Bigeminal rhythm VIII.
ECG of the Month Presentation is on page.
DIAGNOSIS: Sinus rhythm with normal antegrade atrioventricular (A-V) conduction and slow retrograde conduction back to the atria, producing atrial reentry or echo complexes and suggesting dual A-V nodal pathways or an accessory A-V pathway that conducts slowly from the ventricles to the atria.
The P-R interval following each sinus P wave is normal (0.16 s), and the QRS complexes, ST segments and T waves are normal. A P wave that is inverted in the inferolateral leads follows each QRS with a long (0.58 s) R-P interval. This pattern suggests antegrade conduction down the fast pathway and retrograde conduction up the slow pathway in someone with dual A-V nodal pathways. (1) This is an unusual mechanism for atrial reentry, which usually occurs when an atrial premature complex blocks the fast pathway because of its longer refractory period, reaches the ventricles via the slow pathway, and returns to the atria via the no-longer-refractory fast pathway. (2,3) Alternatively, a slowly conducting accessory pathway could be the conduit for the late atrial reentry or echo complexes. Thus, although AV node reentry is typically thought of as causing tachyarrhythmias, in this circumstance, because of resetting of the sinus node and lack of ventricular contraction with the echo beat, it can present as bradyarrhythmia.
The pattern of atrial bigeminy seen in the Figure also could be produced by an automatic focus in the A-V junction or low in the atria. Because of the long R-P intervals and the normal P-R intervals, however, such ectopic impulses would be expected to be conducted to the ventricles. In contrast, conduction back to the atria via a slow nodal pathway might well leave a path of refractorness in the A-V node and transitional tissue that would prevent return of the impulse to the ventricles.
The patient gave a history of hepatitis C and cirrhosis but no history of heart disease. Complete blood count, comprehensive metabolic profile and serum amylase and lipase were normal, as was a computed tomogram of the abdomen. Further gastrointestinal studies will be undertaken in the outpatient clinic.
The temporal sequence, while the patient was in the emergency department, of abdominal pain, lightheadedness, a slow pulse, and the arrhythmia shown in the Figure suggest that reflex vagotonia may have played a role in the patient's arrhythmia. The bigeminal rhythm spontaneously disappeared, and she then had normal sinus rhythm with normal vital signs.
(1.) Josephson ME. Clinical Cardiac Electrophysiology: Techniques and Interpretations. 3rd edition. Philadelphia: Lippincott Williams & Wilkins; 2002.
(2.) Ibid. 171.
(3.) Fisch C, Knoebel SB. Electrocardiography of Clinical Arrhythmias. Armonk, NY: Futura;2000.
Dr. Glancy is a Professor in the Section of Cardiology, Department of Medicine at Louisiana State University Health Sciences Center in New Orleans (LSUHSC-NO). Dr. Lelorier is an Associate Professor of Medicine and Neurology and Director of Electrophyisology Service at LSUHSC-NO. Dr. Atluri is an Assistant Professor of Clinical Medicine at LSUHSC-NO. Dr. Willoughby is a Clinical Instructor of Emergency Medicine at LSUHSC-NO.
D. Luke Glancy, MD; Paul A. Lelorier, MD; Prashanthi Atluri, MD; and Christopher B. Willoughby, MD
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|Title Annotation:||ECG of the Month|
|Author:||Glancy, D. Luke; Lelorier, Paul A.; Atluri, Prashanthi; Willoughby, Christopher B.|
|Publication:||The Journal of the Louisiana State Medical Society|
|Date:||Sep 1, 2011|
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