Validation of impedance cardiography in pulmonary arterial hypertension

Summary Background Non‐invasive methods of measuring cardiac output are highly desirable in pulmonary arterial hypertension (PAH). We therefore sought to validate impedance cardiography ( ICG ) against thermodilution ( TD ) and cardiac magnetic resonance ( CMR ) in the measurement of cardiac output in patients under investigation for PAH. Methods A prospective, cross‐sectional study was performed to compare single‐point measurements of cardiac output obtained by impedance cardiography ( CO ICG ) technology (PhysioFlow ® ) with (i) contemporaneous TD measurements ( CO TD ) at rest and steady‐state exercise during right heart catheterization and (ii) CMR measurements ( CO CMR ) at rest obtained within 72 h. Results Paired CO ICG and CO TD measurements were obtained in 25 subjects at rest and 16 subjects at exercise. CO CMR measurements were obtained in 16 subjects at rest. There was unsatisfactory correlation and agreement between CO ICG and CO TD at rest ( r = 0·42, P = 0·035; bias: 1·21 l min −1 , 95% CI : −2·33 to 4·75 l min −1 ) and exercise ( r = .65, P = .007; bias: 1·41 l min −1 ; 95% CI : −3·99 to 6·81 l min −1 ) and in the change in CO ICG and CO TD from rest to exercise ( r = 0·53, P = 0·033; bias: 0·76 l min −1 , 95% CI : −3·74 to 5·26 l min −1 ). There was also a lack of correlation and unsatisfactory agreement between resting CO ICG and CO CMR ( r = 0·38, P = 0·1; bias: 1·40 l min −1 , 95% CI : −2·48 to 5·28 l min −1 ). In contrast, there was close correlation and agreement between resting CO TD and CO CMR ( r = 0·87, P <0·001; bias: −0·16 l min −1 , 95% CI : −1·97 to 1·65). Conclusions In a representative population of patients under investigation for PAH, ICG showed insufficient qualitative and quantitative value in the measurement of resting and exercise cardiac output when compared with TD and CMR .