ABSTRACT
SE43 (sinus) beat would have occurred (in contrast to escape beats, which arise later than expected). ● Ventricular ectopic beats cause broad QRS complexes (unlike supraventricular ectopics, which usually cause narrow QRS complexes). The ventricular ectopic impulse, having arisen within the ventricular myocardium, has to conduct from myocyte to myocyte in order to depolarize the ventricles – this is slower than conduction via the His-Purkinje system, and hence ventricular depolarization takes longer than it would with a normal sinus beat. ● VEBs arising from the right ventricle have a left bundle branch block morphology, and those arising from the left ventricle have a right bundle branch block morphology. ● On checking the radial pulse of a patient with bigeminy, the VEBs usually feel weaker than the normal sinus beats (because the ventricle has not filled fully by
the compensatory pause after the VEB (‘extrasystolic potentiation’). As a result, VEBs may sometimes be missed on palpation of the radial pulse. Patients with ventricular bigeminy are therefore sometimes mistakenly diagnosed as being bradycardic when their pulse is taken at the wrist, if only the sinus beats are counted. Even automated monitoring equipment (e.g. blood pressure monitors, pulse oximeters) can sometimes underestimate the heart rate by ‘missing’ the VEBs. Careful inspection of an ECG will reveal the correct heart rate. ● For more information on the investigation and management of VEBs, see the commentary on Case 9.
