Search PubMed⌕ Search

Biomedical subjects

T Aherne

Publications and source records attributed to T Aherne.

31 records · Page 2Linked to original sources
PubMed1986

Intracoronary platelet aggregation: pattern of deposition after ischemia, cardioplegia, and reperfusion.

Platelet deposition in the coronary microvasculature has not been completely defined in the temporal relationship to acute myocardial ischemia, the application of crystalloid cardioplegia, and during reperfusion on heart bypass. Twenty-two canine hearts were serially biopsied for the analysis of radioactively tagged platelets. Eleven hearts underwent an isolated heart support preparation with seven followed by potassium cardioplegic arrest and reperfusion while the remaining 4 were maintained on continuous bypass. All 11 hearts undergoing bypass experienced transient (less than 90 sec) ischemia during bypass preparation and produced platelet aggregation in the myocardium (51.12 +/- 24.0 as compared to nonischemic control group 12.3 +/- 4.7; P = 0.005). Potassium cardioplegia did not completely wash out these platelets to the nonischemic control levels (27.8 +/- 14.9; P = 0.04). With the onset of reperfusion after 1 hr of cardioplegic arrest, platelet radioactivity profoundly increased (133.3 +/- 72.8; P = 0.0101) and remained high throughout the hour of reperfusion (324.7 +/- 269.3; P = 0.0369). In summary, intracoronary platelets are activated after transient ischemic episodes during initiation of heart bypass. These ischemia-activated platelet aggregations persist despite the application of cardioplegia during the arrest period. This deposition, in turn, allowed an ongoing pattern of platelet aggregation during the early and subsequent reperfusion. This pattern of ischemia-activated platelet aggregations probably accounts for the progressive reperfusion injury and support of an antiplatelet treatment for coronary microvasculature protection.

Animals↗
PubMed1986

Magnetic resonance imaging of cardiac transplants: the evaluation of rejection of cardiac allografts with and without immunosuppression.

The purpose of this study was to evaluate the potential of magnetic resonance imaging (MRI) in vivo for the characterization of tissue changes associated with acute myocardial rejection after cardiac transplantation. Of 15 dogs that underwent heterotopic cardiac transplantation, six served as untreated controls, and nine received immunosuppressive therapy (25 mg/kg/day cyclosporine, 1 mg/kg/day prednisone). Serial electrocardiographically gated MRI (spin-echo technique) and histologic examinations of allograft biopsy samples were performed for each dog at 2 to 3, 7 to 10, 14 to 17, and 26 to 29 days after transplantation and immediately after animals were killed. Untreated allografts showed a significant increase (p less than .01) in T2 (spin-spin) relaxation time (T2 = 66 +/- 8 msec) and intensity values compared with values in the native hearts (T2 = 44 +/- 6 msec) as early as 1 week after transplantation. The significant difference in T2 values could be observed in vivo as well as on postmortem examination and corresponded to histologic progression of the rejection process. There was no significant difference in T1, T2, or intensity values in cyclosporine-treated allografts and native hearts except in two dogs in which T2 relaxation times and signal intensity in the transplanted hearts increased simultaneously with histologic evidence of rejection, indicating failure of immunosuppressive therapy. There was a significant correlation between histologic grading of severity of rejection and T2 relaxation times of the cardiac transplants (r = .72). Likewise, there was a significant linear relationship between T2 values in vivo and percent water content when the differences between native hearts and allografts were compared (r = .92, p less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Prevention of ischemia-induced myocardial platelet deposition by exogenous prostacyclin.

The antithrombotic effects of prostacyclin infusion on myocardial platelet deposition were studied in a canine model during and after global ischemia. Eleven isolated heart preparations were subjected to 1 hour of cardioplegic arrest under moderate hypothermia (27 degrees to 28 degrees C), including a control group (n = 7) and a prostacyclin-treated group (n = 4). The hearts of four other dogs were continuously perfused for 180 minutes. Platelet deposition was measured at 15 minute intervals throughout the 3 hour study. Serial full-thickness myocardial biopsy specimens were analyzed for activity of 111In-labeled platelets with 99mTc-labeled erythrocyte correction for tissue blood content. The pattern of platelet distribution was determined by scintiscans of each heart, taken with a gamma camera at the end of the 60 minute reperfusion period. Substantial myocardial platelet deposition was found in the control hearts after ischemia but not in the prostacyclin-treated group (p less than 0.05). Furthermore, prostacyclin infusion had a significant disaggregatory effect on intracoronary platelet deposits when the precardioplegic and postcardioplegic biopsy specimens were analyzed (p less than 0.05). Three hours of continuous perfusion did not increase tissue 111In-labeled platelet activity. Ex vivo images showed platelet deposition to be a diffuse patchy process with significantly more 111In activity in the endocardium than in the epicardium after global ischemia (p less than 0.05). These data show the potent antithrombotic properties of prostacyclin in preventing and disaggregating ischemia-induced intracoronary platelet deposition during and after cardioplegic arrest.

Animals↗
PubMed1985

Does prostacyclin (PGI2) cardioplegic infusion improve myocardial protection after ischemic arrest?

To determine whether prostacyclin (PGI2) plays a beneficial role in the blood-perfused heart undergoing global ischemia, 20 isolated canine hearts were studied after sustaining one hour of cardioplegic arrest under moderate hypothermia (27 degrees to 28 degrees C). Left ventricular function (peak systolic pressure, rate of rise of left ventricular pressure [dP/dt], and compliance change in left ventricular volume), myocardial edema, coronary blood flow, and oxygen content were measured during the preischemic period and at 15 and 30 minutes during reperfusion. Results showed an improved hemodynamic recovery (peak systolic pressure, p = 0.018 at 30 minutes; dP/dt, p = 0.020 at 15 minutes) in the group of hearts treated with PGI2 infusion compared with controls. There was no difference in ventricular compliance or myocardial edema between the two groups. This benefit was attributed to a significant increase in myocardial blood flow (p = 0.028 at 15 minutes) and oxygen delivery (p = 0.021 at 15 minutes) during the reperfusion period with PGI2. These data suggest a potential clinical role for PGI2 when applied to the globally ischemic heart in the improvement of myocardial resuscitation during the early reperfusion period.

Animals↗
PubMed1985

Cardiac transplantations in dogs: evaluation with MR.

To assess the potential of magnetic resonance (MR) imaging as an early predictor of cardiac transplant rejection, electrocardiogram-gated (ECG-gated) MR imaging was performed in 12 dogs with heterotopic cardiac transplants. Twenty-two examinations were performed in vivo, and ten postmortem examinations were performed immediately after the dogs were killed. Examinations were performed from 3 days to 14 weeks after transplantation. A 0.35-T superconducting magnet was used with the spin-echo pulse sequence. There was a significant increase (P less than .02 to P less than .001) in T2 relaxation times and intensity values for the transplanted hearts compared with native hearts at all time intervals after transplantation. T1 relaxation times of native and transplanted hearts showed no significant difference on the in vivo ECG-gated studies. However, T1 values calculated on post-mortem studies were significantly longer (P less than .005) in the transplanted compared with the native hearts. With longer pulse repetition and echo delay times, there was an increase in the contrast between the rejecting transplanted heart and the native heart. Thus, ECG-gated MR imaging using the spin-echo technique displays cardiac allograft rejection in vivo. The rejected myocardium in vivo is characterized by a prolonged T2 relaxation time.

Animals↗
PubMedDate not supplied

Coronary artery bypass surgery in the diabetic patient.

Coronary artery and peripheral occlusive arterial disease frequently complicate diabetes mellitus, with death due to atherosclerotic coronary artery disease being three times more likely in diabetic compared to non-diabetic patients. The profile of 32 diabetic patients and 32 matched controls who underwent coronary artery bypass (CABG) is studied and their early and late postoperative outcomes are described. The mean age was 61 +/- 1 year in both groups. The diabetic group comprised 26 non-insulin dependent and 6 insulin dependent diabetics, who had a mean duration of diabetes of 8.5 years (range 2 months--35 years). The median number of grafts per patient performed in the diabetic group and the control group was 3.5 and 3 respectively. There was no mortality in the series, however considerably greater wound morbidity rates were encountered in the diabetic group when compared to matched controls. One renal transplant patient in the diabetic group suffered irreversible acute tubular necrosis and became dialysis dependent post-operatively. Longterm follow-up showed no longterm mortality in either group, with full relief of angina achieved in 75% of diabetic patients compared with 87.5% of matched controls. In addition diabetic patients suffered greater longterm cardiac morbidity than the control group (21.8% versus 12.5%). The results of this study suggest that CABG is a safe operation for the diabetic patient. Diabetic patients receive satisfactory symptomatic relief of angina, but suffer increased perioperative wound complications and greater incidence of longterm cardiac morbidity.

Coronary Artery Bypass↗
PubMedDate not supplied

Quantitation of intracardiac shunts by cine-CT.

Quantitation of intracardiac shunts is important in the evaluation of congenital heart disease and ventricular septal defects postmyocardial infarction. Shunt detection and quantitation is currently performed by either oximetry or radionuclide angiography. Oximetry is an invasive technique and radionuclide angiography, although noninvasive, does not have sufficient spatial resolution to provide detailed anatomic information. The present study evaluated a new technique for quantitating right-to-left shunts by analysis of indicator dilution curves acquired noninvasively using cine-CT. This technique was evaluated in a phantom and in postoperative dogs with a surgically created variable shunt. The phantom model demonstrated the accuracy and reproducibility of the curve analysis algorithm, and the canine model permitted the comparison of oximetry with cine-CT for shunt quantitation. Cine-CT accurately estimated right-to-left shunt fraction when compared with oximetry (r = 0.91) and is more sensitive than oximetry in detecting small shunts. The results of this study suggest that contrast enhanced cine-CT provides a precise noninvasive technique for measuring shunt lesions in congenital and acquired heart diseases.

Animals↗
PubMedDate not supplied

Diagnosis of acute and chronic cardiac rejection by magnetic resonance imaging: a non-invasive in-vivo study.

To evaluate the potential usefulness for characterization of tissue and anatomical changes associated with cardiac transplantation rejection by nuclear magnetic resonance imaging (MRI), sixteen dogs underwent heterotropic cardiac transplantation with six not immunosuppressed serving as controls. Myocardial biopsy and MRI were obtained and compared on a weekly basis. Untreated allografts showed a significant increase in T2 and intensity values by MRI compared to the native heart as early as one week after transplantation. The MRI findings corresponded to the histological progression of acute rejection process in both treated and untreated groups. The linear relationship between histology and MRI was 0.72 while the correlation between T2 and the water content was 0.92. Serial gated MRI correlated with chronic anatomical changes of transplant rejection with evidence of progressive or increasing myocardial wall thickness and decrease in ventricular chamber size.

Animals↗