CVC Highlights: Essentials for interpreting ECGs in practice - Veterinary Medicine
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CVC Highlights: Essentials for interpreting ECGs in practice
ECG evaluation needn't be complicated. In fact, this specialist thinks that most practitioners should be running at least one a day—and a rhythm strip such as lead II is all you really need to assess heart rate and arrhythmias.


Step 5. Summarize the findings and classify the arrhythmia.

What is the predominant rhythm? Is the arrhythmia an abnormality of impulse formation or impulse conduction or both? If either or both, what is the site of the abnormality?

To classify arrhythmias, you need to know two things:
1. The site of origin of the abnormal beat (i.e. the sinoatrial node, the atrial conduction tissue, the AV node-His bundle junction, or the ventricular conduction tissue [bundle branches and Purkinje fibers]).
2. Deviations from the normal rate of automaticity at that site (i.e. tachycardia, bradycardia, block, arrest).

Four types of arrhythmias can be identified on lead II by the following features:

Sinoatrial origin. Increased vagal tone results in sinus arrhythmia and sinus arrest. A lesion in the sinoatrial (SA) node can possibly result in SA block.

Atrial origin. These beats originate from somewhere in the atria other than the SA node. These atrial premature complexes look like a normally conducted beat except their timing is early. A big hint is that the P-wave of the atrial beat is superimposed on the T-wave of the beat before it. Atrial fibrillation (a rapid and irregular heart rate and no P-waves) usually indicates severe heart disease.

Junctional origin. These beats originate near the AV node and have a negative deflection P-wave, or no P-wave, with a normally conducted, short-duration QRS complex.

Ventricular origin. These beats originate somewhere in the ventricles. The QRS complexes are wide and bizarre-appearing and may have positive or negative polarity. Ventricular premature complexes and ventricular tachycardia are the result.

Attendees selected this highlight from CVC lectures. The original paper was published in the proceedings of the 2005 Central Veterinary Conference.


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