A patient's electrocardiogram (ECG) shows periodic QRS complexes that are not preceded by $\mathrm{P}$ waves and that have a bizarre shape. These QRS complexes originated in the

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[Chapter 3, III A]. Because there are no $\mathrm{P}$ waves associated with the bizarre QRS complex, activation could not have begun in the sinoatrial (SA) node. If the beat had originated in the atrioventricular (AV) node, the QRS complex would have had a "normal" shape because the ventricles would activate in their normal sequence. Therefore, the beat must have originated in the His-Purkinje system, and the bizarre shape of the QRS complex reflects an improper activation sequence of the ventricles. Ventricular muscle does not have pacemaker properties.

A Patient's Electrocardiogram (ECG) Shows Periodic QRS Complexes That Are P\mathrm{P}P

A Patient's Electrocardiogram (ECG) Shows Periodic QRS Complexes That Are $\mathrm{P}$