Transvenous temporary pacing, much less painful than the transthoracic method, is required for many indications such as a bridge to permanent pacing, especially for patients who are unable to undergo immediate permanent implantation or for patients whose bradycardia is severe and hemodynamically (blood pressure, pulse rate) unstable. It is required most often in patients with severe infranodal block and less frequently with AV nodal block and sick sinus syndrome (see figures 16, 17). It may be required to treat significant bradycardia due to drugs such as an excess of digitalis. Anticipated or actual bradyarrthythmia during acute myocardial infarction also may require temporary pacing. The onset of a right bundle branch block (RBBB) of the cardiac conductive system (see figure 104B) may precede infranodal block. An abrupt change may occur from 1:1 conduction to Mobitz II second degree block (see figure 17) or complete asystole. The lack of an escape rhythm makes the above possibilities dangerous and warrants temporary pacing, even with only the onset of RBBB in the presence of an acute anterior myocardial infarction.

Temporary pacing of either atrium or ventricle frequently is useful after cardiac surgery, since transient bradyarrhythmias and atrial flutter (see figures 5A, 5B) are common. Also, it can be used in recurrent tachyarrhythmias like torsades de pointe (see figure 13) and incessant ventricular tachycardia (see figure 12).

As in permanent pacing each system requires leads and a pacing generator. Standard transvenous pacing leads are inserted percutaneously into femoral, internal, jugular, or subclavian veins, usually under flouroscopic control.

 

Permanent Pacing

 

Pacing in Congenital Atrioventricular Block

Congenital heart block is usually due to AV nodal block. Patient tend to be asymptomatic and typically have narrow QRS complex rhythms. However, congenital AV block is associated
with serious and possible fatal complications, including syncope and sudden death.In one .study, a mean daytime heart rate
less than 50 beats per minute was associated with sudden death
or need for pacemaker. Exercise testing is useful to assess response at rest and exercise.Other indicators of poor
outcome include prolonged QT interval (corrected for heart rate), cardiomegaly. atrial enlargement. decreased left ventricular systolic function, mean ventricular rates lower than median for age,periods of junctional exit block, and mitral regurgitattion.
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