Syncope, dizziness, and acute heart failure are common. Asystole is a constant threat. With complicating inferior MI, third-degree heart block may respond to atropine and usually resolves spontaneously. When associated with anterior MI, it signifies an extensive MI with serious immediate and late prognoses. Cardiac output usually is maintained by an escape ventricular pacemaker, but its inherent rate may be very low and its rhythmicity unreliable.
Treatment is by emergency insertion of a transvenous pacemaker electrode.
External pacing is possible using a long-duration electrical pulse delivered through large adhesive pads, and this may be a useful support until an endocardial system can be inserted. Isoproterenol should generally be avoided. Long-term management is by permanent pacing. A simple VVI unit will preserve life, but a lack of rate response may significantly impair exercise capacity. However, the sinus node, when undiseased and reliably activating the atria, is the ultimate sensor for heart rate needs.