Atrial fibrillation and stroke: new ideas, persisting dilemmas

Quantification of synchronization during atrial fibrillation by Shannon entropy: validation in patients and computer model of atrial arrhythmias

Atrial fibrillation (AF), a cardiac arrhythmia classically described as completely desynchronized, is now known to show a certain amount of synchronized electrical activity. In the present work a new method for quantifying the level of synchronization of the electrical activity recorded in pairs of atrial sites during atrial fibrillation is presented. A synchronization index (Sy) was defined by quantifying the degree of complexity of the distribution of the time delays between sites by Shannon entropy estimation. The capability of Sy to discriminate different AF types in patients was assessed on a database of 60 pairs of endocardial recordings from a multipolar basket catheter. The analysis showed a progressive and significant decrease of Sy with increasing AF complexity classes as defined by Wells (AF type I Sy = 0.73 +/- 0.07, type II Sy = 0.56 +/- 0.07, type III Sy = 0.36 +/- 0.04, p < 0.001). The extension of Sy calculation to the whole right atrium showed the existence of spatial heterogeneities in the synchronization level. Moreover, experiments simulated by a computer model of atrial arrhythmias showed that propagation patterns with different complexity could be the basis of different synchronization levels found in patients. In conclusion the quantification of synchronization by Shannon entropy estimation of time delay dispersion may facilitate the identification of different propagation patterns associated with AF, thus enhancing our understanding of AF mechanisms and helping in its treatment.

Video-assisted bilateral pulmonary vein isolation and left atrial appendage exclusion for atrial fibrillation

OBJECTIVE

Pulmonary vein isolation is curative in selected patients with atrial fibrillation. The objective of this study was to assess the feasibility and safety (midterm results) of video-assisted thoracoscopic epicardial pulmonary vein isolation.

METHODS

Twenty-seven patients (22 male patients) with atrial fibrillation (18 paroxysmal, 4 persistent, and 5 permanent; average age, 57 years) underwent bilateral video-assisted thoracoscopic off-pump epicardial pulmonary vein isolation and exclusion of the left atrial appendage. All patients had had unsuccessful drug therapy or were intolerant to antiarrhythmic drug therapy or were intolerant to warfarin. The approach included two 10-mm ports and one 5-cm working port (non-rib spreading) bilaterally. Pulmonary vein isolation was achieved bilaterally by using a bipolar radiofrequency device. The left atrial appendage was excised with a surgical stapler.

RESULTS

Bilateral pulmonary vein isolation and left atrial appendage excision was performed successfully in all patients. There were no conversions to sternotomy or thoracotomy. All patients were extubated in the operating room. Postoperative complications in 3 patients were minor and resolved within 48 hours. One morbidly obese patient had more serious complications related to comorbid conditions. Average postoperative follow-up is approximately 6 months (173.6 days). Twenty-three patients have been followed up for greater than 3 months, and 21 of these patients are free of atrial fibrillation (91.3%). The results of magnetic resonance angiography were normal (no pulmonary vein stenosis) in 12 of 12 patients evaluated 3 to 6 months postoperatively.

CONCLUSIONS

Bilateral video-assisted thoracoscopic pulmonary vein isolation with excision of the left atrial appendage is feasible and safe and offers a promising, new, minimally invasive, beating-heart approach for curative surgical treatment of atrial fibrillation.

Prevalence and Clinical Significance of Left Atrial Remodeling in Competitive Athletes

OBJECTIVES

In the present study we assessed the distribution and clinical significance of left atrial (LA) size in the context of athlete's heart and the differential diagnosis from structural heart disease, as well as the proclivity to supraventricular arrhythmias.

BACKGROUND

The prevalence, clinical significance, and long-term arrhythmic consequences of LA enlargement in competitive athletes are unresolved.

METHODS

We assessed LA dimension and the prevalence of supraventricular tachyarrhythmias in 1,777 competitive athletes (71% of whom were males), free of structural cardiovascular disease, that were participating in 38 different sports.

RESULTS

The LA dimension was 23 to 50 mm (mean, 37 +/- 4 mm) in men and 20 to 46 mm (mean, 32 +/- 4 mm) in women and was enlarged (i.e., transverse dimension > or = 40 mm) in 347 athletes (20%), including 38 (2%) with marked dilation (> or = 45 mm). Of the 1,777 athletes, only 14 (0.8%) had documented, symptomatic episodes of either paroxysmal atrial fibrillation (n = 5; 0.3%) or supraventricular tachycardia (n = 9; 0.5%), which together occurred in a similar proportion in athletes with (0.9%) or without (0.8%; p = NS) LA enlargement. Multivariate regression analysis showed LA enlargement in athletes was largely explained by left ventricular cavity enlargement (R2 = 0.53) and participation in dynamic sports (such as cycling, rowing/canoeing) but minimally by body size.

CONCLUSIONS

In a large population of highly trained athletes, enlarged LA dimension > or = 40 mm was relatively common (20%), with the upper limits of 45 mm in women and 50 mm in men distinguishing physiologic cardiac remodeling ("athlete's heart") from pathologic cardiac conditions. Atrial fibrillation and other supraventricular tachyarrhythmias proved to be uncommon (prevalence < 1%) and similar to that in the general population, despite the frequency of LA enlargement. Left atrial remodeling in competitive athletes may be regarded as a physiologic adaptation to exercise conditioning, largely without adverse clinical consequences.

The Modern Management of Minimally Symptomatic Atrial Fibrillation in the Post-AFFIRM Era

Atrial fibrillation is the most common cardiac arrhythmia and presents a unique management challenge for the physician. Given the variability of clinical presentation as well as the variability of clinical sequelae, no single approach meets all patients' needs. This challenging arrhythmia has recently been reviewed in the American College of Cardiology/American Heart Association/European Society of Cardiology guidelines. This comprehensive document goes a long way toward organizing clinical treatment approaches. However, new information gathered in the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) trial further helps the clinician with clinical assessment. Together, these major documents are invaluable to the clinician and provide a rational basis on which to make clinical decisions.

Factor V Leiden mutation and its relation to left atrial thrombus in chronic nonrheumatic atrial fibrillation

The genetic defect of coagulation factor V, known as factor V Leiden, produces a resistance to degradation by activated protein C and increased venous thrombosis. However, the role of factor V Leiden in the formation of left atrial thrombus with nonrheumatic atrial fibrillation has not been studied. We investigated whether factor V Leiden is a risk factor for left atrial thrombus in patients with nonrheumatic atrial fibrillation. We analyzed clinical, echocardiographic, and biochemical data in 105 consecutive patients with nonrheumatic atrial fibrillation. These patients were divided into two groups: group A (n = 37) with left atrial thrombus and group B (n = 68) without left atrial thrombus. The study also included 42 control subjects. Left atrial thrombus was investigated by using both transthoracic echocardiography and transesophageal echocardiography. Blood samples from the patients and controls were analyzed for the factor V Leiden mutation by DNA analysis, using the polymerase chain reaction. There was no significant difference in the prevalence of factor V Leiden between the patients and control subjects. The prevalence of factor V Leiden mutation was 8.1% (3/37) in patients with left atrial thrombus, and 8.8% (6/68) in patients without left atrial thrombus. The prevalence of factor V Leiden was 7.1% (3/42) in control subjects. The prevalance of factor V Leiden was 10% (2/20) in patients with spontaneous echo contrast and 8% (7/85) in patients without spontaneous echo contrast. Multivariate analyses showed that left ventricular ejection fraction was an independent predictor of left atrial thrombus. Factor V Leiden mutation is not a risk factor for left atrial thrombus formation and spontaneous echo contrast in patients with nonrheumatic atrial fibrillation.

Cardioembolic stroke: an update

Cardioembolic stroke accounts for approximately 15% of all strokes and is thought to be one of the more preventable types of strokes. Features that have been reported to support cardioembolism as a mechanism for ischemic stroke have included documented cardiac source of embolism, maximal neurologic deficit at onset, multiple cerebrovascular territories involved, enhanced tendency toward hemorrhagic transformation, enhanced risk of syncope or seizure associated with presentation, and lower likelihood of premonitory transient ischemic attacks. Features that tend to make cardioembolic stroke less likely include significant cerebral atherosclerosis, step-wise progression of the neurologic deficit within a finite period of time, vascular distribution such as entire internal carotid artery territory with combined middle cerebral artery and anterior cerebral artery involvement or watershed distribution, and premonitory transient ischemic attacks. A number of cardiac conditions can promote thromboembolism, and there is risk stratification reflective of the specific condition or coexistent conditions. Anticoagulant therapy generally has been found to be the most effective means of preventing cardiogenic brain embolism, but the intensity of anticoagulation needs to be optimized to reflect the risk-to-benefit ratio for the particular patient.

A method for quantifying atrial fibrillation organization based on wave-morphology similarity

A new method for quantifying the organization of single bipolar electrograms recorded in the human atria during atrial fibrillation (AF) is presented. The algorithm relies on the comparison between pairs of local activation waves (LAWs) to estimate their morphological similarity, and returns a regularity index (rho) which measures the extent of repetitiveness over time of the detected activations. The database consisted of endocardial data from a multipolar basket catheter during AF and intraatrial recordings during atrial flutter. The index showed maximum regularity (rho = 1) for all atrial flutter episodes and decreased significantly when increasing AF complexity as defined by Wells (type I: rho = 0.75 +/- 0.23; type II: rho = 0.35 +/- 0.11; type III: rho = 0.15 +/- 0.08; P < 0.01). The ability to distinguish different AF episodes was assessed by designing a classification scheme based on a minimum distance analysis, obtaining an accuracy of 85.5%. The algorithm was able to discriminate among AF types even in presence of few depolarizations as no significant rho changes were observed by reducing the signal length down to include five LAWs. Finally, the capability to detect transient instances of AF complexity and to map the local regularity over the atrial surface was addressed by the dynamic and multisite evaluation of rho, suggesting that our algorithm could improve the understanding of AF mechanisms and become useful for its clinical treatment.

Oral loading with propafenone for conversion of recent-onset atrial fibrillation: a review on in-hospital treatment

Atrial fibrillation (AF) is a very common arrhythmia. In order to treat acute AF rapidly, effective drug regimens are required. Propafenone is a class IC antiarrhythmic agent that is suitable for oral loading as it reaches peak plasma concentrations within 2 to 4 hours of administration. The use of propafenone loading in patients with AF must be based on appropriate patient selection in view of the negative inotropic effect and the potential proarrhythmic effects of the drug. A series of controlled trials in patients with recent-onset AF without heart failure who were hospitalised with enforced bed rest has shown that orally loaded propafenone (450 to 600 mg as single dose) exerts a relatively quick effect (within 3 to 4 hours) and a high rate of efficacy (72 to 78% within 8 hours). A potentially harmful effect of class IC agents is the risk of transforming AF into atrial flutter (3.5 to 5% of patients). However, atrial flutter with 1 : 1 atrioventricular response was observed in only two of 709 patients receiving propafenone (0.3% incidence). Nevertheless, the potential negative inotropic effect of propafenone demands careful patient selection, with systematic exclusion of patients with left ventricular dysfunction or congestive heart failure. Oral loading with propafenone can be considered as an episodic treatment in patients with AF recurrences, as has been proposed for other drugs in the past. However, the safety of oral loading with propafenone as an outpatient treatment in appropriately selected patients has to be assessed by appropriately designed prospective studies.

Effect of low-intensity warfarin therapy on left atrial thrombus resolution in patients with nonvalvular atrial fibrillation: a transesophageal echocardiographic study

The presence of left atrial thrombus (LAT) is associated with an increased risk of embolic stroke. However, it has yet to be established definitively whether low-intensity warfarin therapy (INR: 1.5-2.0) can prevent LAT formation in patients with nonvalvular atrial fibrillation (NVAF). The present study analyzed the clinical and transesophageal echocardiography (TEE) features of 123 such patients to identify risk factors for LAT formation and the efficacy of prophylactic low-intensity warfarin therapy. Left atrial thrombi were found in 35 patients (28%) in whom systemic hypertension (49% vs 23%; p<0.01) and ischemic heart disease (17% vs 3%; p<0.01) were more frequent. Left ventricular ejection fraction (54+/-14% vs 60+/-11%; p<0.05), left ventricular end-diastolic dimension (51+/-7 mm vs 48+/-5 mm; p<0.05), spontaneous echo contrast (2.2+/-0.7 vs 1.4+/-0.9; p<0.01), left atrial diameter (50+/-6 mm vs 43+/-7 mm; p<0.01), left atrial appendage blood velocity (22.3+/-8.7 cm/s vs 37.2+/-21.5 cm/s; p<0.01) and the incidence of left ventricular hypertrophy (37% vs 15%; p<0.01) were also significantly different between the groups. Fourteen patients received continuous warfarin therapy (target INR: 1.5-2.0) and on the follow-up TEE study the left atrial thrombus resolved in 10 (71%). There were no thromboembolic events or major hemorrhagic complications in these patients, so it was concluded that low-intensity warfarin therapy is efficacious in treating LAT formation in patients with NVAF.

Association of atrial fibrillation and aortic atherosclerosis: a population-based study

OBJECTIVE

To examine the association between atrial fibrillation (AF) and aortic atherosclerosis in the general population.

SUBJECTS AND METHODS

Transesophageal echocardiography was performed in 581 subjects, a random sample of the adult Olmsted County, Minnesota, population (45 years of age or older) participating in the Stroke Prevention: Assessment of Risk in a Community (SPARC) study. The frequency of aortic atherosclerosis was determined in 42 subjects with AF and compared with that in 539 subjects without AF (non-AF group).

RESULTS

Subjects with AF were significantly older than non-AF subjects (mean +/- SD age, 82+/-10 vs 66+/-13 years, respectively; P<.001) and more commonly had hypertension (28 [66.7%] vs 288 [53.4%], respectively; P=.10). The 2 groups were similar in sex and frequency of diabetes mellitus, hyperlipidemia, or smoking history (P>.10). The odds of aortic atherosclerosis (of any degree) were 2.87 times greater (95% confidence interval [CI], 1.41-5.83; P=.004) and the odds of complex atherosclerosis (protruding atheroma >4 mm thick, mobile debris, or plaque ulceration) were 2.71 times greater (CI, 1.13-6.53; P=.03) in the AF group than in the non-AF group. Age was a significant predictor of aortic atherosclerosis (P<.001). After adjusting for age, the odds of atherosclerosis and complex atherosclerosis were not significantly different between the 2 groups (P=.13 and P=.75, respectively).

CONCLUSIONS

In the general population, AF is associated with aortic atherosclerosis, including complex atherosclerosis. This association is related to age since both AF and aortic atherosclerosis are more frequent in the elderly population.

Association of follow-up change of left atrial appendage blood flow velocity with spontaneous echo contrast in nonrheumatic atrial fibrillation

STUDY OBJECTIVES

To evaluate the time-related change of left atrial (LA) appendage flow velocity in chronic atrial fibrillation (AF) by follow-up transesophageal echocardiography (TEE) and to investigate its association with the occurrence of LA spontaneous echo contrast.

DESIGN

Prospective follow-up study.

SETTING

University-based, tertiary referral medical center.

PATIENTS

Forty-seven patients with chronic nonrheumatic AF.

INTERVENTIONS

All studied patients underwent both a baseline and follow-up TEE during a mean period of 13 +/- 7 months.

MEASUREMENTS AND RESULTS

Baseline TEE revealed that LA spontaneous echo contrast was present in 28 patients (group 1) and was absent in 19 patients (group 2). The LA appendage flow velocity profiles at baseline were significantly lower in group 1 than in group 2; on follow-up, the appendage flow velocities decreased significantly in group 2, but were not significantly changed in group 1. Follow-up TEE revealed that spontaneous echo contrast was persistent in all group 1 patients. In group 2, LA spontaneous echo contrast was newly observed in 9 patients (group 2A) but was persistently absent in 10 patients (group 2B). In group 2A, all of the LA appendage flow velocity profiles decreased significantly at the follow-up study. In group 2B, however, only LA appendage inflow velocity integral showed significant decrease on follow-up; there were no significant changes in LA appendage outflow velocity indexes and peak inflow velocity.

CONCLUSIONS

LA appendage flow velocity may decrease with time in some patients with AF, and this change is associated with a new occurrence of LA spontaneous echo contrast. For patients without LA spontaneous echo contrast, serial follow-up of the LA appendage flow velocity profiles may be useful for predicting future development of spontaneous echo contrast. Once LA spontaneous echo contrast occurs in AF patients, it tends to persist with time and the LA appendage is usually under a persistently low flow state.

Bileaflet mechanical prostheses performance in mitral position

OBJECTIVE

The experience with the Carbomedics (CM) and the St. Jude Medical (SJM) bileaflet mechanical prostheses was evaluated to determine thromboembolic and hemorrhagic complications and predictive risk factors.

METHODS

From 1989 to 1994, a total of 625 patients had mitral valve replacement (CM, 240; SJM, 385); 32.5% (203), concomitant procedures and 32.8% (205), previous cardiac surgery, primarily valve replacement procedures.

RESULTS

The pre-operative variables did not distinguish the populations, except for previous surgery CM 37.9% and SJM 29.6% (P < 0.05). The pre-operative variables (type of prostheses, cardiac rhythm, coronary artery bypass, NYHA III/IV, advancing age, gender, urgency status and previous surgery) were not predictive of overall thromboembolism (TE), major TE, minor TE, prosthesis thrombosis and hemorrhage (P not significant; P = NS). The linearized rate of total TE events for overall MVR was 5.0%/patient-year (CM 4.4; SJM 5.4). The < or = 30 day major crude rate was 0.44%, while the > 30 day late major event rate was 2.0%/patient-year. Of the total TE events 91% of < or = 30 days and 75%, > 30 days had an INR < 2.5 at or immediately prior to the event. The thrombosis rate (included in TE events) was 0.63%/patient-year (ten events, four managed successfully with thrombolysis, five successfully with reoperation, and one fatality identified at autopsy). The freedom, at 5 years, from major/fatal TE, thrombosis and hemorrhage from anticoagulation was 88.2%, and 89.5% exclusive of early events.

CONCLUSIONS

This non-randomized prospective observational evaluation of the CarboMedics and St. Jude Medical prostheses has not revealed any differentiation in performance of the prostheses. The study serves as a single institution experience with the potential for future comparative evaluation.

[The etiology and associated risk factors in a sample of 300 patients with atrial fibrillation]

PURPOSE

To analyze the etiology and the prevalence of risk factors in patients with atrial fibrillation.

PATIENTS AND METHODS

Applying an unpaired case controlled study, we examined 300 consecutive patients (143 men) with atrial fibrillation and a mean age of 66 +/- 8 years. This group is compared with a control group of 700 patients (mean age 64 +/- 12 years).

RESULTS

In the group with atrial fibrillation the etiology in 32% was arterial hypertension, in 20% coronary heart disease, in 13% valvular heart disease, in 11% heart failure, in 4% hyperthyroidism and in 20% idiopathic. 50% presented hypertension, 29% tobaccoism, 26% left ventricular hypertrophy, 20% consumption of alcohol, 19% hypercholesterolemia and 16% diabetes. Compared with the control group, patients with atrial fibrillation had coronary heart disease (p < 0.05), VHD (p < 0.01), myocardiopathy (p < 0.05), HT (p < 0.001), left ventricular hypertrophy (p < 0.001), diabetes (p < 0.01) and alcohol consumption (p < 0.01) more frequently. In the multivariant analysis heart failure (odds ratio 2.1 [1.2-3.3]), the valvular heart disease (odds ratio 2.2 [1.4-3.5]), the coronary heart disease (odds ratio 1.8 [1.2-2.6]), the arterial hypertension (odds ratio 1.7 [1.2-2.3]), the left ventricular hypertrophy (odds ratio 2.6 [1.7-3.8]), the diabetes (odds ratio 1.9 [1.2-2.9]) and alcoholic habits (odds ratio 2 [1.3-3.9]) were independent risk factors for atrial fibrillation in our population.

CONCLUSIONS

Atrial fibrillation in our study, is more frequent in patients with arterial hypertension, coronary heart disease or valvular heart disease. There are other risk factors such as arterial hypertension, diabetes and consumption of alcohol too, the modification of which could diminish the risk of the appearance of atrial fibrillation.

A high-temporal resolution algorithm for quantifying organization during atrial fibrillation

Atrial fibrillation (AF) has been described as a "random" or "chaotic" rhythm. Evidence suggests that AF may have transient episodes of temporal and spatial organization. We introduce a new algorithm that quantifies AF organization by the mean-squared error (MSE) in the linear prediction between two cardiac electrograms. This algorithm calculates organization at a finer temporal resolution. (approximately 300 ms) than previously published algorithms. Using canine atrial epicardial mapping data, we verified that the MSE algorithm showed nonfibrillatory rhythms to be significantly more organized than fibrillatory rhythms (p < .00001). Further, we compared the sensitivity of MSE to that of two previously published algorithms by analyzing AF with simulated noise and AF manipulated with vagal stimulation or by adenosine administration to alter the character of the AF. MSE performed favorably in the presence of noise. While all three algorithms distinguished between low and high vagal AF, MSE was the most sensitive in its discrimination. Only MSE could distinguish baseline AF from AF with adenosine. We conclude that our algorithm can distinguish different levels of organization during AF with a greater temporal resolution and sensitivity than previously described algorithms. This algorithm could lead to new ways of analyzing and understanding AF as well as improved techniques in AF therapy.

Left atrial diameter in nonvalvular atrial fibrillation: An echocardiographic study. Stroke Prevention in Atrial Fibrillation Investigators

BACKGROUND

The left atrium (LA) is usually enlarged in patients with nonvalvular atrial fibrillation (AF), but factors associated with LA diameter are incompletely defined.

METHODS AND RESULTS

This transthoracic echocardiographic cohort study includes 3465 participants with nonvalvular AF in 3 multicenter clinical trials. LA diameter determined by M-mode echocardiography was correlated with clinical and echocardiographic features by cross-sectional multivariate regression analyses. The mean LA diameter was 47 +/- 8 mm, on average 6 mm larger in those with AF at the time of echocardiography than in those with sinus rhythm (48 vs 42 mm, P <. 001). Patient age and body weight were independently predictive of LA diameter (P <.0001), but sex, body surface area, and body mass index were not. The estimated independent contribution of atrial rhythm to LA diameter was approximately 2.5 mm. Prolonged duration of AF, left ventricular dilatation and increased muscle mass, mitral regurgitation, annular calcification, and hypertension were additional independent predictors of LA diameter.

CONCLUSIONS

Multiple factors appear to contribute to LA enlargement in patients with nonvalvular AF, including the presence and persistence of the dysrhythmia.

Atrial fibrillation in the elderly

Atrial fibrillation is the most common sustained arrhythmia seen in clinical practice. Although it occurs in any age patients, its frequency increases with age and is very common in the elderly. Atrial fibrillation causes substantial symptoms and morbidity and is an important cause of thromboembolism and stroke. The two approaches for therapy in those patients with intermittent or persistent atrial fibrillation are (1) maintenance of sinus rhythm with an antiarrhythmic drug or nonpharmacologic therapy, and (2) maintenance of atrial fibrillation with rate control. At the present time there are no data about the best approach and therapy must therefore be individualized.

Long-term antithrombotic treatment for atrial fibrillation

Nonvalvular atrial fibrillation (AF) is the most common cardiac disorder causing stroke and systemic emboli. Recent clinical trials have clearly demonstrated the effects of antithrombotic treatment in preventing these devastating complications of AF. This review summarizes the salient findings of the first 5 published studies the Atrial Fibrillation, Aspirin, Anticoagulation Study (AFASAK) from Copenhagen, Denmark; the Boston Area Anticoagulation Trial for Atrial Fibrillation (BATAFF); the Canadian Atrial Fibrillation Anticoagulation study (CAFA); the Stroke Prevention in Non-rheumatic Atrial Fibrillation (SPINAF) study; and the Stroke Prevention in Atrial Fibrillation study (SPAF I) from the United States. These trials emphasize the unequivocal benefits of warfarin therapy compared with no treatment. SPAF II showed that aspirin is quite effective in younger patients (<75 years) who have no risk factors. The European Atrial Fibrillation Trial (EAFT) and SPAF III demonstrated that in older patients (>75 years) who had associated risk factors, warfarin therapy at the target international normalized ratio (INR) of 2-3, is the best treatment; however, a combination of low intensity fixed-dose warfarin and aspirin is ineffective. Thus, the guidelines recommended by the American College of Chest Physicians should be followed in treating patients with AF.

Relation of left atrial spontaneous echo contrast with prethrombotic state in atrial fibrillation associated with systemic hypertension, idiopathic dilated cardiomyopathy, or no identifiable cause (lone)

To investigate the association of left atrial (LA) spontaneous echo contrast with the hemostatic state in nonrheumatic atrial fibrillation (AF), we examined the plasma levels of prothrombin fragment 1+2 and fibrinopeptide A in 73 patients with chronic nonrheumatic AF undergoing transesophageal echocardiography and 38 age-matched normal subjects. The results support the theory that LA spontaneous echo contrast in nonrheumatic AF is associated with a hypercoagulable state, especially in patients with marked LA spontaneous echo contrast.

Stroke prevention and intervention. New options for improved outcomes

Data from recent clinical studies have replaced the empiricism that once pervaded the medical literature regarding stroke. This has created exciting opportunities for optimal management as well as challenges related to the importance of early recognition and intervention. Dr Kelley reviews recent advances in prevention and treatment of stroke and describes a systematic approach that directly affects choice of diagnostic tests and therapeutic options.

Primary stroke prevention in nonvalvular atrial fibrillation: implementing the clinical trial findings

OBJECTIVE

To review the clinical trials evaluating warfarin for primary stroke prophylaxis in nonvalvular atrial fibrillation (NVAF), to discuss the relative benefits and risks of warfarin versus aspirin therapy, and to review the clinical practice guidelines and identify potential barriers to their implementation in clinical practice.

DATA SOURCES

A MEDLINE literature search was performed to identify clinical trials of antithrombotic therapy for NVAF, clinical practice guidelines, studies evaluating physician practices and attitudes, cost-effectiveness studies, and pertinent review articles. Key search terms included atrial fibrillation, stroke, antithrombotic, warfarin, aspirin, and cost-effectiveness.

DATA EXTRACTION

Prospective, randomized clinical trials were selected for analysis. Clinical practice guidelines from recognized panels of experts were reviewed. Comprehensive review articles were selected.

DATA SYNTHESIS

NVAF is a common arrhythmia that is associated with a substantial risk for stroke. Seven prospective, randomized, clinical trials have conclusively demonstrated the efficacy of warfarin for stroke prevention. The greatest benefits are achieved in older patients and those with comorbidities that increase their risk for stroke. The potential benefits of preventing a devastating stroke, however, must be weighed against the potential for bleeding complications. Warfarin has been shown to be cost-effective in high-risk patients, provided the rate of complications is minimized. Nonetheless, many physicians remain hesitant to implement warfarin therapy in older, high-risk patients. The clinical data on aspirin are less consistent than those observed with warfarin. Aspirin appears to be most effective in younger individuals or those considered to be at low risk for stroke.

CONCLUSIONS

In patients with NVAF, the personal, social, and economic consequences of stroke are often devastating. Clinical trials have provided definitive proof that the risks of stroke can be significantly reduced through the use of appropriate antithrombotic therapy. Despite this evidence and the recommendations of a number of clinical practice guidelines, variations in care exist that continue to place patients at risk. Additional outcomes research is needed to evaluate the impact of the clinical trial findings and practice guidelines on clinical practice and to develop methods for overcoming barriers to implementation.

Is anticoagulation therapy underused in elderly patients with atrial fibrillation?

Atrial fibrillation (AF) is found in 0.4% of the adult population and is a common condition in the elderly. Its prevalence increases with age to affect 5 to 14% of those over 74 years. Recent evidence indicates that, compared with sinus rhythm, AF is associated with a 4-to 7-fold increase in the risk of stroke. However, there is strong evidence from randomised trials that full anticoagulation with warfarin substantially reduces the risk of stroke. Elderly patients are among those at higher risk and stand to gain the most from such treatment. They are also at higher risk for complications related to anticoagulant therapy and this sometimes makes clinical decisions difficult. There is a strong rationale for prescribing warfarin for all patients with AF who are over 65 years and free of contraindications. Some concerns exist about the benefit: risk ratio of warfarin in patients aged > 75 years. The answer is probably to use low intensity anticoagulant therapy (international normalised ratio 2.0 to 3.0), which is safer but no less effective than higher intensity regimens. Few data are available in the literature on physicians' attitudes to anticoagulation in elderly patients with AF. Although the results of randomised clinical trials in AF seem to suggest that anticoagulants and/or aspirin (acetylsalicylic acid) are underused in the elderly, over 90% of the patients initially screened were excluded from randomisation, making the sample highly selected. Compared with randomised controlled trials, some observational studies seem to indicate a higher likelihood of using anticoagulation and have targeted the intensity of anticoagulation according to age and clinical scenario.

Prevalence and clinical significance of left atrial thrombus in nonrheumatic atrial fibrillation

The prevalence and clinical significance of left atrial thrombus were prospectively investigated in a consecutive series of 219 patients with chronic nonrheumatic atrial fibrillation using transesophageal echocardiography. Fifteen left atrial thrombi were detected in 15 of the 219 patients (6.8%); 12 of these thrombi (80%) were confined to the left atrial appendage. Left atrial spontaneous echo contrast was visualized in 85 patients (39%). All the thrombi were found in the left atria with spontaneous echo contrast. Patients with left atrial thrombus had significantly lower left ventricular ejection fraction than those without (49 +/- 14% vs. 59 +/- 14%; P < 0.05). Multivariate analysis among clinical and transthoracic echocardiographic variables showed that left ventricular ejection fraction < 50% was the only independent predictor for the presence of left atrial thrombus. A history of thromboembolism was significantly more frequent in patients with left atrial thrombus than in those without (73% vs. 32%; P < 0.005). The presence of left atrial thrombus was more specific than spontaneous echo contrast for predicting history of thromboembolism (97% vs. 80%), but its sensitivity was significantly lower (14% vs. 73%). We conclude that: (1) Transesophageal echo-detected left atrial thrombus is not uncommon in patients with chronic nonrheumatic atrial fibrillation and is exclusively observed in those with left atrial spontaneous echo contrast. (2) Impaired left ventricular systolic function may predispose the left atrial thrombus formation. (3) Left atrial thrombus is a highly specific but insensitive predictor for thromboembolic events.

Atrioventricular junctional ablation and modification for atrial fibrillation

RF catheter ablation is a safe and extremely effective method of achieving complete A-V block in patients with difficult-to-control ventricular rates in atrial fibrillation. In selected patients, A-V junction ablation may improve exercise capacity and functional status while reducing the need for emergency care and hospitalization. Prospective, randomized studies are needed, however, to compare A-V junction ablation as a management strategy to pharmacologic therapy to control ventricular rate or to maintain sinus rhythm. Similarly, additional data are needed to assess methods of achieving A-V junction modification with the lowest risk for A-V block.

Atrial fibrillation in the elderly

The prevalence of atrial fibrillation is 11% in persons older than 70 years and rises to 17% in those aged 84 years or more. One-year mortality ranges from 0.2 to 16%, being highest in elderly patients, and is associated with a 4.8-fold increased risk of stroke. Atrial fibrillation can be cardioverted to normal sinus rhythm electrically or pharmacologically and rapid ventricular rate can be controlled with drugs. While anti-coagulation prevents embolic events in those with atrial fibrillation, the decision to anticoagulate should be based on an assessment of the risk/benefit ratio.

Current recommendations for the anticoagulation of patients with atrial fibrillation

Atrial fibrillation (AF) is the most commonly encountered cardiac rhythm disorder and is strongly associated with stroke. The risk of stroke and the benefit of anticoagulant therapy in patients with AF associated with mitral stenosis has been well accepted. Until recently the risk of stroke and the role of anticoagulant therapy in patients with nonrheumatic AF was unclear. Over the past decade studies have shown an approximate fivefold increase in the risk of stroke in patients with nonrheumatic AF. The results of large clinical trials have shown a benefit of treatment with anticoagulants and, to a lesser extent, aspirin for both the primary and secondary prevention of thromboembolic complications. Other than patients with a low risk of thromboembolic complications (primarily young patients without clinical risk factors), current guidelines recommend anticoagulation of most patients with AF. The studies that form the basis for these recommendations and the currently published guidelines are reviewed.

Clinical epidemiology of stroke

The effect of stroke as a major health issue in the United States is well established. Well-designed epidemiologic studies have contributed important information about the natural history of stroke and its associated risk factors. These cerebrovascular profiles have provided the foundation for many of the current ischemic stroke trials, but the cause and prevention of the hemorrhagic subtypes remain elusive.

Nonpharmacologic approaches to the treatment of atrial fibrillation and atrial flutter

The high prevalence of atrial fibrillation, the associated morbidity and mortality, the absence of safe and effective drug therapy, and an increased understanding of the pathophysiologic basis of atrial fibrillation and flutter have collectively led to the development of novel nonpharmacologic treatments for the management of these arrhythmias, including the CORRIDOR and MAZE surgical procedures, catheter-based ablation and modification of AV conduction, catheter-based ablation of atrial flutter and fibrillation, and internal atrial defibrillation. These surgical and catheter-based techniques offer potentially curative therapy while sparing the long-term risk of antiarrhythmic drug therapy. For patients with typical atrial flutter, catheter ablation affords to cure rate in excess of 70%. As technological innovations further facilitate identification and ablation of the critical isthmus in the floor of the right atrium, success rates should improve substantially. For patients with atrial fibrillation, AV junction ablation with implantation of a rate-responsive ventricular pacemaker should be considered palliative therapy, as should modification of AV junction conduction. The MAZE procedure offers very high cure rates, but because it currently involves open heart surgery, patient selection is critical. Catheter-based procedures emulating aspects of the MAZE procedure may one day offer cure rates comparable to those of the surgery itself, but additional research and technological development are necessary to further define and refine the minimal effective procedure, and then to facilitate the placement of contiguous, full-thickness lesions in precise three-dimensional configurations. In the interim, the implantable automatic atrial defibrillator may offer a means for rapidly restoring sinus rhythm without the risks of long-term antiarrhythmic drug therapy.

Prevalence of intraatrial thrombus in patients with atrial flutter

In summary, left atrial thrombus occurs with disproportionately high frequency in patients hospitalized with atrial flutter. Male gender and a left ventricular ejection fraction < 40% are predictors of left atrial thrombus formation in such patients.

A technique for measurement of the extent of spatial organization of atrial activation during atrial fibrillation in the intact human heart

Atrial fibrillation (AF) is a common clinical problem, associated with considerable morbidity and mortality, for which effective management strategies have yet to be devised. The absence of objective measures to guide selection of antiarrhythmic drug therapy for maintenance of sinus rhythm leaves only clinical endpoints (either beneficial or detrimental) for assessment of drug action, with occasional catastrophic consequences. As part of an attempt to provide an objective framework for the assessment of antiarrhythmic drug action on the electrophysiologic determinants of atrial fibrillation, we have developed a measure of the spatial organization of atrial activation processes during atrial fibrillation. By recording activation sequences at multiple equally spaced locations on the endocardial surface of the atria during atrial fibrillation in humans and determining the degree of correlation between these activation sequences as a function of distance, we have been able to construct spatial correlation functions for atrial activation. We have found that atrial activation remains well-correlated, independent of distance during normal sinus rhythm and atrial flutter. During atrial fibrillation, correlation decays monotonically with distance and the space-constant for this decay may be used to describe the relative spatial organization of atrial fibrillation. We provide examples of the impact of antiarrhythmic agents on the space-constant and suggest that assessment of the relative spatial organization of atrial activation using this methodology may potentially provide an objective framework to guide therapy in patients with AF.

Transesophageal echocardiographic detection of atrial thrombi in patients with nonfibrillation atrial tachyarrhythmias and congenital heart disease

OBJECTIVES

We hypothesized an association between atrial thrombi and nonfibrillation atrial tachyarrhythmias in patients with congenital heart disease.

BACKGROUND

We observed a fatal thromboembolus after direct current cardioversion in an adolescent with atrial flutter and repaired tetralogy of Fallot.

METHODS

Using transesophageal echocardiography, we prospectively studied 19 consecutive patients with congenital heart disease with nonfibrillation atrial tachyarrhythmia (atrial flutter in 18, primary atrial tachycardia in 1) undergoing electrophysiologic procedures (median age 19.6 years, range 7.0 to 53.8; 11 male, 8 female). Transthoracic echocardiograms were available for 17 patients.

RESULTS

All transesophageal examinations were performed without incident. No atrial thrombi were detected in 11 patients who subsequently had uncomplicated direct current cardioversion. Eight solitary atrial thrombi were detected (incidence 42%). Six thrombi were located in the right atrium (Fontan repair in four patients, Ebstein's malformation repair in two), and two were noted in the left atrium (congenital hypertrophic cardiomyopathy and atrial septal defect repair in one patient each). Transthoracic echocardiograms were available in seven of eight patients with thrombus detected by transesophageal echocardiography, with only one study conclusive for an atrial thrombus. Cardioversion was deferred in six of eight patients with thrombus, and anticoagulation therapy was initiated. Uncomplicated electrophysiologic procedures were conducted in two patients at the time of detection of right atrial thrombus (atrioventricular node ablation in one patient, direct current cardioversion in the other).

CONCLUSIONS

Prothrombin conditions exist in patients with congenital heart disease with nonfibrillation atrial tachyarrhythmias, as indicated by a significant incidence of transesophageally detected atrial thrombi. The need for prophylactic anticoagulation and the safety of pharmacologic or direct current cardioversion are issues that remain unresolved.

Should every patient with atrial fibrillation have the rhythm converted to sinus rhythm?

Atrial fibrillation is the most common atrial tachyarrhythmia. Consideration for the potential conversion of atrial fibrillation and the subsequent maintenance of sinus rhythm may be related to underlying pathology. Typically, extra cardiac factors such as thyroid hyperactivity help to determine initial therapy. Intrinsic cardiac factors may also influence the clinician's decision regarding potential cardioversion and maintenance of sinus rhythm. Some acute events such as pericarditis and the effects of cardiac trauma may resolve and result in spontaneous restoration of sinus rhythm. Other cardiac events such as acute myocardial infarction with or without atrial ischemia, valvular disease, and others may result in the precipitation of atrial fibrillation. The major reasons to consider cardioversion, either medically or electrically, are ventricular rate control, hemodynamic improvement, sense of well being, and the avoidance of embolism. Certain clinical situations (e.g., Wolff-Parkinson-White syndrome) require urgent restoration of sinus rhythm in light of the potential for extremely rapid ventricular rates. It has been suggested that all antiarrhythmic drug administration should be initiated in the hospital setting, but the brief period of drug administration in an inpatient setting does not protect the patient from potential, late-onset proarrhythmic events. Both antiarrhythmic drug therapy and electric cardioversion are useful for restoration of sinus rhythm in both acute and chronic atrial fibrillation. The most important negative aspect of drug conversion of atrial fibrillation may be the potential development of a proarrhythmic drug effect. Although controversial, conversion (medical or electrical) is probably indicated in every patient with the first episode of persistent atrial fibrillation, even if the patient is asymptomatic.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical implications of left atrial appendage flow patterns in nonrheumatic atrial fibrillation

Left atrial appendage (LAA) function and flow patterns in 29 patients with chronic nonrheumatic atrial fibrillation were studied by transesophageal echocardiography. These 29 patients (16 men and 13 women; mean age, 63.8 years; range, 38 to 77 years) were classified into two groups according to different LAA flow patterns. Seventeen patients (group 1) had well-defined LAA emptying and filling Doppler flow signals, and the other 12 patients (group 2) had very low LAA flow signals. No significant differences were found in age, sex, mean duration of atrial fibrillation, left ventricular end diastolic dimension, and left ventricular ejection fraction between the two groups. However, group 2 patients had larger left atrial diameter (42.8 +/- 4.2 mm vs 36.6 +/- 8.8 mm; p < 0.05), lower LAA ejection fraction (26.4 +/- 15.2 percent vs 42.6 +/- 14.1 percent; p < 0.05), and lower LAA peak emptying velocity (0.13 +/- 0.03 m/s vs 0.36 +/- 0.16 m/s; p < 0.001). Higher incidence of LAA spontaneous echocardiographic contrast formation in group 2 patients (8/12 vs 1/17; p < 0.001) was noted. In conclusion, a subset of patients with nonrheumatic atrial fibrillation were found to have lower LAA blood flow and poorer LAA function. These patients had higher incidence of left atrial or LAA spontaneous echo contrast formation which had been proved previously to be a marker for future systemic thromboembolism.

Clinical implications of left atrial appendage function: its influence on thrombus formation

This study evaluated the relation between left atrial appendage (LAA) function and LAA spontaneous echo contrast (SEC) or thrombus formation. Seventy-five patients (45 men and 30 women, aged 14-79 years) referred for transesophageal echocardiography (TEE) were examined for LAA area (maximal and minimal), LAA ejection fraction ([LAA maximal area--LAA minimal area]/LAA maximal area), LAA peak emptying velocity, and these patients were classified into three groups by different LAA blood flow patterns: Group 1--25 patients with well-defined biphasic configuration of LAA flow; Group 2--28 patients with multiphasic configuration of LAA flow; Group 3--22 patients with very low LAA blood flow and, sometimes, barely detected Doppler signal. All the 25 patients in Group 1 had a sinus rhythm during TEE study, while the other 50 patients in Groups 2 and 3 were in atrial fibrillation. The patients in Group 3 had the lowest LAA ejection fraction and the lowest peak emptying velocity of these three groups. LAA SEC was present in five of 28 patients in Group 2 and 14 of 22 patients in Group 3, but in none of 25 patients in Group 1 (P < 0.001). LAA thrombus was present in one of 25 patients in Group 1, two of 28 patients in Group 2, and seven of 22 patients in Group 3 (P < 0.05). In conclusion, this study found that patients with poor LAA function, which was represented by lower LAA ejection fraction and lower peak emptying velocity, had higher incidence of LAA SEC or thrombus formation.

Transcranial Doppler evaluation of cerebral blood flow in patients with paroxysmal atrial fibrillation

Cerebral blood flow was measured by transcranial Doppler sonography (TCD) in 15 patients during and after an attack of paroxysmal atrial fibrillation. During the attack the mean flow velocity (MFV) was reduced significantly in the middle cerebral artery (p < 0.05) and nonsignificantly in the other arteries. The pulsatility index (PI) was reduced in all the arteries but not significantly. During the fibrillation phase the MFV and PI tended to decrease as the heart rate increased. None of the patients showed clinical signs of cerebral ischemia during the attacks. The absence of such signs despite the reduced cerebral blood flow in atrial fibrillation is probably due to the activation of mechanisms of autoregulation.

Different risk factor profiles in young and elderly stroke patients with special reference to cardiac disorders

The risk factors of ischemic cerebrovascular disorders in 77 young patients (< or = 40 years) were compared to those in 138 older patients (> 40 years). The risk factor profile of patients with juvenile stroke was considerably different from that of older patients. Migrainous headache and mitral valve prolapse occurred more frequently in the younger age group, whereas hypertension, diabetes mellitus, high levels of cholesterol and triglycerides were found more often in older patients with stroke. 65% of the women under the age of 40 took oral contraceptives which compares to the baseline community value of 28% of women in childbearing age in this country. Cardiac disorders such as atrial fibrillation, left ventricular hypertrophy, coronary heart disease including a history of myocardial infarction, as well as mitral valve disease were demonstrated more often in the group of elderly patients. 7 out of 77 younger patients (9.1%), and 59 out of 138 older patients (42.8%) were considered to belong to a group with "high cardiac risk for stroke". The results of this study indicate that electrocardiographic screening is of prime importance for detecting cardiac risk factors. However, echocardiographic examination often yields additional diagnostic information, particularly in younger patients. The conflicting opinions concerning the relevance of certain risk factors for ischemic stroke could partly be explained by the fact that these risk factors are distributed unevenly depending on age.

Atrial fibrillation: epidemiology and the risk and prevention of stroke

Atrial fibrillation is a common disorder and the incidence increases with each decade of life. Previously, rheumatic mitral valve disease has been the condition most highly associated with atrial fibrillation. However, with the decreasing incidence of rheumatic heart disease, other conditions have assumed greater importance and now congestive cardiac failure, coronary artery disease, and hypertension are the most commonly associated conditions. Nonrheumatic atrial fibrillation is associated with an approximately five-fold increase in the risk of ischemic stroke and a 5% to 7% yearly risk that increases with age. In addition, atrial fibrillation is associated with an increased incidence of silent cerebral infarction and increased mortality. However, whether atrial fibrillation is independently associated with the risk of stroke or is a marker of underlying cardiac disease is contentious. Until recently, the use of preventive therapy has been controversial. However, data from four recently published, prospective randomized studies clearly support the use of warfarin prophylaxis in nonrheumatic atrial fibrillation. Within the diverse group of patients with nonrheumatic atrial fibrillation there are high and low risk subgroups and identification of these may influence decisions regarding antithrombotic prophylaxis. With a few exceptions, however, this remains an area in which there are contradictory findings in the literature. The role of aspirin for prophylaxis in nonrheumatic atrial fibrillation remains unclear and further evaluation awaits the publication of ongoing studies.

Clinical implications of left atrial spontaneous echo contrast in nonrheumatic atrial fibrillation

The prevalence and clinical significance of left atrial (LA) spontaneous echo contrast were investigated in 103 consecutive patients with chronic nonrheumatic atrial fibrillation (AF) using transesophageal echocardiography. LA spontaneous echo contrast was visualized in 25 of 103 patients (24.3%). Age, sex, LA diameter, left ventricular diastolic and systolic dimensions, left ventricular ejection fraction, and the percentage of lone AF were not significantly different between patients with and without LA spontaneous echo contrast; however, those with LA spontaneous echo contrast were less likely to have moderate or severe mitral regurgitation. LA thrombi were observed in 7 patients (6.8%), and all 7 thrombi were found in the atria with spontaneous echo contrast. History of cerebral ischemia or peripheral embolism, or both, was significantly more frequent in patients with than without LA spontaneous echo contrast (84 vs 18%; p less than 0.001). The presence of LA spontaneous echo contrast was highly specific (94%) and predictive for thromboembolic events (positive and negative predictive values of 84 and 82%, respectively). Thus, transesophageal echo-detected LA spontaneous echo contrast is frequently found in patients with chronic nonrheumatic AF. This phenomenon may represent a precursor of thrombus formation, and its presence is associated with an increased thromboembolic risk.