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Patient: n/a
ECG description:
- Sinus tachycardia
- Supraventricular bigemeny
- One premature ventricular contraction
Discussion:
There is a baseline sinus tachycardia with a PR interval of 130ms, regularly interrupted by premature atrial contractions (PAC). Each PAC depolarizes the atria and resets the SA node, causing a change in automaticity and a noncompensatory extrasystolic pause. Judging by the PR interval as well as P axis and morphology of the premature beats, the ectopic pacemaker is atrial. The ectopic PR interval is 130ms, and it is plausible to think that the ectopic pacemaker is located near the SA node. The P wave axis is ca. 30 degrees, and the ectopic P wave axis is ca. 60 degrees, which means that the atria are depolarized anterogradely and in almost the same direction as from the SA node. QRS axis and morphology is slightly different in the QRS complex following the first premature beat and the second and third. Looking closely, we can see that P wave axis and morphology slightly differs from the first PAC to the next two. The PR interval however is the same. This could be due to multifocality, but since the PR interval is quite similar, the two foci must be very close to each other. After the third bigeminal beat, a broad QRS occurs. In spite of the aberrantly looking RBBB-like morphology, this is most likely a premature ventricular contraction (PVC). If this was aberrancy, it would be due a refractory right bundle branch that couldn’t cope with the rapid changes in automaticity caused by the PAC’s. However, the coupling interval before the broad complex is similar to the other coupling intervals, and this demonstrates that the RBB in fact handles the rapid changes in automaticity quite well. In the precordial leads, we can see a P wave following the PVC, suggesting that the atrias have been depolarized retrogradely from the PVC.
July 1, 2009
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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.
January 31, 2009