premature ventricular contractions (PVCs) and bigeminy
introduction
a premature ventricular contraction or ventricular ectopic beat is a cardiac contraction that is generally premature or occurs before the expected sinus QRS complex and arises out of the ventricular tissue.
when a PVC follows every atrial beat, it is called bigeminy
when a PVC occurs every 3rd beat, it is called trigeminy
when 2 PVCs occur in a row, they are called a couplet, when 3 or more occur in a row, then it is called a salvo
PVCs and bigeminy may be a sign that all is not well with the heart and the patient is at risk of a
ventricular fibrillation (VF) when they occur in the setting of acute myocardial ischaemia, hypoxia, prolonged QTc, drug overdoses or metabolic disturbances such as
hypokalaemia
when the PVCs occur near the peak of the T wave of the preceding beat,these beats predispose the patient to ventricular tachycardia or fibrillation. This R-on-T pattern is often seen in patients with acute myocardial infarction or long Q-T intervals. In the latter case, the triggered arrhythmia would be torsade.
couplets, salvos or multifocal PVCs also suggest a higher risk
on the other hand, in patients with no evidence of the above, PVCs and bigeminy are usually
regarded as benign and not treated other than to advise avoidance of stimulants, manage any underlying hypertension, and if symptomatic consider a
beta adrenergic blockers
recently however, evidence suggests that some patients with frequent ventricular ectopy may be at risk of developing dilated cardiomyopathy and that ablation of the ectopic focus appears to reverse this cardiomyopathy
1)
ECG criteria
the QRS complex is wide and often premature with increased amplitude and of a bizarre shape.
the QRS width is 0.12 second or wider.
the T wave is of opposite polarity to QRS complex.
there is no related P wave (unless there is retrograde conduction back through the AV node, which causes the P wave to occur in or after the QRS complex).
usually the PVC is followed by a fully compensated pause.
they may be unifocal (all look the same) or multifocal
Lown grading system
grade | feature |
grade 0 | no PVCs |
grade 1 | occasional PVCs (<30/hr) |
grade 2 | frequent PVCs (>30/hr) eg. bigeminy |
grade 3 | multiform |
grade 4 | repetitive (couplets, salvos) |
grade 5 | R on T PVCs |
Mx of frequent PVCs or bigeminy
Beware of premature ventricular contractions in slow rhythms; they may be an escape focus. Do NOT give lignocaine in this scenario.