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In some cardiac arrest or peri-arrest settings, use of cardiac pacing can be life-saving. Non-invasive pacing can be established rapidly and may be used to maintain cardiac output temporarily while expert help to deliver longer-term treatment is obtained.
Methods of Pacing
- Percussion pacing
- Transcutaneous pacing
- Temporary transvenous pacing
- Permanent pacing (using an implanted pacemaker)
When bradycardia is so profound that it causes clinical cardiac arrest, percussion pacing can be used in preference to CPR because it may produce an adequate cardiac output with less trauma to the patient. It is more likely to be successful when ventricular standstill is accompanied by continuing P wave activity.
Percussion pacing is not as reliable as electrical pacing in stimulating QRS complexes. If percussion does not produce a regular pulse promptly, regardless of whether or not it generates QRS complexes, start CPR immediately.
- With the side of a closed fist deliver repeated firm thumps to the praecordium, just lateral to the lower left sternal edge
- Raise the hand about 20 cm above the chest before each thump
- Monitor the ECG and assess whether a QRS complex is generated by each thump
- If possible a second person should check whether a pulse is generated by each QRS complex
- If initial thumps do not produce a QRS complex, try using slightly harder thumps
- If this still fails to produce a QRS complex, move the point of contact around the praecordium until a site is found that produces repeated ventricular stimulation
Compared with transvenous pacing, non-invasive transcutaneous pacing can be established much more quickly, is easy to perform with minimal training and experience. The main disadvantage in the conscious patient is discomfort. The pacing impulse stimulates painful contraction of chest wall muscles as well as causing some direct discomfort.
- Warn conscious patients that they are likely to experience considerable discomfort during pacing; be ready to give them intravenous analgesia or sedation as required particularly if prolonged pacing is needed
- If necessary, use scissors or a razor to quickly remove excess chest hair from the skin where the electrode is to be applied, and make sure the skin is dry
- If necessary attach ECG monitoring electrodes and leads; these are needed with some transcutaneous pacing devices
- Position the pads in the ‘conventional’ right pectoral and apical positions if possible; one pad over the right pectoral muscle just below the clavicle and one pad in the left-mid-axillary line overlying the V6 ECG electrode position
- If the above positions are not possible, use the anterior-posterior (A-P) pad positions; place the anterior pad on the left anterior chest wall beside the sternum overlying the V2/V3 ECG electrode position, and the posterior pad between the lower part of the left scapula and the spine at the same horizontal level on the trunk as the anterior pad
- Most transcutaneous pacing devices pace the heart in demand mode in which the device will be inhibited if it detects a spontaneous QRS complex and delivers a pacing stimulus only when it is needed; however if there is movement artefact on the ECG this may inhibit the pacemaker
- Select an appropriate pacing rate; usually in the range of 60 – 90 bpm but in some circumstances a slower pacing rate may be appropriate in order to deliver pacing only during sudden ventricular standstill or more extreme bradycardia
- If the pacing device has an adjustable energy output, set this at the lowest value and turn on the pacemaker; gradually increase the output whilst observing the patient and the ECG; as the current is increased the muscles of the chest wall will contract with each impulse and a pacing ‘spike’ will appear on the ECG; increase the current until each pacing spike is followed immediately by a QRS complex indicating electrical capture
- Check that the QRS complex is followed by a T wave; occasionally artefact generated by the pacing current travelling through the chest might look like a QRS complex but such artefact will not be followed by a T wave
- If the highest current setting is reached and electrical capture has not occurred, try changing the electrode positions; continued failure to achieve electrical capture may indicate non-viable myocardium
- Having achieved electrical capture with the pacemaker, check that each paced QRS complex is followed by a pulse; a palpable pulse confirms a mechanical response of the heart to the paced QRS complex; good electrical capture that failures to generate a pulse constitutes PEA, if necessary provide chest compressions
- When transcutaneous pacing produces an adequate cardiac output seek expert help immediately to arrange emergency transvenous pacing
Temporary Transvenous Pacing
It is rarely appropriate to try to attempt to insert a transvenous pacing wire during cardiac arrest. In this setting, use a non-invasive pacing to attempt to achieve a cardiac output and then seek expert help with transvenous pacing.