The ECG was recorded from a 63 year old man admitted to the coronary care unit following an episode of ischaemic cardiac pain.
Rhythm: There are regular QRS complexes at a rate of 45 per minute. No P waves are visible: the rhythm is a
junctional one. There is an isolated ventricular premature beat near the end of the rhythm strip. Morphology: There is ST depression and deep T wave inversion in leads II, III and aVF as well as leads V4 – V6. ‘Reciprocal’ ST elevation is present in lead aVR. The appearance suggests acute inferolateral ischaemia or subendocardial infarction. There is a suggestion of lost R wave in lead V3 and V4 which would be compatible with anterior infarction at some time; the appearances are not sufflciently specific to be diagnostic.
Junctional rhythm (sometimes known as nodal rhythm) is usually an escape rhythm and arises when there is a failure in the generation of sinus beats as may occur in sino atrial block, or when block in the AV junction causes failure in the transmission of sinus beats (ie in complete heart block). In junctional rhythm there may be no P waves if the atria are not activated retrogradely from the AV junction because of the presence of retrograde block. If retrograde activation of the atria does occur P waves may precede, coincide with or follow the QRS complexes depending on the precise site of origin of the rhythm and the rate of propagation in both anterograde and retrograde directions. The polarity of the P wave will usually be the opposite of the P wave recorded in any particular lead during sinus rhythm as atrial activation is occurring in the opposite direction to normal. The rhythm in this patient was not associated with myocardial infarction and sinus rhythm returned shortly after this trace was recorded.