Background: A biomechanical model of the heart can be used to incorporate multiple data sources (ECG, imaging, invasive hemodynamics). The purpose of this study was to use this approach in a cohort of tetralogy of Fallot patients after complete repair (rTOF) to assess comparative influences of residual right ventricular outflow tract obstruction (RVOTO) and pulmonary regurgitation on ventricular health.
Methods: 20 rTOF patients who underwent percutaneous pulmonary valve replacement (PVR) and cardiovascular magnetic resonance (CMR) were included in this retrospective study. Biomechanical models specific to individual patient and physiology (pre-and post-PVR) were created and utilized to estimate the RV myocardial contractility. The ability of models to capture post-PVR changes of RV enddiastolic volume (EDV) and effective flow in pulmonary artery (Qeff) was also compared to expected values. Results: RV contractility pre-PVR (65±17 kPa, mean ± SD) was increased in rTOF patients in comparison to normal RV (39-45 kPa) (p<0.05). The contractility decreased significantly in all patients post-PVR (p<0.05). Patients with predominantly RVOTO demonstrated greater reduction in contractility (median decrease 35%) post-PVR than those with predominant pulmonary regurgitation (median decrease 12%). The model simulated post-PVR decreased EDV for majority and suggested an increase of Qeffboth in line with published data. Conclusions: This study uses a biomechanical model to synthesize multiple clinical inputs and give an insight into RV health. Individualized modeling allows us to predict the RV response to PVR. Initial data suggest that residual RVOTO imposes greater ventricular work than isolated pulmonary regurgitation.
When combining cardiovascular magnetic resonance imaging (CMR) with pressure catheter measurements, the acquired image and pressure data need to be synchronized in time. The time offset between the image and pressure data depends on a number of factors, such as the type and settings of the MR sequence, duration and shape of QRS complex or the type of catheter, and cannot be typically estimated beforehand. In the present work we propose using a biophysical heart model to synchronize the left ventricular (LV) pressure and volume (P-V) data. Ten patients, who underwent CMR and LV catheterization, were included. A biophysical model of reduced geometrical complexity with physiologically substantiated timing of each phase of the cardiac cycle was first adjusted to individual patients using basic morphological and functional indicators. The pressure and volume waveforms simulated by the patient-specific models were then used as templates to detect the time offset between the acquired ventricular pressure and volume waveforms. Time-varying ventricular elastance was derived from clinical data both as originally acquired as well as when time-synchronized, and normalized with respect to end-systolic time and maximum elastance value (E N orig (t), E N t-syn (t), respectively). E N t-syn (t) was significantly closer to the experimentally obtained E N exp (t) published in the literature (p<0.05, L 2 norm). The work concludes that the model-driven time-synchronization of P-V data obtained by catheter measurement and CMR allows to generate high quality P-V loops, which can then be used for clinical interpretation.
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Ethics approval and consent to participateThe data collections for single-ventricle patients were performed under the ethical approvals of the Institutional Review Boards of UT Southwestern Medical Center Dallas (STU 032017-061). The data collections for rTOF patients were performed under the ethical approvals of the Institutional Review Boards of UT Southwestern Medical Center Dallas (STU-2020-0023) and UT Austin (IRB 2020-06-0128). The IRBs waived the need for a consent to use the anonymized retrospective data.
Biomechanical models coupled with cardiovascular MRI (CMR) have the potential to provide non-invasively physiological parameters of clinical interest. The approach is presented and validated on a group of 10 patients who underwent CMR and invasive catheterization. Patient-specific models are built based on CMR data and maximum/minimum arterial pressure. The stroke work, derived from ventricular pressure-volume (P-V) loops, was comparable between the measured and simulated P-V loops, suggesting the high quality of the in silico loops. An excellent correlation of the model-derived myocardial contractility with maximum time-derivative of ventricular pressure gives an opportunity for the non-invasive characterization of patients’ inotropic state.
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