Bradycardia
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Introduction
Bradycardias are defined as symptomatic heart rhythm disorders resulting in a inappropriately low heart rhythm during during physiologic conditions. Generally this results in a cut-off value of <60 beats per minute, however variation of normal heart rate may exist. For instance, during sleep and in athletes the heart rate can be as low as 40 beats per minute.
Bradycardia can be caused by a variety of intrinsic and extrinsic causes.
To understand the pathophysiologic basis of most conduction disorders or disorders of impulse formation it is important to understand the physiology of cardiac conduction and mechanisms of arrhythmia as detailed in the general cardiac arrhythmia section [Link].
Sinus Node Dysfunction
Sinus Bradycardia
Sinus bradycardia is a slow hearth rhythm of <60 beats per minute. It can be
Sinus Node Exit Block
In the case of sinus node exit block, an impulse generated from the sinus node is blocked at one of the exit sides of the sinus node. However impulse formation is not affected, therefore the interval between two subsequent beats should be similar to 2 times the P-P interval.
Sinus Arrest
If the sinus node has a problem with impulse formation it is defined as a sinus arrest. There can be the appearance of a irregular rhythm, however sinus P-waves are clearly present.