Reading Between the (M-mode) Lines
Image Modality: Illustration Table Figure
A 77-year-old woman with a history of cerebrovascular accident (CVA), hypertension, hyperlipidemia, and atrial fibrillation (AF) on warfarin presented to her primary care physician for complaints of nocturnal bilateral leg numbness without involuntary movements. During the visit, she was incidentally found to be bradycardic with a heart rate of 41 bpm. Her physical exam was otherwise unremarkable. She was not on any medications known to cause bradycardia and was otherwise asymptomatic from a cardiovascular perspective. Although, the electrocardiogram clearly showed a diagnosis of AF, diagnosis on transthoracic echocardiogram may be more difficult due to the use of a single-lead rhythm strip. M-mode imaging may be helpful in making a more definitive diagnosis; however, it is important to distinguish coarse AF from flutter. Coarse versus fine AF is dependent on the height of the fibrillatory wave amplitude.1 Fine AF is diagnosed by an amplitude of <1 mm in amplitude. The amplitude of the wave can be used to predict the risk of thromboembolism, whereas coarse AF has been independently associated with CVA.2 In this patient's case, the cycle length of the F waves (where "F" is onset of diastasis) from the M-mode tracing were around 130 ms, corresponding to at atrial depolarization rate of 461 bpm. Coupled with an irregularly irregular conduction interval between the R waves, findings are more suggestive of AF than atrial flutter.3
- Pourafkari L, Baghbani-Oskouei A, Aslanabadi N, et al. Fine Versus Coarse Atrial Fibrillation in Rheumatic Mitral Stenosis: The Impact of Aging and the Clinical Significance. Ann Noninvasive Electrocardiol 2018;23:e12540.
- Yamamoto S, Suwa M, Ito T, 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.
- Jang WI, Park JH, Lee JH, Choi SW, Jeong JO, Seong IW. Cardiocascular Images. M-mode Echocardiographic Demonstration of Atrial Flutter. Circ Cardiovasc Imaging 2009;2:e20-e21.
Date: June 30, 2020
Clinical Topics: Anticoagulation Management, Arrhythmias and Clinical EP, Dyslipidemia, Noninvasive Imaging, Prevention, Anticoagulation Management and Atrial Fibrillation, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Echocardiography/Ultrasound, Hypertension
Keywords: Diagnostic Imaging, Cardiac Imaging Techniques, Echocardiography, Arrhythmias, Cardiac, Atrial Fibrillation, Warfarin, Atrial Flutter, Heart Rate, Bradycardia, Hyperlipidemias, Physicians, Primary Care, Hypesthesia, Electrocardiography, Thromboembolism, Stroke, Hypertension, Dyskinesias