Verapamil use with caution; may cause fetal bradycardia
Atropine safe for acute use; crosses placenta but transient fetal tachycardia only
Pacemaker in pregnancy
Symptomatic bradycardia requiring pacing: fluoroscopy minimized with lead placement guided by echocardiography
Femoral approach preferred to minimize fetal radiation exposure
Geriatric
First-degree AV block in elderly patients
Epidemiologic significance
Prevalence increases markedly from 5th-6th decade due to degenerative fibrosis
In patients >= 85 years, first-degree AV block is the strongest single ECG predictor of mortality
Associated with 1.45x increased risk of AF, 1.39x increased risk of heart failure
Degenerative causes predominate
Lev disease: calcification extending from cardiac skeleton
Lenegre disease: primary fibrotic degeneration of His-Purkinje system
Assess for coexisting bundle branch block
Polypharmacy considerations
Review all AV-nodal blocking agents including ophthalmic preparations
Digoxin toxicity more likely at lower levels due to decreased renal clearance
Non-dihydropyridine CCB and beta-blocker combinations potentiate AV block
Pacemaker in elderly patients
Symptomatic pseudo-pacemaker syndrome: Class IIa indication regardless of age
Comorbidity and life expectancy guide shared decision-making
Falls risk assessment before and after pacemaker implantation
Syncope in elderly
High consequence injury risk from falls
Lower threshold for admission and monitoring
Pediatrics
First-degree AV block in children and adolescents
Normal variants in pediatric population
PR interval normal values age-dependent: shorter in children than adults
Normal upper limit of PR: 140 ms in infants, 160 ms in children, 200 ms in adolescents
Athletes with high vagal tone commonly show PR prolongation
Congenital causes
Congenitally corrected transposition of great arteries
Progressive AV block; pacemaker often required
Maternal anti-Ro/SSA or anti-La/SSB antibodies
Maternal SLE associated with congenital complete heart block
First-degree AV block in fetus warrants serial monitoring
Lyme carditis in children
Common presentation in endemic areas
Doxycycline approved for >= 8 years of age; 4.4 mg/kg/day in 2 divided doses, maximum 100 mg/dose
Amoxicillin 50 mg/kg/day in 3 divided doses for < 8 years
Ceftriaxone 50-75 mg/kg/day IV for high-degree block, maximum 2 g/day
Athletic clearance
Per AHA/ACC 2015 statement: athletes with isolated first-degree AV block and normal heart structure can participate in all competitive sports
Annual evaluation recommended
Exercise testing to exclude infranodal disease before clearance if PR >= 300 ms
Background
Epidemiology
Prevalence and incidence
Population prevalence
Prevalence 0.65-1.1% in the general population
Increases from < 1% in young adults to > 5% in patients > 60 years
J-shaped age distribution: peak in athletes and in the very elderly
Sex distribution
Slightly more prevalent in males across most age groups
Risk associations
Framingham Heart Study: first-degree AV block associated with 2-fold increased risk of AF and 3-fold increased risk of pacemaker implantation
Meta-analysis: 1.45x increased risk of AF, 1.39x increased risk of heart failure, 1.24x increased risk of mortality
Heart and Soul Study: patients with stable CAD and first-degree AV block had 2.3x increased risk of HF hospitalization and 1.6x increased risk of mortality
Cheng et al (JAMA 2009): long-term follow-up confirmed excess mortality with PR prolongation
Pathophysiology
Mechanisms of PR prolongation
AV nodal delay
Most common anatomic location
Calcium channel-dependent slow conduction
Reversible with atropine or exercise
Benign prognosis when isolated
Infranodal delay
Less common but higher risk
His bundle or bundle branch level
Wide QRS suggests infranodal involvement
Does not improve or worsens with exercise
Combined AV nodal and infranodal delay
EPS required to differentiate
HV interval > 100 ms indicates infranodal disease
Molecular and structural mechanisms
Degenerative fibrosis
Progressive replacement of conduction tissue with fibrous tissue
Age-related calcium deposition in cardiac skeleton
Your ECG shows that electrical signals travel more slowly than normal from the upper chambers (atria) to the lower chambers (ventricles) of your heart
This is a delay in the electrical pathway but every signal still gets through — your heart is beating in a coordinated way
In most people this is a benign finding that does not require treatment
Activity instructions
Activity guidance
Most patients with isolated first-degree AV block may continue normal activity
Discuss return to competitive sports with your doctor if you are an athlete
Avoid activities that put others at risk (driving, operating heavy machinery) if you have experienced syncope or near-syncope until cleared by your doctor
Medication instructions
Medication guidance
Take all prescribed medications as directed
Do not stop any heart medications without consulting your doctor
If a medication was adjusted today, follow the new dose instructions provided
Keep a list of all medications, including eye drops (timolol eye drops can affect heart rate)
Follow-up instructions
Outpatient follow-up
Follow up with your family doctor or cardiologist within 2-4 weeks
Bring your medication list to your follow-up appointment
A repeat ECG will likely be performed at your follow-up visit
Tell your doctor about any new symptoms before your scheduled appointment
Return to emergency department
Return immediately for any of the following
Fainting or loss of consciousness (syncope)
Near-fainting or sudden lightheadedness
Severe chest pain or pressure
Sudden shortness of breath
Palpitations with dizziness
New weakness, difficulty speaking, or facial droop
Heart rate below 40 beats per minute or irregular pulse
References
Guidelines and key sources
ACC/AHA/HRS 2018 Bradycardia Guideline
Kusumoto FM, Schoenfeld MH, Barrett C, et al
2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay
Journal of the American College of Cardiology, 2019
Primary guideline source for pacemaker indications, Class I, IIa, IIb, III recommendations
Executive Summary
Kusumoto FM et al, Journal of the American College of Cardiology, 2019
PMID 30412710
Landmark observational studies
Framingham Heart Study
Cheng S, Keyes MJ, Larson MG, et al
Long-Term Outcomes in Individuals With Prolonged PR Interval or First-Degree Atrioventricular Block
JAMA 2009; 10.1001/jama.2009.888
2-fold adjusted risk of AF, 3-fold risk of pacemaker implantation
Kwok CS et al meta-analysis
Prolonged PR Interval, First-Degree Heart Block and Adverse Cardiovascular Outcomes: A Systematic Review and Meta-Analysis
Heart 2016; PMID 26879241
1.45x AF, 1.39x HF, 1.24x mortality risk
Heart and Soul Study
Crisel RK, Farzaneh-Far R, Na B, Whooley MA
First-Degree Atrioventricular Block Is Associated With Heart Failure and Death in Persons With Stable Coronary Artery Disease
European Heart Journal 2011; PMID 21606074
2.3x HF hospitalization risk, 1.6x mortality risk in stable CAD
Additional references
Lyme carditis
Yeung C, Baranchuk A
Diagnosis and Treatment of Lyme Carditis: JACC Review Topic of the Week
Journal of the American College of Cardiology 2019; PMID 30765038
Drug-induced arrhythmias
Tisdale JE, Chung MK, Campbell KB, et al
Drug-Induced Arrhythmias: A Scientific Statement From the American Heart Association
Circulation 2020
Athlete recommendations
Zipes DP, Link MS, Ackerman MJ, et al
Eligibility and Disqualification Recommendations for Competitive Athletes With Cardiovascular Abnormalities: Task Force 9
Circulation 2015
Geriatric arrhythmias
Curtis AB, Karki R, Hattoum A, Sharma UC
Arrhythmias in Patients >= 80 Years of Age: Pathophysiology, Management, and Outcomes
Journal of the American College of Cardiology 2018; PMID 29724357
Cardiac pacemakers
Mulpuru SK, Madhavan M, McLeod CJ, Cha YM, Friedman PA
Cardiac Pacemakers: Function, Troubleshooting, and Management
Journal of the American College of Cardiology 2017; PMID 28081829
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.