Coronary occlus: Resulting heart blk

In most patients who have no previous heart block, myocardial ischemia resulting in conduction abnormalities usually occurs from injury to the AV node. Thus, the SA node is functioning normally but there can be delay of signal transmission through the AV node or the distal bundles. Most commonly following MI, this is seen due to occlusion of the right coronary artery (RCA). In 90% of patients the AV Nodal Branch Artery (AVNBA) arises off of the RCA. Occlusion of the RCA manifests as junctional escape rhythms, 2nd degree AV block or even complete heart block. Beta or calcium channel blockade in these patients can be devastating.

There are various other injuries that can cause heart block in a patient with MI or undergoing cardiac surgery. Damage to the distal RCA below the take-off of the AVNBA leading to RBBB or in a patient with pre-existing LBBB can lead to complete heart block but below the level of the AV Node manifesting as heart block with ventricular escape. If the patient has baseline RBBB and there is damage to the PDA or the LAD, a resultant complete heart block can occur or a bifasicular block can occur. This can be hard to predict since there are two L bundles with varied coronary blood supply.