• A premature beat occurs when an irritable automaticity focus either from the atria, AV junction, or ventricles sends out impulse (1) earlier than the next expected sinus beat (2).
• If the premature beat occurs frequently, a geminy rhythm, in which there the premature beat is coupled with one or more sinus beat(s), is formed.
Bigeminy = 1 premature beat + 1 sinus beat
Trigeminy = 1 premature beat + 2 sinus beats
Quadrigeminy = 1 premature beat + 3 sinus beats
• Causes of atrial and junctional premature beats:
SANS overstimulation
PANS understimulation
Drugs/ Toxin (e.g. caffeine, amphetamine, cocaine, alcohol, digitalis, epinephrine, norepinephrine)
Hyperthyroidism
Mechanical stretch
Hypoxia
• Causes of ventricular premature beats:
Hypoxia
Hypokalemia
Mechanical stretch (cardiomyopathy)
Myocarditis
Beta-1 agonists (epinephrine, norepinephrine)
• Examples of premature beats are listed below.
