Dopexamine attenuates microvascular perfusion injury of the small bowel in pigs induced by extracorporeal circulation

BACKGROUND

Cardio-thoracic surgery with the use of extracorporeal circulation may lead to an impairment of splanchnic perfusion. The aim of this study was to investigate the effect of dopexamine on gastrointestinal microvascular perfusion failure due to extracorporeal circulation.

METHODS

Twenty landrace pigs served as laboratory animals. A loop of the terminal ileum was exteriorized for microscopic observation. In 13 animals a partial left-heart bypass (pLHB), with a non-pulsatile pump flow of approximately 50% of the cardiac output, was established for 2 h. Seven animals received a continuous i.v. infusion of 3 micrograms kg-1 min-1 dopexamine from the beginning of pLHB to the end of the experiment. Seven sham-operated animals served as controls. The microcirculatory network was analysed by means of intra-vital microscopy prior to, during pLHB, and 2 h after bypass.

RESULTS

Despite normal haemodynamics measured by arterial pressure and cardiac output, pLHB led to significant impairment of microvascular perfusion characterized by arteriolar vasoconstriction, reduction of functional capillary density (FCD) to 30% 2 h after weaning off bypass and diminished blood-cell velocities in submucous venules. Dopexamine attenuated this perfusion impairment, preventing arteriolar vasoconstriction. FCD remained normal.

CONCLUSION

Our data demonstrate that treatment with the vasoactive drug dopexamine leads to a significant reduction of the perfusion injury of the small bowel.

The index of pulmonary vascular disease in children with congenital heart disease: relationship to clinical and haemodynamic findings

OBJECTIVE

We asked whether a scoring system [index of pulmonary vascular disease (IPVD)] that quantifies the individual pulmonary vascular pathology would relate to postoperative survival in patients with congenital heart disease and pulmonary hypertension (PH).

METHODS

Lung biopsy specimens from 28 patients at a median age of 6 months (1 month to 21 years) were analysed qualitatively and morphometrically. The IPVD and other morphometric parameters were related to haemodynamic findings and survival.

RESULTS

Mean pulmonary artery pressure (PAP) was 44 mmHg (15-72 mmHg), and the resistance to pulmonary perfusion was 5 U x m(2) (0.9-14 U x m(2)). There were three early (in-hospital) and three late deaths during the follow-up period of 2.5 years (6 months to 7 years). Incipient plexiform lesions were observed in one infant with trisomy 21 and complete atrioventricular septal defect (cAVSD). An IPVD score above the upper critical limit (>2.2) was not observed during the first year of life. On discriminant analysis, morphometric parameters could not predict mortality ( P=0.08).

CONCLUSIONS

The IPVD is not helpful to predict surgical mortality during the first year of life. Patients with trisomy 21 and cAVSD may show advanced pulmonary vascular disease in infancy.

[Preoperative administration of new GPIIb/IIIa inhibitors]

The influence of preoperative abciximab treatment on perioperative risks was analyzed. Six groups were formed in consecutive patients (n = 957, 1/1994-3/2000) operated upon for CABG according to the urgency of the intervention and the type of preoperative haemostaseological treatment. Thirty-one patients underwent urgent/emergency CABG with preceding abciximab treatment. After pretreatment with abciximab the surgical results did not differ from patients with other types of preoperative haemostaseological treatment. CABG can be performed with similar results in abciximab pretreated patients as in patients with other types of preoperative haemostaseological treatment.

Myocardial performance after brain death: studies in isolated hearts

OBJECTIVES AND METHODS

Brain death related hemodynamic instability and/or cardiac dysfunction is frequently described in the potential organ donor which may lead to exclusion of the heart from transplantation. The underlying mechanisms are controversely discussed. Therefore, in the present study, potential brain death associated cardiodepressant factors were evaluated separately in cross-circulated canine heart models. Brain death was induced by inflation of a subdural balloon catheter. Loading conditions and coronary perfusion pressure were kept identical in all cross-circulated hearts throughout the experiment.

RESULTS

Induction of brain death led to a significant hyperdynamic response in all groups, with a maximal effect by the combination of neural and humoral pathways. After the initial reaction all hemodynamic parameters returned to baseline and remained stable until the end of experiments. Even if the hearts were explanted from brain dead donors with typical hemodynamic deterioration in vivo, they showed no significant differences in comparison to the other groups including healthy controls ex vivo.

CONCLUSIONS

Therefore we conclude, that hemodynamic instability in the potential donor may rather reflect altered loading conditions and impaired coronary perfusion than neuro-humorally mediated direct myocardial injury.

[Stability of the Euro-score as an identification tool for patient risk groups -- dependency of the applied documentation system]

From the different methods for risk adjustment, scores allow a rough classification of the patients. The Euroscore represents one of the most modern scores. The most recent version of the documentation system of the German Society for Thoracic and Cardiovascular Surgery may be used without extended extra-work to evaluate the Euroscore despite the presence of various limitations. The investigation of the scores with nearly complete adaptation of the variables of the quality assurance documentation to the original definition showed no substantial differences between the score groups. However, many methodological implications favor the development of self-evaluated models to obtain a most recent weight for each risk factor and to be able to take into account new therapeutical options. These models can be evaluated by the existing database and extended by the most recent data.

Effects of trifluoperazine on the contraction kinetics of the isolated intact tracheal and pulmonary artery smooth muscle

BACKGROUND

We studied the effect of the calmodulin antagonist trifluoperazine (TFP) on isolated intact rat tracheal and pulmonary artery smooth muscle contractile behaviour.

METHODS

Experimental series: 1) TFP-dose-response curves for TFP's effect on force generation were constructed using rat tracheal smooth muscles and rat pulmonary artery preparations (n = 8). A concentration of 1 micromol/l TFP was chosen for the subsequent experimental series. 2) Tracheas and pulmonary arteries (n = 14) were dissected in three segments. One of them was used immediately for experiments ("native"), the other two were treated for 12 h in 4 degrees C Tyrode solution without ("12 h cold storage") or with 1 micromol/l TFP ("12 h cold storage + TFP"). These preparations contracted after supramaximal effective electrical field stimulation. The force-clamping technique was used to analyse kinetic and mechanical parameters of smooth-muscle contraction in both types of preparation (measurement conditions: resting tension 2 mN, 37 degrees C, modified Krebs-Henseleit solution).

RESULTS

1) TFP decreased developed force dose-dependently in pulmonary artery and tracheal smooth muscle. 2) During sustained tonic activation, the contraction kinetics become slower both with and without TFP treatment (p < 0.0001). 3) TFP caused a dramatic retardation of the velocity of force generation in both types of preparation for any given time interval during the course of a tonic activation (p < 0.0005). 4) The dramatic effects of TFP on the contraction kinetics were not associated with effects on the extent of force generation.

CONCLUSIONS

These results support the assumption that tracheal and pulmonary artery smooth muscle cross-bridge rates are controlled by a calcium-calmodulin-dependent myosin light chain kinase. This finding suggests the involvement of a calmodulin-independent regulator process responsible for the changes observed in the cross-bridge cycling rates during sustained tonic activation. A direct intervention on the contractile apparatus level is a measure for reduction of smooth-muscle tone without negative inotropic side effects.

[Myocardial revascularization after pretreatment with the GPIIb/IIIa receptor blocker abciximab]

AIM

The present prospective study analysis whether preoperative abciximab treatment 1) increases perioperative risks, 2) alters the quality of the surgical treatment, 3) whether secondary organ complications occur and 4) whether and how the perioperative surgical management has to be modified.

METHODS

The perioperative results of patients operated upon after preoperative abciximab treatment (n = 31, 1/1994-4/2000) were compared with an optimal control group (elective patients and no preoperative intervention in the hemostaseological system) and with other patients (elective, urgent, emergency operations) receiving different strategies of preoperative hemostaseological interventions (n = 926, 1/1994-4/2000). All patients were operated upon with a well-defined strategy (one surgeon). 1100 perioperative items/patient were prospectively recorded and analyzed. The 30-day and 6 month follow-up was complete.

RESULTS

The mean time interval between end of abciximab therapy and onset of operation was 4.3 h (range: 36-0.5 h, median: 2 h). As compared with the optimal control group (n = 81), perioperative blood loss and the need for substitution of blood and blood products was increased. However, as compared with those patients receiving any type of preoperative intervention in the hemostaseological system (the majority of the patients), no difference was observed regarding intraoperative parameters (duration of extracorporeal circulation and of the operation) and postoperative results (neurological, renal complications, myocardial infarction, psychiatric disturbances, etc.) when abciximab patients were compared with the reference populations. No patient of the abciximab group died within 30 days or during the 6 month follow-up period.

CONCLUSION

The data show that coronary artery bypass grafting can be performed with similar results in abciximab-pretreated patients as in patients with other types of preoperative anticoagulation. Only slight modifications of the surgical management are recommended. As indicated by similar use IMA-grafts the quality of surgical treatment was not reduced.

Does the completeness of revascularization contribute to an improved early survival in patients up to 70 years of age?

OBJECTIVE

In the era of a renewal of incomplete revascularization approaches, the controversy reappears as to whether the approach for complete revascularization is of prognostic value. The clear advantage of complete revascularization in elderly patients has recently been published. However, for the younger patient group, there is no conclusive information available so far. The aim of our study was to investigate the effect of complete vs. incomplete revascularization in patients up to 70 years of age.

PATIENTS AND METHODS

6531 patients underwent isolated CABG. 5003 of these patients were aged up to 70 years at the time of operation.

RESULTS

Incomplete revascularization was performed in 534 (10.7 %) patients. The most common reasons for incomplete revascularization were small vessels and massive calcification. The differences in mortality up to the 180(th) day after CABG are statistically significant. By Kaplan-Meier analysis, the time relationship between incomplete revascularization and death affects predominantly the very early period after CABG. By logistical regression, incomplete revascularization was found to be an independent risk factor for death after CABG.

CONCLUSION

Incomplete revascularization affects the early outcome after CABG in patients up to 70 years of age as an independent risk factor for death. In view of recent approaches for primarily incomplete CABG, our results indicate the necessity to reconsider the advantages of complete revascularization.

Capillary endothelia and cardiomyocytes differ in vulnerability to ischemia/reperfusion during clinical heart transplantation

OBJECTIVE

The development of accelerated graft arteriosclerosis is a major cause of late death after orthotopic heart transplantation. The influence and the extent of peritransplant injury, especially of cardiomyocyte or capillary endothelial cell edema is discussed.

METHODS

A morphometric ultrastructural analysis of myocardial biopsies from 29 donor hearts (21 male, age 34+/-11 years) was performed. Right ventricular biopsies were obtained before cardioplegia (A), immediately following cardioplegia (B) (Custodiol, Dr. F. Köhler Chemie GmbH, Alsbach-Hähnlein, Germany), before implantation (C), after 30 (D) or 60 (E) min of reperfusion and 1 week after transplantation (F). Mean ischemic time was 185+/-68 min. Quantitative electron microscopy was carried out in five samples per heart and time point and in 30 test fields per sample by 'random systematic sampling' and 'point and intersection counting'. As parameters for cell edema the volume density of myofibrils in cardiomyocytes and the mean barrier thickness of capillary endothelia were analyzed. P-values of less than 0.05 were regarded as significant. Significant differences in contrast to the previous values are marked by *.

RESULTS

The volume density of myofibrils (vol.%) was as follows: (B) 63.6+/-3.2, (C) 61.8+/-3.2, (D) 62.9+/-3.2, (E) 63.6+/-4.5. The mean barrier thickness (nm) was as follows: (A) 353+/-21, (B) 376+/-59, (C) 416+/-71*, (D) 473+/-45*; (E) 453+/-50*, (F) 379+/-39.

CONCLUSIONS

Apart from a generally accepted edema of cardiomyocytes a relevant capillary endothelial cell edema develops during clinical heart transplantation. In contrast to cardiomyocytes the cell edema of endothelia shows a more pronounced and significant progression during cold ischemia and early reperfusion. After 60 min of reperfusion it is still significantly more pronounced than at the onset of ischemia. After 1 week there are no statistical differences compared to the initial values. Thus, an edema of capillary endothelia probably will trigger inhomogeneities in capillary perfusion. Peritransplant injury of endothelia may contribute to the later development of accelerated allograft arteriosclerosis.

Influence of steroids on microvascular perfusion injury of the bowel induced by extracorporeal circulation

BACKGROUND

Extracorporeal circulation is associated with gastrointestinal complications. By means of intravital microscopic methods, we investigated whether preoperative treatment with steroids can attenuate the impairment of the bowel microcirculation.

METHODS

In 20 pigs, a partial left heart bypass (pLHB) was established. A loop of the terminal ileum was exteriorized for intravital-microscopic observation. Seven sham-operated animals served as controls. In 13 animals, pLHB was established for 2 hours with a flow rate of 2,000 mL per minute; 7 of the animals received 20 mg/kg body weight prednisolone preoperatively. The microcirculatory network was analyzed before, during pLHB, and 2 hours after bypass.

RESULTS

Despite unchanged macro-hemodynamics, pLHB resulted in a significant microvascular perfusion injury of the small bowel. Arteriolar vasoconstriction and a reduction of perfused capillaries per unit area (functional capillary density) to 30% of prebypass values could be found. Blood cell velocities were reduced in submucuous collecting venules. In the steroid-treated animals, the functional capillary density remained normal. In addition, arteriolar vasoconstriction could be prevented.

CONCLUSIONS

Treatment with prednisolone largely prevents the microcirculatory alterations in the small bowel induced by extracorporeal circulation.

Near-fatal hemoptysis and emergency surgical repair after aortic patch-plasty

A 38-year-old man presented with massive hemoptysis followed by hemorrhage shock. The patient's history revealed a Dacron patch repair for aortic coarctation and recoarctation carried out twice, once 23 and once 10 years ago. Diagnosis of a ruptured descending aortic aneurysm with an aortobronchial fistula into the left lower lobe was established using CT scan. Emergency surgery consisted of left pneumonectomy and descending aortic graft replacement during deep hypothermic circulatory arrest. The patient was discharged 12 days later.

A novel perfusion catheter for hybrid procedures in minimally invasive bypass surgery

BACKGROUND

Combined off-pump bypass grafting and percutaneous coronary intervention (hybrid procedures) is supposed to be beneficial for high-risk patients. We developed a novel perfusion catheter to facilitate these hybrid interventions.

METHODS

First, we tested coagulatory activation in vitro. Afterwards, 6 landrace pigs underwent active coronary perfusion of the LAD. In a second study, 15 pigs underwent off-pump bypass surgery (LIMA to LAD grafting) and the catheter was used to provide myocardial perfusion and prevent bleeding at the site of the coronary anastomosis.

RESULTS

In the in vitro perfusion studies, no activation of coagulation or clotting occurred. Active coronary perfusion was feasible without signs of regional myocardial ischemia or coagulation over a 50-minute period. During off-pump bypass surgery, the catheter prevented bleeding in the operation field and facilitated the surgical procedure.

CONCLUSION

The new perfusion catheter can optimize the conditions of off-pump bypass surgery by preventing bleeding in the operation field, maintaining myocardial perfusion and allowing direct angiographic control of the anastomosis. Therefore, this new technique could be an important tool to facilitate hybrid interventions.

3D evaluation of myocardial edema: experimental study on 22 pigs using magnetic resonance and tissue analysis

BACKGROUND

Myocardial edema (ME) adversely affects ventricular function. Thus, we performed an animal study to demonstrate (1) 3D-ME using magnetic resonance imaging (MRI), which can show ME depending on myocardial location, (2) type of cardioplegic solution, and (3) quantification tools.

METHODS

Pig hearts (n = 22) were perfused using Bretschneider's solution (BRET, n = 8), butanedionemonoxime (BDM, n=8), or no cardioplegia as controls (CTRL, n = 6). Hearts underwent MRI (T(1)-inversion recovery). Myocardial water content (MWC, reference method) was determined from left ventricle anterior, posterior (PW), lateral wall, interventricular septum, papillary muscle, right ventricle wall. Images underwent 3D reconstruction using ray-tracing. Gray-value analysis was performed on "virtual" samples. For statistical analysis, ANOVA, Student's t-test, and the Student-Newman-Keuls test were used.

RESULTS

(1) ME was induced (p < 0.0001 vs. control). Localization differed in MWC, p = 0.003 (BRET), p = 0.023 (BDM), highest at PW (p < 0.01). (2) Differences between the cardioplegia groups were not significant. (3) "Virtual" samples showed equal distribution (BRET: p = 0.007, BDM: p = 0.003), highest at PW (p < 0.01).

CONCLUSIONS

We validated 3D assessment of induced ME in pig hearts using MRI. The method may therefore become an exact tool in monitoring cardioplegia.

[Aortic dissection--when operative treatment, when endoluminal therapy?]

GOAL

To demonstrate the Heidelberg results of the previous 2 years in patients referred for acute aortic dissection.

MATERIAL AND METHODS

93 patients referred for acute aortic dissection were treated by cardiac surgery, vascular surgery and interventional radiology according to a novel therapeutic algorithm including stent-grafts and combined open and interventional procedures and conservative medical therapy when no malperfusion syndrome was present or patients were considered prohibitive for even minor surgical procedures. Stent-graft placements were done assisted by short term cardiac arrest to facilitate correct device deployment.

RESULTS

36 patients presented with type A and the other 57 with type B dissection. 32 of the A patients were operated and 20 of the B patients, respectively. 12 patients with B dissection were treated with stent-grafts. 3 required additional interventional therapy for organ malperfusion. The mortality was 0% in these 12 patients The overall mortality rate in the A group was close to 40% mainly as a result of postoperative organ malperfusion while it was 15% in the B group. In both groups mortality was highest in the respective untreated patient subgroup (3/4 and 8/37, respectively). The main mortality factor was visceral (mesenteric or liver) ischemia. Paraplegic complications occured in neither group. In 4 patients a combined approach applying cardiac surgery of the ascending aorta and endluminal stent-graft placement for the residual B dissection was successfully performed. In one patient this was done simultaneously.

DISCUSSION

Acute aortic dissection of type A with or without valve involvement, coronary artery ischemia can be treated with high technical success rates. However, remaining distal aortic dissection associated with true lumen collapse and organ malperfusion is the main causative factor for clinical failures. Successful combination of open proximal aortic surgery with endoluminal treatment of residual B dissection encourages further use of this novel approach. Acute B type dissection appears to be effectively and safely treated by endoluminal approach in selected cases. Unsolved questions of this less invasive therapeutic approach focus mainly on the design of the proximal anchoring part of the devices.

Downregulation of myocardial contractility via intact ventriculo--arterial coupling in the brain dead organ donor

OBJECTIVE

To test the hypothesis that altered loading conditions play a key role in hemodynamic instability and cardiac dysfunction in the brain dead (BD) organ donor.

METHODS

BD was induced by inflation of a subdural balloon catheter. In the first part of the study, left ventricular function was assessed in a canine in situ cross-circulated heart model (n=6). Pre- and afterload and coronary perfusion pressure were kept identical in all hearts throughout the experiment. In the second part of the study, hearts (n=6) were investigated in vivo allowing the interaction between left ventricular contractility and arterial load. Left ventricular pressure--volume loops were obtained by a combined conductance-pressure catheter and the slope of the endsystolic pressure--volume relationship (Ees), arterial elastance (Ea), stroke work (SW), pressure--volume area, ventriculo--arterial coupling ratio (VAC) and mechanical efficiency (Eff) were calculated.

RESULTS

Induction of BD led to a hyperdynamic response in both models with a significant increase of most hemodynamic parameters. In the in situ isolated heart model, left ventricular contractility returned to baseline without any further deterioration. In contrast, in the intact circulation the hemodynamic parameters declined significantly in comparison to baseline 4 h after BD (Ees: 4.07+/-0.51 vs. 8.06+/-1.09 mmHg/ml, P<0.05, Ea: 3.17+/-0.39 vs. 4.42+/-0.30 mmHg/ml, P<0.05). However, VAC (0.78+/-0.09 vs. 0.65+/-0.14 n.s.) and Eff (73.4+/-2.1 % vs. 76.8+/-3.7 %, n.s.) remained constant over the time.

CONCLUSION

BD induction leads to an initial hyperdynamic reaction followed by hemodynamic instability. The facts that no cardiac dysfunction occurred if loading conditions were kept constant and the ventriculo--arterial coupling ratio and mechanical efficiency remained constant in the intact animal model indicate that decreased contractility reflects to decreased arterial elastance after brain death. Therefore, reduced contractile function after brain death at a decreased afterload may contribute to stroke work optimization.

Does the completeness of revascularization affect early survival after coronary artery bypass grafting in elderly patients?

OBJECTIVE

Usefulness and risks of incomplete versus complete revascularization are still matters of ongoing discussions. Because an increasing number of elderly patients are undergoing coronary artery bypass grafting (CABG), the question arises whether a less extensive surgical approach is more prudent than complete revascularization.

METHODS

Of 6531 patients undergoing isolated CABG, 859 were 75 and older at the time of operation. Mean age of the 859 patients was 77+/-2.7 years (median: 76 years); 65% were men. Follow-up enquiry by questionnaire was performed at the 180th postoperative day with a completeness of 95.6%. Assessment of the impact of incomplete revascularization utilized both multivariable analysis and propensity score matching to account for selection factors.

RESULTS

Incomplete revascularization was performed in 133 patients (16%). The most common reasons for incomplete revascularization were small vessels (55%) and massive calcification (32%). Mortality until 180 days after CABG was higher (n=32; 24%) after incomplete than after complete revascularization (n=105; 15%; P=0.005). By logistic multivariable regression, incomplete revascularization was identified as an independent risk factor for death (Odds ratio, 1.8; P=0.015). By time-related analysis, incomplete revascularization predominantly affected the early period after CABG (P=0.001). Aortic cross clamping time was only slightly shorter for the group with incomplete (59+/-27 min (median: 55 min) vs. 63+/-26 min (median: 58 min); P=0.1).

CONCLUSIONS

Incomplete revascularization increases the early risk of death after CABG in patients aged 75 years and older. The potential compensating benefit of the shorter aortic cross clamping time does not outweigh the advantages of complete revascularization. Thus, in the era of high-volume interventional approaches and minimally invasive techniques, the advantages of complete revascularization need to be considered.

Hirudin protects from leukocyte/endothelial cell interaction induced by extracorporeal circulation

BACKGROUND

The clinical complications of Extracorporeal Circulation (ECC) have been linked to disturbances in the microcirculation. In order to prevent these deleterious effects, a biodegradeable agent to coat the extracorporeal circuit was tested.

METHODS

Intravital fluorescence microscopy was used on the hamster skinfold chamber model in permanently instrumented, awake animals. ECC was introduced via a micro-roller-pump and a silicon tube shunted between the carotid artery and the jugular vein. The ECC-tube system was coated with PEG-Hirudin-Iloprost, two additional groups received either Iloprost i.v. (0.8 mg/kg/h) or Hirudin i.v. (1 mg/kg b.w.).

RESULTS

ECC for 20 minutes resulted in an increase in rolling and adherent leukocytes in postcapillary venules (Roller 9 to 36 [%]; Sticker 24 to 330 [n/mm2]). Use of the coated tube system reduced L/E cell interaction (Roller 9 to 24* [%], Sticker 28 to 194* [n/mm2]; *p<0.05), whereas Hirudin i.v. nearly abolished it.

CONCLUSIONS

The protective effects of the coating and of Hirudin i.v are probably a result of an attenuated activation of the coagulation-fibrinolytic system.

The role of endothelin-B receptors in myocardial and endothelial reperfusion injury after heart transplantation

BACKGROUND

This study was designed to investigate the effects of the selective endothelin-B (ET-B) receptor agonist IRL1620 and the selective ET-B receptor antagonist BQ788 on myocardial and endothelial function after reversible deep hypothermic ischemia and reperfusion.

METHODS

Isogenic intraabdominal heterotopic heart transplantation was performed on Lewis rats. After one hour of cold ischemic preservation, reperfusion was started either after application of saline vehicle or IRL1620 or BQ788 or both. Left ventricular pressure-volume relations and myocardial blood flow were assessed after one and 24 hours of reperfusion. Endothelium-dependent vasodilatation to acetylcholine (ACH) and endothelium-independent vasodilatation to sodium nitroprusside (SNP) were also determined.

RESULTS

IRL1620 attenuated and BQ788 improved myocardial contractility significantly as indicated by the left or upward shift of the systolic pressure-volume relation, respectively, and significantly changed myocardial blood flow during early reperfusion (p<0.05). Although myocardial function and baseline myocardial blood flow were similar in both groups after 24 hours of reperfusion, endothelium-dependent vasodilatation was still significantly lower in the IRL1620 and higher in the BQ788 group (p<0.05).

CONCLUSIONS

These results suggest that activation of the ET-B receptors contributes to reperfusion injury after cardiac preservation in a rat heart transplant model.

Systolic and Diastolic Properties and Myocardial Blood Flow in the Heterotopically Transplanted Rat Heart during Acute Cardiac Rejection

The aim of the study was to characterize the course of systolic and diastolic function, myocardial blood flow, and histologic changes during acute rejection in a model of heterotopic transplantation in rats. For this purpose isogenic Lewis-to-Lewis and allogenic DA (Dark Agouti)-to-Lewis rat cardiac transplants were studied 1 hour and 1, 3, and 5 days, respectively, after heterotopic intraabdominal transplantation. Myocardial tissue blood flow (MBF) was assessed by the hydrogen-clearance method. An implanted balloon was used to measure pressure-volume relations in the transplanted heart. Myocardial water content was determined at the end of the experiments, and histologic examinations were performed. The MBF recovered during the first day postoperatively in both groups and decreased again in the allogenic group after 3 and 5 days (p < 0.05); it remained stable in the isogenic group. Myocardial relaxation was already prolonged in the allogenic group after 3 days and deteriorated further. Left ventricular end-diastolic pressure progressively increased in the allogenic group, whereas it remained unchanged in the isogenic group up to 5 days. After recovery from ischemia, the left ventricular peak systolic pressure was stable in the isogenic group for the entire further observation period, but it significantly decreased in the allogenic group after 5 days (p < 0.05). Myocardial water content showed a significant increase in the allogenic group compared to that in the isogenic group after 5 days. In the allogenic group histologic examination confirmed mild to moderate rejection after 3 days and severe acute rejection after 5 days. Thus, after recovery from ischemia, mild to moderate cardiac rejection was associated with reduced MBF and impaired relaxation. In a typical sequence, generation of edema and impaired diastolic compliance were terminally followed by systolic dysfunction during severe rejection.