Ventricular premature complexes (VPCs) in couplet

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Ventricular premature complexes seen as wide bizarre QRS complexes not preceded by a P wave. Initial two VPCs are isolated while the last two occur in rapid sequence as a couplet. Couplets may be a forerunner of ventricular tachycardia. Isolated VPCs and the couplet are followed by a compensatory pause. All the VPCs have same morphology (monmorphic) indicating the same focus of origin (unifocal). Unifocal VPCs usually have the same coupling interval. Coupling interval is the interval from the onset of the preceding sinus beat to the onset of the ectopic beat. Unifocal VPCs from a parasystolic focus can have varying coupling interval. Parasystolic focus is a protected focus with entrance block. It captures the ventricle whenever it finds that the ventricle is not refractory from a conducted beat. The interectopic intervals in a parasystole have a common denominator.