Analysis of the relationship between left ventricular pressure and motor current for evaluation of native cardiac function during left ventricular support with a centrifugal blood pump

Control of the ventricular assist device (VAD) for native heart preservation should be attempted, and the VAD could be one strategy for dealing with the shortage of donors in the future. In the application of nonpulsatile blood pumps for ventricular assistance from the ventricular apex to the aorta, bypass flow and hence the motor current of the pumps change in response to the ventricular pressure change. Utilizing these intrinsic characteristics of the continuous-flow pumps, in this study we investigated whether motor current could be used as an index for continuous monitoring of native cardiac function. In study 1, a centrifugal blood pump (CFP) VAD was installed between the apex and descending aorta of a mock circulatory loop. In this model, a baseline with a preload of 10 mmHg, afterload of 40 mmHg, and LV systolic pressure of 40 mmHg was used. The pump speed was fixed at 1300, 1500, and 1700 rpm, and LV systolic pressure was increased up to 140 mmHg by steps of 20 mmHg while the changes in LV pressure, motor current, pump flow, and aortic pressure were observed. In study 2, an in vivo experiment was performed using three sheep. A left heart bypass model was created using a centrifugal pump from the ventricular apex to the descending aorta. The LVP was varied through administration of dopamine while the changes in LV pressure, pump flow, and motor current at 1500 and 1700 rpm were observed. An excellent correlation was observed in both in vitro and in vivo studies in the relationship between motor current and LV pressure. In study 1, the correlation coefficients were 0.77, 0.92, and 0.99 for 1300, 1500, and 1700 rpm, respectively. In study 2, they were 0.88 (animal no. 1), 0.83 (animal no. 2), and 0.88 (animal no. 3) for 1500 rpm, and 0.95 (animal no. 2) and 0.93 (animal no. 3) for 1700 rpm. These results suggest that motor current amplitude monitoring could be useful as an index for the control of VAD for native heart preservation.     

Preload sensitivity of the Jarvik 2000 and HeartMate II left ventricular assist devices

The in vitro sensitivity of continuous flow pumps to preload and afterload pressure has been well characterized. We compared flow in the Jarvik 2000 and HeartMate II continuous flow left ventricular assist devices (LVADs) at different inflow and outflow pressures and different pump speeds. This allowed us to measure the impact of a changing inflow pressure on the pump flow rate at different speeds but against a constant afterload. The resulting preload sensitivity curves showed that, overall, both LVADs have a mean preload sensitivity of 0.07 L/min/mm Hg in the physiologic ranges of pressures and flows encountered during normal operation. The HeartMate II pump had an increased preload sensitivity (up to approximately 0.1 L/min/mm Hg) as the preload was increased. The preload sensitivity of the Jarvik 2000 LVAD was more variable, having several peaks and troughs as the preload was increased. In future LVADs, improved preload sensitivity may allow passive regulation of pump output, optimize ventricular unloading, and decrease the risk of ventricular suction by the pump.     

一种植入式磁悬浮离心血泵的体外流体力学实验研究

通过体外模拟循环实验台对一种植入式磁悬浮离心血泵进行体外流体力学实验。以新鲜羊血为循环介质,通过体外循环台测定在后负荷为100 mmHg,血泵在不同转速下的输出量;通过控制血泵的转速,测定在固定泵速下不同后负荷下的输出量。血泵测试工作电压为24 V,电流波动于0.3～0.75 A。血泵功率为7.2～18 W。在后负荷为100 mmHg下,泵速在2 900～3 900 rpm,输出流量为3～7.1 L/min。泵速为2500～3 500 rpm,血泵在后负荷69～163 mmHg下输出流量为1.02～5.87 L/min。在固定的转速下血泵的压力-流量呈负相关关系。体外实验血泵工作性能稳定,可以满足成人心室辅助的需求。血泵功率偏高仍需要进一步改进。     

Development of a small implantable right ventricular assist device

The purpose of this program is to design, develop, and clinically evaluate a new, implantable right ventricular assist device (RVAD) that can be used as a component of an implantable biventricular assist device for patients with severe biventricular heart failure. The initial phase of this program resulted in a prototype RVAD, named DexAide, a modified version of the CorAide left ventricular assist device. In vitro testing was performed in a stand-alone circuit and in a true RVAD mode to evaluate pump performance. Pump flow and power were measured under various afterload and pump speed conditions. The pump performance requirements of 2 to 6 l/min and a pressure rise of 20 to 60 mm Hg were successfully met with pump speeds between 1,800 and 3,200 rpm. The nominal design point of 4 l/min and 40 mm Hg pressure rise was achieved at 2,450 +/- 70 rpm with a power consumption of 3.0 +/- 0.2 W. The initial in vitro testing met the design criteria for the new DexAide RVAD. Initial in vivo testing is under way, which will be followed by preclinical readiness testing and a pilot clinical trial in this 5-year program.     

Initial acute in vivo performance of the Cleveland Clinic PediPump left ventricular assist device

The PediPump is a small ventricular assist device (VAD) with a hydraulic output range designed to support children from newborns to adolescents. The present report describes our initial evaluation of the PediPump as a left VAD in an acute sheep model. The PediPump was implanted in two sheep (50.8 and 62.7 kg). Pump speed was adjusted to achieve a flow of 2 L/min with the naturally occurring preload and afterload conditions to evaluate pump performance under a steady hemodynamic state for 4 hours. Upon completion, pump performance was evaluated under various blood pressure and heart rate conditions. During steady-state evaluations, the ascending aortic flow and pump speed varied slightly depending on systemic arterial pressure variations. During the hemodynamic manipulation studies, flows ranged between 0.5 and 3.2 L/min with pump speeds of 5,200-16,200 rpm and motor current of 0.06-0.75 A. The PediPump demonstrated good initial hemodynamic performance for use as an implantable left VAD. However, some depositions were detected at the time of explanation, mainly at the rear of the pump. We are continuing with further acute studies to evaluate pump performance in anticipation of beginning chronic studies to evaluate long-term biocompatibility.     

The isolated working mouse heart: methodological considerations

 Our aim was to develop a working isolated murine heart model, as the extensive use of genetically engineered mice in cardiovascular research requires development of new miniaturized technology. Left ventricular (LV) function was assessed in the isolated working mouse heart perfused with recirculated oxygenated Krebs-Henseleit bicarbonate buffer (37 °C pH 7.4) containing 11.1 mM glucose and 0.4 mM palmitate bound to 3% albumin. The hearts worked against an afterload reservoir at a height equivalent to 50 mmHg, and heart rate was controlled by electrical pacing of the right atrium. LV pressure was measured with a micromanometer connected to a small steel cannula inserted through the apex of the heart. The experimental protocol consisted of two interventions. First, following instrumentation and stabilization, the preload reservoir was raised from a pressure equivalent of 7 to 22.5 mmHg, while pacing at 390 beats·min^–1. Thereafter the height of the preload reservoir was set to 10 mmHg, and the pacing rate was varied from 260 to 600 beats·min^–1. Aortic and coronary flows were measured by timed collections of effluent from the afterload line and that dripping from the heart, respectively [aortic+coronary flow=cardiac output (CO)]. Elevation of LV end-diastolic pressure (LVEDP) from approximately 5 to 10 mmHg resulted in a twofold increase in average cardiac power [product of LV developed pressure (LVDevP) and CO], whereas myocardial contractility (first derivative of LV pressure, dP/dt) and LVDevP (LV systolic pressure–LVEDP) increased only minimally (5–10%). Measured LVEDP was lower than the equivalent height of the preload reservoir by an amount that was related to the heart rate. Cardiac power, LVDevP and dP/dt were stable at heart rates up to 400 beats·min^–1, but declined markedly with higher rates, consistent with the decrease in LVEDP. Thus, cardiac power was reduced to 50% of its maximum value when stimulated at approximately 500 beats·min^–1, and at even higher rates there was little ejection. By systematic manipulation of the height of the preload reservoir and heart rate, we conclude that LV afterload and preload can be assessed only by high-fidelity measurement of intraventricular pressures. The heights of the afterload column and the preload reservoir are unreliable and potentially misleading indicators of LV afterload and preload. Received: 28 September 1998 / Accepted: 25 January 1999     

Pitfalls in the development of a rotary blood pump controller

The controller presents a major obstacle in the development of the rotary blood pump as a left ventricular assist device (LVAD). Clinically, LVAD flow is a good indicator in the regulation of circulatory conditions and pump flow changes, depending on pump preload and afterload. Many investigators have tried estimating pump flow by referencing the motor current. There have been pitfalls in in vitro experimental settings, however. Using a test loop with a pneumatically driven LV chamber and a centrifugal pump as an LVAD, we monitored pump flow and pressure head to evaluate the pump performance curve (H-Q curve). Under pulsatile LV conditions, the H-Q curve was a loop that changed, depending on LV contractility. The pneumatically driven LV chamber cannot mimic the Starling phenomenon, so the developed LV pressure does not change according to the LV preload. Rotary pump flow estimation is the most effective control method. In pulsatile conditions, however, the H-Q curve is a loop that changes under various LV contractility conditions, complicating determination of linear equation for calculating flow. In addition, the LV chamber in the test loop cannot mimic native heart contractility as described by Starling's law. This finding can lead to a misanalysis of the H-Q curve under pulsatile conditions.     

Global parametric search and left ventricular identification

A mathematical model of left ventricular (LV) function in the dog has been developed. Based on a time-varying systolic elastance, the fitting procedure combined a local search according to a second-order method with a global heuristic search and provided beat-to-beat uncertainty intervals for each of the model parameters. Experiments were performed on anesthetized open-chest dogs in which the LV pressure and aortic flow were measured. The model formulated for the LV elastance appeared to be satisfactory for different contracting conditions including isovolumic or auxobaric beats. The study was focused on the maximal isovolumic elastance which, unlike the end-systolic elastance, has been found to be independent of both the preload and afterload and closely dependent on the contractile state of the LV.     

Influence of right ventricular pre- and afterload on right ventricular ejection fraction and preload recruitable stroke work relation.

When right ventricular (RV) afterload is abnormally increased, it correlates inversely with right ventricular ejection fraction (RVEF). We tested, whether this would be different with normal afterload. Additionally, we investigated whether previous studies on the slope of RV preload recruitable stroke work (SW) relation, which used rather non-physiological measures to change RV preload, could be transferred to more physiological loading conditions. RV volumes were determined by thermodilution in 16 patients with stable coronary artery disease and normal pulmonary artery pressure (PAP) at rest. Pre- and afterload were varied by body posture, nitroglycerin (NTG) application and by exercise at different body positions. At rest, the change from recumbent to sitting position decreased PAP, cardiac index (Ci), RV diastolic and systolic volumes, and RVEF. Additionally, mean pulmonary artery pressure (MPAP) correlated positively with both RVEF and cardiac index. After correction for mathematical coupling, the RV preload recruitable SW relation was: right ventricular stroke work index (RVSWi) (103 erg m-2)= 8.1 x (RV end-diastolic volume index -4.9), with n=96, r=0.57, P< or =0.001. Exercise abolished this correlation and led to an inverse correlation between RV end-systolic volume (ESV) and RVSW. In conclusion, (i) RVEF correlates positively with RV afterload when afterload varies within normal range; (ii) the slope of the RV preload recruitable SW relation, which is obtained at steady state under normal loading conditions, is substantially flatter than previously described for dynamic changes of RV preload. With increasing afterload, preload loses its determining effect on RV performance, while afterload becomes more important. This puts earlier assumptions of an afterload independent RV preload recruitable SW relation into question.     

Hemodynamic properties of the hemopump HP14.

BACKGROUND: The Hemopump HP14 is a catheter-mounted, transvalvular, left ventricular assist device intended for femoral percutaneous insertion. The pump was developed for patients with postoperative or postinterventional low cardiac output and for CABG surgery on the beating heart. Little is known about the effect of afterload and hematocrit on the pump performance. METHODS: The influence of hematocrit and afterload on the pump flow was tested using an in vitro model filled with heparinized bovine blood. Regression analysis of the pump flow with respect to three hematocrit values (20%, 30%, 40%) and ten afterload levels (30 mmHg-120 mmHg in 10 mmHg increments) was performed for all pump speed levels (n = 7). RESULTS: At all pump speed levels reduction of afterload and hematocrit were significant predictors for increasing pump flow (p<0.001). For hematocrit values between 40% and 20% and highest pump speed, mean pump flow at lowest afterload ranged between 2.34 and 2.53 L/min; and at highest afterload between 1.31 and 1.53 L/min. For speed level 1, afterload of 120 mmHg and hematocrit of 40% there was a maximal retrograde flow of 230+/-35 ml/min. CONCLUSIONS: Pump performance is significantly improved by both afterload and hematocrit reduction. In the weaning phase and during the removal of the device, the pump should run at a speed level of at least three to prevent retrograde flow in the pump. Estimates for pump flow in vivo can be extrapolated from our diagrams. Our results show that the Hemopump HP14 is a valuable alternative to intra-aortic balloon counterpulsation.     

A Novel Multi-objective Physiological Control System for Rotary Left Ventricular Assist Devices

Various control and monitoring algorithms have been proposed to improve the left-ventricular assist device (LVAD) therapy by reducing the still-occurring adverse events. We developed a novel multi-objective physiological control system that relies on the pump inlet pressure (PIP). Signal-processing algorithms have been implemented to extract the required features from the PIP. These features then serve for meeting various objectives: pump flow adaptation to the perfusion requirements, aortic valve opening for a predefined time, augmentation of the aortic pulse pressure, and monitoring of the LV pre- and afterload conditions as well as the cardiac rhythm. Controllers were also implemented to ensure a safe operation and prevent LV suction, overload, and pump backflow. The performance of the control system was evaluated in vitro, under preload, afterload and contractility variations. The pump flow adapted in a physiological manner, following the preload changes, while the aortic pulse pressure yielded a threefold increase compared to a constant-speed operation. The status of the aortic valve was detected with an overall accuracy of 86% and was controlled as desired. The proposed system showed its potential for a safe physiological response to varying perfusion requirements that reduces the risk of myocardial atrophy and offers important hemodynamic indices for patient monitoring during LVAD therapy.     

Hemodynamic modes of ventricular assist with a rotary blood pump: continuous, pulsatile, and failure

Pulsatile operation of rotary blood pumps (RBPs) has received interest due to potential concern with nonphysiological hemodynamics. This study aimed to gain insight to the effects of various RBP modes on the heart-device interaction. A Deltastream diagonal pump (Medos Medizintechnik GmbH) was inserted in a cardiovascular simulator with apical-to-ascending aorta cannulation. The pump was run in continuous mode with incrementally increasing rotating speed (0-5000 rpm). This was repeated for three heart rates (50-100-150 bpm) and three levels of left ventricular (LV) contractility. Subsequently, the Deltastream was run in pulsatile mode to elucidate the effect of (de)synchronization between heart and pump. LV volume and pressure, arterial pressure, flows, and energetic parameters were used to evaluate the interaction. Pump failure (0 rpm) resulted in aortic pressure drops (17-46 mm Hg) from baseline. In continuous mode, pump flow compensated by diminished aortic flow, thus yielding constant total flow. High continuous rotating speed resulted in acute hypertension (mean aortic pressure up to 178 mm Hg). In pulsatile mode, unmatched heart and pulsatile pump rates yielded unphysiologic pressure and flow patterns and LV unloading was found to be highly dependent on synchronization phase. Optimal unloading was achieved when the minimum rotating speed occurred at end-systole. We conclude that, in continuous mode, a perfusion benefit can only be achieved if the continuous pump flow exceeds the preimplant (baseline) cardiac output. Pulsatile mode of support results in complex pressure and volume variations and requires accurate triggering to achieve optimal unloading.     

Hydrodynamic characterisation of ventricular assist devices

A new mock circulatory system (MCS) was designed to evaluate and characterise the hydraulic performance of ventricular assist devices (VADs). The MCS consists of a preload section and a multipurpose afterload section, with an adjustable compliance chamber (C) and peripheral resistor (Rp) as principal components. The MCS was connected to a pulse duplicator system for validation, simulating a wide range of afterload conditions. Both pressure and flow were measured, and the values of the different components calculated. The data perfectly fits a 4-element electrical analogon (EA). The MCS was further used to assess the hydrodynamic characteristics of the Medos VAD as an example of a displacement pump. Data was measured for various MCS settings and at different pump rates, yielding device specific pump function graphs for water and pig blood. Our data demonstrate (i) flow sensitivity to preload and afterload and (ii) the effect of test fluid on hemodynamic performance.     

婴幼儿心室辅助泵——20mL罗叶泵体外测试平台的建立和性能研究

目的 设计并制作基于婴幼儿心室辅助泵——罗叶泵的体外测试平台,分别完成20 mL婴幼儿罗叶泵的流体性能实验和耐疲劳实验。方法 将罗叶泵驱动装置、20 mL婴幼儿罗叶泵、前负荷腔、前负荷压力传感器、后负荷腔、前负荷压力传感器、心电监护器、阻尼器和流量计等按不同的实验目的组装成不同的测试平台,流体温度控制为37 ℃,分别用来完成20 mL婴幼儿罗叶泵的流体性能实验和耐疲劳实验。结果 所制作的流体性能实验平台能较好的模拟人体前后负荷;在固定泵输出压力时,测量了20 mL婴幼儿罗叶泵泵频率与泵前压力（前负荷）、泵后压力（后负荷）和流量的关系;所组装的耐疲劳实验平台能够测试罗叶泵的耐疲劳性能;20 mL婴幼儿罗叶泵在连续搏动70 d后,其形变率仅为4 %。结论 所组装的搏动泵测试平台能测试20 mL婴幼儿罗叶泵的流体性能和耐疲劳性能;所制作的20mL婴幼儿罗叶泵具有较好的稳定性和耐疲劳性。 更多还原     

The effect of decreased intrathoracic pressure on ventricular function

SUMMARY  Large decreases in inspiratory intrathoracic pressure (ITP) occur during obstructive apnoeas. The cardiac effects of apnoea-associated decreased ITP come from the interaction of increased preload (venous return) on the right ventricle (RV) and increased afterload on the left ventricle (LV), and are modulated by the autonomic effects of shifts in blood volume and hypoxaemia. During obstructed breathing, venous return increases by as much as three-fold during inspiration even though mean flow may change little. This leads to a substantial inspiratory increase in RV end-diastolic and stroke volume. Because of ventricular interdependence, there is a decrease in LV diastolic compliance and corresponding decrease LV preload.
Sustained decreases in ITP (Müller manoeuvre) inhibit LV ejection, and hence increase LV afterload. However, breathing against an obstructed airway (repetitive short Müller manoeuvre) is not necessarily modelled by the sustained manoeuvre. Animal studies indicate that with airway obstruction, for the first beat or two of inspiration the primary effect on the LV is a reduction in stroke volume related to a decrease in preload, and afterload, if anything, decreases. In fact, afterload only increases during early expiration when stroke volume increases. When obstructive and central apnoeas are paired for duration and blood-gas alterations, there are increases in pulmonary blood volume with central apnoeas and in RV volume with obstructive apnoeas, consistent with the postulation that the primary effect of obstructive apnoeas is on venous return.
In conclusion, the putative role of decreased ITP in increasing LV afterload under conditions appropriate to OSA is not well supported by experimental studies. However, effects with very large swings in ITP as might be seen under the most extreme forms of OSA, and differences in timing of the swings between diastole and systole have yet to be investigated.     

Development of compact ventricular assist device for chronic use

A compact and reliable mechanical ventricular assist device is expected for chronic use. A magnetically suspended centrifugal pump (MSCP) is a seal-less, bearingless pump that can be operated for a long time with-out fear of leak or thrombus formation around the shaft. This paper reports recent progress with the MSCP, including pulse-pressure generation: In three sheep with acute heart failure induced by injection of beta-blockers, left ventricular assist was instituted with an inflow cannula into the left atrium (LA) and left ventricle (LV), and the outflow cannula to the descending aorta. The timing of the pulsation was synchronized with the electrocardiogram. Cardiac performance was evaluated by a conductance catheter and a tipped manometer in the LV. As pump speed increased, the pump flow became almost continuous. After application of pulsation, the pulse pressure increased from 5 to 25 mmHg, irrespective of the inflow cannulation site and the timing of pulsation. With LA cannulation, LV pressure at copulsation was slightly higher than at counterpulsation. Chronic animal trial: The MSCP was implanted in three sheep. The inflow cannula was inserted into the LV. The native heart was kept intact. The inner surface was coated with heparin. Continuous hemodynamic monitoring as well as periodic blood sampling was performed. The duration of running of the pump was 60, 140, and 248 days. The causes of termination were infection and failure of magnetic suspension due to electrical short. No thrombus or embolic findings were observed in the whole body after sacrifice. Renal and hepatic functions were within normal range throughout the experiment. It is concluded that the MSCP can produce pulsation irrespective of the inflow cannulation site and timing of synchronization. It is a promising device for chronic ventricular support.     

Right ventricular function in rats with hypoxic pulmonary hypertension

The function of the hypertrophic right ventricle (RV) was studied in adult rats with hypoxic pulmonary hypertension induced by intermittent high-altitude (IHA) exposure. The isolated RV working heart preparation that was employed enabled us to estimate ventricular contractile and pump performance under controlled loading conditions. In rats exposed to IHA hypoxia the elevated RV systolic pressure and maximum rate of pressure development were observed at various levels of preload or afterload. The peak indices of mechanical performance were almost doubled in these animals when compared with the normoxic group, while the index of contractility remained unchanged. Maximum ventricular performance was found to be a linear function of the relative RV weight. No evidence of RV pump dysfunction was detected in rats exposed to IHA; moreover, the ability of the ventricle to maintain cardiac output against increased pulmonary resistance was markedly improved. The prevention of tricuspid regurgitation by using an artificial valve did not influence the functional curves and the peak ventricular performance. The regression of hypertrophy was accompanied by a reversal of ventricular function to control values, except for the persisting slight increase of peak RV pressure. It may be concluded that the increase of the RV mass in IHA-exposed rats serves to improve maximum ventricular performance, which aids in overcoming an elevated pulmonary resistance without disturbing the pump function.     

Recovery directed left ventricular assist device: a new concept

To promote cardiac recovery, we developed a recovery directed left ventricular assist device (RDLVAD) that consists of a valved apical conduit, an afterload controlling chamber (ACC), and a pump. We evaluated its efficacy by comparison with an ordinary LVAD. In each of six pigs with ischemia-induced heart failure, flow and pressure measurements were made while maintaining the total blood flow and arterial pressure equal in the two groups. RDLVAD was able to direct all the blood ejected from the LV into the ACC (0-15 mm Hg) but not into the aorta (73 mm Hg). In the ordinary LVAD, however, some ejection occurred into the aorta despite vigorous suction of the LV. Thus, RDLVAD increased DPTI/SPTI 2.3 times (p < 0.005) and decreased left ventricular end-diastolic pressure by 40% and maximum dP/dt by 20% (p < 0.05). Even the apical valve, at approximately half the diameter of the aortic valve, was able to allow all the blood ejected from the LV to enter the ACC. In one control group pig that achieved almost no ejection into the aorta, left ventricular relaxation and dilatation was extremely limited. RDLVAD may promote cardiac recovery by ensuring less LV work, a greater blood supply/demand ratio in the coronary circulation, and full ventricular relaxation.     

In vitro evaluation of the PUCA II intra-arterial LVAD

The "pulsatile catheter" (PUCA) pump is a minimally invasive intra-arterial left ventricular assist device intended for acute support of critically ill heart failure patients. To assess the hydrodynamic performance of the PUCA II, driven by an Arrow AutoCat IABP driver, we used a (static) mock circulatory system in which the PUCA II was tested at different loading conditions. The PUCA II was subsequently introduced in a (dynamic) cardiovascular simulator (CVS) to mimic actual in vivo operating conditions, with different heart rates and 2 levels of left ventricular (LV) contractility. Mock circulation data shows that PUCA II pump performance is sensitive to afterload, pump rate and preload. CVS data demonstrate that PUCA II provides effective LV unloading and augments diastolic aortic pressure. The contribution of PUCA II to total flow is inversely related to LV contractility and is higher at high heart rates. We conclude that, with the current IABP driver, the PUCA II is most effective in 1:1 mode in left ventricles with low contractility.     

Axial flow pump treatment during myocardial depression in calves: an invasive hemodynamic and echocardiographic tissue Doppler study

The aim of this study was to investigate flow characteristics and myocardial function after implantation of an axial pump left ventricular assist device while varying afterload and during progressive myocardial depression. Ten calves were included, seven of which fulfilled the protocol. Invasive hemodynamic monitoring and echocardiography with color-coded systolic tissue Doppler velocity (TD velocity) were used during prepump conditions, at three different pump speeds, during modification of the systemic vascular resistance (SVR), and during increasing degrees of beta-blockade. The TD velocity decreased with the myocardial function whereas left ventricular size, fractional shortening, and pump speed did not correlate significantly with the TD velocity. The TD velocity correlated significantly with native stroke volume, heart rate, SVR and cardiac output but none of these alone could explain more than 20% of the changes in TD velocity. The axial flow pump studied is effective in unloading the severely depressed heart and has a high capacity for maintaining an adequate cardiac output, regardless of differing hemodynamic conditions, pump speed or decreasing LV function. Echocardiography with volumetric rendering and TD velocity imaging are valuable tools for monitoring and quantifying residual myocardial function during pump treatment.