established one is often needed to see whether they agree sufficiently for the new to replace the old. Such investigations are often analyzed inappropriately, notably by using correlation coefficients. Our objective is to present an alternative approach, suggested by D. G. Altman and J. M. Bland, based on graphical techniques and simple calculations, for evaluation of the agreement of two methods--intermittent thermodilution (recognized and accepted as a "gold standard" for hemodynamic monitoring) and impedance cardiography (newly introduced method).
Patients and methods: A total of 34 patients (20 (58.8%) men and 14 (41.2%) women) were investigated according to the study protocol at Kaunas University of Medicine Hospital. A prospective controlled study was designed to compare two different methods--intermittent thermodilution and impedance cardiography--of cardiac output measurement simultaneously in patients with acute myocardial infarction. Statistical analysis was performed with Bland-Altman and linear regression.
Results: A total of 34 paired measurements were carried out in 34 patients at the initiation of hemodynamic monitoring and 30 paired measurements in 32 patients after subsequent improvement or stabilization of clinical status. Correlation coefficient ranged from 0.37 to 0.98.
Conclusions: Bland-Altman analysis is an alternative method for assessing the agreement between two methods of clinical measurement. According to our data, noninvasive technique--impedance cardiography--is a reliable method for hemodynamic monitoring in noncomplicated cases of acute myocardial infarction.