Is first-degree atrioventricular (AV) block serious?

From the Guidelines

First-degree atrioventricular (AV) block is generally not serious and usually doesn't require treatment. It's characterized by a prolonged PR interval on an electrocardiogram (ECG), meaning there's a slight delay in electrical conduction from the atria to the ventricles of the heart. Most people with first-degree heart block have no symptoms and can live normal, active lives without restrictions. The condition is often discovered incidentally during routine medical examinations. Unlike more advanced forms of heart block, first-degree heart block rarely progresses to more serious conditions and doesn't typically affect heart function or cardiac output. However, in some cases, it may be a sign of underlying heart disease or medication effects. Certain medications like beta-blockers, calcium channel blockers, and digoxin can cause first-degree heart block as a side effect. If you're diagnosed with first-degree heart block, your doctor will likely monitor your heart health periodically but won't recommend specific treatments unless there are other cardiac concerns present.

Some key points to consider:

• First-degree AV block is usually a benign condition, and most people with this condition do not require treatment 1.
• A very long PR interval may exacerbate symptoms, especially during moderate or mild exercise 1.
• Marked first-degree AV block, PR interval >0.3 s, in rare cases may result in symptoms similar to those associated with retrograde (ventriculoatrial) conduction 1.
• Small, uncontrolled trials have suggested some symptomatic and functional improvement by pacing of patients with PR intervals >0.30 seconds by decreasing the time for AV conduction 1.
• The decision regarding implantation of a pacemaker must be considered with respect to whether AV block will be permanent, and reversible causes of AV block should be corrected first 1.

In general, the management of first-degree AV block is focused on monitoring and addressing any underlying conditions that may be contributing to the condition, rather than treating the condition itself. The most recent and highest quality study, published in 2019, supports this approach, and recommends that patients with first-degree AV block be monitored periodically, but not treated unless other cardiac concerns are present 1.

From the Research

First-Degree Atrioventricular (AV) Block Severity

• First-degree AV block is not always a benign condition, as it can be associated with an increased risk for heart failure, pacemaker implantation, and death 2, 3.
• Studies have shown that patients with first-degree AV block are at a higher risk for developing more severe conduction disease, which may require pacemaker implantation 2.
• The presence of first-degree AV block can also be a marker for underlying heart disease, and its association with heart failure and mortality has been observed in patients with stable coronary artery disease 3.

Clinical Manifestations and Indications for Pacing

• Marked first-degree AV block (PR > 0.30 s) can produce symptoms similar to those of the pacemaker syndrome, and clinical evaluation may require a treadmill stress test to assess the patient's condition 4.
• Pacemaker implantation is recommended for patients with first-degree AV block who experience symptoms similar to those of pacemaker syndrome or have hemodynamic compromise 5, 4.
• The choice between preserving intrinsic AV conduction and delivering right ventricular pacing in patients with pacemakers and first-degree AV block depends on various factors, including the optimal AV delay and the risk of heart failure 6.

Outcomes and Prognosis

• Patients with first-degree AV block who receive pacemaker implantation may have a poorer outcome compared to those without the condition, due to factors such as electrical desynchronization and concealed resynchronization 4.
• The risk of heart failure may be increased with right ventricular pacing in patients with first-degree AV block, particularly if the E/E' ratio is high during intrinsic AV conduction or right ventricular pacing 6.
• Further studies are needed to determine the optimal management strategy for patients with first-degree AV block and to identify patient subgroups that are at risk for developing more severe conduction disease 2, 6.