Atrial Unimorph Bigeminy with Left Anterior Fascicle Block
Click to see full scale version (will open in a new window)
Click to see full scale version (will open in a new window)
Patient: n/a
ECG description:
- Sinus arrhythmia / sinus rhythm with varied rate. V-rate varies from 45-110 bpm.
- Left Axis Deviation (LAD). Cardiac axis approx. – 40°
- Left Anterior Fascicle Block
- Premature Atrial Contractions (PAC) in bigeminal pattern
- Widespread T wave abnormalities. T flat/negative in leads II, III, aVF, V5, V6
- Deep Q-wave in lead V1
Detection of Atrial Bigeminy
The 12 lead ECG displays multiple supraventricular extrasystoles. Each sinus beat is followed by a supraventricular extrasystole with a fixed coupling interval throughout the recording. Since the coupling interval is fixed and the P’ waves are morphologially similar, the term unimorph is used. Unimorph complexes signal that all the premature beats arise from the same automaticity focus, insinuating ectopic unifocality. Though, there is always a possibility that unimorph complexes can originate in different foci. Therefore, the term unimorph is used instead of unifocal.
Determining from the P wave axis and morphology, the ectopic focus is not sinoatrial. The narrow QRS suggests that the ectopic impulse is being conducted normally through the His-Purkinje fibers, ruling out a ventricular ectopy. The PR interval measures 120 ms, which lets us conclude that the irritable focus is atrial, not junctional. The inverted P waves suggests that the ectopic impulse is spreading retrogradely and inferiorly from its focus.
Each premature complex is followed by a postextrasystolic pause, slowing down the rhythm. By measuring the pause, the coupling interval and the normal sinus interval, the pause can be labeled compensatory or noncompensatory, with the latter being the normal finding with premature atrial contractions. As premature atrial impulses normally depolarize the whole atrium and thereby resets the SA Node, sinus pacing is usually interrupted, causing a pause after the extrasystole. This pause is a result of the sinoatrial slowing and is longer than, but not a multiple of the normal interval. With noncompensatory pauses, the coupling interval + the postextrasystolic pause is less than twice the normal interval. With compensatory pauses, the sum of the coupling interval and the postextrasystolic pause is exactly twice the normal interval length. Because of the bigeminal pattern here, there is no “normal” sinus cycle, making it difficult to establish whether the pauses are compensatory or non-compensatory.
Leave a Comment January 31, 2009