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Bronze Level Electrocardiography

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Aims

1. Brief summary of relevant clinical electrophysiology

2. Indications for taking an electrocardiogram (ECG)

3. How to obtain a diagnostic ECGAll Covered in Part 1

4. Basic ECG interpretation

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Section 4 – basic ECG interpretation

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Premature QRS complexes – wide or narrow QRS morphology

Trace 1

Trace 2

Both of these traces show premature QRS complexes. These are complexes with a shorter R-R interval than the preceding sinus beats

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Trace 1

Trace 1: The first 4 complexes show sinus rhythm. The 5th QRS complex is a premature beat with no associated P wave and a wide bizarre QRS morphology which suggests that it is not being conducted through the ventricles via the normal conduction system. As this beat originates in the ventricles it is termed a ventricular premature beat or VPC. The remainder of the trace shows sinus rhythm.

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Trace 2

Trace 2: Shows premature narrow QRS complex beats (the 2nd, 5th, 8th, 11th and 14th beats). These are supraventricular premature beats or SPC.

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Escape beatsSinus rhythm

Sinus arrest with ventricular escape rhythm

Escape beats are less common than premature beatsEscape beats occur after an interval GREATER than the normal R-R interval (cf premature beats occur after an interval LESS than the normal R-R interval) Escape beats have a wide and bizarre complex morphology as they originate from the ventricles. Escape beats maintain cardiac output during sinus arrest.

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Potentially life threatening ECGs

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Potentially life threatening ECGs – ventricular tachycardia

Sinus rhythm Ventricular tachycardia

Characteristics of VT:• Rapid (>180bpm) • Generally regular• More than 6 consecutive wide, bizarre QRS complexes• Seen in animals with severe cardiac and/or systemic disease (eg gastric dilation torsion,

pancreatitis, splenic disease, IMHA, etc).• Of particular concern in Boxers, Dobermanns and Great Danes

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Potentially life threatening ECGs – coarse ventricular fibrillation

Ventricular fibrillation is characterised by very rapid baseline undulations.

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Potentially life threatening ECGs – fine ventricular fibrillation

Usually a terminal rhythmRapid baseline undulations of lower amplitude to coarse VT.In this cases progresses to complete asystole and death around 11:27.

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Potentially life threatening ECGs - asystole

Flatline as there is no organised atrial or ventricular activity

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Potentially life threatening ECGs – high grade second degree atrioventricular block

P QRS T

PP P P P P P P

Large number of consecutive unconducted P waves (blocked at atrioventricular node or AVN). Finally a P wave is conducted through the AVN resulting in a normal QRS complex.There are then 13 consecutive unconducted P waves before the next P-QRS-T complex.

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Potentially life threatening ECGs – sinus arrest with very slow escape rhythm

During this 10 second period only a single beat is seen therefore the heart rate is very slow during this recording. The beat seen has a bizarre QRS morphology and is not preceded by a P wave suggesting that it is ventricular in origin.

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