What are the possible complications of first-degree atrioventricular (AV) block?

Updated: Jan 06, 2020
  • Author: Jamshid Alaeddini, MD, FACC, FHRS; Chief Editor: Jose M Dizon, MD  more...
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Patients with first-degree AV block can occasionally progress to higher-grade AV blocks. Usually, such a progression is only to Mobitz 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 AVN 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.

Other potential complications include reduction in left ventricular stroke volume and cardiac output due to loss of the atrial contribution to ventricular contraction, as well as pacemaker syndrome. [22]

In pacemaker syndrome, which can follow placement of a pacemaker, patients with very prolonged PR interval, especially in those with PR intervals longer than 300 msec, may experience the atrial contraction occuring too close to the previous ventricular contraction (ie, loss of AV synchrony). [23] If the atrial contraction occurs while the atrioventricular valves are closed, it can result in a significant increase in atrial pressures, which leads to a reversal of blood flow and abnormal pressure waves. Most of the signs and symptoms of pacemaker syndrome are nonspecific, but it may present as dizziness, near syncope, syncope, shortness of breath, chest pain, a feeling of neck tightness, and hypotension.

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