Synergistic Model of Cardiac Function with a Heart Assist Device

The breakdown of cardiac self-organization leads to heart diseases and failure, the number one cause of death worldwide. The left ventricular pressure–volume relation plays a key role in the diagnosis and treatment of heart diseases. Lumped-parameter models combined with pressure–volume loop analysis are very effective in simulating clinical scenarios with a view to treatment optimization and outcome prediction. Unfortunately, often invoked in this analysis is the traditional, time-varying elastance concept, in which the ratio of the ventricular pressure to its volume is prescribed by a periodic function of time, instead of being calculated consistently according to the change in feedback mechanisms (e.g., the lack or breakdown of self-organization) in heart diseases. Therefore, the application of the time-varying elastance for the analysis of left ventricular assist device (LVAD)–heart interactions has been questioned. We propose a paradigm shift from the time-varying elastance concept to a synergistic model of cardiac function by integrating the mechanical, electric, and chemical activity on microscale sarcomere and macroscale heart levels and investigating the effect of an axial rotary pump on a failing heart. We show that our synergistic model works better than the time-varying elastance model in reproducing LVAD–heart interactions with sufficient accuracy to describe the left ventricular pressure–volume relation

Preclinical Efficacy of an Epicardial Heart Assist Device

Of the millions of Americans with heart failure, a significant portion are end-stage and experience symptoms even at rest. Moreover, around half of people with heart failure die within 5 years of diagnosis. The ideal treatment option for these patients is a heart transplant. However, fewer than 3000 donor hearts are available for transplant in North America each year. Given the significant disparity in number of donor hearts and end-stage failure patients, there is great clinical need for heart assist technology that supports heart function, and for improved approaches that lead to heart recovery. The current leading device therapy for advanced heart failure patients is a Ventricular Assist Device (VAD). While these devices have been clinically available in the United States since 2003, they are associated with severe complications – including a high risk for stroke and gastrointestinal bleeding. As an alternative to mechanical blood pumps, direct cardiac compression (DCC) devices have been developed for heart assist. The investigation described herein includes the development, simulation, and preclinical testing of a novel DCC device – coined the EpicHeart™ (Epicardial Heart Assist Device). First, engineering design improvements were required to allow for synchronization between device activation and the native contraction of the heart. The methods to accomplish this goal are described with results of in vivo testing. Then, the hemodynamic effects of the device in an acute heart failure model were investigated. Finally, the results of the in vivo testing of the device were applied for technical specification verification of a simulation platform developed to model the clinical effects of the EpicHeart™ Device. The outcomes of this study have yielded an improved preclinical medical device that will proceed with future investigations over longer study durations as well as other heart failure etiologies – while continuing to explore potential for heart recovery. Additionally, the pilot study of simulating this technology is unique and has provided support for future validation of a clinical simulation tool. This simulation is anticipated for use in a clinical environment to predict patient outcomes of the EpicHeart™ Device for treatment of heart disease

Preclinical Efficacy of an Epicardial Heart Assist Device

Of the millions of Americans with heart failure, a significant portion are end-stage and experience symptoms even at rest. Moreover, around half of people with heart failure die within 5 years of diagnosis. The ideal treatment option for these patients is a heart transplant. However, fewer than 3000 donor hearts are available for transplant in North America each year. Given the significant disparity in number of donor hearts and end-stage failure patients, there is great clinical need for heart assist technology that supports heart function, and for improved approaches that lead to heart recovery. The current leading device therapy for advanced heart failure patients is a Ventricular Assist Device (VAD). While these devices have been clinically available in the United States since 2003, they are associated with severe complications – including a high risk for stroke and gastrointestinal bleeding. As an alternative to mechanical blood pumps, direct cardiac compression (DCC) devices have been developed for heart assist. The investigation described herein includes the development, simulation, and preclinical testing of a novel DCC device – coined the EpicHeart™ (Epicardial Heart Assist Device). First, engineering design improvements were required to allow for synchronization between device activation and the native contraction of the heart. The methods to accomplish this goal are described with results of in vivo testing. Then, the hemodynamic effects of the device in an acute heart failure model were investigated. Finally, the results of the in vivo testing of the device were applied for technical specification verification of a simulation platform developed to model the clinical effects of the EpicHeart™ Device. The outcomes of this study have yielded an improved preclinical medical device that will proceed with future investigations over longer study durations as well as other heart failure etiologies – while continuing to explore potential for heart recovery. Additionally, the pilot study of simulating this technology is unique and has provided support for future validation of a clinical simulation tool. This simulation is anticipated for use in a clinical environment to predict patient outcomes of the EpicHeart™ Device for treatment of heart disease

The development and investigation of a novel pulsatile heart assist device

Cardiovascular diseases (CVD) contributed to almost 30% of worldwide mortality; with heart failure being one class of CVD. One popular and widely available treatment for heart failure is the intra-aortic balloon pump (IABP). This heart assist device is used in counterpulsation to improve myocardial function by increasing coronary perfusion, and decreasing aortic end-diastolic pressure (i.e. the resistance to blood ejection from the heart). However, this device can only be used acutely, and patients are bedridden. The subject of this research is a novel heart assist treatment called the Chronic Intermittent Mechanical Support (CIMS) which was conceived to offer advantages of the IABP device chronically, whilst overcoming its disadvantages. The CIMS device comprises an implantable balloon pump, a percutaneous drive line, and a wearable driver console. The research here aims to determine the haemodynamic effect of balloon pump activation under in vitro conditions. A human mock circulatory loop (MCL) with systemic and coronary perfusion was constructed, capable of simulating various degrees of heart failure. Two prototypes of the CIMS balloon pump were made with varying stiffness. Several experimental factors (balloon inflation/deflation timing, Helium gas volume, arterial compliance, balloon pump stiffness and heart valve type) form the factorial design experiments. A simple modification to the MCL allowed flow visualisation experiments using video recording. Suitable statistical tests were used to analyse the data obtained from all experiments. Balloon inflation and deflation in the ascending aorta of the MCL yielded favourable results. The sudden balloon deflation caused the heart valve to open earlier, thus causing longer valve opening duration in a cardiac cycle. It was also found that pressure augmentation in diastole was significantly correlated with increased cardiac output and coronary flowrate. With an optimum combination (low arterial compliance and low balloon pump stiffness), systemic and coronary perfusions were increased by 18% and 21% respectively, while the aortic end-diastolic pressure (forward flow resistance) decreased by 17%. Consequently, the ratio of oxygen supply and demand to myocardium (endocardial viability ratio, EVR) increased between 33% and 75%. The increase was mostly attributed to diastolic augmentation rather than systolic unloading

Structural analysis of implantable biomedical heart assist device fixation

University of Minnesota Ph.D. dissertation. December 2013. Major: Mechanical Engineering. Advisor: Ephraim M. Sparrow. 1 computer file (PDF); ix, 154 pages.This thesis presents how experimentation, numerical simulation, optimization, and mathematical analysis, can be applied to study and improve the fixation of left-ventricle leads within a cardiac vein. Left-ventricle cardiac leads for implantable pacemakers can lose fixation within a cardiac vein and dislodge. A common lead-fixation mechanism for left-ventricle leads was investigated that used a two- or three-dimensional shape at the distal end. The lead and the distal end are constructed from a metal coil that is pre-formed into a two- or three-dimensional shape. Analytical beam approximations of a coil were developed to determine how coil stiffness is affected by coil geometry and material. In-vitro experimentation with a radial force tester was used to measure the overall force between a two- or three-dimensional distal shape within a straight cylindrical tube. Data processing techniques using a moving average were applied to interpret the force data. Numerical simulation using a beam approximation for the coil determined the overall force between a distal shape and a straight cylindrical tube. The distribution of force along the distal shape, including tip force was also obtained from the simulation. The simulation models were validated with experimental data. Using numerical simulation, the model of the distal shape was changed to a spiral shape and then optimized. Since actual cardiac veins are curved, the simulation model was updated with a curved tube to determine how the distal shapes would perform. A mathematical analysis using engineering principles was also applied to obtain a simple analytical equation relating a deformed distal shape to force

A monitoring device for pressurised-air-driven diaphragm-based artificial heart assist devices

A non-invasive device has been developed to monitor the diaphragm position and the blood flow in artificial heart assist devices equipped with a pressurised-air-driven diaphragm. Light scattering from the diaphragm is used as a mechanism for measuring. Information about the position of several points of the diaphragm can be obtained. The completely empty or filled situation can be detected and used for control purposes. Flow data can be extracted and bending characteristics of the diaphragm during operation can be studied

The development and investigation of a novel pulsatile heart assist device

Cardiovascular diseases (CVD) contributed to almost 30% of worldwide mortality; with heart failure being one class of CVD. One popular and widely available treatment for heart failure is the intra-aortic balloon pump (IABP). This heart assist device is used in counterpulsation to improve myocardial function by increasing coronary perfusion, and decreasing aortic end-diastolic pressure (i.e. the resistance to blood ejection from the heart). However, this device can only be used acutely, and patients are bedridden. The subject of this research is a novel heart assist treatment called the Chronic Intermittent Mechanical Support (CIMS) which was conceived to offer advantages of the IABP device chronically, whilst overcoming its disadvantages. The CIMS device comprises an implantable balloon pump, a percutaneous drive line, and a wearable driver console. The research here aims to determine the haemodynamic effect of balloon pump activation under in vitro conditions. A human mock circulatory loop (MCL) with systemic and coronary perfusion was constructed, capable of simulating various degrees of heart failure. Two prototypes of the CIMS balloon pump were made with varying stiffness. Several experimental factors (balloon inflation/deflation timing, Helium gas volume, arterial compliance, balloon pump stiffness and heart valve type) form the factorial design experiments. A simple modification to the MCL allowed flow visualisation experiments using video recording. Suitable statistical tests were used to analyse the data obtained from all experiments. Balloon inflation and deflation in the ascending aorta of the MCL yielded favourable results. The sudden balloon deflation caused the heart valve to open earlier, thus causing longer valve opening duration in a cardiac cycle. It was also found that pressure augmentation in diastole was significantly correlated with increased cardiac output and coronary flowrate. With an optimum combination (low arterial compliance and low balloon pump stiffness), systemic and coronary perfusions were increased by 18% and 21% respectively, while the aortic end-diastolic pressure (forward flow resistance) decreased by 17%. Consequently, the ratio of oxygen supply and demand to myocardium (endocardial viability ratio, EVR) increased between 33% and 75%. The increase was mostly attributed to diastolic augmentation rather than systolic unloading.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Barnes Hospital Bulletin

https://digitalcommons.wustl.edu/bjc_barnes_bulletin/1063/thumbnail.jp

Mechano-electric effect and a heart assist device in the synergistic model of cardiac function

The breakdown of cardiac self-organization leads to heart diseases and failure, the number one cause of death worldwide. Within the traditional time-varying elastance model, cardiac self-organization and breakdown cannot be addressed due to its inability to incorporate the dynamics of various feedback mechanisms consistently. To face this challenge, we recently proposed a paradigm shift from the time-varying elastance concept to a synergistic model of cardiac function by integrating mechanical, electric and chemical activity on micro-scale sarcomere and macro-scale heart. In this paper, by using our synergistic model, we investigate the mechano-electric feedback (MEF) which is the effect of mechanical activities on electric activity—one of the important feedback loops in cardiac function. We show that the (dysfunction of) MEF leads to various forms of heart arrhythmias, for instance, causing the electric activity and left-ventricular volume and pressure to oscillate too fast, too slowly, or erratically through periodic doubling bifurcations or ectopic excitations of incommensurable frequencies. This can result in a pathological condition, reminiscent of dilated cardiomyopathy, where a heart cannot contract or relax properly, with an ineffective cardiac pumping and abnormal electric activities. This pathological condition is then shown to be improved by a heart assist device (an axial rotary pump) since the latter tends to increase the stroke volume and aortic pressure while inhibiting the progression (bifurcation) to such a pathological condition. These results highlight a nontrivial effect of a mechanical pump on the electric activity of the heart