Bradycardia is a condition of the heart in which the pulse rate (heart beat) falls to a level, which causes the patient to have symptoms of fainting as well as easy fatigue, dizziness, etc.

A very slow pulse rate can be tolerated,so long as the amount of blood pumped out of the left side of the heart per minute is adequate to oxygenate the brain and the other parts of the body. Once the heart is unable to fullfill this requirement fainting will occur.

For example, the 24 hour EKG Holter recording of an asymptomatic 18 year old male athlete shows a slow heart rate of 30 per minute, while he was sleeping (the parasympathetic nerve was stimulated to cause the heart rate slowing with one junctional slowing escape beat).

But during exercise his rate went up to 180 a minute with a normal PR interval.No symptoms developed during long term followup (see figure 93b).

Normal Heart Rate

Normal range of heart rates in the afternoon has been reported to be 46 to 93 beats per minute for men, and 51 to 95 beats per minute for women.

Nocturnal rates are slower, decreasing during sleep by an average of 24 beats per minute in young adults and by 14 beats in those over 80 years of age.

Trained athletes are prone to bradycardia (slow pulses) with heart rates below 40 beats per minute common at rest.

In view of these findings, the American Heart Association current guidelines for pacemaker implantation (a battery powered,lithium-iodine type, electronic,pulse generating device embedded under the skin of the chest, just below the right clavicle usually, and connected to the right atrium and/or ventricle by a sterile wire, which is guided through the cephalic vein) advise the following:

1. Episodes of sinus bradycardia with heart rates as low as 30 beats per minute, which cause no symptoms, are to be considered with in the normal range.

2.Also,normal are sinus pauses (no P waves) of up to 3 seconds (see fig 16, second EKG) and atrioventricular nodal Wenckebach block, where the PR interval successively increases until a P wave is finally not followed by a QRS on the EKG (see fig 17, second EKG).

Types of Bradycardia

1. Sinus Node Dysfunction:
   a. Sinus Bradycardia
   b. Sinus Arrest
   c. Sinoatrial Exit Block
   d. Bradycardia - Tachycardia syndrome
2. Atrioventricular Conductive Disturbances:
   a. 1st Degree Atrioventricular AV block
   b. 2nd Degree AV block Mobitz type I
   c. 2nd Degree AV block Mobitz type II
   d. 2nd Degree High Grade AV Block
   e. 3rd Degree AV Block

Causes of Bradycardia (see table )

Bradycardia Evaluation

Bradycardia Managment