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  •    Markers of autonomic dysfunction can predict new onset AF after acute MI
    Anand Deshmukh M.D., Creighton University, Omaha, NE.

    Risk on new onset atrial fibrillation (AF) is thought to be multifactorial including due to structural and neurohormonal changes in the myocardium. Electrophysiological test measuring various properties of the atrium have a role to play in the detection of patients at high risk for the development of AF.

    Jons et al. studied the risk of new onset AF using various electrophysiological parameters in 271 patients surviving acute myocardial infarction (MI) and left ventricular ejection (LVEF) ? 40 % that were enrolled in the original Cardiac Arrhythmias Risk Stratification After Myocardial Infarction (CARISMA) study. Echocardiograms were performed at baseline and at 6 weeks post MI. Implantable Loop Recorder (ILR) was implanted within 21 days of MI and interrogated at regular intervals for 2 years to detect AF episodes. Twenty-four hour Holter monitoring was performed to assess measures of heart rate variability (HRV) and heart rate turbulence (HRT). Programmed electrophysiological stimulation was performed 6 weeks post MI to assess basic intervals and inducibility of AF. Bruce protocol stress test was performed 6 weeks post MI.

    Of the study population, 101 (37%) patients developed new onset AF. Patients with AF were older, with higher incidence of chronic obstructive pulmonary disease, ? 2 NYHA class heart failure symptoms and lower incidence of percutaneous coronary intervention. The highest predictive values for predicting new onset AF were obtained using HRV and HRT at Holter monitoring. A turbulence slope of ? 2.5 ms/RR, the lower tertile of the low-frequency power (LFIn) < 4.60 and lower tertile of the short term scaling exponential from fractal HRV analysis (DFA 1 < 1.0) were consistently associated with increased risk of AF at baseline and 6 weeks even after adjustment for the important baseline covariates. Risk score by using these parameters had incremental predictive value in development of AF. Thus, in patients with acute MI and left ventricular systolic dysfunction, new onset AF is associated with an altered autonomic regulation reflected in electrophysiologic parameters that can predict its risk.

    Even though this study is novel in identifying new predictors for development of AF after acute MI, its clinical significance is questionable due to short duration of atrial fibrillation (16 beats) used to identify new onset AF. AF duration lasting more than 2 minutes was not recorded by ILR. Longer follow up is needed to assess the clinical significance of short episodes of AF in this patient population.

    Reference:

    Jons C, Raatikainen P, Gang UJ, Huikuri HV, Joergensen RM, Johannesen A, Dixen U, Messier M, McNitt S, Thomsen PE; Cardiac Arrhythmias and Risk Stratification after Acute Myocardial Infarction (CARISMA) Study Group. Autonomic dysfunction and new-onset atrial fibrillation in patients with left ventricular systolic dysfunction after acute myocardial infarction: a CARISMA substudy. J Cardiovasc Electrophysiol. 2010 Sep;21(9):983-90.


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