Changes in left ventricular systolic wall stress during biventricular circulatory assistance

Extracorporeal membrane oxygenation (ECMO) reduces the systolic stress integral (SSI) in the normal left ventricle. We tested the hypothesis that the SSI does not decrease in poorly contracting, dilated, ejecting hearts during ECMO. In 14 sheep, four pairs of ultrasonic crystals measured changes in left ventricular (LV) wall thickness and three LV diameters. Volume calculations were validated by balloon distention of the ventricles after death (slope = 0.85; r = 0.85). SSI was measured during ECMO flows of 20 to 100 ml/kg/min in both normal and dilated, poorly contracting hearts produced by 30 minutes of warm ischemia. After warm ischemia, end-systolic elastance, an index of contractility, decreased from 8.3 +/- 0.6 mm Hg/ml to 2.9 +/- 0.4 mm Hg/ml (p = 0.001) and peak systolic pressure decreased from 47.4 +/- 0.7 mm Hg to 37.5 +/- 0.08 mm Hg (p = 0.01). In normal hearts, as ECMO flow increased, SSI decreased from 10.5 +/- 2.2 mm Hg.sec to 7.7 +/- 0.8 mm Hg.sec at 60 ml/kg/min (p = 0.001). However, in postischemic hearts, SSI progressively increased from 6.6 +/- 0.3 mm Hg.sec before ECMO to 12.4 +/- 1.8 mm Hg.sec at ECMO = 100 ml/kg/min. These studies indicate that the initial effect of ECMO on the poorly contracting, dilated heart increases LV wall stress and that the increase in stress is proportional to ECMO flow. The increase in stress is primarily due to an increase in afterload, which more than offsets decreases in systolic and diastolic volumes.     

Experimental studies of prolonged circulatory maintenance with a left ventricular assistance in cardiac arrested goats

Recently, various types of left ventricular assist systems (LVAS) have become available to treat the patients in profound heart failures beyond the limit of the effects of IABP. However, the occurrence of an intractable severe bi-ventricular failure, ventricular fibrillation (VF) or cardiac arrest during the time with left ventricular assistance became a more serious problem. Since during the usage of these assist devices, pulmonary venous return will decrease, consequently, LVAS will not be able to maintain sufficient systemic circulation over a extended duration. This study was intended to develop a method of prolonged circulatory maintenance only with a LVAS in cardiac arrested goats until the time when heart transplantation will be performed. In this study, our LVAS was implanted between the left atrium and the aorta in twelve goats in which the hearts were fibrillated. We have followed the principle of circulatory maintenance only with our LVAS in cardiac arrest based on the pressure gradient between the right and left atria and at the same time the pump suction effect through the lungs. The results showed that when pulmonary vascular resistances (PVRs) were kept within normal ranges (less than 15,000 dynes.sec.cm-5), systemic circulations were well maintained only with LVAS as long as RAPs were kept in 14-18 mmHg. Under these conditions, the systemic circulatory flows have fluctuated between 80-140 ml/kg/min depending on the animals demands. The mean arterial pressures were kept above 80 mmHg and the goats have shown quite normal behaviors. However, in goats which showed the presence of pleural effusions and ascites were found to be more difficult to maintain prolonged normal circulation. In our study, the maintenance of total serum protein level above 6.0 g/dl was found to be essential to prevent the development of both pleural effusions and ascites . The authors have achieved the longest survival goat for a duration of 38 days after implantation with our LVAS. We have concluded that when PVRs may be kept in normal ranges, our LVAS can maintain normal systemic circulation even in arrested hearts for a prolonged duration during which time heart transplantation or total artificial heart replacement can be performed.     

Methods of acute postcardiotomy left ventricular assistance

OBJECTIVE: Despite many technological advances in cardiovascular surgery, some patients still experience postcardiotomy left ventricular (LV) failure that is refractory to both inotropic support and intra-aortic balloon pump (IABP) placement. The primary author (MJR) recently changed from inflow cannulation at the right superior pulmonary vein/left atrial junction to inflow cannulation at the dome of the left atrium. The purpose of this study was to compare data collected during placement of a left ventricular assist device (LVAD) at the junction of the right superior pulmonary vein with positioning the device in the dome of the left atrium. Experimental design, setting, and participants: the medical records of all patients undergoing cardiac surgery by one author (MJR) between 1994 and 1997 were retrospectively reviewed, and 4 patients requiring LVAD placement for short term postcardiotomy support were identified. Each patient's chart was reviewed for duration of LVAD support, average LVAD blood flows, pulmonary capillary wedge pressures (PCWP), preoperative characteristics, postoperative complications, and final outcome for the patients. RESULTS: Accessing the left atrium through the dome resulted in excellent blood flow through the LVAD and allowed for good LV decompression. Hemostasis remained the most common complication regardless of the technique employed; however, the enhanced visibility provided by accessing the left atrium via the dome made repairs less technically difficult. Three patients (75%) were able to be weaned from the LVAD and were discharged from the hospital to home. Two of these patients were cannulated via the left atrial dome making removal of the LVAD easier, thus exposing the patients to less additional operative time. One patient could not be weaned from LVAD support secondary to development of right ventricular failure requiring RVAD insertion and subsequent development of multiple organ failure syndrome. CONCLUSIONS: Patients requiring LV assistance following cardiopulmonary bypass surgery traditionally have high levels of morbidity and mortality. In spite of the complications associated with the placement of an assist device, we remain encouraged by the excellent LV decompression and systemic flows we achieved following implantation of the LVAD through the dome of the left atrium. The superior ease of implantation and decannulation provided better operative care and postoperative management for our patients.     

Left ventricular assistance without thoracotomy: mediastinal and transseptal approaches to the left heart.

Two methods to cannulate the left atrium for initiating mechanical left ventricular circulatory assistance using a centrifugal pump were investigated in 25 sheep. A modified Dennis transatrial septal approach produced flow rates of 88.6 +/- 14 mL.kg-1.min-1 through 21F catheters inserted during fluoroscopy through the jugular vein. In 8 animals the septal perforation was plugged after decannulation with a modified Rashkind umbrella plug. Fibroendothelial tissue covered the plug by 4 week. In 7 other animals, the septal defect was not plugged. The septal defect reached pinpoint size by 2 weeks and was completely closed by 4 weeks. In 10 sheep, the left atrium was cannulated from the neck through the mediastinum. Left ventricular assistance flow averaged 71.6 +/- 14 mL.kg-1.min-1. Mean blood loss during 1 hour of left ventricular assistance was 47 mL. In 8 animals, the atrial perforation was plugged with a mean blood loss of 253 +/- 194 mL. In 2 animals, the perforation was intentionally not plugged; mean blood loss was 700 mL. All animals survived. The modified Dennis transatrial method is recommended as a safe, expeditious, cost-effective method to implement left ventricular assistance without thoracotomy. The mediastinal approach, which is technically possible in humans, is more difficult but feasible. Left ventricular assistance has been proven to be the most effective way to rest the failing, ejecting left ventricle. Implementation without thoracotomy potentially expands applications of left ventricular assistance for temporary support of patients with severe manifestations of ischemic heart disease.     

Left ventricular diastolic function of the reperfused postischemic donor heart

This study examined the pathophysiological relationship between left ventricular diastolic function and myocardial biochemical changes during reperfusion following hypothermic cardioplegic preservation of the donor heart. Isolated canine hearts (n=47) were preserved for 6 h at 5°C, followed by normothermic reperfusion for 2 h. Regression analysis demonstrated a highly significant correlation between: Left ventricular maximum –dp/dt and the left ventricular end-diastolic pressure (r=–0.56, P=0.001); myocardial concentrations of adenosine triphosphate (ATP) and Ca²⁺ (r=–0.59, P=0.0001); maximum –dp/dt and myocardial concentrations of: (1) ATP, (2) Ca²⁺, and (3) total adenine nucleotide with left ventricular volume loading (r=–0.53, P=0.003, r=0.51, P=0.002; and r=0.52, P=0.002, respectively); and left ventricular end-diastolic pressure and myocardial Ca²⁺ (r=0.66, P=0.0001). These results suggest that left ventricular relaxation, as assessed by maximum –dp/dt, has a negative correlation with left ventricular stiffness, as determined by the end-diastolic pressure in preserved donor hearts. Furthermore, increased myocardial Ca²⁺ concentrations reflect exhaustion of myocardial ATP. Thus, the myocardial Ca²⁺ concentration correlates directly with wall stiffness and inversely with ventricular relaxation, while ATP concentration correlates directly with ventricular relaxation.     

Left ventricular function during support with an asynchronous pulsatile left ventricular assist device.

BACKGROUND: Left ventricular assist devices (LVADs) are frequently used to maintain patients with severe heart failure until heart transplantation becomes possible. Some patients may experience recovery of LV function during such support. Therefore, it is essential to be able to monitor changes in LV function in this setting. METHODS: We studied LV function in 10 patients (median age 34 years, 9 male) who had LVADs implanted because of severe heart failure due to dilated cardiomyopathy a median of 4 months previously. Median pre-implant ejection fraction was 27% and all patients had been on maximal medical therapy, including intravenous inotropic support, prior to insertion of the LVAD. RESULTS: During LVAD support there were cyclical variations in LV dimensions, fractional shortening (FS) and transmitral flow, related to changes in the phase relationship of the LV and the LVAD. The "best" FS occurred when LV systole coincided with device filling and the "worst" FS when LV systole coincided with device ejection. Median FS with the pump switched off was 18% (10% to 32%). Pump-off FS was significantly greater than the "worst" FS with the pump on (5%, p = 0.002), and similar to the "best" pump-on FS (19%, p = NS). CONCLUSIONS: LV function could be studied echocardiographically during LV support and brief periods of interruption in support. Function varied according to the phase relationship of the LV and LVAD. The "best" FS measured during LVAD support was more closely related to the FS with the device switched off than the "worst" pump on FS. The "best" pump-on LV function is therefore most representative of intrinsic LV performance and can be used as a guide to recovery and the potential need for pump-off studies.     

Left ventricular pressure and volume unloading during pulsatile versus nonpulsatile left ventricular assist device support

BACKGROUND: Nonpulsatile axial or centrifugal pumps are the latest generation of left ventricular assist devices (LVAD). Whether left ventricular (LV) unloading and outcome in these devices is similar to pulsatile LVADs during long-term support has not been investigated. We compared LV unloading and mortality between different types of LVAD support (pulsatile versus nonpulsatile). METHODS: In 31 patients undergoing long-term LVAD implantation (nonpulsatile = 10, pulsatile = 21) preoperative and postoperative echocardiographic and hemodynamic assessment with right heart catheterization had been obtained. RESULTS: All patients had similar echocardiographic, hemodynamic, and clinical heart failure characteristics at baseline. The degree of LV pressure unloading was the same in both device types, caused by similar reduction of mean pulmonary pressure (18.6 +/- 5.1 versus 18.3 +/- 7.5 mm Hg) and pulmonary capillary wedge pressure (8.9 +/- 4.4 versus 8.0 +/- 7.0 mm Hg). Left ventricular volume unloading was pronounced with a pulsatile device owing to a statistically significant higher pump output (5.1 +/- 1.0 L/min) in comparison with nonpulsatile LVADs (3.6 +/- 0.9 L/min, p < 0.001). Echocardiographic-determined end-systolic indicators confirm this augmentation in pulsatile LVADs. Etiology or the time interval of hemodynamic reassessment had no impact in left ventricular pressure unloading, but LV volume unloading decreased between day 60 and 120 in patients with nonpulsatile LVADs. The preoperative and postoperative transplant mortality was comparable in both groups. CONCLUSIONS: Left ventricular pressure unloading is similar in patients with nonpulsatile as compared with pulsatile implantable long-term assist devices. Left ventricular volume unloading is pronounced in pulsatile LVADs.     

Analysis of the arterial blood pressure waveform during left ventricular nonpulsatile assistance in animal models

When the rotary blood pump is used as a left ventricular assist device (LVAD), the arterial blood pressure waveform changes with the LVAD condition. Based on evidence from an in vitro study, the change of the arterial blood pressure waveform during left ventricular assistance was evaluated using animal models. After the left pleural cavity was opened through the fifth intercostal space under general anesthesia, a rotary blood pump was implanted as an LVAD into 6 healthy calves. The direct left carotid arterial blood pressure waveform was measured and recorded by an oscilloscope. The Fast Fourier Transform technique was utilized to analyze the arterial blood pressure waveform and calculate the pulsatility index (PI) and the pulse power index (PPI). Similar to the in vitro study, the PI and PPI decreased exponentially with the increase of the LVAD assist ratio. By using this analysis methodology, a physiologically effective ventricular assistance might be achieved.     

Closed chest resection of left ventricular myxoma through thoracoscopic assistance

We performed a totally endoscopic resection of a left ventricular myxoma using the Heart Port Endoclamp System and conventional endoscopic instruments in a young male patient. It is a feasible and safe procedure with good clinical results and an excellent cosmetic outcome.     

Changes in hemodynamics and coronary blood flow during left ventricular assistance with the Hemopump.

The Hemopump, a catheter-mounted left ventricular assist device, has been demonstrated to be effective in supporting patients with potentially reversible cardiac failure. The mechanism of recovery of the hearts with this device is not fully understood. The effects of the Hemopump on hemodynamics and coronary blood flow with and without myocardial ischemia and failure have been studied in 8 anesthetized open-chest dogs. Coronary blood flow in the left circumflex artery was assessed with an intracoronary Doppler catheter. Myocardial ischemia was induced by ligation of the left anterior descending and diagonal branches. The effects of maximum support were compared with those of minimum support. The effects of the Hemopump varied according to cardiac function. When cardiac dysfunction was mild, the Hemopump support slightly reduced myocardial O2 demand (assessed by pressure-work index) by volume unloading. When cardiac dysfunction was severe, total bypass was achieved and myocardial O2 demand decreased by 45%, owing to both volume and pressure unloading. Coronary blood flow was incompletely auto-regulated, and the ratio of blood flow to O2 demand increased.     

Left ventricular diverticulum with hypertrophy of the left ventricular apex.

A surgical case of diverticulum in the left ventricular apex is presented. A two-dimensional echocardiogram and magnetic resonance image showed a calcified tumor buried in the marked hypertrophied apex of the left ventricle. Enucleation of the oval and hard tumor (4 x 2.5 x 2.5 cm) was performed through the apex, and the defect was anastomosed by buttress sutures. Histologic examination demonstrated that the tumor cavity was filled with a thrombus encapsulated by thickened and calcified endocardium that extended to the left ventricular cavity. In this report, the etiology of the diverticulum with a hypertrophied myocardium is discussed.     

Glucose-insulin-potassium solution improves left ventricular mechanics in diabetes

BACKGROUND: The mechanism by which glucose-insulin-potassium solutions enhance recovery of left ventricular function after myocardial ischemia in diabetic patients is not well understood. We evaluated the effect of glucose-insulin-potassium on ventriculoarterial coupling and left ventricular mechanics in a chronic ovine model of diabetes. METHODS: Diabetes was induced in 6 sheep with streptozotocin. After 6 months of diabetes, the response of the left ventricular pressure-volume relationship to 60 minutes of intravenous glucose-insulin-potassium solution (1,000 mL of 5% dextrose in water, 100 IU of regular insulin, 90 mmol of KCl at 1.5 mL x kg(-1) x h(-1)) was determined. RESULTS: Glucose-insulin-potassium solution increased end-systolic elastance 68% (p = 0.01) and improved ventriculoarterial coupling (1.7+/-0.3 to 1.0+/-0.1; p < 0.01). Potential energy decreased 35% (p = 0.01), and pressure-volume area decreased 20% (p = 0.01). However, stroke work did not change; therefore stroke work efficiency increased from 50.1%+/-3.5% to 60.2%+/-5.1% (p = 0.01). CONCLUSIONS: Glucose-insulin-potassium solution improves left ventricular contractility and ventriculoarterial coupling in diabetes. Left ventricular mechanics is improved by decreasing total mechanical work without significantly affecting stroke work, resulting in improved stroke work efficiency. Improved efficiency facilitates understanding of the enhanced tolerance to myocardial ischemia afforded by glucose-insulin-potassium solution.     

Long-term transplant outcomes of donor hearts with left ventricular dysfunction

Objective

Despite small single-center reports demonstrating acceptable outcomes using donor hearts with left ventricular dysfunction, 19% of potential donor hearts are currently unused exclusively because of left ventricular dysfunction. We investigated modern long-term survival of transplanted donor hearts with left ventricular dysfunction using a large, diverse cohort.

Left ventricular performance after patch reconstruction of the left ventricular wall for postinfarction left ventricular aneurysms]

Left ventricular performance in patients with a left ventricular aneurysm (LVA) treated with patch reconstruction is largely unknown. This study consisted of 15 patients, 14 men and 1 woman, with the average age of 59 +/- 8.5 years. The resected area of LVA was 40 +/- 27 cm2. The area of the woven Dacron patch used for reconstruction was 57 +/- 19% of the resected area including the sewing rim. The EF (Ejection Fraction, 1/3FF (Filling Fraction) and PFR (Peak Filling Rate) were calculated by 99mTc equilibrium cardiac pool scintigraphic images. The A/R ratio (peak velocity during atrial kick phase/peak velocity during the rapid filling phase) was measured using Doppler echocardiography, at the mitral orifice level. These parameters were determined before and 1 to 2 months after the operation. The time course was followed for A/R ratios. The preoperative resting global EF was 0.28 +/- 0.14 (0.44 +/- 0.13 for the contractile area) and the EF during exercise was 0.31 +/- 0.14. Resting and exercise EFs improved significantly (p < 0.01) to 0.40 +/- 0.11 and 0.43 +/- 0.10 postoperatively. The 1/3FF (%) and PFR (/sec) were low before operation (1/3FF, 11.3 +/- 8.3; PFR, 1.2 +/- 0.47). Postoperatively, the 1/3FF rose to 14.8 +/- 9.3 and the PFR showed a significant (p < 0.05) increase to 1.6 +/- 0.6. The A/R ratio significantly (p < 0.05) improved from preoperative 1.76 +/- 0.46 to 0.95 +/- 0.11 on the 3rd postoperative day. This improvement was maintained until the late postoperative period, with a value of 1.14 +/- 0.29 at month 16.(ABSTRACT TRUNCATED AT 250 WORDS)     

Left ventricular performance before and after left ventriculotomy and removal of a left ventricular aneurysm

The effects of left ventriculotomy on left ventricular performance were studied in seven patients with ventricular tachyarrhythmia (VT) and nine patients with left ventricular aneurysm (LVA). Hemodynamic and left ventriculographic findings were evaluated before and after operations. In VT the non-contracting areas, measured at end-diastole, as mean 10.8 +/- 7.1% of the left ventricular internal surface area. There was no significant fall in left ventricular ejection fractions (EF), cardiac indexes (CI) and left ventricular end-diastolic volume indexes (LVEDVI) after left ventriculotomy. In LVA, the non-contracting areas decreased from 31.0 +/- 7.4% to 13.7 +/- 13.5% (p less than 0.01) in association with a reflex decrease in LVEDVI from 117 +/- 31.8 ml/m2 to 90.4 +/- 24.7 ml/m2 (p less than 0.05). EF increased from 40.8 +/- 7.00% to 54.6 +/- 10.7% (p less than 0.01). There was no significant change in CI and left ventricular stroke volume index after left ventricular aneurysmectomy. The observations indicate that left ventriculotomy of limited size is an acceptable and a safety approach to the ventricular tachyarrhythmias and another cardiac operations.