Towards a Personalized and Dynamic CRT-D

Background: In spite of cardiac resynchronization therapy (CRT) benefits, 25 – 30% of patients are still non responders. One of the possible reasons could be the non optimal atrioventricular (AV) and interventricular (VV) intervals settings. Our aim was to exploit a numerical model of cardiovascular system for AV and VV intervals optimization in CRT.

Methods: A numerical model of the cardiovascular system CRT-dedicated was previously developed. Echocardiographic parameters, Systemic aortic pressure and ECG were collected in 20 consecutive patients before and after CRT. Patient data were simulated by the model that was used to optimize and set into the device the intervals at the baseline and at the follow up. The optimal AV and VV intervals were chosen to optimize the simulated selected variable/s on the base of both echocardiographic and electrocardiographic parameters.

Results: Intervals were different for each patient and in most cases, they changed at follow up. The model can well reproduce clinical data as verified with Bland Altman analysis and T-test (p > 0.05). Left ventricular remodeling was 38.7% and left ventricular ejection fraction increasing was 11% against the 15% and 6% reported in literature, respectively.

Conclusions: The developed numerical model could reproduce patients conditions at the baseline and at the follow up including the CRT effects. The model could be used to optimize AV and VV intervals at the baseline and at the follow up realizing a personalized and dynamic CRT. A patient tailored CRT could improve patients outcome in comparison to literature data.

Continuous-flow pump model study: the effect on pump performance of pump characteristics and cardiovascular conditions

This model study evaluates the effect of pump characteristics and cardiovascular data on hemodynamics in atrio-aortic VAD assistance. The model includes a computational circulatory sub-model and an electrical sub-model representing two rotary blood pumps through their pressure-flow characteristics. The first is close to a pressure generator-PG (average flow sensitivity to pressure variations, -0.047 l mmHg(-1)); the second is closer to a flow generator-FG (average flow sensitivity to pressure variations, -0.0097 l mmHg(-1)). Interaction with VAD was achieved by means of two interfaces, behaving as impedance transformers. The model was verified by use of literature data and VAD onset conditions were used as a control for the experiments. Tests compared the two pumps, at constant pump speed, in different ventricular and circulatory conditions: maximum ventricular elastance (0.44-0.9 mmHg cm(-3)), systemic peripheral resistance (781-1200 g cm(-4) s(-1)), ventricular diastolic compliance C p (5-10-50 cm(3) mmHg(-1)), systemic arterial compliance (0.9-1.8 cm(3) mmHg(-1)). Analyzed variables were: arterial and venous pressures, flows, ventricular volume, external work, and surplus hemodynamic energy (SHE). The PG pump generated the highest SHE under almost all conditions, in particular for higher C p (+50 %). PG pump flow is also the most sensitive to E max and C p changes (-26 and -33 %, respectively). The FG pump generally guarantees higher external work reduction (54 %) and flow less dependent on circulatory and ventricular conditions. The results are evidence of the importance of pump speed regulation with changing ventricular conditions. The computational sub-model will be part of a hydro-numerical model, including autonomic controls, designed to test different VADs.

Acoustic system for the estimation of the temporary blood chamber volume of the POLVAD heart supporting prosthesis

BACKGROUND

The paper presents a newly researched acoustic system for blood volume measurements for the developed family of Polish ventricular assist devices. The pneumatic heart-supporting devices are still the preferred solution in some cases, and monitoring of their operation, especially the temporary blood volume, is yet to be solved.

METHODS

The prototype of the POLVAD-EXT prosthesis developed by the Foundation of Cardiac Surgery Development, Zabrze, Poland, is equipped with the newly researched acoustic blood volume measurement system based on the principle of Helmholtz's acoustic resonance. The results of static volume measurements acquired using the acoustic sensor were verified by measuring the volume of the liquid filling the prosthesis. Dynamic measurements were conducted on the hybrid model of the human cardiovascular system at the Foundation, with the Transonic T410 (11PLX transducer - 5% uncertainty) ultrasound flow rate sensor, used as the reference.

RESULTS

The statistical analysis of a series of static tests have proved that the sensor solution provides blood volume measurement results with uncertainties (understood as a standard mean deviation) of less than 10%. Dynamic tests show a high correlation between the results of the acoustic system and those obtained by flow rate measurements using an ultrasound transit time type sensor.

CONCLUSIONS

The results show that noninvasive, online temporary blood volume measurements in the POLVAD-EXT prosthesis, making use of the newly developed acoustic system, provides accurate static and dynamic measurements results. Conducted research provides the preliminary view on the possibility of reducing the additional sensor chamber volume in future.

Hybrid model analysis of intra-aortic balloon pump performance as a function of ventricular and circulatory parameters

We investigated the effects of the intra-aortic balloon pump (IABP) on endocardial viability ratio (EVR), cardiac output (CO), end-systolic (V(es)) and end-diastolic (V(ed)) ventricular volumes, total coronary blood flow (TCBF), and ventricular energetics (external work [EW], pressure-volume area [PVA]) under different ventricular (E(max) and diastolic stiffness) and circulatory (arterial compliance) parameters. We derived a hybrid model from a computational model, which is based on merging computational and hydraulic submodels. The lumped parameter computational submodel consists of left and right hearts and systemic, pulmonary, and coronary circulations. The hydraulic submodel includes part of the systemic arterial circulation, essentially a silicone rubber tube representing the aorta, which contains a 40-mL IAB. EVR, CO, V(es), and V(ed), TCBF and ventricular energetics (EW, PVA) were analyzed against the ranges of left ventricular E(max) (0.3-0.5-1 mm Hg/cm(3)) and diastolic stiffness V(stiffness) (≈0.08 and ≈0.3 mm Hg/cm(3), obtained by changing diastolic stiffness constant) and systemic arterial compliance (1.8-2.5 cm(3)/mm Hg). All experiments were performed comparing the selected variables before and during IABP assistance. Increasing E(maxl) from 0.5 to 2 mm Hg/cm(3) resulted in IABP assistance producing lower percentage changes in the selected variables. The changes in ventricular diastolic stiffness strongly influence both absolute value of EVR and its variations during IABP (71 and 65% for lower and higher arterial compliance, respectively). V(ed) and V(es) changes are rather small but higher for lower E(max) and higher V(stiffness). Lower E(max) and higher V(stiffness) resulted in higher TCBF and CO during IABP assistance (∼35 and 10%, respectively). The use of this hybrid model allows for testing real devices in realistic, stable, and repeatable circulatory conditions. Specifically, the presented results show that IABP performance is dependent, at least in part, on left ventricular filling, ejection characteristics, and arterial compliance. It is possible in this way to simulate patient-specific conditions and predict the IABP performance at different values of the circulatory or ventricular parameters. Further work is required to study the conditions for heart recovery modeling, baroreceptor controls, and physiological feedbacks.