Bradycardia can arise from two basic mechanisms. Very first, decreased automaticity from the sinus node can result in sluggish heart prices or pauses. If sinus node pacemaker action ceases, the heart will generally be activated at a slower rate by other cardiac tissues with pacemaker action.
Decreased sinus node automaticity can occur throughout periods of elevated vagal tone (sleep, carotid sinus massage, “common faint”), with increasing age and secondary to medicines (beta-blockers, calcium channel blockers). 2nd, sluggish heart rates can occur if the cardiac impulse is prevented from activating the ventricles normally due to blocked conduction.
Simply because the fibrous valvular annulus is electrically inert, the AV node and His bundle normally form the only electrically active connection between the atria and also the ventricles. Although this arrangement is useful for preventing feedback between the two chambers, it also makes the AV node and His bundle vulnerable websites for obstructed conduction in between the atria and ventricles.
Although prevent could be observed in possibly the left or right bundle branches, bradycardia doesn’t necessarily happen, because the ventricles can nevertheless be activated by the contralateral bundle. Atrioventricular prevent has been classified as first degree when there’s an abnormally long atrioventricular conduction time (PR interval > 0.22 s) but activation from the atria and ventricles nevertheless demonstrates 1:1 association.
In second-degree atrioventricular block, some but not all atrial impulses are conducted to the ventricles. Lastly, in third-degree block, there’s no association in between atrial and ventricular action. Atrioventricular prevent can occur with increasing age, with increased vagal input, and being a side effect of particular drugs.
Atrioventricular block can occasionally be observed also in congenital disorders such as muscular dystrophy, tuberous sclerosis, and maternal systemic lupus erythematosus and in acquired disorders such as sarcoidosis, gout, Lyme disease, systemic lupus erythematosus, ankylosing spondylitis, and coronary artery illness. Bradycardia resulting from possibly decreased automaticity or obstructed conduction calls for evaluation to detect reversible causes.
Nevertheless, implantation of the permanent pacemaker is frequently required.