Arrhythmias and Electrocardiogram Interpretation

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What is an EKG?

An electrocardiogram (EKG/ECG) is a graphic recording of electrical potentials produced by the cardiac tissue and measured by electrodes placed at different sites on the body.

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How does electrical activity travel through the heart?

Cardiac conduction typically starts at the sinoatrial (SA) node near the top of the right atrium ( Fig. 14.1 ). This impulse carries across the atria until it reaches the atrioventricular (AV) node, which is located near the junction of the atria and ventricles. The impulse is slightly delayed here as the atria contract. Conduction then continues down the bundle of His to the left and right bundle branches, which then break into Purkinje fibers in the ventricles. Heart rate is usually controlled by the fastest firing pacemaker. This should be the SA node at 60–100 beats per minute (bpm), but the controlling pacemaker activity may drop to lower sites in the setting of conduction system problems.

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How do you interpret an EKG?

The key is to be systematic! Read every EKG the same way every time. For prehospital purposes, the most critical points of EKG interpretation are identifying rate, rhythm, and evidence of myocardial ischemia.

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What is a normal heart rate?

The rate should normally be between 60 and 100. A heart rate <60 is considered bradycardia. A heart rate >100 is considered tachycardia.

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How do you identify the rhythm?

We will examine specific rhythms later. To understand rhythm, it is essential to ask four questions:

• Is the rate fast or slow?

• Are the QRS complexes narrow or wide?

• Are the QRS complexes spaced regularly or irregularly?

• Are there P waves present and what is their relation to the QRS complex?

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What is a normal rhythm?

Normal sinus rhythm (NSR) has a rate of 60–100, narrow and regular QRS complexes, P waves present, and every P wave associated with a QRS complex with a regular PR interval ( Fig. 14.2 ).

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What are the important bradycardias to know?

You should be able to identify sinus bradycardia, AV blocks, and junctional and idioventricular rhythms ( Fig. 14.3 ).

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What is sinus bradycardia?

Sinus bradycardia has a rate less than 60, narrow and regular QRS complexes, P waves present, and every P wave associated with QRS complex ( Fig. 14.4 ). This is just NSR with a slower rate.

This can be a normal variant seen during sleep or in young healthy adults or athletes. It may also be seen in the setting of pathologic processes such as myocardial infarction, beta-blockers or calcium channel blockers, hypothermia, hypoxia, or Cushing’s reflex with high intracranial pressure. Arrhythmia treatment is usually not required. Address underlying causes if needed.

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