摘要:

Background The upper limit of vulnerability is the stimulus strength above which electrical stimulation cannot induce ventricular fibrillation even when the stimulus occurs during the vulnerable period of the cardiac cycle.The purpose of this study was to test the hypothesis that the upper limit of vulnerability can accurately predict the defibrillation threshold in patients undergoing implantable cardioverter-defibrillator (ICD) implantation using nonthoracotomy lead systems.15 J.Conclusions When tested with three shocks on and before the peak of the T wave, the upper limit of vulnerability accurately predicted the defibrillation threshold in patients undergoing ICD implantation using nonthoracotomy lead systems.This method required either one or no episodes of ventricular fibrillation in most patients. (Circulation. 1994;90: 2308-2314.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Atherosclerotic coronary artery disease, complicated by acute thrombosis, is the usual cause of sudden death in adults.This study addresses the pathology of coronary arteries in sudden death in the young (<=35 years old).Methods and Results Among 200 consecutive cases of sudden death in youth in the Veneto region of Italy, 37 (33 men and 4 women, age 18 to 35 years; mean, 29.4 years) showed obstructive atherosclerotic coronary artery disease in the absence of other cardiac pathological conditions and causes of death. No patient had previous angina pectoris or myocardial infarction. Cardiac arrest occurred at rest in 30 subjects and was related to effort in 7. A histological study was carried out on the obstructive coronary plaques. Degree of lumen stenosis and extension of lipid core and intimal fibrocellular hyperplasia facing the lumen were calculated morphometrically. Immunohistochemistry and electron microscopy were used to further characterize the plaque cell population. Single-vessel disease was found in 33 patients and triple-vessel disease in 4, with an overall total of 45 obstructive plaques, 34 of which were located in the proximal left anterior descending coronary artery. At histological study, only 10 plaques from 10 patients showed acute thrombosis (occlusive in 5 and subocclusive in 5); the remaining 35 were uncomplicated. Thirty-one plaques were fibrous in nature, while the other 14 were atheromatous. Compared with the atheromatous lesions, the fibrous plaques were rarely complicated by thrombosis (3% versus 64%; P<.001) and distinctly exhibited a fairly well-preserved tunica media (81% versus 21%; P<.001) as well as a stratum of neointimal fibrocellular hyperplasia (68% versus 7%; P<.001), which on immunohistochemistry and electron microscopy appeared to be proliferating smooth muscle cells.Conclusions In our study population, sudden death was precipitated by acute coronary thrombosis in only 27% of patients with obstructive coronary atherosclerotic plaque.Most of the young victims of sudden death with obstructive coronary atherosclerosis showed single-vessel disease that affected the left anterior descending coronary artery and was due to fibrous plaques with neointimal smooth muscle cell hyperplasia and a preserved tunica media in the absence of acute thrombosis. (Circulation. 1994;90:2315-2323.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Resting cardiac function does not necessarily affect exercise capacity.However, to determine whether it affects early dynamics of oxygen uptake (Vo2) during exercise, we measured Vo2during a constant work rate and during incremental exercise testing in patients with a history of myocardial infarction. Vo2=35%, group 1) and those with lower ejection fractions (LVEF<35%, group 2).Methods and Results Forty patients with a history of prior myocardial infarction (age, 57+-10 years) were monitored during 6 minutes of moderate constant work rate testing (40+-8 W) and during symptom-limited incremental exercise testing with a cycle ergometer. Vo2was calculated from respired gas analysis on a breath-by-breath basis. Cardiac output determinations were made with a computerized cadmium telluride detector every 10 seconds during exercise. The Vo2time constant during constant work rate exercise was slower in group 2 (58.0+-7.6 seconds) compared with group 1 (45.8+-10.5 seconds, P=.0002), indicating slower kinetics in group 2. The time constant for the rise in cardiac output during exercise was also slower in patients with lower EFs (63.0+-12.8 versus 50.0+-12.2 seconds). However, there were no differences in exercise capacity parameters, such as the Vo2or cardiac output at peak exercise, obtained during incremental exercise testing among the two groups.Conclusions The prolonged time constant of Vo2, which is primarily determined during early parts of exercise, reflects delayed cardiac output response in patients with severely impaired LV function.The time constant of Vo2during submaximal constant work rate exercise can be used as a sensitive and discriminant measure of impaired cardiac reserve in these patients. (Circulation. 1994;90:2324-2332.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The cardiovascular response to beta -adrenergic stimulation is markedly blunted with advancing age, and this blunting may underlie some of the prominent age-associated changes in the hemodynamic profile during dynamic exercise. To examine this hypothesis, we administered the nonselective beta -adrenergic receptor blocker propranolol (0.15 mg/kg IV) to 25 healthy normotensive men ages 28 to 72 years from the Baltimore Longitudinal Study of Aging (BLSA) immediately before maximal upright cycle ergometry with Technetium-99m gated cardiac blood pool scintigraphy. Their hemodynamic responses to exercise were compared with those of 70 age-matched healthy unmedicated male BLSA control subjects. The maximal cycle work rate achieved was similar in propranolol-treated men (158+-32 W) and control subjects (148+-32 W) and declined similarly with age in both groups. Hemodynamics at seated rest were not age-related in either group; however, propranolol-treated men had lower heart rates (HR), systolic blood pressure (SBP), ejection fraction, and cardiac index than control subjects but higher end-diastolic volume index (EDVI) and end-systolic volume index (ESVI) by covariance analysis. At maximal effort, several striking age-drug interactions were evident: Propranolol caused a greater reduction in HR and greater increases in EDVI and stroke volume index (SVI) in younger than in older men. Hence, at maximal work rate, HR declined less with age in the propranolol group (0.46 versus 1.09 beats per minute per year, P<.05 by covariance analysis); EDVI and SVI decreased with age (0.27 and 0.48 mL/m (2) per year, respectively) after propranolol compared with increases of 0.47 and 0.16 mL/m2per year in control subjects, respectively, each P<=.05 by covariance analysis. The left ventricular contractility index, SBP/ESVI, at exhaustion was reduced by propranolol to a greater extent in younger than older men. Thus, acute beta -adrenergic blockade reverses the age-associated ventricular dilation at end diastole and end systole observed during upright cycle exercise and blunts the decline in maximal HR and myocardial contractility. These data suggest that the age-associated declines in maximal HR and left ventricular contractility during vigorous exercise are manifestations of reduced beta -adrenergic responsivity with advancing age which is partially offset by exercise-induced ventricular dilation. (Circulation. 1994;90:2333-2341.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background and Purpose Heterotopic cardiac transplantation is a valuable surgical technique that maximizes the use of donor organs.However, recipient heart function may decline steadily postoperatively with resulting clinical deterioration. Paced linkage has the potential of reducing afterload and enhancing coronary flow of both hearts, thereby improving recipient- and donor-heart function. This may have long-term as well as short-term benefits.Methods and Results The study was performed on 11 heterotopic transplant recipients.The two hearts were linked with a pacemaker (paced linkage) to produce recipient heart systole during different periods of donor-heart diastole. The recipient ventricular contraction was timed to occur during early, mid, and late diastole of the donor heart. Hemodynamic baseline measurements were compared with the optimal counterpulsated data. Paced linkage produced significant improvements in total cardiac output, 5.0+-0.9 compared with baseline 4.5+-0.8 L/min (P=.021); recipient coronary sinus flow, 278+-145 versus 186+-108 mL/min (P=.022); and aortic systolic pressure, 135+-27 versus 123+-27 mm Hg (P=.005). There was an overall improvement in systolic ventricular performance in the recipient heart when pace linked, as evidenced by a significant increase in left ventricular systolic pressure of 118+-36 compared with the baseline value of 108+-33 mm Hg (P=.016), an increase in ejection period from 174+-30 versus 203+-48 (P=.046), and a decrease in the pre-ejection period of 147+-37 when paced versus 181+-39 milliseconds (P=.013). The metabolic studies showed a significant decrease in hypoxanthine release from a baseline level of 0.4 micromole/L to a paced value of -0.06 micromole/L (P=.002); these very low values would suggest that there is no evidence of ischemia. Hemodynamic changes in the donor heart included a significant reduction in the left ventricular end-diastolic pressure from 6.8+-4.4 versus baseline of 10.5+-5.8 mm Hg (P=.029) and in maximum -dP/dT from 3.2+-1.7 versus baseline of 2.1+-1.1.Conclusions Paced linkage after heterotopic cardiac transplant produces significant functional improvements in both hearts.Permanent pacemaker implantation may sustain these acute benefits and prevent the premature deterioration of the recipient heart. (Circulation. 1994;90:2342-2347.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Serial quantitative coronary angiography is used to assess progression of coronary disease; however, pathology studies have demonstrated angiographic insensitivity for determining atheroma.Intracoronary ultrasound (ICUS) can define and measure the components of the arterial wall and offers the potential for precise quantitative assessment of disease progression on serial examinations. The present study was done to test the feasibility of serially assessing intimal proliferation at the same coronary site with ICUS imaging in cardiac transplant recipients.Methods and Results ICUS imaging was done with a 30-MHz, 5F or 4.3F ultrasound imaging catheter at the time of angiography in 70 cardiac allografts (3.8 sites per patient) initially and 1 year later. Mean intimal thickness (IT), luminal area (LA), and total area (TA) of lumen plus intima and an index of intimal thickness (II=TA-LA/TA) were measured at each site. Additionally, vessels were graded using a scale incorporating criteria of intimal thickness and circumferential involvement. Side-by-side comparisons of paired angiograms were performed both to verify the similarity of ICUS imaging site and to detect new angiographic abnormalities. At least one site could be assessed serially by ICUS in 100% of patients, but only 189 of the original 263 coronary sites (72%) (2.7 sites per patient) could be matched satisfactorily on the second study. Thirty-nine patients (56%) had mild IT and 31 patients (44%) had moderate or severe IT on the initial study. Both groups showed the same IT progression the following year (Delta = 0.05+-0.13 versus 0.07+-0.15 mm; P=NS). Twenty-seven of the 70 patients (39%) showed progression by ICUS. The 23 patients with ICUS progression and angiographically normal vessels had the same progression in intimal thickening as the 4 patients with ICUS progression but showing angiographic disease (Delta =0.17+-0.13 versus 0.22+-0.10 mm; P=NS).Conclusions Replication of the intracoronary imaging site by judgment of two observers at an initial study and at a second study 1 year later was possible in at least one vessel site in 100% of the 70 patients and in 72% (189 of 263) of the original imaging sites (2.7 sites per patient). Serial ICUS demonstrates progression of intimal thickening at specific sites in only some cardiac transplant patients. Progression of intimal proliferation can occur in individuals in the presence or absence of initially increased intimal thickening or of angiographic disease at the time of the initial studies. Angiography is insensitive for recognizing early intimal thickening of the coronary vessels. (Circulation. 1994;90:2348-2355.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Imaging of myocardial glucose metabolism using (Fluorine-18)fluorodeoxyglucose (FDG) with positron emission tomography (PET) has been proposed for identification of tissue viability in patients with advanced coronary artery disease. This study was designed to evaluate the predictive value of flow and metabolic imaging for functional recovery after revascularization in myocardial segments of varying degrees of dysfunction.Methods and Results Thirty-seven patients (mean age, 59+-11 years) with coronary artery disease and impaired left ventricular function (ejection fraction, 34+-10%) were studied with PET using FDG and (Nitrogen-13)ammonia before surgical coronary revascularization (3+-1 grafts per patient). Tissue was scintigraphically characterized as normal, nonviable (concordant reduction of perfusion and FDG uptake), viable without discordance of perfusion and metabolism (mildly reduced perfusion and metabolism), or ischemically compromised (mismatch of reduced perfusion and maintained FDG uptake). Functional outcome was assessed by serial radionuclide ventriculography before and at 13+-13 weeks (median interval of 8 weeks) after coronary revascularization. Preoperatively impaired regional wall motion improved significantly in ischemically compromised (mismatch) revascularized segments but not in nonviable myocardium or in viable myocardium without discordance of perfusion and metabolism. The negative predictive value of PET for functional recovery was 86%, whereas the positive predictive value in revascularized regions ranged from 48% to 86% depending on severity of baseline wall motion abnormalities.Conclusions PET identifies metabolically active tissue, which benefits from revascularization.Although the negative predictive value of PET for recovery was high, functional improvement of viable but ischemically compromised tissue was less frequent than previously reported. The predictive value of PET was highest in left ventricular segments with severe dysfunction and a mismatch or reduced perfusion but preserved metabolism. Integration of PET, angiographic, and functional data is necessary for the optimal selection of patients with advanced coronary artery disease and impaired left ventricular function for revascularization. (Circulation. 1994;90:2356-2366.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Superior patency rates for internal mammary artery (IMA) grafts compared with vein coronary bypass grafts have been demonstrated by retrospective studies.This difference may have been affected by selection bias of patients and coronary arteries for IMA grafting.Methods and Results To estimate the difference between IMA and vein grafts, we analyzed graft patency data of 912 patients who entered a randomized clinical drug trial.In this trial, 494 patients received both IMA and vein grafts (group 1) and 418 only vein grafts (group 2). Occlusion rates of IMA grafts and IMA plus vein grafts in group 1 were compared with those of vein grafts in group 2. Multivariate analysis was used to compare occlusion rates of IMA and vein grafts while other variables related to graft patency were controlled for. In addition, 1-year clinical outcome was assessed by the incidence of myocardial infarction, thrombosis, major bleeding, and death. Occlusion rates of distal anastomoses in group 1 versus group 2 were 5.4% (IMA grafts) versus 12.7% (vein grafts) (P<.0001) and 10.4% (IMA plus vein grafts) versus 12.7% (vein grafts) (P=.14). There was no difference in adjusted risk of occlusion between IMA grafts and vein grafts (P=.089). Type and location of distal anastomosis and lumen diameter of the grafted coronary artery were shown to be predictors of occlusion. Clinical events occurred in 17.8% (group 1) and 16.0% (group 2) of patients (P=.53).Conclusions The observed difference in 1-year occlusion rates between IMA and vein grafts can be explained by a maldistribution of graft characteristics by selection of coronary arteries for IMA grafting rather than being ascribed to graft material. One-year clinical outcome is not improved by IMA grafting. (Circulation. 1994;90:2367-2374.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Background Cardiac tamponade frequently complicates acute proximal aortic dissection and is one of the most common causes of death from aortic dissection.Well-defined strategies for the management of acute aortic dissection now exist; however, little is known about how best to manage the hemopericardium that may complicate it.Methods and Results Using a computer-based review, we retrospectively identified 10 patients presenting to our hospital over a 13-year period who were diagnosed with both aortic dissection and cardiac tamponade. All 10 had proximal dissections. Three of the 10 presented as the sudden onset of fatal electromechanical dissociation, 6 presented with hypotension, and 1 was normotensive on presentation. Of the 7 hypotensive or normotensive patients diagnosed with cardiac tamponade, 4 underwent successful pericardiocentesis while awaiting surgery. At time intervals of 5 to 40 minutes after their pericardiocenteses, 3 of the 4 patients experienced sudden onset of electromechanical dissociation and death; the fourth patient survived and underwent surgical repair. Of the 3 hypotensive or normotensive patients who had either no pericardiocentesis or an unsuccessful pericardiocentesis, all 3 underwent successful surgical repair and survived.Conclusions In this study, patients with an aortic dissection complicated by cardiac tamponade have an early mortality of 60%.While 3 of the 10 died from electromechanical dissociation immediately upon presentation, the 3 other deaths all occurred shortly after successful pericardiocentesis, a procedure undertaken to stabilize them. While the number of patients in this series is small, the observations do raise the possibility that in patients with cardiac tamponade complicating aortic dissection pericardiocentesis could be harmful rather than beneficial. Possible mechanisms for why the performance of pericardiocentesis might destabilize such patients are proposed. (Circulation. 1994;90:2375-2378.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Origin of both coronary arteries from the pulmonary artery is generally a lethal condition from progressive ventricular failure. We report the clinical and surgical course of two infants, ages 3 and 6 months, with this anomaly. One patient had normal intracardiac anatomy with low pulmonary artery pressures (30/12 mm Hg). The second patient had a restrictive subpulmonic ventricular septal defect with a moderately elevated pulmonary artery pressure (50/13 mm Hg). Left ventricular ejection and shortening fractions were profoundly depressed in both patients. The common coronary trunk arose from the right anterior facing sinus in one patient and from the left posterior facing sinus in the other. Both patients underwent repair by direct coronary implantation to the aorta. Left ventricular function improved with shortening fractions near normal at a follow-up of 6 months for one patient and 1 year for the other. Early diagnosis and prompt repair is compatible with survival and return of normal shortening fraction. (Circulation. 1994;90:2379-2384.)

ISSN:0009-7322    

出版商:OVID    

年代:1994

数据来源: OVID