Epicardial left ventricular lead placement for cardiac resynchronization therapy: optimal pace site selection with pressure-volume loops

OBJECTIVES

Patients in heart failure with left bundle branch block benefit from cardiac resynchronization therapy. Usually the left ventricular pacing lead is placed by coronary sinus catheterization; however, this procedure is not always successful, and patients may be referred for surgical epicardial lead placement. The objective of this study was to develop a method to guide epicardial lead placement in cardiac resynchronization therapy.

METHODS

Eleven patients in heart failure who were eligible for cardiac resynchronization therapy were referred for surgery because of failed coronary sinus left ventricular lead implantation. Minithoracotomy or thoracoscopy was performed, and a temporary epicardial electrode was used for biventricular pacing at various sites on the left ventricle. Pressure-volume loops with the conductance catheter were used to select the best site for each individual patient.

RESULTS

Relative to the baseline situation, biventricular pacing with an optimal left ventricular lead position significantly increased stroke volume (+39%, P =.01), maximal left ventricular pressure derivative (+20%, P =.02), ejection fraction (+30%, P =.007), and stroke work (+66%, P =.006) and reduced end-systolic volume (-6%, P =.04). In contrast, biventricular pacing at a suboptimal site did not significantly change left ventricular function and even worsened it in some cases.

CONCLUSIONS

To optimize cardiac resynchronization therapy with epicardial leads, mapping to determine the best pace site is a prerequisite. Pressure-volume loops offer real-time guidance for targeting epicardial lead placement during minimal invasive surgery.

Three-dimensional electromechanical mapping: imaging in the operating room of the future

BACKGROUND

Three-dimensional electromechanical mapping has previously been shown to be a clinically important tool for cardiac imaging and intervention. We hypothesized that this technology may be beneficial as an intraoperative modality for assessing cardiac hemodynamics and viability during cardiac surgery. We report here the use of this technology as an imaging modality for intraoperative cardiac surgery.

METHODS

The tip of a locatable catheter connected to an endocardial mapping and navigating system is accurately localized while simultaneously recording local electrical and mechanical functions. Thus the three-dimensional geometry of the beating cardiac chamber is reconstructed in real time. The system was tested on 6 goats that underwent acute dynamic cardiomyoplasty and on 5 dogs that underwent left anterior descending (LAD) coronary artery ligation.

RESULTS

The electromechanical mapping system provided an accurate three-dimensional reconstruction of the beating left ventricle during cardiomyoplasty. After the wrapping procedure, significant end-diastolic area reduction was noted in the base and mid parts of the heart (948 +/- 194 mm2 vs 1245 +/- 33 mm2, p = 0.021; and 779 +/- 200 mm2 vs 1011 +/- 80 mm2, p = 0.016). The area of the cross-section of the apex did not change during the operation. Acute infarcted tissue was characterized 3 days after LAD ligation by concomitant deterioration in both electrical and mechanical function.

CONCLUSIONS

By providing both a clear view of the anatomical changes that occur during cardiac surgery, and an accurate assessment of tissue viability, electroanatomic mapping may serve as an important adjunct tool for imaging and analysis of the heart during cardiac surgery

Right ventricular support for off-pump coronary artery bypass grafting studied with bi-ventricular pressure--volume loops in sheep

OBJECTIVES

Tilting the heart during off-pump coronary artery bypass grafting (OPCABG) causes a strong decrease in cardiac output. It is hypothesized that this decrease is caused by reduced right ventricular filling and that right ventricular support is thus the best way to restore cardiac output. Simultaneous left and right ventricular pressure-volume loops were used to test this hypothesis.

METHODS

In seven sheep, the heart was tilted with the use of an Octopus device. After unsupported tilting, a novel right ventricular support, the Enabler, was activated at a pulsatile flow of 1.6 l/min. Pressure-volume loops of both ventricles were obtained using conductance catheters, and cardiac output was monitored with an aortic flow probe.

RESULTS

Tilting reduced cardiac output by 31% (4.4--3.1 l/min, P=0.001) and right ventricular end-diastolic volume by 44% (86--51 ml, P=0.005), while right ventricular end-diastolic pressure did not decrease. Left ventricular systolic pressure was not significantly reduced upon tilting and even increased in two animals. During Enabler right ventricular support, the cardiac output remained 23% lower than pre-tilting values (3.4 vs. 4.4 l/min, P=0.001).

CONCLUSIONS

Restricted right ventricular filling is the primary cause of the strong decrease in cardiac output during tilting. The Enabler right ventricular support can currently not restore cardiac output to pre-tilting values, mainly caused by its limited output and a decrease in right ventricular output upon Enabler activation. Constant monitoring of cardiac output is crucial during (unsupported or supported) tilting as blood pressure alone may not reflect the extent of the reduction in cardiac function.

Hemodynamic evaluation of descending aortomyoplasty versus intra-aortic balloon pump performed in normal animals: an acute study

OBJECTIVE

Aortomyoplasty is a surgical procedure that aims to induce hemodynamic benefits similar to those of the intra-aortic-balloon-pump (IABP). The objective of this study was to compare the coronary blood flow augmentation and afterload reduction produced by IABP and descending aortomyoplasty counterpulsation.

METHODS

From a series of fifteen mongrel dogs (18-35 kg), eight underwent acute descending aortomyoplasty and seven had IABP application. Left anterior descending (LAD) coronary artery blood flow was measured using a Doppler flow probe. Left ventricular pressure in addition to aortic pressures both proximal and distal to either the aortomyoplasty site or the IABP position were monitored continuously. All experiments were acute and performed in normal hearts.

RESULTS

Descending aortomyoplasty induced a 27% increase in the LAD blood flow integral during assisted beats (14.0+/-6 ml/min integral compared to 10.8+/-4 ml/min integral in unassisted beats [P<0.001]). This was comparable to an 18% rise in the LAD blood flow integral during IABP counterpulsation (from 8.6+/-3 ml/min to 10.2+/-4 ml/min [P<0.001]). Conversely, while IABP counterpulsation reduced the left ventricular afterload by 16% (from 102+/-23 mmHg to 86+/-26 mmHg [P<0.001]), descending aortomyoplasty did not result in afterload reduction.

CONCLUSIONS

Descending aortomyoplasty produces coronary blood flow augmentation comparable to that achieved by the IABP. This may be important for end-stage ischemic patients. However, afterload reduction achieved by the IABP was not reproduced during descending aortomyoplasty counterpulsation. The surgical technique of descending aortomyoplasty should be modified to attain afterload reduction, thus improving treatment for congestive heart failure patients.

Acute and short-term effects of partial left ventriculectomy in dilated cardiomyopathy: assessment by pressure-volume loops

OBJECTIVES

The aim of this study was to evaluate the short-term effects of partial left ventriculectomy (PLV) on left ventricular (LV) pressure-volume (P-V) loops, wall stress, and the synchrony of LV segmental volume motions in patients with dilated cardiomyopathy.

BACKGROUND

Surgical LV volume reduction is under investigation as an alternative for, or bridge to, heart transplantation for patients with end-stage dilated cardiomyopathy.

METHODS

We measured P-V loops in eight patients with dilated cardiomyopathy before, during and two to five days after PLV. The conductance catheter technique was used to measure LV volume instantaneously.

RESULTS

The PLV reduced end-diastolic volume (EDV) acutely from 141+/-27 to 68+/-16 ml/m2 (p < 0.001) and to 65+/-6 ml/m2 (p < 0.001) at two to five days postoperation (post-op). Cardiac index (CI) increased from 1.5+/-0.5 to 2.6+/-0.6 l/min/m2 (p < 0.002) and was 1.8+/-0.3 l/min/m2 (NS) at two to five days post-op. The LV ejection fraction (EF) increased from 15+/-8% to 35+/-6% (p < 0.001) and to 26+/-3% (p < 0.003) at two to five days post-op. Tau decreased from 54+/-8 to 38+/-6 ms (p < 0.05) and was 38+/-5 ms (NS) at two to five days post-op. Peak wall stress decreased from 254+/-85 to 157+/-49 mm Hg (p < 0.001) and to 184+/-40 mm Hg (p < 0.003) two to five days post-op. The synchrony of LV segmental volume changes increased from 68+/-6% before PLV to 80+/-7% after surgery (p < 0.01) and was 73+/-4% (NS) at two to five days post-op. The LV synchrony index and CI showed a significant (p < 0.0001) correlation.

CONCLUSIONS

The acute decrease in LV volume in heart-failure patients following PLV resulted at short-term in unchanged SV, increases in LVEF, and decreases in peak wall stress. The increase in LV synchrony with PLV suggests that the transition to a more uniform LV contraction and relaxation pattern might be a rationale of the working mechanism of PLV.

New biocompatible polymer surface coating for stents results in a low neointimal response

Clinical studies indicate a more pronounced endothelial response after stent implantation than after balloon inflation. This might be related to the metal surface of the stent, and therefore it is speculated that coating of the stent might partially prevent hyperplasia. One coated and one noncoated Palmaz-Schatz stent were implanted in two separate coronary arteries of seven pigs. The coating was composed of methylmethacrylate (MMA) (hydrophobic, 70 mol %) and 2-hydroxyethyl methacrylate (HEMA) (hydrophilic 30 mol %). After sacrifice (3 weeks), cross sections were made of the stented areas. Vessel wall reaction was calculated both independently and dependently of local vessel wall injury due to the stent struts. Overall, vessel wall reaction of the coated stents was lower than that of the noncoated stents. The degree of hyperplasia was linearly related to the degree of stent-induced vessel wall injury. Analyses of all the struts showed that significantly less hyperplasia occurred in the coated versus noncoated stents. In this porcine coronary artery model, the MMA/HEMA stent coating resulted in significantly reduced vessel wall response. However, it remains to be determined whether this favorable outcome will also be present in humans.

Metallic wires with an adherent lubricious and blood-compatible polymeric coating and their use in the manufacture of novel slippery-when-wet guidewires: possible applications related to controlled local drug delivery

A new procedure was developed for the controlled application of adherent hydrophilic and biocompatible coatings onto the surface of "endless" metallic wires. Use of copolymers of 1-vinyl-2-pyrrolidinone and alkylmethacrylates provided coatings with excellent adherence and lubricity, and markedly low thrombogenicity. Coated wires could be spiralized without damaging the coating; the resulting coils are potentially useful as lubricious guidewires for use in, for example, interventional cardiology or urology. This study demonstrates that the lubricity of the coating is dependent on the composition (hydrophilicity) of the coating biomaterial, as well as on the thickness of the coating. Furthermore, the results imply that the adherence of the hydrophilic coating is essentially due to entanglement of the binder polymer chains and the hydrophilic copolymer chains. Moreover, the idea to use the hydrophilic coating on the wire as a temporary depot for controlled local drug delivery was explored. The coating was loaded with the dye rhodamine, and release of the dye upon immersion of the coated wire in water was studied. This work revealed that release of the drug is dependent on the composition of the coating. The potential utility of such wires with a drug-charged coating for controlled local drug delivery is discussed briefly.

Acute descending aortomyoplasty induces coronary blood flow augmentation

BACKGROUND

Aortomyoplasty is a procedure aimed to improve cardiac output in patients suffering from heart failure. Stimulation of the latissimus dorsi muscle around the aorta produces hemodynamic effects similar to those of the intraaortic balloon pump. These may be maintained without the accompanying complications or the need for anticoagulation. The objective of this study was to test the acute effects of aortomyoplasty on coronary artery blood flow.

METHODS

Eight mongrel dogs (18 to 30 kg) underwent acute descending aortomyoplasty. Several stimulation protocols were applied after wrapping of the latissimus dorsi muscle around the aorta in different surgical configurations. The left anterior descending coronary blood flow was measured using a transonic Doppler flow probe. Left ventricular and aortic pressures, proximal and distal to the aortomyoplasty site, were monitored continuously.

RESULTS

Significant aortic diastolic pressure augmentation was expressed both as an increase in peak values, from 110 +/- 24 mm Hg to 120 +/- 24 mm Hg (p < 0.001) and as an increase in the diastolic integral, from 64 +/- 23 mm Hg x s to 84 +/- 37 mm Hg x s (p < 0.001). Concomitantly, peak left anterior descending coronary blood flow increased from 26 +/- 10 mL/min to 32 +/- 12 mL/min (p < 0.001). This was associated with an increase in the diastolic flow integral from 11 +/- 4 mL to 14 +/- 6 mL (p < 0.001).

CONCLUSIONS

Descending aortomyoplasty induces significant augmentation of coronary blood flow. Optimal timing of muscle stimulation is important in achieving the best assist. This procedure may prove beneficial for end-stage ischemic patients.

The enabler right ventricular circulatory support system for beating heart coronary artery bypass graft surgery

BACKGROUND

Beating heart coronary artery bypass graft surgery of the left anterior descending, diagonal, and right coronary artery can be performed safely with the Octopus Stabilization System. However, tilting of the heart, which is necessary to reach the obtuse marginal and distal right coronary arteries, causes hemodynamic instability. This study was performed to investigate the possible role of the Enabler right ventricular circulatory support system in counteracting this instability.

METHODS

In 8 sheep, the Enabler cannula was introduced via the jugular vein and positioned with the inlet valve in the right atrium and outlet valve in the pulmonary artery. The Octopus was used to expose the inferior wall and the posterior wall of the left ventricle. The hemodynamic effects of this tilting with and without Enabler right ventricular support were recorded, including Pressure Volume (PV) loops measured by conductance catheters in both ventricles.

RESULTS

Tilting caused a reduction in stroke volume (inferior 31%, posterior 17%) and Enabler activation increased stroke volume (inferior 13%, posterior 31%).

CONCLUSIONS

Tilting the heart has severe hemodynamic consequences that can be partially counteracted by the use of the Enabler for right ventricle support.

Ex vivo testing of heparin-coated extracorporeal circuits: bovine experiments

In this study the intrinsic thrombogenicity of the extracorporeal circuits and the benefit of heparin-bonded circuits in an extracorporeal life support system without full systemic heparinization and with minimal interference of the so called material-independent factors was tested in four calves. In two circuits (group A) all blood-contacting surfaces were coated with end-point-attached heparin and the other two were non-coated (group B). Under standardized conditions the calves were perfused at a blood flow rate of 2 L/min. After only one bolus injection of heparin (250 IU/kg body weight) before cannulation, plasma heparin activity rapidly decreased in both groups: half life of about 55 minutes. This decrease of the heparin activity was accompanied by a fall of the activated clotting time (ACT) level to baseline values. The experiments using a heparin-coated circuit, had a runtime of more than 360 minutes, whereas the experiments using a non-coated circuit had to be terminated after a runtime of 255 minutes, because massive fibrin formation was noticed in the circuit. This formation was accompanied by a rapid increase in the line pressure, measured just before the inlet of the oxygenator. The macroscopic inspections after terminating the experiments and rinsing the circuit showed a clean circuit in group A. The fibrinopeptide A (FPA) level increased faster during perfusion with the non-coated circuit than in the heparin coated circuit. Lung histopathological examinations of the lungs of the animals in group A showed no fibrin deposition, whereas most of the blood vessels of the lung preparations of the animals in group B were partially or completely occluded with fibrin. These results suggest that heparin-bonding greatly reduces the thrombogenicity of the extracorporeal circuit, and therefore it can reduce the need for systemic heparinization in an extracorporeal life support system.

Structural alterations in the latissimus dorsi muscles in three patients more than 2 years after a cardiomyoplasty procedure

AIMS

The long-term effects of the use of the latissimus dorsi muscle for dynamic cardiomyoplasty were studied. Skeletal muscle fast fatiguable type II fibres are transformed to highly fatigue-resistant type I fibres in animal models, and is assumed to occur in men. However, it is not known whether this same transformation occurs in patients with chronic heart failure.

METHODS AND RESULTS

Three patients who underwent a cardiomyoplasty procedure (pre-operative NYHA class IV) were studied. The left latissimus dorsi muscle was stimulated, according to routine clinical protocol, with 30 Hz bursts in a 2:1 ratio to cardiac activation. The patients died more than 2 years after surgery and five autopsy samples were obtained at defined places in the wrapped muscle. In the proximal part of the latissimus dorsi muscle, the type I fibres comprised 68-80% in all three patients, whereas peroperatively type I fibres comprised 17-30% indicating significant but not complete transformation. Transformation in the latissimus dorsi muscle as a whole appeared to be inhomogeneous, with type I fibres ranging from 10-80%. An extensive amount of muscle fibre appeared to be replaced by fatty tissue (10%-50%). This occurred at random and resulted in complete loss of muscle structure. A significant increase in the density of small arteries was observed in the latissimus dorsi after transformation.

CONCLUSIONS

In these patients, muscle fibre type transformation was not as complete as that observed in animal experiments, and was accompanied by loss of muscle viability. The stimulation current in the latissimus dorsi muscle appeared not to be the direct cause of local tissue lipomatosis or collagen deposition.

Sustained local drug delivery from a radiopaque implanted reservoir

A new polymeric biomaterial that contains covalently bound iodine, and is therefore radiopaque, was used to construct a sustained local drug-delivery device. A polymeric wall was designed to be porous (i.e., passage of low-molecular-weight molecules across the wall is possible), self-healing, and biocompatible. Once implanted, the sphere cavity can be filled and refilled with a concentrated solution of a (cytostatic) drug, which is subsequently released by slow diffusion into the tissue region surrounding the sphere. This principle of sustained local drug delivery is shown by a series of in vitro experiments on the release of 5-fluorouracil, and in vivo animal experiments, using x-ray fluoroscopic and scintigraphic techniques.

Left ventricular pressure-volume relationships before and after cardiomyoplasty in patients with heart failure

BACKGROUND

The aim of this study was to elucidate whether beneficial effects of cardiomyoplasty (CMP) in patients with dilated cardiomyopathy are the result of a decrease in existing ventricular dilatation or a prevention of further dilatation.

METHODS AND RESULTS

Combined micromanometer-conductance catheters were used to evaluate left ventricular pressure-volume relationships in six patients with dilated cardiomyopathy before and at 6 and 12 months after CMP. Acute changes in preload and afterload were induced by a standardized leg-tilting intervention and a bolus infusion of nitroglycerin. After CMP, end-diastolic volume (EDV) decreased from 138+/-10 to 103+/-18 mL/m2 (P<.01) at 6 months and to 83+/-17 mL/m2 (P<.01) at 12 months. End-diastolic pressure (EDP) decreased from 20.2+/-6.4 to 13.9+/-7.7 mm Hg (P<.01) at 6 months after CMP. Peak ejection rate and ejection fraction increased at 6 months after CMP from 594+/-214 to 799+/-214 mL/s (P<.05) and from 26.6+/-4.7% to 40.1+/-8.3% (P<.05), respectively. Peak dP/dt decreased at 12 months after CMP from -842+/-142 to -712+/-168 mm Hg/s (P<.05). Leg-tilting before CMP increased EDP from 20.2+/-6.4 to 25.6+/-5.2 mm Hg (P<.01), end-systolic pressure (ESP) from 118+/-17 to 122+/-17 mm Hg (P<.05), and tau from 50.8+/-2.8 to 53.8+/-2.3 ms (P<.05). Six months after CMP, leg-tilting also increased EDV from 103+/-18 to 110+/-22 mL/m2 (P<.05) and ESV from 62+/-14 to 66+/-14 mL/m2 (P<.05). Before CMP, nitroglycerin decreased EDP from 20.2+/-6.4 to 10.4+/-3.8 mm Hg (P<.01), ESP from 118+/-17 to 96+/-11 mm Hg (P<.05), ESV from 100+/-11 to 89+/-7 mL/m2 (P<.05), and tau from 50.8+/-2.8 to 44.5+/-3.7 ms (P<.05). Six months after CMP, nitroglycerin decreased EDP, ESP, and tau to similar values.

CONCLUSIONS

Our findings show that up to 1 year after CMP, marked decreases in left ventricular volume are present. Our measurements suggest that CMP actively reduced the dilated ventricle but did not prevent a higher EDV on an increased venous return. The latissimus dorsi muscle wrap contraction results in better synchronization of contraction and more rapid emptying of the left ventricle.

Distal embolization during thrombectomy with use of the hydrolyser (hydrodynamic thrombectomy catheter): in vitro testing

PURPOSE

To evaluate distal embolization while using the Hydrolyser (hydrodynamic thrombectomy catheter) with special attention to the severity of the stenosis and temporary distal or proximal flow obstruction.

MATERIALS AND METHODS

The Hydrolyser procedure was assessed in plastic tubes (5-8 mm) with a 70% or 90% diameter stenosis with or without temporary distal flow obstruction and a 72-hour-old clot proximal to the stenosis. The weight of the embolized particles was established after passage through filters of 1,000, 500, 100, and 10 microm. To evaluate the influence of the absolute inner diameter of the stenosis 1.0-, 2.1-, and 3.0-mm stenoses were compared in 10-mm tubes.

RESULTS

Thrombus removal was greater than 99.9% in all but one of the cases in the 5-8-mm tubes. Embolization with a weight of more than 1 mg was only found in tubes with a relative stenosis of 70% and a stenosis inner diameter of greater than 1.5 mm. There was a positive relationship between inner diameter of the stenosis and the amount of distal embolization. In the presence of a proximal or distal temporary flow obstruction during thrombectomy, no distal embolization greater than 1 mg was found.

CONCLUSION

In this in vitro study, the Hydrolyser thrombectomy device demonstrated minimal distal embolization. The amount of distal embolization that did occur was related to the absolute stenosis diameter and could be prevented by a severe distal stenosis and/or a temporary proximal or distal flow obstruction.

Cardiomyoplasty as an isolated procedure to treat refractory heart failure

OBJECTIVE

Cardiomyoplasty represents a controversial therapy for chronic heart failure. The aim of this study is to review our experience of such a surgical procedure as an isolate approach to treat refractory left ventricular dysfunction.

METHODS

Twenty-two patients were considered candidates for cardiomyoplasty because of chronic heart failure. Mean age was 58.7 +/- 5.3 (range 48-71 years), 19 patients were male and 3 were female. Ischemic or idiopathic etiology was present in 11 cases, respectively. Traditional as well as innovative techniques were used to assess hemodynamic function. Pre-operative hemodynamic profile included mean left ventricular ejection fraction of 20 +/- 5.8% (9-28%), absence of severe right ventricular failure, and mean left ventricular end-diastolic diameter of 75.5 +/- 7.4 mm (range 61-92 m). All patients were in New York Heart Association Class III or Intermittent IV despite conventional medical therapy.

RESULTS

There was no intra-operative death. No additional surgery was performed. Left latissimus dorsi (LD) muscle was used in 20 cases, and right LD in two patients. Early mortality occurred in one patient (low cardiac output syndrome), whereas late mortality in five patients (three sudden deaths, one lung cancer, one heart failure). Mean follow-up is 20.7 +/- 16.7 months (3-51 months). Actuarial survival at 4 years is 70%. Cardiac index increased at 6 months (3.08 +/- 0.5 l/min per m2, P = 0.04), but no other significant changes were observed in the long term (3.03 +/- 0.7 l/min per m2, 3 +/- 0.7 l/min per m2, and 2.85 +/- 0.7 l/min per m2, at 12, 24 and 36 months, respectively). Ejection fraction improved at 6 and 12 months (29.1 +/- 1.03%, P = 0.0017; and 27.3 +/- 5.6%, P = 0.0091, respectively), while no substantial augmentation was documented at 2 and 3 years (25.6 +/- 2.5% and 25.1 +/- 4.0%, respectively). Left ventricular end-diastolic diameter was markedly reduced at 6 (73.2 +/- 8.0 mm, P = 0.0176), 12 (69.4 +/- 8.5 mm, P = 0.002) and 24 months (71.1 +/- 7.0 mm, P = 0.011), and was then stable (74.0 +/- 9.1 mm, P = 0.47) at 36 months. Postoperative pressure/volume loop evaluation showed some improvement of hemodynamic function from skeletal muscle assistance. Acute pulmonary edema episodes, as well as number of hospitalizations, were considerably reduced following cardiomyoplasty.

CONCLUSIONS

In our experience, cardiomyoplasty was shown to exert moderate beneficial influence on left ventricular performance, to significantly reduce cardiac dilatation and to promote the stabilization of the disease course.

In vivo tissue compatibility of two radio-opaque polymeric biomaterials

Polymeric biomaterials featuring intrinsic radio-opacity continue to attract considerable scientific attention. This work focusses on two polymers that contain covalently bound iodine, rendering the materials radio-opaque. The first material is hard, transparent and glass-like, and consists of methyl methacrylate, 2-(2'-iodobenzoyl)-ethyl methacrylate (1) and 2-hydroxyethyl methacrylate (HEMA), in the molar ratio 65:20:15, respectively. The second material is a cross-linked hydrophilic network, consisting of HEMA and 1, in the molar ratio 80:20, respectively. Both materials were characterized by means of different physico-chemical techniques, including magic-angle-spinning solid state NMR spectroscopy, infrared spectroscopy and differential scanning calorimetry. Moreover, both materials were implanted subcutaneously in rats for 24 days. Upon explanation and histological examination, it appeared that both materials were well tolerated. No tissue necrosis, abscess formation or inflammation were observed. The samples were found to be surrounded by a vascularized capsule consisting of connective tissue cells. The results reveal excellent tissue compatibility for both materials. This is an important observation, since tissue compatibility is absolutely necessary for the applications which are foreseen for this type of radio-opaque biomaterials.

A versatile three-iodine molecular building block leading to new radiopaque polymeric biomaterials

A methacrylic monomer containing three iodine atoms, 2- [2',3',5'-triiodobenzoyl]-ethyl methacrylate (compound 1), was prepared in pure form. Compound 1 can be reacted with other methacrylates, such as methyl methacrylate (MMA), and 2-hydroxyethyl methacrylate (HEMA) with high conversion. Typically, less than 0.5% of free monomer is left after polymerization. For example, compound 1 was reacted with MMA and HEMA in the molar ratio 7:73:20, respectively. This yielded a terpolymer with Tg = 86 degrees C, Mw = 47,000 g/ mol and Mn = 22,800 g/mol. This material was characterized by various physicochemical techniques, including gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis, and nuclear magnetic resonance (NMR) spectroscopy (1H at 400 MHz, DMSO-d6 solution). In addition the material was found to exhibit low surface thrombogenicity in vitro and a low propensity to activate contacting blood platelets. Furthermore it was found that the terpolymer is markedly radiopaque: even thin objects (< 0.5 mm) could be easily visualized using X-ray fluoroscopic techniques as are routinely used in the clinic, e.g., during coronary angiography. The combined results obtained with the present terpolymer (particularly its in vitro hemocompatibility and its radiopacity) leads to the suggestion that this type of polymer could be used as cardiovascular biomaterials, for instance for the construction of a new type of endovascular stents. These would be expected to show improved biocompatibility if compared with metallic stents which are currently used, for instance in conjunction with percutaneous transluminal coronary angioplasty (PTCA). A stent prototype, constructed from the present radiopaque terpolymer, is shown and discussed briefly.

Comparison of arterial wall reaction after passage of the Hydrolyser device versus a thrombectomy balloon in an animal model

PURPOSE

This study was designed to compare the reaction of the vessel wall after application of the Hydrolyser hydrodynamic thrombectomy device to the reaction after use of a balloon thrombectomy catheter. The influence of the vessel inner diameter on vessel wall reaction was evaluated after passage of the Hydrolyser.

MATERIALS AND METHODS

After measurement of the vessel inner diameter with intravascular ultrasound (US), 102 segments of femoral and carotid arteries of goats were treated with one of the following four procedures: passage of the intravascular US catheter alone; passage of the Hydrolyser without or with an activated jet; or passage of an inflated thrombectomy balloon. Histologic evaluation was performed after 3 weeks.

RESULTS

Intimal thickening (more than five cell layers of neointima) 3 weeks after treatment occurred more frequently after passage of the balloon than after any of the other procedures (P < .001). For vessels with a diameter of 3-4 mm, 4-5mm, or more than 5 mm, no significant difference in vessel wall reaction was observed following Hydrolyser passage.

CONCLUSION

In this model, passage of the Hydrolyser device resulted in less intimal reaction compared with the thrombectomy balloon.

Beat-to-beat analysis of left ventricular pressure-volume relation and stroke volume by conductance catheter and aortic Modelflow in cardiomyoplasty patients

BACKGROUND

Since the clinical introduction of dynamic cardiomyoplasty, a discrepancy has been observed between unchanged measurements of cardiac function and improved clinical outcome.

METHODS AND RESULTS

We performed a beat-to-beat analysis of cardiac performance at rest in nine cardiomyoplasty patients 6 to 24 months after operation. Conductance and micromanometer catheters were placed in left ventricle and aorta and used for measurements over a 15-second period, during which the wrapped latissimus dorsi (LD) muscle was stimulated for 10 seconds in a 1:2 synchronization mode followed by a 5-second period without LD stimulation. The synchronization delay between start of the QRS complex and the LD contraction was changed from 4 up to 125 ms at the patient's clinical stimulation strength and at an increased supramaximal amplitude. Comparing the LD assisted period to the unassisted period, at the clinical settings no significant changes in stroke volume (SV) as measured by the conductance technique and the aortic Modelflow technique were observed. A significant (P < .05) rise in left ventricular end-diastolic pressure (LVEDP) was observed directly after the assisted 10-second period. The peak ejection rate (PER) of left ventricular volume increased (P < .05), with a mean of 28 +/- 23% during the LD stimulated beats. At the patient's individual best setting, SV of the stimulated beats increased (P < .01) by a mean of 20 +/- 15%. Systolic aortic pressure increased (P < .01) by a mean of 7 mm Hg, peak negative dP/dt increased (P < .01), and PER increased, with a mean of 68 +/- 24% (P < .01). LVEDP was similar in stimulated and unstimulated beats and increased (P < .05) in the nonpaced 5-second period. The delay for the best setting ranged from 25 to 125 ms; the stimulus strength was 1.5 to 3 V higher than the clinical setting. At the patient's individual worst setting, SV remained unchanged and PER was higher, with a mean of 30 +/- 25% (P < .05). The worst setting was observed at the 1.5- to 3-V-higher stimulus strength; in six patients, it was at a short delay (4 to 25 ms) and in three patients, at the longest delay (100 to 125 ms).

CONCLUSIONS

By the left ventricular conductance catheter and aortic Modelflow methods, improvement in cardiac function by dynamic cardiomyoplasty was demonstrated in this patient group. The synchronization interval, stimulus strength, and stimulus duration appeared to be critical for obtaining optimal improvement.

Studies on a new radiopaque polymeric biomaterial

A new radiopaque polymeric biomaterial has been synthesized. The material, which actually represents an entire family of analogous radiopaque materials, is composed of 2-(p-iodobenzoyl)-ethyl methacrylate (compound 1, 21 mol%), methyl methacrylate (MMA, 60 mol%), and 2-hydroxyethyl methacrylate (HEMA, 19 mol%). The terpolymer was synthesized in a radical polymerization reaction at elevated temperature in N,N-dimethylformamide (DMF). The product was subjected to a set of physicochemical characterization techniques (gel permeation chromatography, 500 MHz 1H NMR in deuterated dimethylsulphoxide (d6-DMSO) solution, differential scanning calorimetry, dynamic water contact angle measurements), as well as to an in vitro thrombogenicity assay. Furthermore, scanning electron microscopy was used to study interactions of the material with blood platelets. The most important findings are: (a) the material is a genuine polymer with excellent X-ray visibility, even in the form of thin (0.4 mm) drawn fibres. This was established under realistic conditions. (b) The material exhibits low in vitro thrombogenicity, i.e. comparable to polyvinyl chloride, which is known as a passive material. These observations lead us to the suggestion that this type of radiopaque polymer holds promise with respect to application as a construction material for a new type of endovascular stent. This could be relevant in particular to stents to be used in conjunction with percutaneous transluminal coronary angioplasty (PTCA), also known as Dottering. Currently there is a clear trend away from metallic stents towards all-polymeric stents, since the latter have superior biocompatibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on two new radiopaque polymeric biomaterials

Two new polymeric materials (polymers A and B) containing covalently bound iodine were prepared. These polymers were evaluated with respect to their possible use as radiopaque implant biomaterials--that is, materials that are visible in a noninvasive manner using routine X-ray absorption imaging techniques. Polymer A is a copolymer of methyl methacrylate (MMA) and 1 (80 and 20 mol%, respectively). Polymer B was prepared from MMA, 1, and 2-hydroxyethyl methacrylate (HEMA) (mol ratio 65:20:15, respectively). Compound 1 was synthesized from 4-iodophenol and methacryloyl chloride. The resulting polymers were characterized with GPC, DSC, NMR, and by measuring both the advancing and receding contact angles. Thrombogenicity of the polymers was determined by an in vitro thrombin generation test procedure. The maximum concentration of free thrombin was 76 +/- 1 nM for polymer A, and 64 +/- 3 nM for polymer B. The lag times (i.e., time onset of thrombin generation) were 392 seconds for polymer A and 553 seconds for polymer B. For PVC-T, which is known as a passive material, a lag time of 583 seconds was found. This indicates that polymer B is comparable to PVC-T, and more passive than polymer A. Polymer A exhibited minor activation of platelets. Polymer B did not induce platelet activation at all. The polymers exhibited, even as fibers with a diameter of ca. 0.3 mm, good radiopacity with routine imaging X-ray techniques in the clinic.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo evaluation of the Hydrolyser hydrodynamic thrombectomy catheter

PURPOSE

The authors evaluated a 7-F double-lumen thrombectomy catheter (Hydrolyser) in vivo.

MATERIALS AND METHODS

To evaluate efficacy, thrombectomy was performed 1, 4, or 8 days after local denudation in peripheral arteries (n = 18) and veins (n = 29) of nine goats. To evaluate safety, the reaction of the vessel wall to a functioning and nonfunctioning Hydrolyser catheter was evaluated in the peripheral arteries and veins of three goats 10 days after the procedure.

RESULTS

Reopening was achieved in all vessels with residual thrombus in 11% of arteries (two of 18) and 55% of veins (16 of 29). Slight intimal thickening was observed, but no difference was seen between the passage of a functioning versus nonfunctioning catheter.

CONCLUSIONS

The Hydrolyser device can remove intravascular thrombus up to 8 days after induction. There was no difference in vessel wall reaction after the passage of a functioning and nonfunctioning catheter.

Circulatory models in assessment of cardiac enzyme release in dogs

Cardiac ischemia causes interstitial leakage of cellular enzymes followed by release of these enzymes into plasma. Quantitative interpretation of these data requires a specific circulatory model, and the performance of such models was investigated. Plasma activities of cardiac enzymes were measured for increasingly abrupt forms of ischemic heart injury in the dog: 1) permanent ligation of the left anterior descending coronary artery (LAD); 2) reperfusion after 2 h of ligation of the LAD; and 3) calcium-free perfusion of the LAD during 10 min (calcium-paradox injury). Release into plasma of a rapidly (41%/h) and a slowly (2.2%/h) catabolized enzyme was calculated from the plasma activities, using a detailed circulatory model with compartments for heart, plasma, muscle, skin, and viscera. The time course of cellular enzyme leakage into interstitial space in the heart was calculated from release into plasma and a range of reported values for transendothelial permeability. Simplification to one- and two-compartment models introduced, respectively, 10 and 2% error in calculated cumulative release. Considering the other sources of error, this implies adequate performance of the two-compartment model. Protein washout from the heart is strongly influenced by expansion of interstitial protein space with dead myocyte volume and depends on the microheterogeneity of necrotic tissue areas. Accelerated release of enzymes into plasma after reperfusion reflects accelerated cellular leakage rather than enhanced washout.

The importance of muscle relaxation in dynamic cardiomyoplasty

During the last decade dynamic cardiomyoplasty has been introduced as a new method to treat patients with severe heart failure. This procedure consists of the wrapping of the latissimus dorsi (LD) muscle around the heart with electrical stimulation of the muscle synchronous to cardiac contraction. The optimal pacing mode of the muscle, during the conditioning and working period of the LD muscle, is still unclear. The pace protocol, currently used worldwide, has a maximal number of muscle tetanic contractions of 100 per minute. Data are presented on the LD muscle contraction characteristics using that protocol. Both force measurements from six in situ stimulated goat LD muscles and x-ray evaluation of the movement of metallic clips on wrapped LD muscles in two patients were used. Results demonstrate that LD muscle force is well maintained at the maximal rate of 100 contractions per minute but relaxation is severely hampered. This may lead to diminished support of the failing heart and damage of the wrapped muscle. A pacing protocol is proposed using a lower maximal stimulation rate.

Differences in metabolic response of dog and goat latissimus dorsi muscle to chronic stimulation

The latissimus dorsi (LD) muscle is considered suitable to assist ventricular mechanical function in either cardiomyoplasty or extra-aortic-assist devices. Such application requires that this mixed-type skeletal muscle be transformed into a fatigue-resistant muscle, the adaptation of which can be elicited by chronic stimulation. In this study the LD muscles of dog and goat were subjected in situ to 12 wk of continuous electrical stimulation through intramuscular electrodes, and their myofibrillar and metabolic adaptations were compared. A gradual increase in the contraction rate of the muscle (in 10 wk from 30 to 80 contractions/min) caused the proportion of immunohistochemically identified type I fibers to increase in dog muscle from 30 to 74% and in goat muscle from 21 to 99%. Correspondingly, the anaerobic-glycolytic activity (fructose-6-phosphate kinase and lactate dehydrogenase activities) decreased by approximately 75% in both dog and goat muscles, whereas the oxidative capacity (fatty acid oxidation and citrate synthase activity) increased two- to threefold in goat LD muscle but remained unaltered in dog LD muscle. Muscular contents of high-energy phosphates and endogenous substrates were maintained, but the L-carnitine content decreased by 43% in both dog and goat. Our data further indicate that, for the monitoring of the metabolic adaptation of skeletal muscle, the ratio of activities of the oxidative and anaerobic-glycolytic pathways (e.g., citrate synthase to fructose-6-phosphate kinase activities) is a useful parameter in both dog and goat.(ABSTRACT TRUNCATED AT 250 WORDS)

Imipramine induced heart failure in the dog: a model to study the effect of cardiac assist devices

OBJECTIVE

The value of intravenous imipramine in creating a reversible model of short term heart failure was evaluated in anaesthetised dogs.

METHODS

Acute effects of imipramine were studied in 11 dogs using invasive haemodynamic pressure measurements and two dimensional echo evaluation.

RESULTS

After a 30 min imipramine infusion (7.5 mg.kg-1.h-1), positive left ventricular dP/dtmax decreased from 1368(SEM 108) to 909(119) mm Hg.s-1 (p < 0.05), left ventricular end diastolic pressure increased from 8(1) to 12(2) mm Hg (p < 0.05), while left ventricular pressure decreased from 106(4) to 87(6) mm Hg (p < 0.05). Cessation of imipramine administration resulted within 60 min in partial restoration of cardiac function. This deterioration and subsequent recovery was also demonstrated with echocardiographic measurements, which showed a decrease in ejection fraction from 54(3)% to 28(2)% (p < 0.05). During administration of imipramine neither significant electrophysiological changes nor supraventricular/ventricular arrhythmias were seen. Repeated infusions of imipramine in three anaesthetised dogs with a two week interval showed the reproducibility of the haemodynamic effects and the recovery of ventricular function. Since the model was developed to evaluate the use of cardiomyoplasty in heart failure, the effect of imipramine was also evaluated on latissimus dorsi muscle contraction. Administration of imipramine did not affect skeletal muscle force development at the dosage used to create heart failure.

CONCLUSIONS

This model can be used to produce short term reversible heart failure in anaesthetised animals to test the efficacy of supportive interventions like dynamic cardiomyoplasty, intra-aortic balloon pumping, and mechanical cardiac assist devices.

Changes in canine latissimus dorsi muscle during 24 wk of continuous electrical stimulation

To study functional, structural, and biochemical adaptations to electrical stimulation of striated muscle in a large animal, the canine latissimus dorsi (LD) muscle was conditioned continuously for 24 wk with an increasing number of pulse bursts (burst duration 250 ms, burst frequency 30 Hz). Force measurements in vivo after 12 wk showed a significant decrease in the ripple, the ratio of interstimulus to peak force amplitude, from 0.94 +/- 0.03 to 0.13 +/- 0.08 (SE; n = 8, P less than 0.05), indicating reduction in contractile speed. Also the steep part of the force-frequency relation shifted to lower frequencies. A significant change in fiber-type composition was seen with both enzyme- and immunohistochemistry, manifested by an increase of type I fibers from 29.5 +/- 2.9 to 83 +/- 8% (SE; n = 8, P less than 0.05). During this period a transient rise in the number of type IIc/Ic fibers (from 3 to 10%) was seen. In the stimulated muscle, capillary-to-fiber ratio increased from 1.9 +/- 0.4 to 2.7 +/- 0.1 (P less than 0.05). A significant increase in mitochondrial volume was also seen, especially in the peripheral part of the fiber. Both creatine kinase and lactate dehydrogenase revealed a significant decline in activity within 12 wk. At the same time a shift in lactate dehydrogenase-isozyme pattern was observed toward the cardiac composition. No additional changes occurred after 12 wk of stimulation, indicating that conversion of the canine LD muscle was complete within this period.

Complications after intracoronary stent implantation: three cases

Complications after implantation of articulated Palmaz-Schatz stents in coronary arteries of 3 patients are reported. In 1 patient, embolization of the stent occurred during the acute phase, and in the other 2 patients, we observed restenosis after 4 and 5 months, respectively. Late restenosis was located in the midportion and the distal end of the stent in 1 patient. In the other patient a severe subtotal occlusion was found 1 cm proximal to the stent. These findings suggest that adaptation of the stent delivery system is needed to prevent loss of the stent and scraping of the vessel wall.

Adaptation of energy metabolism of canine latissimus dorsi muscle in response to chronic electrical stimulation

Transformation of the latissimus dorsi (LD) muscle from a fast-twitch, fatigue-prone to a fatigue-resistant ("heart-like") muscle, necessary to allow its application in cardiac assist devices, can be induced by chronic electrical stimulation. In adult dogs we studied the nature and time course of myofibrillar and metabolic adaptations in the LD muscle when exposed in situ to 24 weeks of continuous electrical stimulation. In addition, the metabolic properties of the stimulated muscle were compared with those of canine cardiac muscle. The proportion of immunohistochemically identified type I fibres increased on stimulation from 28% to 80%, while that of type II fibres decreased from 69% to 16%. Fibres of intermediate type (IIC and IC) appeared transiently; the highest levels were found between 4 and 8 weeks of stimulation. The activities of fructose-6-phosphate kinase and lactate dehydrogenase (LDH), which before stimulation were similar to those in heart, decreased to 18% and 34% of their initial values respectively. However, the LDH isozyme pattern changed towards that typical for cardiac muscle. These changes indicate a markedly decreased flux capacity through the glycolytic pathway which, however, is directed more towards the oxidative conversion of substrates. The mitochondrial capacity (maximal palmitate oxidation and pyruvate dehydrogenase complex activities) of the muscle did not change and remained at a level less than half of that of cardiac ventricular muscle. Contents of adenine nucleotides and endogenous substrates were maintained during stimulation. No further changes in the observed adaptations occurred after week 12 of stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Percutaneous implantation of a new intracoronary stent in pigs

Sixty-two self-expanding parallel wire stainless steel stents were implanted in normal coronary arteries of 31 young pigs using a newly developed delivery system. In 57 of 62 procedures, the percutaneous coronary implant of the stent was successful; five stents were released in side branches. Implants remained in place for a few hours to 6 months. In spite of correct sizing, two stents migrated out of the coronary arteries. Seven pigs died prematurely; in six of them death might be stent-related. Although no anticoagulant and antiplatelet aggregation drugs were administered during the follow-up period, at autopsy thrombi were observed in only seven arteries (nonobstructive in four of seven arteries). All arteries except for three were patent; these three vessels occluded probably due to oversizing of the stent. Complete neointimal coverage was found within 3 weeks. Important hyperplasia was not seen. It was concluded that coronary implantation of this stent usually was easy. Obstructive thrombus formation was rather uncommon despite the absence of chronic anticoagulant and antiplatelet aggregation therapy. Hyperplasia was rare.

What is the ideal pulse frequency for skeletal muscle stimulation after cardiomyoplasty?

Routinely the latissimus dorsi (LD) muscle is stimulated with bursts of pulses at 30 pulses/sec after cardiomyoplasty to assist the failing heart. At a lower pulse frequency the contractile force decreases and at higher frequencies the energy demand of the pacemaker increases rapidly. We investigated the effect of the stimulus frequency variation on contractile force in untrained LD muscles and in muscles after 12 weeks of continuous cyclic electrical stimulation. In six dogs, two electrodes (Medtronic SP5528) were implanted in the left LD muscle together with an Itrel muscle stimulator. The LD muscle was stimulated with 30 pulses/sec in bursts to deliver initially 30 and after 10 weeks 80 contractions per minute. Both before and after training of the LD muscle maximum force was observed by stimulating with a frequency of 36 to 130 pulses/sec in a burst. However, training induced a shift in the steep part of the force-frequency relation to lower frequencies. In particular, at 15 pulses/sec 60% of the maximal force was obtained in contrast to 40% before training. A fatigue test of 8 minutes duration was performed specified by 100 bursts/min and a burst duration of 0.25 sec at pulse frequencies of 30, 36, 50, and 85 pulses/sec. The contractile force decreased significantly during the course of the test at all frequencies. However, the force obtained with 30 pulses/sec stimulation was lower during the initial phase and approximately 10% higher at the end of the fatigue test as compared to 36, 50, and 85 pulses/sec stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Canine-specific adaptation of energy metabolism of latissimus dorsi muscle in response to chronic electrical stimulation

Continuous electrical stimulation ot canine latissimus dorsi (LD) muscle in situ during 24 weeks induced an increase of immunohistochemically assayed type I fibers from about 30 to 80%. Concomitantly, the activity of fructose-6-phosphate kinase, a key enzyme of the glycolytic pathway, declined markedly, but the capacity for fatty acid oxidation remained unaltered. With respect to myofibrillar and metabolic properties the dog LD muscle initially resembled soleus muscle, and after 24 weeks of stimulation had acquired the properties of gastrocnemius muscle. It is concluded that in the dog, unlike the rat, the LD muscle has an inherently fixed capacity for oxidative energy production. Further expansion of its resistance to fatigue, as induced by chronic stimulation, most likely results mainly from a more efficient coupling between tension development and energy production.

A new method to select stimulus strength after cardiomyoplasty

At present, there is no technique available for the determination of optimal stimulus strength in patients after cardiomyoplasty. To stimulate the latissimus dorsi (LD) muscle, we implanted Itrel stimulators in two goats and cardiomyostimulators in three goats following the routine cardiomyoplasty procedure. During the following 3 months, these LD muscles were conditioned at 2.5-4.0 volts (V). After conditioning, LD muscle shortening was measured on x-ray films using the distance between two stimulation electrodes as references. LD muscle shortening increased rapidly at higher stimulus strength and reached 13% +/- 2% at 2.0 V. Shortening was calculated in one patient at 4, 6, and 9 weeks following surgery. The increase in the number of pulses per burst (2, 3, and 6, respectively) had a positive effect on muscle shortening between the two stimulation electrodes (10%, 14%, and 20%, respectively). Also, muscle shortening was measured between two clips attached to the distal part of the LD muscle. Muscle shortening in the area wrapped around the left ventricle was 15% after 9 weeks. In a second patient, shortening between the electrodes was 16% at 14 months after surgery, and distal muscle shortening was 11%. We concluded that optimal stimulation after cardiomyoplasty could be detected more accurately by measurement of LD muscle shortening using the stimulation electrodes or surgical clips as markers.

Time course of cellular enzyme release in dog heart injury

The transport time of enzyme from heart to plasma was studied in two experimental models. First, the enzyme alanine aminotransferase was slowly infused into the left ventricular wall in open-chest dogs. The half-life for the washout of alanine aminotransferase activity into plasma was 20 +/- 4 minutes (mean +/- SEM, n = 8) and was not different in ischemic and normally perfused tissue. From measurements of arteriovenous differences in alanine aminotransferase activity and left ventricular blood flow, it was concluded that 77 +/- 14% of total enzyme washout from ischemic tissue occurred by direct entry into the bloodstream. The corresponding value for the vascular permeability-surface area product was 264 +/- 55 ml.kg-1.hr-1. For a second model, we studied myocardial enzyme release into plasma after abrupt heart injury induced by 10 minutes of calcium-free coronary perfusion followed by reintroduction of calcium (calcium-paradox mechanism). The half-life for the release into plasma was 1.9 +/- 0.2 hours (mean +/- SEM, n = 6) and was again not influenced by sustained ischemia. Slower washout, as observed for this second model, is consistent with increased interstitial protein space and corresponds to a permeability--surface area product between 135 and 285 ml.kg-1.hr-1. These results were used to calculate the time course of cellular enzyme leakage from the rate of enzyme release into plasma in various forms of heart injury. Significant shifts between the time curves of evolving cellular injury and enzyme release into plasma are observed after 2 hours of ischemia followed by coronary reperfusion, but not after permanent ischemia.

Changes in myocardial high-energy phosphate stores and carbohydrate metabolism during intermittent aortic crossclamping in dogs on cardiopulmonary bypass at 34 degrees and 25 degrees C

The effect of cooling to 25 degrees C on myocardial metabolism was studied during four periods of global ischemia (10 minutes each) followed by 15 minutes of reperfusion in dogs on cardiopulmonary bypass. Systemic and heart temperature at normothermia (group N, 34 degrees C; n = 15) was compared with general hypothermia (group H, 25 degrees C; n = 16). Before and at the end of each aortic crossclamp period in small myocardial biopsy specimens the adenosine triphosphate, creatine phosphate, inorganic phosphate, glycogen, and lactate content was analyzed. Also, lactate and inorganic phosphate were measured in the coronary effluents during the repetitive periods of reperfusion. Hemodynamic function was not different at 60 minutes after cardiopulmonary bypass compared with pre-cardiopulmonary bypass values, and was not different between the groups N and H. The tissue content of adenosine triphosphate and glycogen decreased progressively during the experimental period, resulting in slightly depressed values in both groups at the end of cardiopulmonary bypass. Pronounced effects of ischemia and reperfusion on tissue content of creatine phosphate, inorganic phosphate, and lactate were observed after each period of ischemia. The net decrease in tissue creatine phosphate content was not different between groups N and H (41 +/- 4 versus 38 +/- 4 mumol.gm-1 dry weight; mean +/- standard error of the mean) after 10 minutes of ischemia. However, during ischemia the net inorganic phosphate increase in myocardial tissue was significantly higher in group H (70 +/- 7 mumol.gm-1) than in group N (44 +/- 3 mumol.gm-1). These findings do not support the notion that myocardial protection is improved during hypothermia. Moreover, quantitatively the release of inorganic phosphate and lactate did not correlate with the amount accumulated in the myocardial tissue during the preceding periods of ischemia. The release appeared to be temperature dependent, that is, significantly reduced at 25 degrees C. The present data demonstrate why clinical outcome is satisfactory in both surgical procedures, when in general the periods of aortic crossclamping do not exceed 10 minutes each and the reperfusion periods in between the ischemic episodes last about 15 minutes. Besides, the findings indicate that hypothermia is not strictly necessary under these circumstances.

Complete recovery in plasma of enzymes lost from the heart after permanent coronary artery occlusion in the dog

Plasma activities of creatine kinase (CK) and alpha-hydroxybutyrate dehydrogenase (HBD) were measured after permanent coronary artery occlusion in the dog. Cumulative release of enzymes in plasma was calculated from these data by using a previously validated two-compartment model for circulating enzymes. Regional myocardial ischemia was measured by injection of radiolabeled microspheres. After 48 hours, the dogs were killed, and a detailed map of left ventricular enzyme activity was obtained from 108 tissue samples. Cumulative release into plasma of CK and HBD was 96 +/- 20% and 112 +/- 26%, respectively, of the total activities depleted from the heart (mean +/- SD, n = 11). The scatter in these values is inherent to the calculations, and it is concluded that both enzymes are recovered completely in plasma and, thus, can be used as quantitative markers of injury. Discrepancies between this result and earlier reports on the recovery of CK are only partly apparent and can be explained partly by underestimation of the elimination rate of CK from plasma, irregardless of tissue edema and incomplete extraction of enzyme activity from tissue.

Myocardial blood flow and oxygen consumption after aortic cross-clamping

The effect of four repetitive periods of 10 min global ischemia, followed by 15 min of reperfusion on myocardial blood flow and oxygen consumption at 34 degrees C (group N) and 25 degrees C (group H) were studied in comparison with that of 60 min continuous ischemia combined with multidose St. Thomas Cardioplegia (group C) in dogs on cardiopulmonary bypass (CPB). Two groups, in which a protocol comparable to the groups N and H, respectively, but without repetitive periods of ischemia was followed, served as control. In all groups a hyperemic response was observed after release of aortic cross-clamping (AC). Myocardial blood flow was not diminished at the end of CPB as compared to the values at the start of CPB. We conclude that the no-reflow phenomenon did not occur after these procedures of intermittent or continuous AC. Immediately following release of AC the arterial-coronary sinus difference of oxygen content reached a peak value in groups N and H indicating rapid replenishment of the low tissue oxygen content. These peak values appeared to be much smaller after cardioplegia. After 10 min of reperfusion a significant lower oxygen consumption was observed at 25 degrees C (0.2 mumole.g-1.min-1 O2) as compared to 34 degrees C (1.5 mumole.g-1.min-1 O2). This difference cannot be explained by temperature alone because oxygen consumption did not decrease below 0.5 mumole.g-1.min-1 in the control group of dogs put on CPB at 25 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic and haemodynamic changes in the heart during the early phase of cardiopulmonary bypass: II. Animal experiments

A significant release of lactate instead of uptake was observed during the first 10 min of cardiopulmonary bypass preceding aorto-coronary bypass surgery in human patients. To clarify these findings in more detail, myocardial lactate and oxygen metabolism was studied in healthy dog hearts subjected to a protocol similar to the clinical situation. In one group (n = 11) normothermia at 34 degrees C was used with an empty beating heart, and in the other group (n = 11) hypothermia with ventricular fibrillation was applied. Within the first 10 min of bypass no significant changes in high energy phosphates were observed in myocardial biopsies. However, a marked decrease in mean aortic blood pressure and a simultaneous lowering in oxygen consumption was observed in both groups after instalment of bypass. An initial shift from lactate uptake to lactate release occurred while on bypass in the normothermia group. After 10 min of bypass, lactate uptake was restored in hearts of both groups. Therefore, the lactate release during the initial phase of bypass in patients originates both from the instalment of the bypass and from (local) inadequate perfusion, which is most likely to be due to stenosed coronary arteries.

Metabolic and haemodynamic changes in the heart during the early phase of cardiopulmonary bypass: I. Clinical observations

Knowledge of the effects of cardiopulmonary bypass on the myocardium and on cardiac function is limited. We therefore studied changes in haemodynamics and myocardial metabolism during the initial phase of cardiopulmonary bypass in two patient groups. In one group "normothermia" (34 degrees C) was used while on bypass, with an empty beating heart; in the other group hypothermia (range 27-33 degrees C) with ventricular fibrillation was used. Mean aortic pressure and myocardial oxygen consumption decreased significantly in both groups after instalment of CPB. The arterial-coronary sinus differences in lactate changed to negative values within 5 min of the start of bypass, indicating release instead of uptake of lactate. This release was maintained during the observation period and increased significantly in the hypothermic patient group when the ventricles were fibrillating. Therefore in patients undergoing aorto-coronary bypass surgery, detrimental changes in the myocardium must be anticipated during the initial phase of cardiopulmonary bypass prior to aortic cross clamping.

Recovery of hypertrophied rat hearts after global ischemia and reperfusion at different perfusion pressures

The ability to resist transient ischemia was studied in isolated hearts of 18 months old spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Both types of hearts showed optimal performance during the preischemic period when perfused at a diastolic perfusion pressure of 8.0 (WKY) and 13.3 (SHR) kPa. Hemodynamic recovery of WKY hearts during reperfusion at 8.0 kPa, following 45 min global ischemia, was satisfactory. coronary perfusion completely normalized, contractility (dPlv/dtmax) was slightly depressed and cardiac output returned, on the average, to 40% of the preischemic values. In contrast, hemodynamic function of SHR hearts reperfused at 13.3 kPa was greatly depressed, as evidenced by almost complete abolition of cardiac output, severe reduction of dPlv/dtmax and persistent underperfusion of the endocardial layers. In addition, the postischemic release of lactate dehydrogenase was retarded and enhanced. The release patterns of degradation products of adenine nucleotides showed a shift to the endstage products xanthine and uric acid. The enhanced vulnerability of the hypertrophied heart to ischemia was even more expressed when the SHR hearts were reperfused at 8.0 kPa. Postischemic function was characterized by electrical instability, loss of contractility and cardiac output, and noreflow in the endocardial layers. Persistent accumulation of lactate and degradation products of adenine nucleotides in the postischemic hearts are in line with the lack of reperfusion. The present results indicate that a detailed mechanistic explanation for the reduced ability to withstand ischemia of SHR cannot be based on differences in ATP content or an altered anaerobic glycolitic activity prior and during ischemia. It is suggested that a defect on the circulatory level, probably caused by enhanced reactivity of the coronary vessels towards ischemia-elicited factors, is responsible for the higher vulnerability of hypertrophied heart to an ischemia insult.

Myocardial enzyme depletion in infarcted human hearts: infarct size and equivalent tissue mass

Myocardial activities of several enzymes were measured in infarcted and non-infarcted areas of heart sections obtained from eight patients who died after acute myocardial infarction. Similar data were obtained from four patients with cardiovascular disorders who died from causes other than myocardial infarction and from six patients without previously known heart disease. It was found that both non-infarcted and infarcted tissue samples contained considerably altered enzyme activities. This finding explains the low correlations between enzymatic and histological estimates of infarct size previously reported. However, when the residual myocardial activities of different enzymes were compared with each other, a close correlation was found between creatine kinase, alpha-hydroxybutyrate dehydrogenase, and aspartate aminotransferase. It appears that the pathological changes in the myocardial activities of these enzymes may be explained by the phenomenon of diluted myocardium. This indicates that myocardial injury, as estimated from plasma enzyme activities, may still be expressed meaningfully in gram equivalents of healthy myocardium.

A biochemical and ultrastructural study on myocardial changes during aorto-coronary bypass surgery: St. Thomas Hospital cardioplegia versus intermittent aortic cross-clamping at 34 and 25 degrees C

The changes induced by continuous aortic cross-clamping in combination with multidose ice-cold St. Thomas Hospital cardioplegia (myocardial temperature below 16 degrees C), or intermittent aortic cross-clamping at 34 or 25 degrees C were evaluated in a randomized study on 72 patients undergoing extensive aorto-coronary bypass surgery. The cumulative release of heart-specific enzymes was very small and no marked ultrastructural changes in mitochondria of both the subepi- and the subendocardial layer of the left ventricular free wall occurred. No differences between the three operation techniques could be observed on the basis of the above-mentioned parameters. Myocardial ATP and glycogen contents were decreased in post-ischaemic tissue in both the normothermic and hypothermic intermittent aortic cross-clamp groups. This decrease was associated with a release of lactate and inorganic phosphate during the repetitive periods of reperfusion. No change in myocardial ATP and glycogen content could be observed in the cardioplegia-treated hearts. St. Thomas Hospital cardioplegia is obviously most effective in preventing changes in myocardial metabolism such as reduction of ATP and carbohydrate stores during the reversible phase of ischaemic insult.

Enzymatic assessment of myocardial necrosis after cardiac surgery: differentiation from skeletal muscle damage, hemolysis, and liver injury

Plasma activities of various (iso)enzymes were measured in patients after cardiac surgery (n = 114) and after acute myocardial infarction (n = 40). From these activities, the cumulative release of enzymes in plasma was calculated with a two-compartment circulatory model. This model was adapted to transient postoperative changes in plasma volume and similar changes in the transcapillary escape rate of proteins, observed after cardiac surgery and verified in dogs after cardiopulmonary bypass (CPB). Comparison of cumulative release of enzymes with the enzyme content of myocardium, skeletal muscle, and blood cells allows identification of the various sources of enzyme release. Cardiac injury after uncomplicated bypass surgery is only 1.5 +/- 1.5 (mean +/- SD) gram equivalents (gmEq) of myocardium, compared to a loss of 31 +/- 13 gmEq of myocardium after AMI. Peroperative hemolysis is estimated at 68 +/- 15 ml of blood. Total loss of skeletal muscle amounts to 13 +/- 10 gmEq. Some hepatic enzyme release is observed after AMI but not after surgery. Large differences in time course exist between the release of enzymes from myocardium and skeletal muscle and also between myocardial release in the surgery group and in the AMI group. The accuracy of estimations is discussed and indicated as a function of the extent of cardiac injury.

The effect of different proportions of casein in semipurified diets on the concentration of serum cholesterol and the lipoprotein composition in rabbits

The effect of different proportions of casein in semipurified diets on the concentration of serum cholesterol and the lipoprotein composition was studied in rabbits. Low-casein diets (10% w/w) resulted in serum cholesterol levels and growth rates that were lower than high-casein diets (40%). An intermediate proportion of casein (20%) produced intermediate concentrations of serum cholesterol, but only minor differences in food intake and weight gain, compared with the high-casein group. In the animals with the highest values of total serum cholesterol (the 40% casein group), most of the serum cholesterol was transported in the very low density lipoproteins, whereas with moderate hypercholesterolemia (the 20% casein group), the low density lipoproteins were the main carriers of cholesterol. Elevation in lipoprotein cholesterol was associated in all groups with an increased ratio of cholesterol to protein, suggesting the formation of particles relatively rich in cholesterol. When the rabbits on the diet containing 10% casein were subsequently transferred to the 40% casein diet, a steep increase in the level of serum cholesterol occurred. Conversely, switching the rabbits on the 40% casein diet to the 10% casein diet resulted in a decrease in the level of serum cholesterol.