Pacemaker Therapy                                                                             

Indications

ACC/AHA Guidelines 1998

The most common indication for pacing in children is complete heart block although the sick sinus syndrome following atrial switch procedures (Senning and Mustard operations) is still relatively common. 

Transvenous Pacing

When permanent pacing is required, the usual approach is via the left sublcavian vein. A pacing wire is fed into the ventricle and connected to a programmable generator (“pacing box”) implanted under the skin. The generators are now very small  (approximately  50 mm in diameter and 8 mm thick. In dual chamber pacing an additional atrial lead is used. A pacing check is performed at implantation, one day later and then at regular intervals thereafter.

The generator can be programmed for different rates, voltage output, mode, sensitivity and rate responsiveness using a transmitter placed close to the skin. It can also be interrogated for patient events. The life of a generator is variable and depends on its output and frequency of use but is usually 5-10 years.

Epicardial Pacing

If small infants require pacing then the morbidity from a tranvenous approach may be considerable. The surgeon can then place a lead on the ventricle (epicardium) and the generator in the abdomen. These can readily be removed when the child is older and a transvenous system implanted.

Settings

Pacing modes follow an internationally agreed convention. Four letters are used. The first letter refers to the paced chamber, the second to the chamber where intrinsic activity is detected (sensing). The third refers to how the pacemaker reacts to the heart’s intrinsic electrical activity – usually inhibited. The fourth letter is "R" and denotes rate responsiveness to exercise. The common modes are VVI (paces & senses ventricle, inhibited by ventricular contraction), VVIR and DDD (paces & senses atrium & ventricle, inhibited by atrial &  ventricular contraction). This is the most physiological mode. AAI mode may be used in the sick sinus syndrome provided the AV node is normal.

Pacing is reflected on the ECG with a spike preceding the paced chamber. The above example shows a pacing spike initiating ventricular contraction (VVI mode in a patient with complete heart block). 

Troubleshooting

Pacemakers may become infected. This is most common around the time of implantation. It presents with fever, local inflammation, pain swelling and tenderness if the infection is sited around the pacemaker box or lead insertion site. It may also present as infective endocarditis with vegetations on the pacing lead (arrow). The system may need to be explanted to enable antibiotics to control the infection.

Failure to pace successfully may present with syncope or presyncope or be asymptomatic and noted at the pacemaker check or a routine ambulatory ECG. It may be due to generator failure (e.g. low battery), exit block (fibrosis between lead and myocardium), lead displacement or fracture (arrow). No pacing spikes are seen on the ECG.

Inappropriate sensing may also cause difficulties. If oversensing occurs the pacemaker may fail to pace when required. If undersensing the pacemaker may fail to sense at all pace when not required.

Temporary Pacing

Temporary pacing is most often required in the immediate postoperative period. It is such a common problem that temporary leads are placed on the atrium and ventricle and passed out through the chest wall at the time of surgery. They are removed by traction when no longer needed. Outside of the immediate post-operative period temporary pacing is rarely indicated. If necessary a lead (arrow) is inserted via the subclavian, jugular or femoral vein and connected to an external pacemaker box.
 

This page was last edited 14/2/2004