<P> Hyperkalemia in those with previous cardiac disease and Lyme disease can also result in third - degree heart block . </P> <P> The prognosis of patients with complete heart block is generally poor without therapy . Patients with 1st and 2nd degree heart block are usually asymptomatic . </P> <P> Treatment in emergency situations ultimately involves electrical pacing . Pharmacological management of suspected beta - blocker overdose might be treated with glucagon, calcium channel blocker overdose treated with calcium chloride and digitalis toxicity treated with the digoxin immune Fab . </P> <P> Third - degree AV block can be treated by use of a dual - chamber artificial pacemaker . This type of device typically listens for a pulse from the SA node via lead in the right atrium and sends a pulse via a lead to the right ventricle at an appropriate delay, driving both the right and left ventricles . Pacemakers in this role are usually programmed to enforce a minimum heart rate and to record instances of atrial flutter and atrial fibrillation, two common secondary conditions that can accompany third - degree AV block . Since pacemaker correction of third - degree block requires full - time pacing of the ventricles, a potential side effect is pacemaker syndrome, and may necessitate use of a biventricular pacemaker, which has an additional 3rd lead placed in a vein in the left ventricle, providing a more coordinated pacing of both ventricles . </P>

Where does the action potential begin in a 2nd degree av block