Ventricular parasystole

Ventricular Parasystole

 * 1) An ectopic ventricular pacemaker activates the ventricle concurrently with, but independent of, the impulse of the basic rhythm.
 * 2) It is protected from the impulse of the basic rhythm by entrance block.
 * 3) Its own impulse is able to depolarize the ventricle.
 * 4) Probably due to increased automaticity.
 * 5) EKG findings:
 * 6) * varying coupling intervals
 * With PVCs there is usually fixed coupling
 * 1) * RR intervals of the ectopic beats being mathematically related to each other
 * The interectopic forum is variable, are multiples of the shorter interval
 * Although the ectopic focus fires regularly, only those that find the ventricles responsive are manifested electrocardiographically.
 * The ratio between the intervals is seldom exact whole numbers (3:1) and more often 3:2 etc.
 * Parasystolic rates vary from 20 to 400 BPM
 * In most patients the rate varies between 30 to 56 BPM
 * Parasystolic rates greater than 70 BPM is called parasystolic VT.
 * 1) * the presence of fusion beats
 * May discharge at the same time that an impulse of the basic rhythm arrives at the ventricles.
 * The ventricles are then depolarized by the two wavefronts.
 * Can occur with regular PVCs, but with parasystole more frequently.
 * 1) It is relatively uncommon
 * 2) * Seen in 1 to 1.5/1000 EKGS
 * 3) * Long rhythm strip required to demonstrate variability in coupling interval