First degree heart block
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First-Degree Heart Block: Clinical Significance and Implications
Prevalence and General Characteristics
First-degree heart block, also known as first-degree atrioventricular (AV) block, is characterized by a prolonged PR interval on an electrocardiogram (ECG). It is relatively common, with a prevalence of approximately 4% in the general population. In asymptomatic young individuals, the prevalence ranges from 0.65% to 1.1%. The condition is often considered benign, especially when the PR interval prolongation is moderate (0.22 to 0.23 seconds).
Association with Heart Failure and Mortality
Recent studies have challenged the notion that first-degree AV block is entirely benign. In patients with stable coronary artery disease (CAD), first-degree AV block has been associated with an increased risk of heart failure (HF) hospitalization and mortality. Specifically, patients with a PR interval ≥220 ms were found to have a higher risk of HF hospitalization (age-adjusted HR 2.33) and all-cause mortality (age-adjusted HR 1.58). This association persisted even after adjusting for various confounders, including heart rate and medication use.
Impact on Patients with Heart Failure
Among patients with heart failure, the presence of first-degree AV block is notably higher, ranging from 15% to 51%. This condition is linked to worse outcomes, including increased mortality and HF hospitalization. Cardiac pacing in these patients is associated with poorer outcomes compared to those with normal AV conduction. Optimization of atrioventricular delay in patients undergoing cardiac resynchronization therapy (CRT) is crucial, although the best method for AV resynchronization remains undetermined.
Prognostic Implications in Hypertrophic Cardiomyopathy
In patients with hypertrophic cardiomyopathy (HCM), first-degree AV block is associated with a higher risk of HCM-related death, including sudden death and potentially lethal arrhythmic events. A study involving 414 HCM patients found that those with first-degree AV block had an adjusted hazard ratio of 2.41 for HCM-related death. This suggests that first-degree AV block may serve as a significant prognostic marker in this patient population.
Long-Term Prognosis in Healthy Individuals
In healthy individuals without organic heart disease, the long-term prognosis of first-degree AV block appears to be more favorable. A 30-year longitudinal study of 3983 healthy men found no significant differences in all-cause mortality between those with and without first-degree AV block. However, the study noted a slightly higher, though not statistically significant, rate of ischemic heart disease in those with the condition.
Advanced Conduction Abnormalities and Rheumatic Fever
First-degree AV block is also a minor manifestation of acute rheumatic fever. More advanced conduction abnormalities, such as second- and third-degree AV block, are less common but can be highly suggestive of rheumatic fever in certain populations.
Conclusion
While first-degree heart block has traditionally been viewed as a benign condition, emerging evidence suggests it may be associated with adverse outcomes in specific patient populations, such as those with CAD, heart failure, and HCM. Understanding these associations is crucial for improving the management and therapeutic strategies for affected individuals. Further research is needed to refine the optimal monitoring and treatment approaches for patients with first-degree AV block.
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