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  •    Atrial fibrillatory Rate does not Increase the Risk of Stroke in Patients with Atrial Fibrillation
    Raj Guda, MD (JAFIB- News Bureau)

    Atrial fibrillation is the most common cardiac arrhythmia that affects more than 10 million people across the world. Atrial fibrillation [AF] is an important risk factor for stroke and adds significant morbidity to the affected patients. Evaluating the risk of stroke and appropriate treatment with antiplatelet and Warfarin have become standard of care in patients with AF

    The most commonly identified risk factors known to cause stroke in patients with AF are congestive heart failure, hypertension, age of over 75, diabetes, and prior history of stroke or transient ischemic attack [CHADS2]. In addition to these, some other non clinical parameters like reduced left atrial appendage [LAA] flow velocity and occurrence of spontaneous echocardiographic contrast [SEC] were known to influence the incidence of stroke in this group of patients. Prior studies that assessed the impact of atrial fibrillatory wave amplitude on the LAA flow velocity, thrombus formation and risk of stroke were inconclusive.

    Some of the recent studies have also demonstrated a possible relation between the Atrial fibrillatory rate and the left atrial appendage flow velocity. These findings have generated interest among the researchers to find out the importance of the atrial fibrillatory rate in predicting the future incidence of stroke among AF patients. Recently Andreas Bollman from the Department of Cardiology in Lund University, Sweden studied patients for relation between atrial fibrillatory rate and stroke (Andreas Bollmann, Daniela Husser, Arne Lindgren, Martin Stridh et al  Atrial fibrillatory rate and risk of stroke in atrial fibrillation Europace (2009) 11, 582–586)

    The digital EKG’s of patients with embolic stroke who had AF(group-1)  were studied and compared with those of patients with AF  and no stroke (group-2). Group-1 comprised of 79 consecutive patients aged more than or equal to 65 with persistent non valvular AF who were admitted to that institution. The patients in both the groups were matched for age, gender and CHADS2 score. The atrial fibrillatory rate was determined from EKG readings in lead v1.After high-pass filtering to remove baseline wander; atrial fibrillatory activity was extracted in lead v1. Frequencies were converted to fibrillatory rates with its unit fps (rate=frequency x60). Mean fibrillatory rate (in fpm) defined as an average of instantaneous fibrillatory rate over the 10s ECG segment was determined.
         
    The study has not found any significant difference in the atrial fibrillatory rate between the patients with stroke and controls. One of the interesting outcomes of this study was the inverse correlation between the age of the patients and the atrial fibrillatory rate.  When analysing patients and controls together, there was an inverse correlation between fibrillatory rate and age. Individuals aged 85 years and more had a significantly lower fibrillatory rate than individuals aged 65–74 years and individuals aged 75– 84 years. In those subgroups, fibrillatory rates were, however, also similar in patients and controls. This change in atrial fibrillatory rate and LAA flow velocity is thought to be related to ageing mediated structural change in the cardiac muscle. Increased deposition of fat, collagen, and amyloid in atrial tissue is observed in eighth decade.

    Though this study did not find any correlation between the atrial fibrillatory rate and the stroke incidence, it was an attempt to find the role of EKG variables in determining the stroke incidence in AF patients. More than the rate, the mere presence of prolonged episodes of AF increases the risk of stroke in these patients. Clinicians should routinely try to incorporate CHADS2 in their armamentarium for risk stratification of stroke while treating patients with AF

    References

    1. Fuster V, Ryden LE, Cannom DS, Crijns HJ, Curtis AB, Ellenbogen KA et al. ACC/AHA/ESC 2006 Guidelines for the Management of Patients With Atrial Fibrillation— Executive Summary. A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Revise the 2001 Guidelines for the Management of Patients With Atrial Fibrillation).Circulation 2006;114:e257–354.

    2. Mugge A, Kuhn H, Nikutta P, Grote J, Lopez JA, Daniel WG. Assessment of left atrial appendage function by biplane transesophageal echocardiography in patients with nonrheumatic atrial fibrillation: identification of a subgroup of patients at increased embolic risk. J Am Coll Cardiol 1994;23:599–607.

    3. Li YH, Hwang JJ, Tseng YZ, Kuan P, Lien WP. Clinical significance of fibrillatory wave amplitude—a clue to left atrial appendage function in nonrheumatic atrial fibrillation. Chest 1995;108:359–63.

    4. Yamamoto S, Suwa M, Ito T, Murakami S, Umeda T, Tokaji Y et al. Comparison of frequency of thromboembolic events and echocardiographic findings in patients with chronic nonvalvular atrial fibrillation and coarse versus fine electrocardiographic fibrillatory waves. Am J Cardiol 2005;96:408–11.

    5. Blackshear JL, Safford RE, Pearce LA. F-amplitude, left atrial appendage velocity, and thromboembolic risk in nonrheumatic atrial fibrillation. Stroke Prevention in Atrial Fibrillation Investigators. Clin Cardiol 1996;19:309–13.

    6. Bollmann A, Husser D, Mainardi L, Lombardi F, Langley P, Murray A et al. Analysis of surface electrocardiograms in atrial fibrillation: techniques, research, and clinical applications. Europace 2006;8:911–26.


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