[Show abstract][Hide abstract] ABSTRACT: Accurate prediction of recovery of dysfunctional myocardium would optimize risk/benefit analysis among patients with coronary artery disease and decreased ventricular function. Tissue-tagged magnetic resonance imaging permits quantitative assessment of changes in ventricular function and may improve the prediction of myocardial recovery after coronary artery bypass grafting.
Thirteen patients underwent preoperative and postoperative stress magnetic resonance imaging with strain analysis at rest with 5 and 10 microg x kg(-1) x min(-1) dobutamine. Two-dimensional strain analysis was performed on a single midventricular short-axis image divided into 6 regions for each patient (n = 78). Regional minimum principal, circumferential, and radial strain values were calculated at each stress level. Regional changes in postoperative strain were correlated with changes in preoperative dobutamine stress by means of logistic regression. Receiver operating characteristic curves were created to determine the accuracy of preoperative dobutamine stress for the prediction of postoperative myocardial recoverability.
Minimum principal, circumferential, and radial strain values at 5 and 10 microg of dobutamine differed significantly from baseline strains (P < .05). Receiver operator characteristic curves found minimum principal strain to be 75% accurate for prediction of recoverability at both stress levels. Circumferential strain was 72% and 70% accurate at 5 and 10 microg, respectively, whereas radial strain was 77% and 64% accurate at 5 and 10 microg, respectively.
Dobutamine-stressed tissue-tagged magnetic resonance imaging with strain analysis is feasible to quantitatively predict myocardial recoverability after coronary artery bypass grafting. Further study is required to determine the optimal strain parameter for predicting myocardial recoverability after surgical revascularization.
The Journal of thoracic and cardiovascular surgery 06/2008; 135(6):1342-7. · 3.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Melagatran, the active form of ximelagatran, is a novel, direct thrombin inhibitor that does not have a narrow therapeutic window regarding hemorrhagic and thromboembolic events. We aimed to determine whether melagatran would be effective in preventing thrombus formation on heterotopically placed mechanical heart valves.
A graft containing a bileaflet mechanical heart valve was implanted in the descending thoracic aorta of domestic swine. Two groups of 6 animals received daily subcutaneous injections of either melagatran (2.4 mg/kg, 3 times per day) or dalteparin (175 U/kg, 2 times per day) for 30 days. Four control animals received no anticoagulation therapy. Fecal HemoQuant and serum hemoglobin levels were recorded. Thirty days after the procedure, platelets were labeled with indium 111, the abdominal organs were inspected, and thrombi and platelets deposited on the valve were measured.
Median thrombus burden on the valves was 0.4 mg (interquartile range, 0.15-5.45 mg) with melagatran, 0.5 mg (interquartile range, 0-14.5 mg) with dalteparin, and 168 mg (interquartile range, 32.5-665.75 mg) for controls (melagatran vs dalteparin and control; P = .04). Median platelet deposition on the valves was 0 (interquartile range, 0-8.9 x 10(4)) with melagatran, 49.9 x 10(4) (interquartile range, 27.9 x 104-191.8 x 10(4)) with dalteparin, and 115.2 x 10(4) (interquartile range, 9.6 x 10(4)-243 x 10(4)) for controls (melagatran vs dalteparin and control; P = .02). Melagatran did not increase the risk of thromboembolism or bleeding.
Thrombus and platelet accumulation on the prosthetic valves was decreased by melagatran and dalteparin. The use of melagatran or other related direct thrombin inhibitors warrants further study in prophylaxis of thromboembolism in patients with mechanical heart valves.
The Journal of thoracic and cardiovascular surgery 09/2007; 134(2):359-65. · 3.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The pacing model of heart failure produces heterogeneous changes in wall stress and myocyte diameter. The purpose of this study was to measure regional changes in cardiotrophin-1 (CT-1), a cytokine thought to play a role in LV remodeling, and regional changes in LV strain as measured with magnetic resonance imaging.
Dilated cardiomyopathy was induced in nine mongrel dogs over 4 wk by rapid pacing using a right ventricular epicardial lead. Baseline CT-1 was measured from an apical myocardial biopsy, and regional CT-1 was measured from anterior, lateral, inferior, and septal walls after the induction of heart failure and in six control dogs. Tissue tagged images were divided into similar regions and minimal principal strain (MPS), ejection fraction, and ventricular volumes were compared after induction of heart failure.
After induction of heart failure, LV ejection fraction and end-diastolic volume differed significantly from baseline (P < 0.01 and P = 0.02, respectively). Additionally, regional CT-1 and MPS were significantly different (P < 0.01 for both). Cardiotrophin-1 increased significantly in the inferior and septal walls (both P < 0.01) but not in the anterior or lateral walls (both P = NS). Minimum principal strain decreased significantly in the inferior and septal walls (both P < 0.01) but not in the anterior or lateral walls (both P = NS).
The pacing model of heart failure produces heterogeneous changes in regional CT-1 and wall motion as measured by MPS. The greatest regional changes are closest to the pacemaker site: the inferior and septal walls. These differences in regional CT-1 may account for previously noted myocyte hypertrophy and preserved ventricular function in these regions.
Journal of Surgical Research 08/2007; 141(2):277-83. · 2.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Irrigated bipolar radiofrequency ablation has been used to replicate Cox maze surgical scars in pig hearts ex vivo. Impedance monitoring accurately predicted complete transmurality for all lesions. This study aimed to assess the feasibility and reliability of irrigated radiofrequency ablation and impedance monitoring to produce electrically isolating Cox maze lesions in vivo.
A modified Cox maze procedure was performed in 8 adult sheep during cardiopulmonary bypass using irrigated bipolar and unipolar radiofrequency ablation. For bipolar radiofrequency ablation, atrial tissues were clamped between opposing electrodes; ablation was terminated at the plateau in impedance decline. Unipolar radiofrequency ablation lesions were painted on the endocardium, and transmurality was assessed visually. Animals survived 30 days.
Bipolar lesions (n = 48) were thinner (7.4 +/- 2.4 mm versus 12.7 +/- 3.2 mm) and required less time (14.1 +/- 3.4 seconds versus 41.4 +/- 21.8 seconds) and energy (377.5 +/- 99.2 W.s versus 995.1 +/- 547.1 W.s) to create despite being longer (31.7 +/- 8.6 mm versus 19.2 +/- 5.6 mm) than unipolar lesions (n = 26). The left atrial pacing threshold across selected bipolar lesions increased at least fivefold above baseline (1.6 +/- 0.2 mA) at 1 hour (18.4 +/- 4.6 mA; n = 8; p < 0.001) and 30 days (17.2 +/- 5.2 mA; n = 6; p < 0.001), indicating functional conduction block. Bipolar lesions had no adherent thrombus or endocardial defects. Cross-section examination confirmed transmurality in 100% of bipolar lesions and 98.7% of unipolar lesions.
Irrigated bipolar radiofrequency ablation with impedance monitoring safely and reliably produces electrically isolating, transmural Cox maze lesions in vivo.
The Annals of thoracic surgery 12/2005; 80(6):2263-70. · 3.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To compare myocardial enhancement during first-pass myocardial perfusion imaging at 3.0 Tesla (T) and 1.5T.
First-pass myocardial perfusion imaging was performed on twelve normal subjects at 3T and 1.5T using an interleaved notched saturation recovery gradient echo pulse sequence. Subjects received either 0.10 mmol/kg for both scans (group 1), 0.075 mmol/kg for both scans (group 2), or 0.075 mmol/kg for the 3T scan and 0.10 mmol/kg for the 1.5T scan (group 3).
Contrast enhancement was significantly greater at 3T than at 1.5T for the 12 subjects whether enhancement was normalized to baseline signal intensity (2.58 +/- 0.76 vs. 1.52 +/- 0.37, p < 0.0001) or to noise (57.6 +/- 19.7 vs. 14.7 +/- 7.8, p < 0001). For each of the three groups, contrast enhancement was significantly greater at 3T versus 1.5T (p < 0.0001, p < 0.001, p < 0.008 when normalized to baseline signal; p < 0.0001 for all groups when normalized to noise).
3T improves contrast in first-pass myocardial perfusion imaging at either 0.10 mmol/kg or 0.075 mmol/kg.
Journal of Cardiovascular Magnetic Resonance 02/2005; 7(3):559-64. · 5.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The contemporary risk of reoperative aortic valve replacement is ill-defined. We therefore compared the recent early results of reoperative and primary aortic valve replacement in our institution.
Between January 1993 and January 2001, a total of 162 patients underwent reoperative aortic valve replacement with or without coronary artery bypass grafting, and 2290 underwent primary aortic valve replacement with or without coronary artery bypass grafting. The reoperative and primary groups were similar with regard to gender (37% female in both), preoperative New York Heart Association functional class (2.8 +/- 1 vs 2.8 +/- 1), and ejection fraction (58% +/- 15% vs 57% +/- 15%). Patients undergoing reoperative aortic valve replacement were younger than those undergoing primary aortic valve replacement (64 +/- 15 years vs 70 +/- 13 years, P < .001). Previous prostheses were xenografts in 77 patients (48%), homografts and autografts in 25 (15%), and mechanical prostheses in 60 (37%). Mean time to reoperation was 9.7 +/- 6.8 years.
Early mortality for reoperative aortic valve replacement (8/162, 5%) was not statistically different from that for primary aortic valve replacement (71/2290, 3%, P = .20). Endocarditis was more common in the reoperative group (22% vs 3%, P < .001); when endocarditis was excluded from the analysis, early mortality was 3% in both groups. Multivariate predictors for early mortality were prosthetic valve endocarditis ( P < .001, odds ratio 9.8), advanced preoperative functional class ( P < .001, odds ratio 2.0), peripheral vascular disease ( P = .008, odds ratio 2.0), preserved left ventricular ejection fraction ( P = .004, odds ratio 0.98), and male gender ( P = .009, odds ratio 0.49). After adjustment for these factors, there was no difference in early mortality between the groups ( P = .095).
The risk of reoperative aortic valve replacement is similar to that for primary aortic valve replacement. These data support the expanded use of bioprosthetic valves in younger patients.
Journal of Thoracic and Cardiovascular Surgery 01/2005; 129(1):94-103. · 3.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Advances in tissue prosthetic valve design and manufacturing have stimulated renewed interest in the use of biological valves in younger patients. This approach, however, risks reoperation. We therefore reviewed our recent experience with repeat mitral valve replacement to better define its contemporary risks.
Using a computerized database, we identified and compared 106 patients undergoing repeat mitral valve replacement with 562 control patients undergoing primary mitral valve replacement between January 1993 and December 2000 at our institution.
There were no significant differences between repeat and primary surgery groups with respect to age (mean 66 +/- 12 vs 64 +/- 13 years), gender distribution (women 65% vs 64%), preoperative functional class, ejection fraction, or active endocarditis (6.6% vs 3.4%). The indication for reoperation in the repeat group was structural dysfunction in 49 patients (46%), paravalvular leak in 21 patients (20%), nonstructural dysfunction in 11 patients (10%), and progression of other native valve disease in 8 patients (8%). Prior prostheses were mechanical in 46 patients (43%). Mean time to reoperation was 11.5 +/- 7.1 years. There were 5 deaths out of 106 patients in the repeat group (4.7%) and there were 23 deaths out of 562 patients in the control group (4.1%) (p = NS). Multivariate analysis identified prior myocardial infarction (p = 0.014, odds ratio 2.9) and nonelective surgical status (p = 0.004, odds ratio 2.3) as significant predictors of operative mortality.
The risk of repeat mitral valve replacement was low suggesting that there should be less reluctance to recommend patients choose a bioprosthesis over a mechanical prosthesis. Given the expected durability of current designs, bioprosthetic use may be explored in younger patients without subjecting those individuals to excessive risk.
The Annals of thoracic surgery 08/2004; 78(1):67-72; discussion 67-72. · 3.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Magnetic resonance imaging with radiofrequency tissue tagging permits quantitative assessment of regional systolic myocardial strain. We sought to investigate the utility of this imaging modality to quantitatively determine preoperative impairment and postoperative improvement in ventricular function in patients with ischemic heart disease.
Magnetic resonance imaging with radiofrequency tissue tagging was performed on 6 patients (average age 60.2 +/- 13.7 years) with coronary artery disease and 32 control subjects with no known heart disease. Patients with coronary artery disease underwent imaging before and 3 months after coronary artery bypass grafting. The ventricle was divided into 6 segments within a midventricular plane. Regional 2-dimensional left ventricular circumferential strain was calculated from tagged magnetic resonance images throughout systole. Circumferential strain results were compared in patients before and after and 3 months after coronary artery bypass grafting and also in control subjects.
Before the operation circumferential strain identified 100% (10/10) of all regional wall motion abnormalities seen by preoperative ventriculography. Postoperatively, improvements were demonstrated in 56% (20/36) of the regions, and these improvements agreed with viability testing by single-photon emission computed tomography when available. Additionally, preoperative global circumferential strain for the ischemic group was significantly depressed relative to that in control subjects (0.11 +/- 0.05 vs 0.20 +/- 0.03, P <.001). Global circumferential strain correlated with ejection fraction by ventriculography (r = 0.84, P <.01) and improved after coronary artery bypass grafting (0.14 +/- 0.05 vs 0.11 +/- 0.05, P <.01).
Magnetic resonance imaging with radiofrequency tissue tagging permitted circumferential strain calculation. This technology quantitatively demonstrated improvements in left ventricular wall motion after coronary artery bypass grafting for both individual regions and the entire ventricle. This noninvasive method may prove useful in preoperative evaluation and postoperative serial assessment of left ventricular wall motion.
Journal of Thoracic and Cardiovascular Surgery 07/2004; 128(1):76-82. · 3.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nonirrigated radiofrequency ablation (RFA) has been used to replicate the surgical scars of the Cox-Maze procedure. This study aimed to demonstrate that an irrigated, bipolar RFA energy source could also effectively replicate Cox-Maze lesions with impedance monitoring to predict the transmurality of ablated tissue.
A complete Cox-Maze lesion pattern was created ex vivo on fresh porcine atria using an irrigated, bipolar RFA system. Tissues were clamped between opposing electrodes with steady pressure to ensure an intimate tissue-electrode interface during ablation. A proprietary feedback and control algorithm monitored tissue impedance and terminated ablation when lesions were deemed transmural by a plateau in impedance decline. Ablation time and power, lesion width and length, and tissue thickness were recorded. Lesions were stained with 1% triphenyltetrazolium chloride and sectioned for gross assessment of transmurality.
One hundred thirty-seven lesions were created on 11 porcine hearts. The total ablation time per lesion was 14.8 +/- 1.2 seconds (range, 10.0-19.0 seconds). Lesions averaged 4.2 +/- 1.3 mm (range, 1.3-10.2 mm) in width. Average tissue thickness was 3.0 +/- 1.7 mm (range, 0.5-9.9 mm). Crosssectional examination revealed that 100% of lesions were transmural (n = 718), and no tissue defects were observed.
These results indicate that irrigated bipolar RFA energy can produce transmural Cox-Maze lesions ex vivo on intact porcine atria and that impedance monitoring is a reliable predictor of lesion transmurality. Additional in vivo studies are under way to further demonstrate the efficacy and safety of irrigated, bipolar RFA technology.
Heart Surgery Forum 02/2003; 6(5):418-23. · 0.56 Impact Factor