++

Sinus Node Dysfunction (“Sick Sinus Syndrome”)

++

  • Sinus bradycardia: Sinus rate of less than 60 bpm.
  • Sinoatrial exit block, type I: Progressively shorter P-P intervals, followed by failure of occurrence of a P wave.
  • Sinoatrial exit block, type II: Pauses in sinus rhythm that are multiples of basic sinus rate.
  • Sinus arrest, sinus pauses: Failure of occurrence of P waves at expected times.

++

Atrioventricular (AV) Block

++

  • First degree: Prolonged PR interval more than 0.2 seconds.
  • Second degree
    • • Type I: Progressive increase in PR interval, followed by failure of AV conduction and nonoccurrence of a QRS complex
    • • Type II: Abrupt failure of AV conduction not preceded by increasing PR intervals.
  • High degree: AV conduction ratio 3:1 or greater.
  • Complete: Independent atrial and ventricular rhythms, with failure of AV conduction despite temporal opportunity for it to occur.

++

General Considerations

++

The clinical presentation of patients with conduction system disease is determined by the existence of three underlying abnormal conditions: bradycardia, inability to increase the heart rate in response to increases in metabolic needs, and atrioventricular (AV) dyssynchrony (inappropriately timed atrial and ventricular depolarization and contraction sequences).

++

Pathophysiology & Etiology

++

Sinus Node Dysfunction

++

Sinus node dysfunction (“sick sinus syndrome”) is usually due to a degenerative process that involves the sinus node and sinoatrial (SA) area (Table 22–1). Often, the degenerative process and associated fibrosis also involve the AV node and its approaches as well as the intraventricular conduction system; as many as 25–30% of patients with sinus node dysfunction have evidence of AV and bundle branch conduction delay or block.

++
Table Graphic Jump Location
Table 22–1. Causes of Sinus Node Dysfunction. 
++

Respiratory sinus arrhythmia, in which the sinus rate increases with inspiration and decreases with expiration, is not an abnormal rhythm and is most commonly seen in young healthy persons. Nonrespiratory sinus arrhythmia, in which phasic changes in sinus rate are not due to respiration, may be accentuated by the use of vagal agents, such as digitalis and morphine, and is more likely to be observed in patients who are older and who have underlying cardiac disease, although the arrhythmia is not itself a marker for structural heart disease; its mechanism is unknown. Ventriculophasic sinus arrhythmia is an unusual rhythm that occurs during high-grade or complete AV block; it is characterized by shorter P-P intervals when they enclose QRS complexes. The mechanism is not known with certainty but may be related to the ...

Want access to your institution's subscription?

Sign in to your MyAccess Account while you are actively authenticated on this website via your institution (you will be able to tell by looking in the top right corner of any page – if you see your institution’s name, you are authenticated). You will then be able to access your institute’s content/subscription for 90 days from any location, after which you must repeat this process for continued access.

Ok

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess account, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessMedicine Full Site: One-Year Subscription

Connect to the full suite of AccessMedicine content and resources including more than 250 examination and procedural videos, patient safety modules, an extensive drug database, Q&A, Case Files, and more.

$995 USD
Buy Now

Pay Per View: Timed Access to all of AccessMedicine

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.