Levels of agreement between cardiac magnetic resonance and conductance catheter measurements of right ventricular volumes after pulmonary artery banding

Right ventricular volume-strain loops using 3D echocardiography-derived mesh models: proof-of-concept application on patients undergoing different types of open-heart surgery

BACKGROUND

Right ventricular (RV) function can be quantified by right heart catheterization-derived pressure-volume loops. While this technique is invasive, echocardiography-based volume-strain loops (VSLs) potentially reflect a non-invasive alternative. In this study, an approach to generate VSLs from volume and multidimensional strain data of 3D echocardiography-derived RV mesh models is evaluated with regard to feasibility and reproducibility.

METHODS

In a retrospective cohort study design, 3D intraoperative transesophageal echocardiograms of twenty-three patients undergoing aortic valve surgery (AVS) and eighteen patients undergoing off-pump coronary artery bypass (OPCAB) grafting were available prior to sternotomy and after sternal closure. RV meshes were generated using 3D speckle-tracking. Custom-made software quantified the meshes' volumes, global longitudinal (RV-GLS) and global circumferential strain (RV-GCS) for VSL generation. Linear regression of systolic VSLs yielded slopes, intercepts and systolic areas. Polynomial regression of two orders was used to analyze systolic-diastolic coupling at 10% increments of the RV end-diastolic volume (RVEDV). Reproducibility was analyzed by fourfold double-measurements of four datasets.

RESULTS

VSL calculation was feasible from all included 3D datasets. RV-GLS remained unaltered, but RV-GCS worsened in AVS [abs. diff. (∆) 3.9%, P<0.01] and OPCAB patients (∆4.5%, P<0.001). While RV-GCS systolic areas were markedly reduced at the end of AVS (∆268mL%, P<0.01) and OPCAB (∆185mL%, P<0.001), RV-GCS slopes did not change. Systolic-diastolic uncoupling was not observed, but in trend, decreased diastolic RV-GCS after AVS (P=0.06) and increased diastolic RV-GCS after OPCAB (P=0.06) were observed. Intraclass correlation coefficients (0.84-0.98) and coefficients of variation (6.4-11.8%) indicated good reproducibility.

CONCLUSIONS

RV VSL generation using 3D echocardiography-derived mesh models is feasible. Longitudinal and circumferential strain vectors yield intrinsically different VSL indices. In future investigations, VSLs of multidimensional strains could provide further insight into periprocedural changes of RV mechanics.

Effects of Mechanical Ventilation Versus Apnea on Bi-Ventricular Pressure-Volume Loop Recording

Respiration changes intrathoracic pressure and lung volumes in a cyclic manner, which affect cardiac function. Invasive ventricular pressure-volume (PV) loops can be recorded during ongoing mechanical ventilation or in transient apnea. No consensus exists considering ventilatory mode during PV loop recording. The objective of this study was to investigate the magnitude of any systematic difference of bi-ventricular PV loop variables recorded during mechanical ventilation versus apnea. PV loops were recorded simultaneously from the right ventricle and left ventricle in a closed chest porcine model during mechanical ventilation and in transient apnea (n=72). Variables were compared by regression analyses. Mechanical ventilation versus apnea affected regression coefficients for important PV variables including right ventricular stroke volume (1.22, 95% CI [1.08-1.36], p=0.003), right ventricular ejection fraction (0.90, 95% CI [0.81-1.00], p=0.043) and right ventricular arterial elastance (0.61, 95%CI [0.55-0.68], p<0.0001). Right ventricular pressures and volumes were parallelly shifted with Y-intercepts different from 0. Few left ventricular variables were affected, mainly first derivatives of pressure (dP/dt(max): 0.96, 95% CI [0.92-0.99], p=0.016, and dP/dt(min): 0.92, 95% CI [0.86-0.99], p=0.026), which might be due to decreased heart rate in apnea (Y-intercept -6.88, 95% CI [-12.22; -1.54], p=0.012). We conclude, that right ventricular stroke volume, ejection fraction and arterial elastance were mostly affected by apnea compared to mechanical ventilation. The results motivate future standardization of respiratory modality when measuring PV relationships.