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Biomedical subjects

J L Blackshear

Publications and source records attributed to J L Blackshear.

At least 37 records · Page 2Linked to original sources
PubMed1996

Thoracoscopic obliteration of the left atrial appendage: potential for stroke reduction?

BACKGROUND: In a review of all relevant articles describing the site of left atrial thrombus in patients with atrial fibrillation, the thrombus was localized to the left atrial appendage in 43% of patients with rheumatic heart disease and in 91% of patients with nonrheumatic atrial fibrillation. This study was designed to test the feasibility of thoracoscopic obliteration of the left atrial appendage as a means of reducing thromboembolic stroke. METHODS: Thoracoscopic obliteration of the left atrial appendage was undertaken in 10 dogs, 5 with staples and 5 with an endoloop. Obliteration also was attempted in 8 fresh human cadavers. RESULTS: In all dogs, the appendage was rapidly obliterated (21.3 +/- 7.6 minutes) and confirmed at euthanasia at 11 weeks. In 3 cadavers, anatomic and disease factors prevented visualization of the left atrial appendage; in 1 the appendage tore, and in the remainder the appendage was obliterated. CONCLUSIONS: Obliteration of the left atrial appendage is feasible and may be considered as an additional surgical procedure to reduce stroke. The group of patients in whom it offers the greatest potential are those with atrial fibrillation deemed ineligible for warfarin, those without atrial thrombus and with a free pericardial and pleural space.

Animals↗
PubMed1996

Appendage obliteration to reduce stroke in cardiac surgical patients with atrial fibrillation.

BACKGROUND: Left atrial appendage obliteration was historically ineffective for the prevention of postoperative stroke in patients with rheumatic atrial fibrillation who underwent operative mitral valvotomy. It is, however, a routine part of modern "curative" operations for nonrheumatic atrial fibrillation, such as the maze and corridor procedures. METHODS: To assess the potential of left atrial appendage obliteration to prevent stroke in nonrheumatic atrial fibrillation patients, we reviewed previous reports that identified the etiology of atrial fibrillation and evaluated the presence and location of left atrial thrombus by transesophageal echocardiography, autopsy, or operation. RESULTS: Twenty-three separate studies were reviewed, and 446 of 3,504 (13%) rheumatic atrial fibrillation patients, and 222 of 1,288 (17%) nonrheumatic atrial fibrillation patients had a documented left atrial thrombus. Anticoagulation status was variable and not controlled for. Thrombi were localized to, or were present in the left atrial appendage and extended into the left atrial cavity in 254 of 446 (57%) of patients with rheumatic atrial fibrillation. In contrast, 201 of 222 (91%) of nonrheumatic atrial fibrillation-related left atrial thrombi were isolated to, or originated in the left atrial appendage (p < 0.0001). CONCLUSIONS: These data suggest that left atrial appendage obliteration is a strategy of potential value for stroke prophylaxis in nonrheumatic atrial fibrillation.

Aged↗
PubMed1996

Management of atrial fibrillation in adults: prevention of thromboembolism and symptomatic treatment.

Because of its prevalence in the population and its associated underlying diseases and morbidity, atrial fibrillation (AF) is an important and costly health problem. Advancing age, diabetes, heart failure, valvular disease, hypertension, and myocardial infarction predict the occurrence of AF within a population. The management of AF is complex and involves prevention of thromboembolic complications and treatment of arrhythmia-related symptoms. Stroke occurs in 4.5% of untreated patients with AF per year. Independent risk factors for stroke in nonrheumatic patients with AF are advanced age; a history of prior embolism, hypertension, or diabetes; and echocardiographic findings of left atrial enlargement and left ventricular dysfunction. Warfarin decreases stroke by two-thirds and death by one-third; aspirin is only about half as effective overall and is insufficient therapy for those with risk factors for stroke. Options for thromboembolic prophylaxis are use of warfarin for all in whom it is safe or, alternatively, warfarin for those with risk factors and aspirin for those without risk factors. One-half of the patients with AF are 75 years of age or older. The uniform applicability and relative safety of warfarin therapy in this age-group are controversial. Specific therapy for the arrhythmia should be dictated by the need to control symptoms. Symptomatic treatments include rate-control medications and strategies designed to terminate and prevent arrhythmia recurrence. Digoxin, beta-adrenergic blockers, verapamil, and diltiazem slow excessive ventricular rates in patients with AF and may favorably manage comorbid conditions. The efficacy of anti-arrhythmic medications is only 40 to 70% per year in preventing recurrences of AF, and these agents, except amiodarone, may increase the risk of sudden death in patients with certain types of organic heart disease and AF. The use of nonpharmacologic symptomatic therapies such as atrioventricular node modification or ablation with a rate-response pacemaker or surgical intervention is increasing.

Adrenergic beta-Antagonists↗
PubMed1996

Valve replacement in aortic stenosis with preoperative mean gradient < 50 mmHg: hemodynamic outcome.

BACKGROUND AND AIMS OF THE STUDY: No prior studies have defined pre- versus postoperative hemodynamics of large numbers of patients with low mean transvalvular gradients. This was our objective. METHODS: Retrospective analysis was undertaken of preoperative and postoperative echo/Doppler data in 294 patients who underwent aortic valve replacement (AVR) for aortic stenosis (AS). Some 136 patients had a preoperative mean gradient of < 50 mmHg. The relationship of preoperative to pre- minus postoperative (delta) mean gradient (GRAD), peak valvular velocity (V2), left ventricular outflow tract velocity (V1), V1/V2 ratio, V2-V1, and aortic valve area (AVA) were plotted and analyzed such that a 'zero-benefit threshold' from surgery could be estimated. RESULTS: Strong relationships (r > 0.80) were noted for GRAD to delta GRAD, V2 to delta V2, and (V2-V1) to delta (V2-V1) with zero-benefit thresholds of 16 mmHg for GRAD, 2.6 m/s for V2 and 1.7 m/s for V2-V1. These thresholds were lower in patients who received homografts (11 mmHg, 2.2 m/s, and 1.1 m/s respectively), p < 0.02. The relationship of pre operative V1/V2 to delta V1/V2 and AVA-delta AVA were weaker (r = 0.52 and 0.33 respectively) with zero-benefit thresholds of 0.41 and 2.0 cm2. Among patients with depressed preoperative fractional shortening, improvement was confined to those without coexistent coronary artery disease. CONCLUSION: This analysis of thresholds of mean gradient benefit suggests that most patients with low gradient AS improve hemodynamically from AVR. The hemodynamic 'break-even' point averages a mean gradient of 16 mmHg.

Aged↗
PubMed1995

Nocturnal dyspnea and atrial fibrillation predict Cheyne-Stokes respirations in patients with congestive heart failure.

BACKGROUND: Cheyne-Stokes respirations have frequently been noted in highly selected groups of patients with congestive heart failure, but their prevalence in an unselected population with congestive heart failure is undefined. METHODS: One hundred consecutive unselected outpatients or stable inpatients with clinical congestive heart failure encountered by three clinical cardiologists during a 6-month period were screened for Cheyne-Stokes respirations with overnight oximetry. RESULTS: The mean age (+/- SD) of the patients was 70 +/- 8.6 years. Of the 100 patients, 33% had had previous coronary bypass surgery, 77% were men, 57% had hypertension, and 32% had atrial fibrillation. The mean ejection fraction (+/- SD) was 34% +/- 13%. Periodic breathing was assessed qualitatively as Cheyne-Stokes respirations in 27% of patients, nonspecific sleep-disordered breathing (apneas and/or hypopneas) in 43%, and normal in 30%. For patients with Cheyne-Stokes respirations, patients with nonspecific sleep-disordered breathing, and normal subjects, the mean numbers of oxyhemoglobin desaturation events per hour were 24, 10, and 2, and the total numbers of desaturations of 4% or more that lasted less than 3 minutes were 172, 74, and 13. Independent predictors of Cheyne-Stokes respirations vs non-Cheyne-Stokes respirations included a history of nocturnal dyspnea (odds ratio, 4.00; 95% confidence interval, 1.33 to 12.04; P = .01) and atrial fibrillation (odds ratio, 3.24; 95% confidence interval, 1.21 to 8.48; P = .02). CONCLUSIONS: Cheyne-Stokes respirations and nonspecific sleep-disordered breathing are common in unselected patients with congestive heart failure, and Cheyne-Stokes respirations are predicted by a history of nocturnal dyspnea and the presence of atrial fibrillation. Techniques designed to modify the nocturnal breathing pattern of patients with congestive heart failure may be applicable to a large portion of the congestive heart failure population.

Aged↗
PubMed1995

Prevalence, age distribution, and gender of patients with atrial fibrillation. Analysis and implications.

The prevalence of atrial fibrillation (AF) is related to age. Anticoagulation is highly effective in preventing stroke in patients with AF, but the risk of hemorrhage may be increased in older patients. We reviewed the available epidemiologic data to define the age and sex distribution of people with AF. From four large recent population-based surveys, we estimated the overall age- and gender-specific prevalence of AF. These estimates were applied to the recent US census data to calculate the number of men and women with AF in each age group. There are an estimated 2.2 million people in the United States with AF, with a median age of about 75 years. The prevalence of AF is 2.3% in people older than 40 years and 5.9% in those older than 65 years. Approximately 70% of individuals with AF are between 65 and 85 years of age. The absolute number of men and women with AF is about equal. After age 75 years, about 60% of the people with AF are women. In contrast to people with AF in the general population, patients with AF in recent anticoagulation trials had a mean age of 69 years, and only 20% were older than 75 years. The risks and benefits of antithrombotic therapy in older individuals are important considerations in stroke prevention in AF.

Adult↗
PubMed1995

Improved detection of silent cardiac ischemia with a 12-lead portable microprocessor-driven real-time electrocardiographic monitor.

OBJECTIVE: To compare a microprocessor-driven real-time 12-lead electrocardiographic monitoring device with Holter monitoring for detection of ischemia. DESIGN: Electrocardiographic monitoring was conducted in 110 patients at bed rest or undergoing surgical procedures. MATERIAL AND METHODS: In three groups of patients, simultaneous monitoring with a 12-lead real-time device and a 2-channel Holter system was performed to detect ischemic episodes. The differences in the number of ischemic events and the total time of ischemia revealed by the two devices were analyzed statistically. RESULTS: In patients with coronary artery disease, more ischemic ST-segment shifts were detected by the 12-lead device than by Holter monitoring (44 versus 16 events; P < 0.05). Total time of ischemia was also greater with the 12-lead device (879 versus 273 minutes; P < 0.05). Ischemia was detected by both techniques in 6 patients, only by the 12-lead device in 12, and only by Holter monitoring in 1. Neither device detected ischemia in control subjects. The 12-lead device had an advantage in detecting inferior ischemia, and it identified an additional 13 patients with unstable angina who had changes in T-wave polarity but did not exhibit ST-segment shifts. CONCLUSION: The 12-lead real-time electrocardiographic monitoring device is superior to Holter monitoring in detecting and facilitating real-time identification of myocardial ischemia in patients at bed rest.

Angina, Unstable↗
PubMed1994

Obstructive sleep apnea manifesting as suspected angina: report of three cases.

OBJECTIVE: To describe three cases of obstructive sleep apnea that resembled coronary artery disease and to suggest features that might distinguish these two syndromes. DESIGN: We present three detailed case reports of patients with severe obstructive sleep apnea and discuss similar cases from the literature. MATERIAL AND METHODS: Two obese women and one obese man with previously undiagnosed obstructive sleep apnea had chest discomfort, episodic dyspnea, and palpitations, most prominent at night. All three patients had multiple cardiac risk factors and had previously undergone cardiac evaluations, including at least two prior cardiac catheterizations each. Repeated cardiac catheterization revealed less coronary occlusive disease than expected on the basis of the symptoms in all three patients and a small atrial septal defect in one patient. When reassessed, the medical histories suggested obstructive sleep apnea. RESULTS: Overnight polysomnography documented the presence of severe sleep apnea; the three patients had mean values of 56 disordered breathing events per hour and 44% minimal oxygen saturation. Although bi-level or continuous positive airway pressure yielded initial improvement, all patients had difficulty with routine use of this therapy after 1 1/2 years of follow-up. CONCLUSION: The initial manifestations of severe obstructive sleep apnea may simulate angina, suggest arrhythmia, or mimic heart failure. Failure to inquire about snoring and daytime somnolence in patients with chest pain may prevent the identification of clinically significant disordered breathing during sleep.

Aged↗
PubMed1994

Making the diagnosis when the patient has 'blue toes'.

Painful "blue toes" describes a physical sign whose meaning may be discovered through a carefully taken history, physical, and laboratory evaluation. Accurate diagnosis is important, because therapy for one specific condition may be contraindicated for another. When embolism is suspected, ultrasound examination of the heart, aorta, and periphery may be useful prior to angiography in order to avoid exacerbation of cholesterol crystal embolization. Transesophageal echocardiography or MRI may be needed to exclude a thoracic aortic source. The differential diagnosis can be divided into three categories: emboli from the cardiac and arterial system, acquired hypercoagulability disorders, and syndromes that lead to peripheral vascular pathology. A clinical approach to the evaluation of patients is presented, with case reports.

Aged↗
PubMed1993

Digital embolization from plaque-related thrombus in the thoracic aorta: identification with transesophageal echocardiography and resolution with warfarin therapy.

A 71-year-old man had painful blue toes after an episode of protracted vomiting. Abdominal, cardiac, and transesophageal ultrasound studies were performed before angiography was considered. A large mobile mass in the proximal descending thoracic aorta, which suggested thrombus, was identified by transesophageal echocardiography. With no further evaluation, anticoagulant therapy with heparin and warfarin was initiated. Three months later, repeated transesophageal echocardiography demonstrated only a tiny vestige of the plaque-related mass. The pain and discoloration of the toes resolved completely. The advantages and disadvantages of the various diagnostic and therapeutic approaches to peripheral embolization are discussed.

Aged↗
PubMed1992

Antiarrhythmic drug therapy and cardiac mortality in atrial fibrillation. The Stroke Prevention in Atrial Fibrillation Investigators.

BACKGROUND AND OBJECTIVES: The relation between cardiac mortality and antiarrhythmic drug administration has not been fully determined. This relation was analyzed in 1,330 patients enrolled in the Stroke Prevention in Atrial Fibrillation Study, a randomized clinical trial comparing warfarin, aspirin and placebo for the prevention of ischemic stroke or systemic embolism in patients with nonvalvular atrial fibrillation. METHODS: Patients who received antiarrhythmic drug therapy for atrial fibrillation in this study were compared with patients not receiving antiarrhythmic agents. The relative risk of cardiac mortality, including arrhythmic death, in patients receiving antiarrhythmic drug therapy was determined and adjusted for other cardiac risk factors. RESULTS: In patients receiving antiarrhythmic drug therapy, cardiac mortality was increased 2.5-fold (p = 0.006, 95% confidence interval [CI] 1.3 to 4.9) and arrhythmic death was increased 2.6-fold (p = 0.02, 95% CI 1.2 to 5.6). Among patients with a history of congestive heart failure, those given antiarrhythmic medications had a relative risk of cardiac death of 4.7 (p less than 0.001, 95% CI 1.9 to 11.6) compared with that of patients not so treated; the relative risk of arrhythmic death in the treated group was 3.7 (p = 0.01, 95% CI 1.3 to 10.4). Patients without a history of congestive heart failure had no increased risk of cardiac mortality (relative risk 0.70, 95% CI 0.2 to 3.1) during antiarrhythmic drug therapy. After exclusion of 23 patients with documented ventricular arrhythmias and adjustment for other variables predictive of cardiac death, patients receiving antiarrhythmic drugs were not at increased risk of cardiac death or arrhythmic death. However, in patients with a history of heart failure who received antiarrhythmic drug therapy, the relative risk of cardiac death was 3.3 (p = 0.05, 95% CI 0.99 to 11.1) and that of arrhythmic death was 5.8 (p = 0.009, 95% CI 1.5 to 21.7) compared with the risk in patients not taking antiarrhythmic medications. CONCLUSIONS: Although antiarrhythmic drug therapy was not randomly determined in this trial, the data suggest that in patients with atrial fibrillation and a history of congestive heart failure, the risk of such therapy may outweigh the potential benefit of maintaining sinus rhythm.

Anti-Arrhythmia Agents↗
PubMed1992

Ambulatory monitoring of silent myocardial ischemia: what is its utility?

In patients with angina pectoris, ambulatory ST segment monitoring has documented that asymptomatic myocardial ischemic episodes occur with greater frequency than previously suspected. During such episodes, ischemia has been verified by nuclear, echocardiographic, and biochemical techniques. Painless ST segment depression is consistent with severe coronary artery disease when detected by ambulatory monitoring in patients with angina and portends a worsened prognosis in patients about to have vascular surgical procedures. On the other hand, ST depression without angina has a better prognosis than ST depression with angina during treadmill exercise testing. Silent ischemia of prolonged duration per 24-hour period suggests a poor prognosis in patients with a history of unstable angina or myocardial infarction.

Angina, Unstable↗
PubMed1991

Reversibility of blue-gray cutaneous discoloration from amiodarone.

A 45-year-old man had severe blue-gray cutaneous discoloration during amiodarone therapy for atrial fibrillation. Therefore, this drug regimen was discontinued, and long-term anticoagulation and digoxin therapy were used. The patient was advised to avoid exposure of his skin to sunlight, and a bleaching agent was prescribed. After 18 months of follow-up, the blue-gray hyperpigmentation had diminished. Although photosensitivity reactions from amiodarone occur in more than 50% of patients, blue-gray cutaneous discoloration occurs in less than 10% of patients on prolonged therapy with amiodarone. The presence of high concentrations of iodine, detected by electron probe analysis, suggests that the cutaneous deposits are amiodarone itself or a metabolite. The slow rate of elimination of amiodarone and a high uptake by fat-associated tissues may explain the delayed disappearance of cutaneous photosensitivity and late resolution of the blue-gray discoloration. Our current case supports the reversibility of these adverse effects on long-term follow-up.

Amiodarone↗
PubMed1991

Constrictive effect of serotonin on visible renal arteries: a pharmacoangiographic study in anesthetized dogs.

Serotonin (5HT) has been implicated in the pathogenesis of several arterial disorders. Experimental intrarenal infusion of 5HT has produced initial decreases, and later sustained increases in total renal blood flow in the dog, and flow limiting renal artery spasm in other species. We assessed renal angiographic responses to 5HT infused into one renal artery of nine dogs before and after treatment with indomethacin (I). On blinded assessment of arteriograms, 5HT-induced narrowing was detected (p less than 0.001), and the effect was accentuated by I (p less than 0.001). Ketanserin (K), a 5HT-2 receptor antagonist, reversed the arteriographic vasoconstrictor effect of 5HT in five I-treated dogs (p less than 0.05). Linear cortical defects and decreased contrast intensity were seen in the nephrogram phase during 5HT infusion after I. This appearance resembled the arteriographic findings in hemorrhagic shock, suggesting profound impairment of renal cortical perfusion. This study suggests that 5HT constricts visible renal arteries via interaction with the 5HT-2 receptor, and that this in vivo effect is modified by arterial synthesis of vasodilator prostaglandins in the anesthetized dog.

Angiography↗