Temporary pacing (1)

When the heart’s intrinsic pacemaking ability fails, temporary internal or external pacing can be instituted. Internal electrodes can be endocardial (inserted via a central vein) or epicardial (placed on the external surface of the heart at thoracotomy). The endocardial wire may be placed under fluoroscopic control or ‘blind’ using a balloon flotation catheter. External pacing can be rapidly performed by placement of two electrodes on the front and rear chest wall when asystole or third degree heart block has produced acute haemodynamic compromise. It is often used as a bridge to temporary internal pacing. It can also be used as a prophylactic measure, e.g. for Mobitz type II second degree heart block.

Indications

• Third degree heart block.

• Mobitz type II second degree heart block when the circulation is compromised or an operation is planned.

• Overpacing (rarely; more successful with internal pacing).

• Asystole.

Complications

Internal pacing

• As for central venous catheter insertion.

• Arrhythmias.

• Infection (including endocarditis).

• Myocardial perforation (rare).

External pacing

• Discomfort.

Failure to pace

1 No pacemaker spikes seen: check connections, check battery.

2 No capture (pacing spikes but no QRS complex following): poor positioning/dislodgement of wire. Temporarily increase output as this may regain capture. Reposition/replace internal pacing wire.

General

1 Check threshold daily as it will rise slowly over 48–96h, probably due to fibrosis occurring around the electrodes.

2 Overpacing may be used for a tachycardia unresponsive to anti-arrhythmic therapy or cardioversion. For SVT, pacing is usually

attempted with the wire sited in the right atrium. Pace at rate 20–30bpm above patient’s heart rate for 10–15s, then either decrease

rate immediately to 80bpm or slowly by 20bpm every 5–10s.

3 If overpacing fails, underpacing may be attempted with the wire situated in either atrium (for SVT) or usually ventricle (for either SVT

or VT). A paced rate of 80–100bpm may produce a refractory period sufficient to suppress the intrinsic tachycardia.

4 Epicardial pacing done during cardiac surgery uses either two epicardial electrodes or one epicardial and one skin electrode (usually

a hypodermic needle). The pacing threshold of epicardial wires rises quickly and may become ineffective after 1–2d.

5 In asystole, paced rhythm does not guarantee cardiac output.