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Biomedical subjects

K L Yun

Publications and source records attributed to K L Yun.

At least 19 recordsLinked to original sources
PubMed2000

Pulmonary abnormalities after coronary arterial bypass grafting operation: cardiopulmonary bypass versus mechanical stabilization.

BACKGROUND: Cardiopulmonary bypass has been implicated in causing poor pulmonary gas exchange postoperatively in patients undergoing coronary artery bypass grafting procedures. This randomized prospective study was conducted to determine whether patients undergoing coronary artery bypass grafting operations using cardiac stabilization and thereby avoiding cardiopulmonary bypass will have improved pulmonary function postoperatively. METHODS: Fifty-eight patients were randomized to one of two groups: coronary artery bypass grafting operation with stabilization or coronary artery bypass grafting operation with cardiopulmonary bypass. Preoperative and postoperative pulmonary gas exchange measurements were performed on intubated patients, including the arterial partial pressure of oxygen on 100% inspired oxygen, the alveolar-arterial oxygen gradient, and pulmonary shunt. Static and dynamic lung compliance measurements were performed postoperatively. Hemodynamic variables (including creatine kinase-MB and troponin levels), intubation time, postoperative bleeding, and blood transfusions were compared. RESULTS: Both study groups had a large decrease in arterial partial pressure of oxygen on 100% inspired oxygen (p < 0.0001) and a significant postoperative increase in the alveolar-arterial oxygen gradient (p < 0.0001). There was no statistical difference in the postoperative gas exchange between the two groups; however, the postoperative pulmonary shunt was significantly better in the stabilization group (24% versus 31%, p = 0.03). The patients were extubated in the intensive care unit earlier in the stabilization group (8.2 hours versus 9.2 hours, not significant). The mean static and dynamic lung compliance postoperatively was lower in the stabilization group, although not statistically significant (p = 0.06). CONCLUSIONS: Coronary artery bypass grafting operation using cardiac stabilization technique is safe and avoids the risk of cardiopulmonary bypass. The pulmonary gas exchange postoperatively is comparable to standard cardiopulmonary bypass procedures, but a reduced postoperative pulmonary shunt was seen in the stabilization group.

Blood Transfusion↗
PubMed1999

Aortic valve replacement with the freestyle stentless bioprosthesis: five-year experience.

BACKGROUND: Stentless aortic valves were designed to provide a more physiological flow pattern and lower transvalvular gradient, which may have an important bearing on postoperative left ventricular function and remodeling. In this study, we prospectively analyzed the 5-year clinical results with the Freestyle valve (Medtronic, Inc) and its hemodynamic performance by serial echocardiography. METHODS AND RESULTS: Between January 1993 and August 1997, 95 patients with a mean age of 75 years underwent aortic valve replacement with the Freestyle prosthesis. Sixty-four percent of patients received valves </=23 mm, and 37% had concomitant coronary artery bypass grafting. Average follow-up was 44+/-18 months (mean+/-SD), and echocardiography was performed preoperatively, at discharge, at 3 to 6 months, and annually thereafter. The 30-day operative mortality rate was 3%, with an overall actuarial survival rate of 80+/-6% (mean+/-SEM) at 5 years. Of the 10 late deaths, only 2 were cardiac related, thereby yielding a freedom from cardiac mortality of 94+/-3% after 5 years. No patient required reoperation on the aortic valve for any reason, including structural degeneration, nonstructural dysfunction, or prosthetic valve endocarditis. There were 9 thromboembolic and 3 anticoagulant-related bleeding events, none of which was fatal. The actuarial freedom from valve-related morbidity and mortality was 79+/-4% at 5 years. Hemodynamically, the mean transvalvular gradient significantly decreased after valve replacement and was reduced further by 41% by 6 months with a corresponding increase in effective orifice area. Left ventricular mass index fell to 75% of the preoperative value by 2 years. CONCLUSIONS: The Freestyle stentless valve can be implanted safely in the elderly with excellent midterm clinical results. It has superb hemodynamics in terms of residual transvalvular gradient, effective orifice area, and regression of left ventricular hypertrophy.

Aged↗
PubMed1999

Randomized trial of partial versus complete chordal preservation methods of mitral valve replacement: A preliminary report.

BACKGROUND: The merits of retaining the subvalvular apparatus during mitral valve replacement for chronic mitral regurgitation have been demonstrated in numerous clinical and laboratory investigations. In this preliminary report, we analyzed the early effects of complete versus partial chordal preservation on left ventricular mechanics. METHODS AND RESULTS: Fifty patients undergoing isolated surgical correction of mitral insufficiency were prospectively randomized to either total or partial chordal-sparing mitral valve replacement. Of the first 19 patients studied, 8 had preservation of the posterior leaflet only, and 11 had complete preservation of all chordal structures. A comparison group consisted of 6 patients who had primary mitral valve repair. Echocardiography was performed preoperatively and at discharge from the hospital to determine dimensions, wall stress, and ejection fraction. Preservation of the posterior leaflet only resulted in a reduction in end-diastolic volume, an increase in end-systolic volume (P=0.058), a rising trend in end-systolic stress, a decrease in long-axis fractional shortening, and a fall in ejection fraction from 0.68+/-0.16 to 0. 46+/-0.19 (P=0.001). Although patients who had preservation of all chordal structures also had decreased end-diastolic volume, long-axis fractional shortening, and ejection fraction (0.60+/-0.13 to 0.52+/-0.07, P=0.01), end-systolic stress fell and end-systolic volume decreased instead of increased. Compared with the posterior leaflet preservation group, those in the group with completely preserved chordal structures had a larger decline in end-diastolic volume and smaller decreases in long-axis fractional shortening and ejection fraction. Changes in end-systolic volume and stress were also statistically different between the 2 cohorts. No differences were detected between the group with total preserved chordal structures and the mitral repair group in any of the measured parameters. CONCLUSIONS: Compared with posterior chordal preservation only, complete retention of the subvalvular apparatus during mitral valve replacement resulted in improved ejection performance and smaller chamber volumes due to reduced systolic wall stress. These hemodynamic advantages are comparable to those observed with primary mitral reconstruction.

Aged↗
PubMed1999

Time related quality of life after elective cardiac operation.

BACKGROUND: Due to improved operative techniques, myocardial preservation, and perioperative care, open heart procedures are now being performed in older and sicker patients. As a result, the quality of life has become an important issue in the decision making process. METHODS: Between January 1993 and October 1994, 604 patients above 65 years of age who underwent non-emergent open heart operations were followed prospectively over a 2-year period. The Health Status Questionnaire forms were distributed to all patients preoperatively and to hospital survivors at 3, 12, and 24 months. The questionnaire contains 36 questions and is divided into eight categories. Follow-up was 100% complete with 99.6% of questionnaires returned. RESULTS: Significant quality of life improvements were noted in all categories after surgery. After reaching a peak at 12 months, there were small, but significant declines in scores relating to physical health and health perception at 24 months. In contrast, measurements for mental attributes continued to increase with time. By multivariate analysis, diabetes, older age, and female gender had a relatively adverse influence on quality of life despite improvement after operation. Similarly, patients with chronic obstructive pulmonary disease or having redo operations had lower health perception with some physical limitations. While procedure type (coronary artery bypass grafting) was associated with preoperative bodily pain, congestive heart failure symptoms were not an independent factor affecting quality of life. CONCLUSIONS: Quality of life improves with cardiac surgical interventions in this studied age group and should not be denied even in the elderly population.

Aged↗
PubMed1999

Prosthesis-patient mismatch: hemodynamic comparison of stented and stentless aortic valves.

Several centers have reported excellent clinical performance of stentless aortic xenografts. This study reports a hemodynamic comparison of the Medtronic Freestyle stentless and Mosaic stented valves. The prosthetic hemodynamics at discharge and 1 year after insertion in 95 patients who underwent aortic valve replacement with the Freestyle stentless bioprosthesis at Southern California Kaiser Permanente Medical Center were compared retrospectively with 115 unmatched individuals who received the Mosaic stented valve at the University of British Columbia. As assessed by echocardiography, there were no differences in the mean transvalvular gradient, effective orifice area (EOA), or EOA indexed to body surface area (EOAI) at discharge between the two groups. However, after 1 year, all corresponding Freestyle valve sizes had larger EOAs and lower gradients. Furthermore, fewer patients receiving Freestyle xenografts had prosthesis-patient mismatch (19% vs. 64%, P<.001) as defined by EOAI <0.85 cm2/m2. Although the Mosaic stented valve provides comparable immediate hemodynamic performance after implantation, there is significant improvement with the Freestyle bioprosthesis in terms of gradient, EOA, and prosthetic-patient mismatch at 1 year.

Aged↗
PubMed1997

Composite valve graft versus separate aortic valve and ascending aortic replacement: is there still a role for the separate procedure?

BACKGROUND: To ascertain if operative technique has any bearing on outcome, the surgical results after aortic root replacement using either a composite valve graft (CVG) or a separate graft and valve (GV) were analyzed. METHODS AND RESULTS: Three hundred and ninety consecutive, nonrandomized patients treated for aortic valve disease and ascending aortic aneurysm (n=278) or type A dissection (n=112 [45 acute]) between 1965 and 1995 were analyzed retrospectively. One hundred and thirty-five patients received a CVG, and 255 had separate GV replacement. Mean age was 52+/-16 years (+/-1 SD). Eighty-two patients (44% of the CVG group) had the Marfan syndrome (MFS). Follow-up (96% complete) totaled 2247 patient-years and extended to 27 years. The operative mortality rate was 10+/-3% (+/-70% confidence limits) for patients receiving a CVG and 15+/-2% for GV replacement (P=NS). The 15-year actuarial survival estimate was higher for the CVG group (53+/-14% [+/-SEM] versus 36+/-4%, P=.037). Seven patients in the CVG group required reoperation on the aortic valve or ascending aorta, as did 49 in the GV group. The probabilities of freedom from reoperation on the aortic rootwere 82+/-9% and 75+/-4% at 10 years for the CVG and GV group (P=NS). Thirty variables were analyzed in a multivariate model: pulmonary disease, higher New York Heart Association functional class, and longer cardiopulmonary bypass time were linked with higher operative mortality risk; older age, emergency operation, coronary artery disease, and liver dysfunction were independent determinants of late death. Younger age and use of a bioprosthesis were predictors of late reoperation. Type of procedure (GV versus CVG) was not a significant predictor of any outcome variable. CONCLUSIONS: The long-term results after CVG or GV were similar, which reflects proper patient selection. Use of a composite valve graft theoretically confers more protection against recurrent aortic root aneurysm, and, unless one opts for a valve-sparing aortic root replacement procedure, is most appropriate for younger patients, those with the MFS (including acute dissections), and others with marked pathological involvement of the sinuses. On the other hand, use of a separate GV should not be abandoned; in carefully selected patients (and if properly performed, eg, excision of the sinuses), GV also provides satisfactory results.

Adult↗
PubMed1997

Ascending aortic aneurysm and aortic valve disease: what is the most optimal surgical technique?

The merits of separate versus composite valve graft replacement for the treatment of patients with ascending aortic aneurysms or dissections associated with aortic valve disease remain a controversial issue. Considering all available clinical data, the early and late results surprisingly are quite similar between the two procedures. However, patient selection criteria and operative technique are important. In patients with the Marfan syndrome and in those with significantly diseased or destroyed sinuses, composite valve graft replacement is the procedure of choice. The "open" (Carrel button) method of coronary reimplantation is recommended in almost all cases to minimize the risk of late false aneurysm formation. If the aortic leaflets are normal, a valve-sparing aortic root remodeling procedure is a reasonable alternative in certain individuals. Separate valve graft replacement is still a satisfactory option in other (non-Marfan) patients; however, most of the sinuses should be resected, leaving only small tongues of aortic wall surrounding the coronary ostia to reduce the risk of late aortic root aneurysmal degeneration. In patients with complex prosthetic valve endocarditis or multiple paravalvular leaks, homograft aortic root replacement is a good option after radical debridement of all infected or devitalized tissue.

Aortic Dissection↗
PubMed1996

Stanford experience with obliterative bronchiolitis after lung and heart-lung transplantation.

BACKGROUND: Obliterative bronchiolitis (OB) is the main chronic complication after heart-lung (HLTx) and lung transplantation (LTx), limiting the long-term success of both transplant procedures. METHODS: Since 1981, 135 HLTxs and 61 isolated LTxs were performed in 184 patients at Stanford University. RESULTS: The overall prevalence of OB in patients surviving longer than 3 months postoperatively was 64% after HLTx and 68% after LTx. The actuarial freedom from OB was 72%, 51%, 44%, and 29% at 1, 2, 3, and 5 years, respectively, after HLTx and LTx. An analysis of potential risk factors revealed that the frequency and severity of acute rejection episodes (p < 0.001) and the appearance of lymphocytic bronchiolitis on biopsy (p < 0.05) were significantly associated with the development of OB. With regard to diagnosis of OB, pulmonary function tests show early reductions of the forced expiratory flow between 25% and 75% of the forced vital capacity with subsequent decreases in the forced expiratory volume in 1 second. The sensitivity of transbronchial biopsies has increased to 71% since 1993. Current treatment consists of augmented immunosuppression. Concurrent acute rejection episodes or active OB on biopsy have been treated aggressively with high-dose steroid pulses. Analysis of data from 73 patients with OB after HLTx and LTx revealed actuarial 1-, 3-, 5-, and 10-year survival of 89%, 71%, 44%, and 17% versus 86%, 77%, 63% and 56% in patients without OB (p < 0.05 by log-rank analysis). The main complication and cause of death in patients with OB was superimposed respiratory tract infection, which was treated aggressively. CONCLUSIONS: Early diagnosis of OB using pulmonary function tests or transbronchial biopsy is possible and important, because immediate treatment initiation has led to acceptable survival rates, with nearly 50% of affected patients still alive 5 years after transplantation. Current experimental research on OB suggests that immune injury is the main pathogenetic event of airway obliteration in animal models; rapamycin and leflunomide are new immunosuppressive agents that may have the potential to prevent and treat airway obliteration.

Actuarial Analysis↗
PubMed1996

Heart transplantation complicated by a patent foramen ovale of the recipient atrial septum.

A patent foramen ovale after heart transplantation is a relatively uncommon occurrence. We report a case of a 58-year-old man with profound hypoxemia after orthotopic cardiac transplantation for end-stage ischemic cardiomyopathy. Transesophageal echocardiography demonstrated the presence of a patent foramen ovale in the recipient atrial cuff. Primary closure was performed with correction of the right-to-left shunt.

Echocardiography, Transesophageal↗
PubMed1995

Arterial switch and resection of hepatic hemangioendothelioma.

We report on the management of a neonate undergoing arterial switch for transposition of the great arteries and concomitant resection of a hepatic infantile hemangioendothelioma. A preoperative aortogram demonstrated the arterial supply of the hepatic hemangioendothelioma. Pulmonary artery hypertension and myocardial ischemia were noted after separation from cardiopulmonary bypass. Resection of the hepatic malformation produced an immediate reduction in pulmonary hypertension and resolution of the myocardial ischemia. The patient had an uneventful postoperative recovery.

Female↗
PubMed1995

Durability of the Hancock MO bioprosthesis compared with standard aortic valve bioprostheses.

To compare the durability of the Hancock modified orifice (Hancock MO, model 250 [H-MO]) valve with two other commonly used standard aortic valve bioprostheses, a cohort of 1,602 patients undergoing aortic valve replacement using porcine valves between 1971 and 1990 (excluding simultaneous mitral valve replacement) was analyzed retrospectively using Cox model multivariate techniques. Five hundred sixty-one patients received a composite H-MO valve, 652 received a standard Hancock model 242 (H) valve, and 389 received a Carpentier-Edwards model 2625 (C-E) valve. Mean age was 60 +/- 15 years (+/- 1 standard deviation) (71% male). Follow-up (10,247 patient-years) extended to 15 years and was 97% complete. The main focus of this study was bioprosthetic durability, using The American Association for Thoracic Surgery/The Society of Thoracic Surgeons guidelines to define structural valve deterioration (SVD). Multivariate analysis revealed that (younger) age (p < 10(-5), liver disease (p = 0.02), and 1981 to 1985 operative period (p = 0.012) were the only significant, independent predictors of SVD. In concordance with previous reports, the SVD freedom estimate was greater than 90% at 15 years for patients older than 70 years of age. Hepatic dysfunction had an adverse effect on SVD (estimated freedom from event at 10 years was 34 +/- 17% [standard error of mean] versus 78 +/- 2% for those without liver disease), but this affected only 3% of patients. Interestingly, one operative period (1981 to 1985) was associated with a slightly higher risk of SVD compared to the three other 5-year time windows. Valve type did not emerge as a significant risk factor for SVD.(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗
PubMed1994

Left ventricular torsional dynamics immediately after mitral valve replacement.

BACKGROUND: Cardiac operations and cardiopulmonary bypass are associated with a host of unphysiological consequences that have widespread systemic effects. Since previous investigations in human cardiac transplant recipients had demonstrated that left ventricular (LV) torsional deformation was a sensitive method to detect subclinical LV dysfunction during acute rejection, we studied LV systolic torsion and diastolic recoil preoperatively and postoperatively in a canine model using myocardial marker techniques. METHODS AND RESULTS: Seven dogs underwent placement of LV subepicardial myocardial markers and creation of mitral regurgitation. Three months later, the animals underwent high-speed, biplane videofluoroscopic analysis for determination of LV systolic function and regional LV systolic torsional deformation and diastolic recoil. The animals then underwent chordal-sparing mitral valve replacement and were restudied 1 to 2 hours postoperatively. One to 2 hours after the cardiac operation, regional maximal systolic torsional deformation decreased significantly in all three LV regions on the lateral LV wall, as well as in the apical and apical-equatorial regions on the anterior wall. During early systole, minimal regional systolic torsion increased significantly in all regions on the lateral wall, as well as in the apical level of the posterior wall. Heterogeneous decreases in torsional deformation were also seen during the early diastolic filling period. CONCLUSIONS: Regional systolic torsional deformation and diastolic recoil are markedly perturbed early after a cardiac operation and its associated manipulations. Such changes, however, may potentially serve as sensitive tools to assess the impact of different techniques of intraoperative management, including newer methods of myocardial protection.

Animals↗
PubMed1992

Left ventricular mechanics and energetics in the dilated canine heart: acute versus chronic mitral regurgitation.

The effects of volume overload associated with mitral regurgitation on left ventricular systolic mechanics, energetics, mechanical to external stroke work efficiency, and ventriculoarterial coupling were examined in 11 conscious, closed-chest dogs. Miniature radiopaque tantalum markers were implanted into the myocardium to measure left ventricular volume, and biplane cinefluoroscopic images were obtained 1 week and 3 months after creation of mitral regurgitation. Echocardiographically determined left ventricular mass increased from 116 +/- 28 to 152 +/- 29 gm (p less than 0.001). Left ventricular end-diastolic and end-ejection volumes increased by 24% and 27%, respectively. Global left ventricular systolic performance was assessed by the slopes (linear regression) of the end-systolic pressure-volume and end-systolic stress-volume relationships corrected for change in end-diastolic volume; normalized end-systolic pressure-volume relationships fell by 36% (p less than 0.001), and normalized end-systolic stress-volume relationships declined by 21% (p less than 0.005). The normalized end-systolic volume at 100 mm Hg end-systolic left ventricular pressure increased from 0.63 to 0.75 (p less than 0.05). Similar results were observed based on a nonlinear (quadratic) fit of the end-systolic pressure-volume data. In terms of energetics, the slopes of the stroke volume-end-diastolic volume and pressure-volume area-end-diastolic volume relationships fell significantly, indicating reduced external stroke work and mechanical energy at any given level of preload. Additionally, the efficiency of energy transfer from pressure-volume area to external pressure-volume work at matched end-diastolic volume was 25% lower (p = 0.006) at 3 months compared with the 1-week measurements. While overall effective arterial (or total vascular) elastance tended to decrease after a period of time, the effective ventriculovascular coupling ratio increased from 1.6 +/- 0.6 to 2.7 +/- 1.1 (p less than 0.005), indicating a greater degree of mismatch between the left ventricle and the total (forward and regurgitant) vascular load. Therefore the low pressure-volume overload of mitral regurgitation not only resulted in depressed left ventricular systolic mechanics but also was associated with deterioration of global left ventricular energetics and efficiency and exacerbated mismatch in coupling between the left ventricle and the systemic arterial bed and left atrium.

Acute Disease↗
PubMed1991

Dose response of fish oil versus safflower oil on graft arteriosclerosis in rabbit heterotopic cardiac allografts.

With the advent of cyclosporin A, accelerated coronary arteriosclerosis has become the major impediment to the long-term survival of heart transplant recipients. Due to epidemiologic reports suggesting a salutary effect of fish oil, the dose response of fish oil on graft coronary arteriosclerosis in a rabbit heterotopic cardiac allograft model was assessed using safflower oil as a caloric control. Seven groups of New Zealand White rabbits (n = 10/group) received heterotropic heart transplants from Dutch-Belted donors and were immunosuppressed with low-dose cyclosporin A (7.5 mg/kg/day). Group 1 animals were fed a normal diet and served as control. Group 2, 3, and 4 animals received a daily supplement of low- (0.25 mL/kg/day), medium- (0.75 mL/kg/day), and high- (1.5 mL/kg/day) dose fish oil (116 mg n-3 polyunsaturated fatty acid/mL), respectively. Group 5, 6, and 7 animals were supplemented with equivalent dose of safflower oil (i.e., 0.25, 0.75, and 1.5 mL/kg/day). Oil-supplemented rabbits were pretreated for 3 weeks before transplantation and maintained on the same diet for 6 weeks after operation. The extent of graft coronary arteriosclerosis was quantified using computer-assisted, morphometric planimetry. When the animals were killed, cyclosporin A was associated with elevated plasma total cholesterol and triglyceride levels in the control group. While safflower oil prevented the increase in plasma lipids at all dosages, fish oil ameliorated the cyclosporin-induced increase in total cholesterol only with high doses. Compared to control animals, there was a trend for more graft vessel disease with increasing fish oil dose, as assessed by mean luminal occlusion and intimal thickness. A steeper trend was observed for increasing doses of safflower oil; compared to the high-dose safflower oil group, animals supplemented with low-dose safflower oil had less mean luminal occlusion (16.3% +/- 5.9% versus 41.4% +/- 7.6%, p less than 0.017) and intimal thickness (7.9 +/- 1.9 microns versus 34.0 +/- 13.0 microns, analysis of variance: p = 0.054). Low-dose safflower oil also had a slight, but nonsignificant, beneficial effect on graft vessel disease when compared to control rabbits. The same trends were observed in the degree of histologic rejection (0 = none to 3 = severe) in fish oil- and safflower oil-treated animals. Rejection score correlated weakly but significantly (p = 0.0001) with mean luminal occlusion (r = 0.52) and intimal thickness (r = 0.46). Therefore allograft coronary disease in this model appeared to exhibit an unfavorable, direct-dose response to fish oil and safflower oil, independent of effects on plasma lipids.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Regional epicardial and endocardial two-dimensional finite deformations in canine left ventricle.

We evaluated subepicardial and subendocardial two-dimensional finite deformations in the left ventricular (LV) anterior, lateral, and posterior regions in the closed-chest, conscious dog heart. Eight dogs underwent placement of 22 radiopaque markers in the LV myocardium. Sets of three markers were implanted in the anterior, lateral, and posterior subepicardium and subendocardium at the mid-ventricular level; reference markers were placed at apical and basal sites. Eight hours later, biplane videofluoroscopy was performed. Finite deformations for each subepicardial and subendocardial region were analyzed during three consecutive beats at end expiration. Circumferential shortening occurred in all layers and regions; similarly, longitudinal shortening occurred in all layers except that of the posterior endocardium. Values of principal strain were -0.19 +/- 0.08 (SD) and -0.10 +/- 0.03 for the anterior subendocardium and subepicardium, -0.20 +/- 0.07 and -0.10 +/- 0.02 for the lateral subendocardium and subepicardium, and -0.13 +/- 0.02 and -0.10 +/- 0.03 for the posterior subendocardium and subepicardium respectively (P less than 0.05 subendocardium vs. subepicardium). Second principal strain tended to be near zero or positive (from -0.01 +/- 0.05 to 0.04 +/- 0.05) in all regions. The end-systolic direction of principal strain was -29 +/- 32 degrees and -34 +/- 29 degrees in the anterior subepicardium and subendocardium, -47 +/- 10 degrees and -30 +/- 37 degrees in the lateral subepicardium and subendocardium, and -4 +/- 29 degrees and +7 +/- 23 degrees in the posterior subepicardium and subendocardium. Anterior and lateral directions of principal strain were similar in the subepicardial and subendocardial layers and oriented along the epicardial fiber axis, but the posterior direction tended to be circumferentially oriented.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Alterations in left ventricular diastolic twist mechanics during acute human cardiac allograft rejection.

BACKGROUND: Contraction of obliquely oriented left ventricular (LV) fibers results in a twisting motion of the left ventricle. The purpose of this study was to assess the effects of acute human cardiac allograft rejection on LV twist pattern and the twist-volume relation. METHODS AND RESULTS: Tantalum markers were implanted into the LV midwall in 15 transplant recipients to measure time-varying, three-dimensional chamber twist using computer-assisted analysis of biplane cinefluoroscopic images. Twist was defined as the mean longitudinal gradient of circumferential rotation about the LV long axis. When plotted against normalized percent ejection fraction (%EF), the resulting twist-normalized %EF relation could be divided into three phases. In systole, LV twist was linearly related to ejection of blood. In contrast, diastolic untwist was characterized by early rapid recoil with little change in LV volume, followed by more gradual untwisting when the bulk of diastolic filling occurred. During 10 acute rejection episodes in 10 patients, maximum twist, peak systolic twist rate, and the slope of the systolic twist-normalized %EF relation did not change. In contrast, the slope of the early (first 15% of filling) diastolic twist-normalized %EF relation (M(early-dia)) decreased significantly (-0.194 +/- 0.062 [prerejection] versus -0.103 +/- 0.054 rad/cm [rejection], p = 0.0003), resulting in a prolonged tau 1/2 (time required to untwist by 50% [20 +/- 5% versus 28 +/- 5% of diastole], p = 0.0003) and decrease in percent untwisting at 15% diastolic LV filling (62 +/- 11% versus 36 +/- 13%, p = 0.0003). Therefore, a greater proportion of LV untwisting occurred later in diastole during rejection, as reflected by an increase in the slope (M(mid-dia)) of the middle to late (from 15 to 90% filling) diastolic twist-normalized %EF relation (-0.018 +/- 0.009 versus -0.030 +/- 0.010 rad/cm, p = 0.0015). Peak rate of untwist was not affected. With resolution of rejection, M(early-dia) and percent untwist during early diastole returned to baseline levels (p = NS versus baseline). There was also a trend for M(mid-dia) to return toward prerejection values (p = NS versus baseline), but this change did not reach statistical significance compared with rejection values. CONCLUSION: Acute cardiac allograft rejection is associated with altered diastolic twist mechanics in the absence of any demonstratable systolic abnormalities. During rejection, myocardial edema and other factors may result in intrinsic changes of the elastic properties of the myocardium, thereby leading to modification of recoil forces responsible for the early, rapid unwinding of the deformed ventricle.

Acute Disease↗