Mechanical Unloading Properties of Axial Flow Pumps and their Effect on Myocardial Stunning

Postischemic myocardial dysfunction affects morbidity and mortality in patients with coronary artery disease. It is known that mechanical unloading of the left heart ventricle can positively influence postischemic myocardial dysfunction. In this respect we tested two miniaturised axial flow pumps, i.e. the 14-F and the 21-F Hemopump®. An experimental study was carried out on 30 open chest sheep where regional myocardial wall motion was followed using sonomicrometry in a preparation of transient coronary artery occlusion. Only the larger 21-F Hemopump® showed hemodynamically significant unloading of the left ventricle. Furthermore, as far as stunning is concerned, systolic wall thickening recovered better when this type of pump was used during reperfusion. Also postejection thickening, which is an indication of diastolic postischemic dysfunction, is reduced significantly in the postischemic area (ANOVA, p<0.05). Thus, the 21F Hemopump®, but not the 14F Hemopump®, provides adequate mechanical unloading in order to beneficially influence myocardial stunning.

Intramyocardial hematoma mimicking abnormal left ventricular trabeculation

Intramyocardial hematoma may present as a tumor or pseudoaneurysm on echocardiography. A 68-year-old man was admitted with a subacute posterior wall infarction complicated by ventricular fibrillation. Echocardiography showed isolated left ventricular abnormal trabeculations, a finding suggesting an associated skeletal muscle disorder, in the lateral wall. At cardiac surgery, performed 6 weeks later because of severe 3-vessel disease, an intramyocardial hematoma of the lateral wall was excised, and myocardial and skeletal muscle biopsies were taken, which showed neither isolated left ventricular abnormal trabeculations nor skeletal muscle disorder. Postoperatively, echocardiography revealed no abnormal trabeculations.

Successful treatment of postoperative right ventricular heart failure with the HIA-Medos-assist system in a 2-year-old girl

One year after total correction of tetralogy of Fallot, reoperation was performed in a 2-year-old infant because of an aneurysm of the right ventricular outflow tract. After removal of the aneurysm, massive right ventricular failure occurred. Maximal medical inotropic support could not reestablish sufficient right ventricular function. Therefore, it was decided to implant the new HIA-Medos system as a right ventricular assist. In the postoperative period, echocardiographic controls showed increasing contractility of the right ventricle. The assist system was removed after 3 days and the infant was discharged in good condition on the 22nd postoperative day.

Haemodynamic changes in patients undergoing high-risk PTCA under protection of transfemoral heart- lung machine support with centrifugal pumps

Patients with a high risk for myocardial revascularization by cardiological or surgical means can be supported during high-risk PTCA with mechanical circulatory support (supp HR-PTCA). Between November 1994 and June 1997 we performed 28 supp HR-PTCA's under protection of a heart-lung machine (HLM) with femoro - femoral cannulation under regional anesthesia. We approached 2.8+/-1.5 stenoses and 1.7+/-0.6 vessels per patient. Primary success rate was 95 percent of the treated vessels. During unloading, pulmonary artery mean pressure fell to 42+/-29% of the starting value, and LVEDP was decreased to 36+/-42%. Mechanical unloading also resulted in a significant reduction of left ventricular volumes (unloaded LVEDVI and LVESVI represent 76.8% and 76.6% of pre-unloaded values, respectively, p<0.05). All patients except one survived the procedure and could be discharged from the hospital. Femoro-femoral cardio-pulmonary bypass under regional anesthesia provides sufficient protection for high risk PTCA procedures and enables high risk patients to benefit from coronary revascularization.

Headache as the initial manifestation of acute aortic dissection type A

The most common initial symptom of aortic dissection is chest pain. Other initial symptoms include pain in the neck, throat, abdomen and lower back, syncope, paresis, and dyspnoea. Headache as the initial symptom of aortic dissection has not been described previously. A 61-year-old woman with a history of migraine and arterial hypertension developed continuous bifrontal headache. Two hours later, right-sided thoracic pain and a diastolic murmur were suggestive of aortic dissection that was confirmed by echocardiography and subsequent surgery. The dissection commenced in the ascending aorta and involved all cervical arteries until the base of the skull. Headache as the initial manifestation of aortic dissection was assumed due to either vessel distension or pericarotid plexus ischemia. Aortic dissection has to be considered as a rare differential diagnosis of frontal headache, especially in patients who develop aortic regurgitation or chest pain for the first time.

Centrifugal pumps as left ventricular assist for coronary revascularization on a beating heart

During recent years, coronary bypass surgery has progressed toward minimizing invasiveness. One important feature of this approach is performing surgery on a beating heart. During the crucial phase of such surgery, the mechanical support of the heart with a left ventricular assist device (LVAD) is a possible option. During the period from October 1, 1994 until June 30, 1997, we employed a centrifugal pump system in 118 cases of coronary artery bypass graft (CABG) procedures with LVAD support (mechanically supported CABG [SUPPCAB]). A total of 179 distal anastomoses with an average of 1.5 +/- 0.5 coronary anastomoses per patient was performed. Three types of pumps were used: 23 BioPump, 87 Isoflow, and 8 Capiox systems. The median time on mechanical support was 44 min (range, 16-116 min). The mean flow rate during support time was 3.5 +/- 0.8 L/min, which results in a calculated flow of 1.7 +/- 0.6 L/min/m2 body surface area (BSA). The average flow was 3.2 +/- 0.8 L/min with the BioPump and 3.7 +/- 0.8 L/min with the Isoflow pump, respectively (p < 0.01). The mean arterial pressure during mechanical support was 75 +/- 12 mm Hg. In 2 patients, the pump system was kept running postoperatively in the ICU. Eight of the patients received operations under resuscitation or in cardiogenic shock. Nine (7.9%) of the patients did not survive the early postoperative phase. For coronary revascularization of the anterolateral and diaphragmatic parts of the heart, the SUPPCAB procedure is feasible with excellent mechanical support of the heart by centrifugal pumps. Especially in high risk cases, this procedure can be recommended.

Pathophysiological considerations concerning uni- and biventricular mechanical cardiac assist

Mechanical assisted circulation by the means of cardiac assist devices is a routine procedure in modern cardiac surgery and cardiology. We investigated the impact of mechanical unloading on regional myocardial "stunning" and the influence of assisted circulation on left heart and right heart failure persevered by an ultimate addition of pulmonary hypertension in experimental set ups. We found that mechanical unloading either during ischemia or in the early reperfusion phase attenuates stunning and enhances the return of synchronous heart performance. In our global dysfunction model we showed that the right heart is dispensable. Sufficient inflow to the left heart is provided unless pulmonary hypertension is present. Also additional left heart support can not overcome the deleterious situation and in select cases only additional right heart support can prevent the "low LVAD output" syndrome. We conclude that mechanical assisted circulation and mechanical unloading are beneficial in case of regional and global dysfunction persevered by pulmonary hypertension, however, the knowledge about interactions of assist systems and the circulation has to be improved in order to optimize clinical assist device performance.

Medos/HIA-assist system: first experiences with mechanical circulatory assist in infants and children

The Medos/HIA-System is a new pneumatically driven system for mechanical circulatory assist. The system is characterized by excellent efficiency at high heart rates and is available with three ventricles of 10, 25 and 60ml stroke volume. It can be used as left-, right- or biventricular assist device. Our preliminary experiences with this novel system for support of infants and children are reported.

A new pneumatic pump for extracorporeal circulation: TPP (true pulsatile pump). Experimental and first clinical results

A pulsatile, membrane type pump, TPP, was developed for use in routine cardiac surgery. The artificial ventricle consists of a polycarbonate housing with an inlet and outlet polyurethane tricuspid valve. The membrane is actuated hydraulically. For pre-clinical studies, we designed a study in sheep. After a pump run of 6 hours the animals were allowed to recover and sacrificed after 72 hours. All clinical parameters returned to normal values (p > 0.05 vs. control values). During pump run we found elevated free plasma hemoglobine. However, these values returned to normal until the end of the observation period. Thereafter, the device was used in ten routine cardiac surgery procedures. All patients survived the procedure and were discharged from hospital. The postoperative course of lab parameters (kidney, liver and blood count) was no different to routine cardiac surgical procedures. This pulsatile pump system can thus be safely employed in cardiac surgery.

Pre-clinical evaluation of a novel, pneumatic, ventricular assist device (Medos HIA-VAD) under pathophysiological conditions

To evaluate a new cardiac assist system, the Medos HIA-VAD, we studied the effects of mechanical unloading on regional and global myocardial dysfunction. As a model for the regional temporary contractile dysfunction we chose an anesthetized, open chest preparation in sheep. We occluded the diagonal coronary artery for 15 minutes and reperfused for 90 minutes. Hemodynamic parameters and wall thickening were monitored. Unloading with the 60-ml Medos HIA-VAD was performed either during ischemia (group II) or during reperfusion (group III). The recovery of non-uniformity indicated by post-ejection wall thickening was significantly faster (p < 0.05) in both groups if compared to the non-assisted group (group I) (all groups n = 4). Recovery of systolic wall thickening in the postischemic region in group I was only 76 +/- 12%, while it was 103 +/- 11% and 92 +/- 11% in groups II and III, respectively (p < 0.05). In a canine model of global left ventricular failure, we occluded the left anterior descending coronary artery for 20 min, and after 5 minutes of reperfusion, the circumflex artery for 45 min (group I, n = 5). After 5 min of CX occlusion in group II we performed assisted circulation for 90 min with the 10-ml (n = 5) and the 25-ml (n = 5) Medos HIA-VAD. In group I, no dog survived, in group II, all survived 4 hours of reperfusion (n = 10). Lactate at the end of the experiment was 1.1 +/- 0.9 mmol/L (10-ml, and 1.1 +/- 0.2 mmol/L (25-ml) (p > 0.05 vs. base line). We conclude that the Medos HIA-VAD is a reliable assist device that enhances myocardial recovery and allows sufficient peripheral circulation in the case of cardiogenic shock.

Autograft aortic valve replacement with downsized pulmonary allograft for right ventricular outflow tract reconstruction

A three-week-old neonate underwent aortic valve replacement with a pulmonary autograft (Ross procedure). The right ventricular outflow tract was reconstructed with a downsized pulmonary allograft. The surgical technique is presented. Six months after operation the girl is doing well and both the autograft and allograft function are excellent.

[Acute and chronic mechanical circulatory support]

Mechanical circulatory support and mechanical unloading of the left ventricle become more and more routine in clinical treatment regimens of both acute and chronic heart failure. Along with increasing availability of different cardiac assist systems one can adjust the degree of support according to the clinical situation. We report about our experience in the period between January 1994 and May 1995 with following assist systems: Hemopump, centrifugal pumps, Medos, HIAVAD and Novacor. We implanted those devices in 21 patients out of following indications: postinfarct--cardiac failure (CF), postcardiotomy CF, elective postcardiotomy support, myocarditis CF and "bridge" to transplant. Ten patients survived the period of mechanical support and could be weaned successfully. Circulatory support was sufficient in all cases, indication, time of implantation, anticoagulation and prevention of infections are discussed.

[Surgical coronary revascularization of the beating heart]

Despite the fact that all the progress in technology, surgical technique and pathophysiological knowledge has made aortocoronary bypass surgery a safe routine procedure, there are certain clinical settings where an alternative approach seems to be advantageous. In 50 patients with age ranging from 51 to 74 years with advanced coronary heart disease and poor left ventricular (LV) function, as well as in patients with good LV function and single or double vessel disease not amenable for PTCA and in patients with acute ischemia or recent myocardial infarction, we performed coronary artery bypass grafting (CABG) without cardioplegic arrest during a short period of left ventricular unloading by means of a left ventricular assist device (LVAD). During LVAD support we administered Esmolol to decrease the heart rate and to keep the heart flaccid to facilitate easier peripheral anastomosis on a breathing heart. Preoperative ejection fraction ranged from 15 to 56%. In two patients of the acute MI-group, we continued the left ventricular mechanical support postoperatively, one of them survived. We performed on average 1,4 distal anastomoses and used in 34 cases the left internal mammary artery. All but three patients survived the procedure in stable conditions and could leave intensive care after a mean stay of 1.5 days. There were no perioperative myocardial infarctions. In our view, CABG during LVAD support without heart lung machine and cardioplegia is a safe and life saving procedure. No ischemic damage is applied to the heart and it can be recommended for cautions use in select patients.

[Percutaneous "high risk" angioplasty with prophylactic cardiopulmonary support. High risk PTCA with mechanical circulatory support]

With improved technology and development of several mechanical assist devices, the indications of percutaneous transluminal coronary revascularization have been extended. In 39 patients (30 men, mean age = 60.1 +/- 8.1 years) with angina pectoris or heart failure, with poor operative risk-benefit ratio and ejection fraction < 35% and/or target vessel supplying > 50% of the viable myocardium, we performed assisted percutaneous transluminal coronary revascularization. Intraortic balloon counterpulsation (n = 16), extracorporal circulation (n = 21), or hemopump (n = 2) were used for mechanical support. Complete 6-week follow up was possible in 27 patients. An improvement of left-ventricular function (patients with EF < or = 35% demonstrated an improvement: 27 +/- 7 vs 36 +/- 10%, p < 0.05), heart failure (patients with EF < or = 35% demonstrated an improvement of maximal oxygen uptake: 14 +/- 4 vs 17 +/- 4 ml/kg/min; p < 0.05) and a marked improvement of angina (23/38 demonstrated CCS-improvement of at least one class) was found. Hospital mortality was as low as 2.6%. Major postinterventional complications included nonfatal myocardial infarction (n = 2), fatal retroperitoneal bleeding (n = 1), pulmonary edema (n = 1), nonfatal ventricular fibrillation (n = 1), cerebrovascular event without residual (n = 1), and deep vein thrombosis (n = 4). In conclusion, assisted percutaneous revascularization was successful in a high risk subset of patients with increased surgical risk and/or poor ventricular function.

Left-ventricular unloading with a new pulsatile assist device: the HIA-VAD system and its influence on myocardial stunning

To assess the mechanical unloading properties of a new pneumatic cardiac assist device (60 ml Medos HIA-VAD) and its possible influence on recovery from myocardial stunning we performed a study in 12 anaesthetized sheep. After left thoracotomy measuring transducers were placed and the assist device connected between the left-atrial appendage and the descending thoracic aorta. Global hemodynamics were measured before and after unloading was performed. Myocardial stunning was induced by transient occlusion of a coronary artery for 15 minutes and regional myocardial wall thickening was measured. A group without unloading served as controls (group I, n = 4). In a second group unloading was performed during the last ten minutes of ischemia (group II, n = 4) and in a third group unloading was performed for 30 minutes starting after ten minutes of reperfusion (group III, n = 4). After starting the Medos HIA-VAD, significant unloading could be demonstrated: left-ventricular dP/dtmax decreased significantly (p < 0.05) to 54% and 61% in groups II and III and left-atrial pressure to 50% and 71%, respectively. Systolic and mean arterial pressure did not change significantly (p > 0.05), while the diastolic pressure increased (p < 0.05) to 134% and 138% in groups II and III. After mechanical unloading whether during ischemia or during reperfusion systolic wall thickening in the postischemic area recovered to 103% and 92% of preischemic control in groups II and III, respectively. Recovery was incomplete in the non-unloaded controls (76%) (p < 0.05 versus groups II and III). Post-ejection thickening, a diastolic measure of stunning, diminished significantly after unloading in both protocols (p < 0.05 for groups II and III versus group I). We conclude that mechanical unloading with the 60 ml Medos HIA-VAD significantly improves recovery from myocardial stunning.

Mechanical unloading properties of axial flow pumps and their effect on myocardial stunning

Postischemic myocardial dysfunction affects morbidity and mortality in patients with coronary artery disease. It is known that mechanical unloading of the left heart ventricle can positively influence postischemic myocardial dysfunction. In this respect we tested two miniaturised axial flow pumps, i.e. the 14-F and the 21-F Hemopump. An experimental study was carried out on 30 open chest sheep where regional myocardial wall motion was followed using sonomicrometry in a preparation of transient coronary artery occlusion. Only the larger 21-F Hemopump showed hemodynamically significant unloading of the left ventricle. Furthermore, as far as stunning is concerned, systolic wall thickening recovered better when this type of pump was used during reperfusion. Also postejection thickening, which is an indication of diastolic postischemic dysfunction, is reduced significantly in the postischemic area (ANOVA, p < 0.05). Thus, the 21F Hemopump, but not the 14F Hemopump, provides adequate mechanical unloading in order to beneficially influence myocardial stunning.

Mechanical unloading with a miniaturized axial flow pump (hemopump): an experimental study

A family of miniaturized axial flow pumps has been developed, including the Hemopump, the 14-F, and the 21-F HP, which were especially designed for cardiological use. We designed an experimental set-up to study the unloading properties of these devices in a model of regional stunning in an anesthetized, open thorax preparation in sheep. Stunning was caused by 15-min occlusion of the diagonal branch of the left anterior descending coronary artery with subsequent 90 min of reperfusion. Regional myocardial function was assessed by sonomicrometry. A control group was compared with 2 groups with either mechanical unloading during part of ischemia (Group 2) or the early phase of reperfusion (Group 3). In either unloading protocol, both Hemopumps were used. It was shown that recovery from asynchrony was significantly faster in Groups 2 and 3 if unloading was performed with the 21-F HP compared with control Group 1 and the groups using the 14-F HP (p > 0.05). Thus, mechanical unloading with the 21-F Hemopump enhances recovery from stunning whereas unloading with the 14-F HP has only minor effects on hemodynamics and no effects on recovery.

Effects of unloaded reperfusion on mitochondrial function in the postischemic myocardium

The effect of mechanical unloading on recovery of postischemic myocardial performance, high energy phosphate content, and mitochondrial function was tested in an isolated working rabbit heart model. After 30 min of global ischemia, prolonged unloaded reperfusion could prevent complete loss of contractility, deterioration of mitochondrial function, and depletion of the ATP pool as was found when only short-term unloading was performed. Aortic flow recovered to 21% of preischemic control, and left ventricular dP/dt max to 46% (p < 0.05 vs. short-term unloading). OPR and ADP/O stabilized at 42 and 72%, respectively (p < 0.05 vs. short-term unloading), and ATP at 33% of control (p < 0.05 vs. short-term unloading). These results show the beneficial effect of prolonged unloading in postischemic hearts.

Use of left-ventricular assist with the Hemopump in cardiac surgery

From July 1989 to May 1992 16 patients received circulatory support with a Hemopump assist device in the Department of Cardiac Surgery of the Katholieke Universiteit Leuven. The mean age of those patients was 56 +/- 13 years (ranging from 23 to 72 years). The mean time of assisted circulation was 60 +/- 46 h (ranging from 2 to 168 h). Group I consists of 13 patients who received the device after postcardiotomy cardiac failure (survival 38%). Group II includes 1 patient who received the pump prior to repair of a large postinfarction ventricular septal defect (survival 10%). Group III consists of 2 patients for whom the Hemopump was used as a bridge to cardiac retransplantation. Both are still alive (survival 100%). If the 21-F Hemopump is implanted following a critical indication it can be used rather successfully for mechanical circulatory support.

Immunology of atherosclerosis. Demonstration of heat shock protein 60 expression and T lymphocytes bearing alpha/beta or gamma/delta receptor in human atherosclerotic lesions

Our previous work revealed the presence of a great number of activated T lymphocytes in early human atherosclerotic lesions, and we were able to induce atherosclerosis in normocholesterolemic rabbits by immunization with Mycobacterium tuberculosis heat-shock protein (HSP) 65. We hypothesized this latter phenomenon to arise from cross-reactivity of mycobacterial HSP 65 with the endogenously expressed homologous 60-kd form of this stress protein. To study HSP 60 expression and the phenotype of intima infiltrating T lymphocytes relative to the T cell receptor (TCR) in human atherosclerotic lesions, specimens of aorta, carotid arteries, and internal mammary arteries and veins, as well as saphenous veins and vena cava from 27 subjects, aged 23 to 80 years, were examined using immunohistochemical and immunofluorescence techniques on serial frozen tissue sections. HSP 60 was detected on endothelium, smooth muscle cells, and/or mononuclear cells of all carotid and aortic specimens, whereas vessels of smaller diameter, serving as reference specimens for normal intima without atherosclerotic lesions and mononuclear infiltration, showed no detectable expression of this stress protein. Furthermore, although the majority of CD3+ cells within the mononuclear cell infiltrates of atherosclerotic lesions bear the alpha/beta TCR, a considerable portion also consisted of gamma/delta TCR+ cells. Thus, 9.7% of T cells in the transition zone between normal intima and fatty streaks carry the gamma/delta TCR, a proportion that decreases to 6.6% and 4.3% in fatty streaks and atherosclerotic plaques, respectively. We conclude that the intensity of HSP 60 expression correlates positively with the atherosclerotic severity and that most lymphocytes participating in atherogenesis bear the alpha/beta TCR, although gamma/delta TCR+ cells are also enriched in atherosclerotic lesions. Expression of HSP 60 by intimal cells, caused, eg, by hemodynamic shear forces, may be responsible for recruitment of HSP-sensitized T cells, thus leading to the induction of an initiating inflammatory process in atherosclerosis. Other risk factors, such as high serum cholesterol levels, contribute to the final outcome of the disease.

Left ventricular assist with an axial flow pump (Hemopump): clinical application

Eighteen patients suffering from acute left heart failure were selected as candidates for Hemopump support. In 6 patients, peripheral atheromatosis prevented insertion of the device. Of the remaining 12 patients, 9 had postcardiotomy shock, 2 had acute rejection after orthotopic heart transplantation, and 1 had acute myocardial infarction complicated by a large postinfarction ventricular septal defect. During Hemopump support, hemodynamics recovered in all patients. Major complications were related to mechanical pump failure, such as fracture of the drive cable and expulsion of the cannula out of the ventricle, or to hemolysis of variable degree. Seven patients (58%) survived and were discharged from the hospital: the 2 patients bridged to heart transplantation and 5 of the 9 postcardiotomy patients, including 1 who could not be weaned but later underwent successful transplantation. The patient with the postinfarction ventricular septal defect died after removal of the device because of hemolysis. These results indicate that the Hemopump is a relatively noninvasive and efficacious left ventricular system of moderate power.

Left ventricular assistance using a catheter-mounted coaxial flow pump (Hemopump) in a canine model of regional myocardial ischaemia

The global and regional effects of left ventricular circulatory assistance were examined in dogs during acute myocardial infarction using a new coaxial flow device (Hemopump). In 12 dogs the left anterior descending coronary artery was occluded for 4 h and subsequently reperfused for 12 h. In six dogs, left ventricular assistance was started 90 min after coronary artery occlusion and maintained for several hours; six control animals received no circulatory support. Survival rate in the animals receiving mechanical support was 100% vs 0% in the control group. The Hemopump reduced left ventricular stroke work up to 80% and maintained blood flows to the brain, kidneys, liver and intestine throughout the experiment. Infarct size, expressed as a percentage of the left ventricle, however, was not modified (12% in supported animals vs 13% in control dogs). Side effects of the coaxial flow pump were thrombocytopaenia, occurring in all six dogs, and haemolysis, which was demonstrated in one animal. It was concluded that the Hemopump provides effective global and regional circulatory support in a canine model of severe cardiogenic shock. However, the value of left ventricular support to modify infarct size could not be demonstrated in this experimental model.

[Possibilities for saving homologous blood in heart surgery]

The risks of blood transfusion in context with the increasing number of operative open-heart procedures and the linked increased demand for blood products present a challenge to find methods of saving homologous blood. On the one hand there is increasingly less blood at the surgeon's disposal and on the other hand there is the threat of infectious complications with viruses of the HIV or the hepatitis group, as well as allergic reactions. At present we are developing the concept of blood saving as a programme which should work without excess demands on the staff and which can be adjusted to the needs of the individual patient. The programme consists of the following components: preoperative self donation, use of cell saver, acceptance of e relatively low hematocrit, medication to alter the coagulation process and blood-less priming.