Radial Artery Tonometry to Determine Cardiac Output in Left Ventricular Assist Device Patients: A Comparison with Transthoracic Echocardiography

Objectives: Measurements of cardiac function parameters such as cardiac output (CO) and stroke volume (SV) are crucial in the follow-up of left ventricular assist device (LVAD) patients. None invasive and easy to use techniques to estimate hemodynamic parameters in outpatient departments are gaining relevance as alternative method.

Methods: For our pilot study, we sought to compare CO estimated from a 3D blood pressure pulse analyzer (BPPA) (DMP-Life, DAEYOMEDI Co., Ltd., Gyeonggi-do, South Korea) to LVAD calculated blood flow (cBF) and to pulsed-wave Doppler (PWD) echocardiography derived parameters in LVAD patients. From July 2016 to April 2017, 32 LVAD patients (10 HeartMate 3, 22 HeartMate II) with a mean age 64 ± 6 (31 males, mean BMI 26 ± 5 kg/m²), who were in a follow-up in our outpatient department, had simultaneously transthoracic echocardiography (TTE), pulse analyses with BPPA and the cBF from the LVAD was also documented. According to TTE findings, patients were then subdivided in two groups: patients with a regular opening aortic valve (OAV) [20 patients] and those with intermittent opening or closed aortic valve (CAV) [12 patients].

Results: In all patients, the comparison of cBF and CO measured by BPPA with Bland-Altmann-test, showed similar results on average, but the bias (difference between the means) was 0.7 with [95%-CI: −3.2 −1.6]. This could be explained by the fact that BPPA measures both cBF and the patients’ own CO, if the patients still have ejection fraction. In the CAV groups, the cBF and BPPA's CO correlated very well (bias only 0.05, [95%-CI: −0.3–0.4]). In OAV group the bias between BPAA's and cBF was 1.3 [95%-CI: −3.7 −1.03]. In the OAV group, 16 patients had an accurate TTE to measure PWD derived CO. mean PWD derived CO was 1.5 ± 1.0 L/min. In these 16 patients after adding the PWD's CO to the cBF derived from the LVAD, BPAA's CO and cBF + TTE's CO correlated very well with only a bias of 0.04 [95%-CI: −0.3 −0.2], indicating that BPAA measures both cBF and patients own cardiac output accurately.

Conclusion: Blood pressure pulse analyzer is a relative quick and simple method, which facilitates the collection of cardiac function parameters in LVAD patients in the outpatient departments. BPPA provide sufficient information about patients own cardiac output and correlate very well with blood flow calculated by the LVAD. Further analyses are necessary to detect aortic valve opening in LVAD patients through the pulse wave analyses.