Bradycardia

The normal heart rate (ventricular rate) at rest is 60–100 beats min^-1. A bradycardia is defined as a heart rate slower than 60 min^-1.

Bradycardia may be:

• A physiological state in very fit people or during sleep
• An expected result of treatment (e.g. with a ß-blocker).

Pathological bradycardia may be caused by malfunction of the SA node or from partial or complete failure of atrioventricular conduction. Other pathological causes include vasovagal and other neurally-mediated syncope and presyncope and hypothyroidism.

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When you assess any patient with an arrhythmia address two factors:

1. The condition of the patient (presence or absence of adverse features)
2. The nature of the arrhythmia

Experience and expertise may be needed to identify some rhythm abnormalities with complete precision. However, a simple, structured approach to interpreting the rhythm on any ECG recording will define any rhythm in sufficient detail to enable the most appropriate treatment to be chosen.

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The 6-stage approach was covered in detail in the module Monitoring, Rhythm Recognition and 12-lead ECG.
Apply this to the analysis of any rhythm on an ECG:

1. Is there any electrical activity?
2. What is the ventricular (QRS) rate?
3. Is the QRS rhythm regular or irregular?
4. Is the QRS width normal (narrow) or broad?

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Any cardiac rhythm can be described accurately and managed safely and effectively using the first four stages.

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5. Is atrial activity present? (If so, what is it: Typical sinus P waves? Atrial fibrillation? Atrial flutter? Abnormal P waves?)
6. How is atrial activity related to ventricular activity? (e.g. 1:1 conduction, 2:1 conduction, etc, or no relationship)

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Extreme bradycardia may also cause such a severe fall in cardiac output to effectively cause cardiac arrest.

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