         |
Premature Ventricular Contractions Premature Ventricular Contractions (PVCs) (Example 1) Premature Ventricular Contractions (PVCs) (Example 2) Premature Ventricular Contractions (PVCs) (Example 3) A Premature Ventricular Contraction (PVC) occurs when a focus in the ventricle generates an action potential before the next scheduled SA nodal action potential. There are four main characteristics of PVCs: 1) They are premature. That is they occur earlier than you would expect if you were to measure the previous R to R intervals. 2) They are ectopic. Meaning originating outside of the SA node. Thus the QRS morphology would be different than the normal QRS morphology when the action potential travels through the normal conduction system.. 3) They are wide complexes. Since they come from the ventricles and do not use the normal ventricular conduction system, the action potential needs to travel from myocyte to myocyte instead which is much slower, thus the QRS complex is wide. Unlike a premature atrial contraction, which is usually narrow-complexed since it uses the normal ventricular conduction system (unless a baseline right or left bundle branch block is present). 4) There is a compensatory pause after the PVC. The extra action potential causes the SA node to become refractory to generating its next scheduled beat. Thus it must "skip a beat" and it will resume exactly 2 P to P intervals after the last normal sinus beat. Ventricular bigeminy occurs when every other beat is a PVC. |
|
|
Home | Cardiology Review
| ECG Review
| Book Review
| Cardio News
Contact Us | About Us | Disclaimer LearnTheHeart.com is Copyright 2004-2009 ALL RIGHTS RESERVED |
