The human heart is made up of four chambers, two atria and two ventricles. These chambers are responsible for pumping blood to the entire body. The heart sends signals to these chambers to contract and relax periodically, thus, ensuring that there is smooth functioning of the heart. However, sometimes, there may be an abnormality in the electrical conduction system of the heart. When the impulse conducted from the atria to the ventricles through the AV node is delayed and travels slowly than normal, it leads to a condition known as the first degree AV block. This is the most common type of conduction disturbance and is seen to occur in both healthy as well as diseased hearts.
There are many different factors that can lead to a block of the first degree. These include, the presence of an AV nodal disease and an enhanced vagal tone. In cases of people, who have an enhanced vagal tone, the block may be physiologic in nature, as is seen in well trained athletes. Other causes of this type of AV block include, myocarditis, side effect of any drug or medication, electrolyte disturbances in the body (like hyperkalemia), and even severe conditions like myocardial infarctions. The drugs that can cause slowing down of the AV node functioning include, calcium channel blockers, beta blockers, and all the drugs that fall under the class of drugs that increase the cholinergic activity in the body.
A first degree heart block is rarely symptomatic and no treatment is generally required for this condition. It is seen in nearly 1% of the population and is seen to have an increased incidence rate with an increase in age. Thus, it is actually a benign condition, with no real threat to the person's life, thereby, with no increase in morbidity or mortality rate. The heart rate and heart rhythm are normal, thus, producing no discernible symptoms. One of the signs of this condition on ECG is that, the PR interval is increased beyond the normal 0.20 seconds. Thus, as there are no physical findings in the individual, most cases of the block of first degree are noticed incidentally on the ECG. However, at times, this condition may also be symptomatic. Also, further investigation and tests may become necessary if this condition is seen accompanying any another heart disease.
If the condition is being aggravated due to the intake of certain drugs, then the drugs need to be discontinued immediately and other drugs that do not have such an effect on the AV node should be prescribed. Although the use of drugs and medications is not advisable for patients that have such a type of block, if a person also has bradycardia or a significant risk of the block becoming a second degree AV block, then medication can be used. Medicines like atropine, which increase the heart rate and have a vagolytic effect on the body can be given in such cases.
This condition is generally asymptomatic and hence, does not require any kind of active treatment. This is primarily because, despite reaching slowly, the conduction signals do reach the ventricles of the heart. Other types of heart blocks, the second degree heart block and the third degree heart block are more severe types of blocks, which need to be addressed on an emergency level.