ECG Interpretation

1. Site of origin. They are either ventricular or supraventricular. Supraventricular ectopics may be subclassified into either: (a) atrial (originating in the atria) or (b) junctional or nodal (originating in the AV node or bundle of His). 2. Timing. Ectopic complexes that occur before the next normal complex would have been due are termed premature, and those that occur following a pause such as a period of sinus arrest or in complete heart block are termed escape complexes. 3. Morphology. If all the ectopics in a tracing have a similar morphology to each other they are referred to as uniform and those in which there are different shapes as multiform. 4. Number of ectopics. Premature ectopic complexes may occur singly, in pairs or in runs of three or more; the latter is referred to as a tachycardia. A tachycardia may be continuous, termed persistent or sustained, or intermittent, termed paroxysmal. 5. Frequency. The number of premature ectopic complexes in a tracing may vary from occasional to very frequent. When there is a set ratio such as one sinus complex to one ectopic complex it is termed bigeminy and one ectopic to two sinus complexes is termed trigeminy.