Читать книгу Practical Cardiovascular Medicine - Elias B. Hanna - Страница 140

The sinus nodal artery originates from the proximal RCA (60%) or the LCx (40%). The AV nodal artery originates from the AV groove con- tinuation of a dominant RCA (90%) or a dominant LCx (10%).

In inferior MI, sinus bradycardia and AV blocks may develop in the first 24 hours, at which time they are usually brief and result from the increased vagal tone that accompanies inferior MI. Beyond 24 hours, the AV block is due to ischemia and edema of the AV node and is more persistent, but eventually resolves within a few days (<1 week). The AV node is resistant to ischemia, and therefore it almost never infarcts. When AV block is seen along with a fast P-wave rate, the block is due to nodal ischemia or edema, rather than a high vagal tone.

The AV block being at the nodal level, it may manifest as first-degree AV block, second-degree type I AV block, or complete AV block with a junctional rhythm (rate 40–100). Those blocks are usually well tolerated, develop gradually (first-degree to second-degree then third-degree AV block), and resolve gradually. Complete AV block is seen in ~4-5% of inferior MIs, mostly on the first day.^150,151

Complete AV block is associated with a larger MI, more RV MI, and a 2-fold higher in-hospital mortality.^150,151 Patients who survive to hospital discharge, however, do not have an increase in long-term mortality in some,¹⁵² but not all studies.¹⁵⁰

Treatment – AV block that occurs in the first 24 hours responds to atropine, which should be used in case of hemodynamic instability. Since it is not driven by a high vagal tone, later AV block (>24 hours) does not typically respond to atropine but may respond to aminophylline (adenosine-receptor blocker) (ACC); being usually well tolerated with a good escape, complete AV block does not require pacing. It only requires temporary transvenous ventricular pacing in case of shock, HF, or low-output signs.

Symptomatic sinus bradycardia or pauses are initially treated with up to 2 mg of atropine. Transcutaneous or transvenous pacing may be used if symptomatic bradycardia persists.