Echocardiographic imaging and ventricular mechanics in pulsatile-flow LVAD pediatric patients: a systematic approach.

Echocardiography plays a crucial role in determining the eligibility for left ventricular assist device (LVAD) placement in patients experiencing advanced heart failure (HF) and in monitoring patient care after the implantation procedure. Because of its unique nature, pediatric population and pulsatile-flow LVADs used in pediatrics require specific skills so that pediatric echocardiographers must develop a systematic approach in order to image the patients pre and post LVAD implantation. Therefore, the purpose of this narrative review is to delineate a systematic echocardiographic approach for pediatric patients supported by pulsatile-flow LVADs.

Sensitivity Analysis of Single Beat Left Ventricular Elastance Estimation by Chen Method.

INTRODUCTION: Left ventricular (LV) end-systolic elastance (Ees) can be estimated using single-beat (Ees(sb)) Chen method, employing systolic and diastolic arm-cuff pressures, stroke volume (SV), ejection fraction and estimated normalized ventricular elastance at arterial end-diastole. This work aims to conduct a sensitivity analysis of Chen formula to verify its reliability and applicability in clinical scenario. METHODS: Starting from a baseline condition, we evaluated the sensitivity of Ees(sb) to the parameters contained in the formula. Moreover, a mathematical model of the cardiovascular system was used to evaluate the sensitivity of Ees(sb) to end-diastolic LV elastance (Eed), Ees, arterial systemic resistance (Ras) and heart rate (HR). RESULTS: In accordance with Ees definition, Ees(sb) increases by increasing aortic pressure and pre-ejection time, reaching the highest value for a pre-ejection time = 40 ms, and then decreases. In contrast with Ees definition, Ees(sb) increases (from 3.21 mmHg/mL to 12.15 mmHg/mL) by increasing the LV end-systolic volume and decreases by increasing the SV. In the majority of the analysis with the mathematical model, Ees was underestimated using the Chen method: by increasing Ees (from 0.5 to 2.5 mmHg/mL), Ees(sb) passes only from 0.56 to 1.54 mmHg/mL. Ees(sb) increases for higher Eed (from 1.03 to 2.33 mmHg/mL). Finally, Ees(sb) decreases (increases) for HR < 50 bpm (< 50 bpm), and for Ras < 1100 mmHg/gcm4 (> 1100 mmHg/gcm4). CONCLUSION: Unexpectedly Ees(sb) increases for higher LV end-systolic volume and decreases for higher SV. These results contrast with Ees definition, which is the ratio between the LV end-systolic pressure and the LV end-systolic volume. Moreover, Ees(sb) is influenced by cardiocirculatory parameters such as LV Eed, HR, Ras, ejection time, and pre-ejection time. Finally, Ees(sb) computed with the model output often underestimates model Ees.

Evolution of Ventricular Energetics in the Different Stages of Palliation of Hypoplastic Left Heart Syndrome: A Retrospective Clinical Study.

Hyperplastic left heart syndrome (HLHS) patients are palliated by creating a Fontan-type circulation passing from different surgical stages. The aim of this work is to describe the evolution of ventricular energetics parameters in HLHS patients during the different stages of palliation including the hybrid, the Norwood, the bidirectional Glenn (BDG), and the Fontan procedures. We conducted a retrospective clinical study enrolling all HLHS patients surgically treated with hybrid procedure and/or Norwood and/or BDG and/or Fontan operation from 2011 to 2016 collecting echocardiographic and hemodynamic data. Measured data were used to calculate energetic variables such as ventricular elastances, external and internal work, ventriculo-arterial coupling and cardiac mechanical efficiency. From 2010 to 2016, a total of 29 HLHS patients undergoing cardiac catheterization after hybrid (n = 7) or Norwood (n = 6) or Glenn (n = 8) or Fontan (n = 8) procedure were retrospectively enrolled. Ventricular volumes were significantly higher in the Norwood circulation than in the hybrid circulation (p = 0.03) with a progressive decrement from the first stage to the Fontan completion. Ventricular elastances were lower in the Norwood circulation than in the hybrid circulation and progressively increased passing from the first stage to the Fontan completion. The arterial elastance and Rtot increased in the Fontan circulation. The ventricular work progressively increased. Finally, the ventricular efficiency improves passing from the first to the last stage of palliation. The use of ventricular energetic parameters could lead to a more complete evaluation of such complex patients to better understand their adaptation to different pathophysiological conditions.

A cardiovascular simulator tailored for training and clinical uses.

OBJECTIVE: In the present work a cardiovascular simulator designed both for clinical and training use is presented. METHOD: The core of the simulator is a lumped parameter model of the cardiovascular system provided with several modules for the representation of baroreflex control, blood transfusion, ventricular assist device (VAD) therapy and drug infusion. For the training use, a Pre-Set Disease module permits to select one or more cardiovascular diseases with a different level of severity. For the clinical use a Self-Tuning module was implemented. In this case, the user can insert patient's specific data and the simulator will automatically tune its parameters to the desired hemodynamic condition. The simulator can be also interfaced with external systems such as the Specialist Decision Support System (SDSS) devoted to address the choice of the appropriate level of VAD support based on the clinical characteristics of each patient. RESULTS: The Pre-Set Disease module permits to reproduce a wide range of pre-set cardiovascular diseases involving heart, systemic and pulmonary circulation. In addition, the user can test different therapies as drug infusion, VAD therapy and volume transfusion. The Self-Tuning module was tested on six different hemodynamic conditions, including a VAD patient condition. In all cases the simulator permitted to reproduce the desired hemodynamic condition with an error<10%. CONCLUSIONS: The cardiovascular simulator could be of value in clinical arena. Clinicians and students can utilize the Pre-Set Diseases module for training and to get an overall knowledge of the pathophysiology of common cardiovascular diseases. The Self-Tuning module is prospected as a useful tool to visualize patient's status, test different therapies and get more information about specific hemodynamic conditions. In this sense, the simulator, in conjunction with SDSS, constitutes a support to clinical decision - making.

Tailoring the hybrid palliation for hypoplastic left heart syndrome: A simulation study using a lumped parameter model.

The results of Hybrid procedure (HP) for the hypoplastic left heart syndrome (HLHS) depend on several variables: pulmonary artery banding tightness (PAB), atrial septal defect size (ASD) and patent ductus arteriosus stent size (PDA). A HP complication could be the aortic coarctaction (CoAo). The reverse Blalock-Taussig shunt (RevBT) placement was proposed to avoid CoAo effects. This work aims at developing a lumped parameter model (LPM) to investigate the effects of the different variables on HP haemodynamics. A preliminary verification was performed collecting measurements on a newborn HLHS patient to calculate LPM input parameters to reproduce patient's baseline. Results suggest that haemodynamics is affected by ASD (ASD: 0.15-0.55 cm, pulmonary to systemic flow ratio Qp/Qs: 0.73-1, cardiac output (CO): 1-1.5 l/min and ventricular stroke work SW: 336-577 ml mmHg) and by the PAB diameter (PAB: 0.07-0.2 cm, Qp/Qs: 0.46-2.1, CO: 1.3-1.6 l/min and SW: 591-535 ml mmHg). Haemodynamics was neither affected by RevBT diameter nor by PDA diameter higher than 0.2 cm. RevBT implantation does not change the HP haemodynamics, but it can make the CoAo effect negligible. LPM could be useful to support clinical decision in complex physiopathology and to calibrate and personalise the parameters that play a role on flow distribution.

Experimental integration of Autoregulation Unit for left ventricular assist devices in a cardiovascular hybrid simulator.

In this paper, an Autoregulation Unit (ARU) for left ventricular sensorized assist devices (LVAD) has been used with a cardiovascular hybrid simulator mimicking physiological and pathological patient conditions. The functionalities of the ARU have been demonstrating for the successful receiving and visualization of system parameters, sending of commands for LVAD speed changes, and enabling of the autonomous flow control algorithm. Experiments of speed changes and autoregulation are reported, showing the feasibility of the approach for both local and remote control of a LVAD.

Towards a personalized and dynamic CRT-D. A computational cardiovascular model dedicated to therapy optimization.

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.

Use of a comprehensive numerical model to improve biventricular pacemaker temporization in patients affected by heart failure undergoing to CRT-D therapy.

Cardiac resynchronization therapy by biventricular pacemaker/ICD implantation is a validated therapy for patients affected by heart failure with asynchrony of ventricular contraction. Considering the large number of parameters which play a role in cardiac resynchronization therapy, a comprehensive numerical model of cardiocirculatory system could be a useful tool to support clinical decisions. A variable elastance model of ventricles was updated to model the interventricular septum and to simulate the interventricular and the intraventricular desynchrony, and the effect of the biventricular stimulation. In addition, a numerical model of the biventricular pacemaker, which drives the beginning of the heart chambers and interventricular septum contraction, was also developed. In order to validate the model, five patients affected by dilated cardiomyopathy were analysed by echocardiography and electrocardiography before implantation, 24 h and 3 months after the implantation. The developed numerical model permits to reproduce clinical data and to estimate the trend of parameters that are difficult to measure (i.e. left ventricular systolic elastance). Furthermore, the model permits to study the effect of different biventricular pacemaker temporizations on hemodynamic variables.

Application of a user-friendly comprehensive circulatory model for estimation of hemodynamic and ventricular variables.

PURPOSE: Application of a comprehensive, user-friendly, digital computer circulatory model to estimate hemodynamic and ventricular variables. METHODS: The closed-loop lumped parameter circulatory model represents the circulation at the level of large vessels. A variable elastance model reproduces ventricular ejection. The circulatory model has been modified embedding an algorithm able to adjust the model parameters reproducing specific circulatory conditions. The algorithm reads input variables: heart rate, aortic pressure, cardiac output, and left atrial pressure. After a preliminary estimate of circulatory parameters and ventricular elastance, it adjusts the amount of circulating blood, the value of the systemic peripheral resistance, left ventricular elastance, and ventricular rest volume. Input variables and the corresponding calculated variables are recursively compared: the procedure is stopped if the difference between input and calculated variables is within the set tolerance. At the procedure end, the model produces an estimate of ventricular volumes and Emaxl along with systemic and pulmonary pressures (output variables). The procedure has been tested using 4 sets of experimental data including left ventricular assist device assistance. RESULTS: The algorithm allows the reproduction of the circulatory conditions defined by all input variable sets, giving as well an estimate of output variables. CONCLUSIONS: The algorithm permits application of the model in environments where the simplicity of use and velocity of execution are of primary importance. Due to its modular structure, the model can be modified adding new circulatory districts or changing the existing ones. The model could also be applied in educational applications.