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The presence of multiple P wave morphologies indicates multiple ectopic pacemakers within the atria and/or AV junction. If ≥ 3 different P wave morphologies are seen, then multifocal atrial rhythm is diagnosed:

We therefore interpret this tracing as showing “AV dissociation” – since at least some P waves are unrelated to the QRS complexes that follow them. The term AV dissociation should never be used as a “diagnosis” per se. Instead – it is the result of the underlying rhythm on the tracing. In this case – the underlying rhythm is sinus bradycardia at a rate of 50/minute (the P-P interval is precisely 6 large boxes in duration for each of the P waves on this tracing). AV dissociation occurs by…

If ≥ 3 different P wave morphologies are seen and the rate is ≥ 100, then multifocal atrial tachycardia (MAT) is diagnosed:


Representation of single, normal heart beat. Each waveform & deflection is labeled with a letter. They actually represent heart contractions. The first small vertical bump is known as the "P-wave," when the SA node generates an electrical impulse causing the Atrias (the top) of the heart to contract. Impulse travels down through the heart to the Ventricles. Normally, should be between 0.12-0.20 s. The P-wave & the space between it & next positive (upward) deflection are known as the PR…

Accelerated Junctional Rhythm: occurs when the rate of the AV junctional pacemaker exceeds that of the sinus node. This situation arises when there is increased automaticity in the AV node coupled with decreased automaticity in the sinus node. Causes include myocardial ischaemia, digoxin toxicity, cardiac surgery, myocarditis and beta-agonists (e.g. isoprenaline).

P-waves: 1) Are they present? 2) Do they occur regularly? 3) Is there one P-wave for each QRS complex? 4) Are the P-waves smooth, rounded, and upright? 5) Do all the P-waves have similar shapes?