AUTHOR AND EDITOR INFORMATION

Section 1 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Multimedia
• References

INTRODUCTION

Section 2 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Multimedia
• References

Background

On an electrocardiogram (ECG), the PR interval, which is defined as the time from the initial deflection of the P wave to the start of the QRS complex, should be between 120 and 200 msec. First-degree heart block, or first-degree atrioventricular (AV) block, is defined as prolongation of the PR interval on the ECG to more than 200 msec.

Pathophysiology

With first-degree AV block, every atrial impulse is transmitted to the ventricles, resulting in a regular ventricular rate. This type of AV block can arise from delays in the conduction system in the AV node itself, the His-Purkinje system, or a combination of both. Overall, dysfunction at the AV node is much more common than dysfunction at the His-Purkinje system. If the QRS complex is of normal width and morphology on the ECG, then the conduction delay is almost always at the level of the AV node. If, however, the QRS demonstrates a bundle-branch morphology, then the level of the conduction delay is often localized to the His-Purkinje system.

Frequency

United States

In the United States, the prevalence of first-degree AV block among young adults ranges from 0.65-1.6%. Higher prevalence is reported in studies of trained athletes (8.7%) and medical students (8%). The incidence is 1.13 per 1000 persons. It is more common among African Americans compared with Caucasian populations. The prevalence of first-degree AV block increases with advancing age.

Mortality/Morbidity

In and of itself, first-degree AV block is a benign condition, with no associated increase in morbidity or mortality.

CLINICAL

Section 3 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Multimedia
• References

History

• Patients may have a history of past heart disease, including myocarditis or myocardial infarction (MI).
• Patients may be highly conditioned athletes with a high degree of vagal tone, or they may be on medications that slow conduction through the AV node.
• A history of an infectious disease, such as Lyme disease, may be present.

Physical

No findings on the physical examination are associated with first-degree AV block; it is generally an incidental finding noted on an ECG.

Causes

• The following are the most common causes of first-degree AV block:
• • Intrinsic AV nodal disease
  • Enhanced vagal tone
  • Acute MI, particularly acute inferior wall MI
  • Myocarditis
  • Electrolyte disturbances
  • Drugs (especially those drugs that increase the refractory time of the AV node, thereby slowing conduction)
• Drugs that most commonly cause first-degree AV block include the following:
• • Class Ia antiarrhythmics (eg, quinidine, procainamide, disopyramide)
  • Class Ic antiarrhythmics (eg, flecainide, encainide, propafenone)
  • Class II antiarrhythmics (beta-blockers)
  • Class III antiarrhythmics (eg, amiodarone, sotalol, dofetilide, ibutilide)
  • Class IV antiarrhythmics (calcium channel blockers)
  • Digoxin or other cardiac glycosides
  • Magnesium

DIFFERENTIALS

Section 4 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Multimedia
• References

Other Problems to be Considered

Second-degree AV block
Third-degree AV block (complete heart block)
Junctional escape rhythms

WORKUP

Section 5 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Multimedia
• References

Lab Studies

• Routine laboratory studies are usually not indicated in the evaluation of first-degree AV block.
• Electrolyte and drug screen can be obtained if a metabolic derangement or drug toxicity is suspected.

Imaging Studies

• Routine imaging studies are not indicated.

Other Tests

• Follow-up ECGs may be indicated in patients who are treated with AV nodal agents while in the ED as well as for patients with a concomitant MI.

TREATMENT

Section 6 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Multimedia
• References

Emergency Department Care

No specific therapy is indicated for isolated first-degree AV block. Any associated condition (eg, myocardial infarction digitalis intoxication) should be treated appropriately.

Consultations

No emergent consultation is necessary. Outpatient cardiology follow-up can be arranged, if desired.

FOLLOW-UP

Section 7 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Multimedia
• References

Further Inpatient Care

• Hospitalization specifically for first-degree AV block is not indicated. However, admission may be indicated for associated conditions (eg, myocardial infarction).
• Significant electrolyte abnormalities should be corrected.

Further Outpatient Care

• In the absence of a disease process that requires admission, patients with first-degree AV block may be safely discharged and receive follow-up on an outpatient basis.
• Patients should get serial follow-up ECGs to evaluate for progression to a higher-grade AV block.
• Patients with first-degree AV block and coexistent bundle-branch block should be closely observed.

Complications

• Patients with first-degree block can occasionally progress to higher-grade AV blocks. Usually, such a progression is only to a Mobitz type I, second-degree heart block, but occasionally, higher-grade block can occur. The later scenario is particularly seen in patients with an acute MI, myocarditis, or acute drug overdoses.
• Drugs that slow conduction through the AV nodal system increase the risk of progression to higher-grade heart blocks. Administering such agents to a person with a coexisting first-degree AV block should be done with caution.

Prognosis

• The prognosis for isolated first-degree AV block is very good.

MULTIMEDIA

Section 8 of 9  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Multimedia
• References

Media file 1:  ECG in a patient with first-degree heart block.
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Media type:  ECG

Media file 2:  ECG in a patient with first-degree heart block.
	View Full Size Image
Media type:  ECG

REFERENCES

Section 9 of 9

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Multimedia
• References

• Bexton RS, Camm AJ. First degree atrioventricular block. Eur Heart J. Mar 1984;5 Suppl A:107-9. [Medline].
• Hesler RA. Cardiovascular principles. In: Goldfrank LR, Howland MA, Flomenbaum NE, et al, eds. Goldfrank's Toxicologic Emergencies. 7^th ed. New York: McGraw Hill; 2002:315-34.
• Mymin D, Mathewson FA, Tate RB, Manfreda J. The natural history of primary first-degree atrioventricular heart block. N Engl J Med. Nov 6 1986;315(19):1183-7. [Medline].
• Upshaw CB. Comparison of the prevalence of first-degree atrioventricular block in African-American and in Caucasian patients: an electrocardiographic study III. J Natl Med Assoc. Jun 2004;96(6):756-60. [Medline].
• Yealy DM, Delbridge TR. Dysrhythmias. In: Marx JA, Hockberger RS, Walls RM, eds. Rosen's Emergency Medicine. Concepts and Clinical Practice. 5^th ed. Mosby: 2002:1053-98.
• Zipes DP. Specific arrhythmias: Diagnosis and treatment. In: Braunwald E, ed. Heart Disease: A Textbook of Cardiovascular Medicine. 3^rd ed. WB Saunders Co; 1988:658-716.

Article Last Updated: Sep 5, 2006