a. Causes of Arrhythmia. Arrhythmias develop for various reasons, including acute myocardial infarction (heart attack), trauma, and drug reactions.

Drowning, near drowning, asphyxiation, and the patient’s underlying medical conditions can also cause arrhythmias.

b. Significance of Arrhythmia. There are several reasons why cardiac arrhythmias may be clinically significant.

Heart rates below 40 to 50 beats per minute lead to inadequate cardiac output and often precede electric instability of the heart. If the sinus rate falls below 60 beats per minute, another conduction system may take over. The atrial-ventricular junction (AV junction) has an inherent rate of 40 to 60 beats a minute. The ventricle has an inherent rate of 20 to 40 beats a minute. This may lead to premature ventricular contractions and ventricular arrhythmias.

If a heart rate is over 120 to 140 beats per minute, the heart must work harder. This causes further myocardial ischemia (diminished blood flow). Tachycardia may be linked with a drop in cardiac output which is secondary to decreased stroke volume, this lowered volume being caused by the ventricles having less time to fill between heartbeats.

Finally, ectopic beats (beats located away from the normal position) could be a sign of electric instability of the ventricles. Such heartbeats are an important sign since they may indicate that more serious arrhythmias, such as ventricular tachycardia or ventricular fibrillation, may develop.