First-Degree Atrioventricular Block - Causes, Symptoms, Diagnosis, and Treatment

Introduction

A first-degree atrioventricular block can be defined as a block in the PR interval of the electrocardiography that is greater than 0.20 seconds without any disturbance in the conduction between the atrium and ventricle. The PR interval is the moment of time from the beginning of the P wave to the beginning of the QRS complex. The P wave signifies atrial depolarization and the QRS complex signifies ventricular depolarization.

• An electrocardiogram or an ECG tracks the electrical activity of the heart. Electrodes with electric pads are placed on the limbs and feet of the patient to record the electric signals.

• An electrocardiogram has different electrical intervals denoted by alphabets corresponding to other functions of the heart. One such interval is the PR interval.

• Ventricular depolarization means the event when the ventricles contract, thus increasing the pressure within the ventricles. This applies the same to atrial depolarization.

• In simple terms, the electrical pulse through the AV or atrioventricular node is signified by the P wave.

• The AV node, or the atrioventricular node, is a tiny structure located in the heart. The chief function of this atrioventricular node is to control the flow of the heart’s electrical signals that are getting transmitted from the atrium to the ventricles.

• HPS, or the His-Purkinje System, has the duty to rapidly conduct the electrical signals to the ventricles and are present in the inner walls of the ventricles.

When the atrioventricular node or, alternately, the His-Purkinje System does not work efficiently due to some obstruction, it leads to a condition called AV block or atrioventricular block of first-degree.

What Causes First-Degree Atrioventricular Block?

There are several causes that can result in a first-degree atrioventricular block. Most of them are due to an underlying cardiovascular condition that has been ignored or not diagnosed correctly, leading to the formation of the atrioventricular coalition over time. Following are the conditions that lead to a first-degree atrioventricular block.

• Increased vagal tone.

• Fibrotic changes in the heart.

• Myocardial infarction.

• Hypokalemia.

• Hypomagnesemia.

• Lyme disease.

• Diphtheria.

• Imbalance in the body’s electrolyte system.

• Rheumatic fever.

• Endocarditis.

• Chagas disease.

• Collagen vascular disease.

• Scleroderma.

• Rheumatoid arthritis.

• Lenegre and Lev diseases.

• Antiarrhythmic drugs such as Digoxin.

• Sarcoidosis.

• Coronary heart disease.

• Degenerative heart changes.

• Bezold- Jarisch condition

What Are the Signs and Symptoms of First-Degree Atrioventricular Block?

As age increases, an individual is more prone to this condition. But it is generally seen in healthy young adults who are very active in their lifestyle. Wear and tear, or overuse of the cardiac muscles during strenuous exercise might also be one of the reasons that lead to this cardiovascular condition at such a young age. A first-degree atrioventricular block is more common in males as compared to females. Young athletes show more prevalence as compared to other same-age patients. Below are some of the signs and symptoms of first-degree atrioventricular block. It should be noted that, a patient suffering from a first-degree atrioventricular block, generally does not manifest any explicit symptoms. Nevertheless, the below mentioned are a few of the signs that the patient may or may not experience before being diagnosed with a first-degree atrioventricular block.

• Difficulty in breathing.

• Lightheadedness.

• Slight discomfort.

• Syncope.

• Clubbing or bluish discoloration of the fingertips.

It should be known that there are multiple causes of the first-degree atrioventricular block that show no symptoms at all.

How to Diagnose First-Degree Atrioventricular Block?

Laboratory studies, electrocardiography, and other additional diagnostic modalities help in the diagnosis of atrioventricular block. Below are some of the diagnostic tools used for the diagnosis of atrioventricular obstruction. The healthcare provider must check if there is a familial prevalence of this condition or any other underlying cardiovascular disorder.

• To check the presence of hyperkalemia, the electrolyte levels of the patient are checked.

• Levels of the drug Digoxin must be checked in case the patient is taking it.

• Potassium and any other drug toxicity should be evaluated.

• Electrocardiograph recording of 12-lead.

• An implantable loop recorder is also a vital tool in the diagnosis of atrioventricular block.

• Electrophysiological tests are done to find the location of the block and any other present arrhythmia.

• Echocardiography is done to evaluate the ventricular function of the heart.

• An exercise test is conducted to check if the heart condition improves or worsens during exercise.

How to Treat Atrioventricular Block?

There are multiple treatment modalities for the treatment of atrioventricular block. In the majority of cases, there is no need to treat first-degree atrioventricular block. This is mainly because they show no signs or symptoms at first, and even after diagnosis, the clinical manifestations can be managed under emergency conditions. In case there is another underlying cardiovascular condition, it should be addressed and corrected first. Permanent pacemakers are not indicated for first-degree atrioventricular block patients. In case the block on the electrocardiogram shows a prolonged interval for multiple episodes, only then the healthcare provider and team can make a decision for a pacemaker or another long-term heart monitor. Overall, the underlying cardiovascular disease must be treated, which will eventually help in treating first-degree atrioventricular block.

Conclusion

An atrioventricular block is directly proportional to the degree of the underlying cardiovascular condition or any other medical problem. Patients with advanced atrioventricular obstruction need prompt treatment, while asymptomatic patients need monitoring. Patients with first-degree atrioventricular block have no clinical consequences. They do not show symptoms in the majority of cases. An electrocardiograph is likely to detect the presence of a first-degree atrioventricular block. In case of any slight signs, the patient should seek immediate medical attention. Patient education is vital, and there should be aware of the reversible causes of atrioventricular block and thus avoid or limit those causes. Patients can generally lead a normal life post-treatment and must have regular follow-ups with their doctors. A symptom-free life without the presence of the progressions of the first-degree atrioventricular block is possible.