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Cardiac monitoring part 3: External pacing

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Phil Jevon

PGCE, BSc, RN, is resuscitation officer/clinical skills lead, Manor Hospital, Walsall

Cardiac pacing is the delivery of a small electrical current to the heart to stimulate myocardial contraction. External (transcutaneous or percussion) pacing can be established quickly and easily during cardiopulmonary resuscitation (CPR). It gives time for the spontaneous recovery of the conduction system or for more definitive treatment to be established, for example, transvenous pacing. This article describes two methods of external pacing.

Related anatomy and physiology

The conduction system of the heart is detailed in Fig 1.

The SA node (pacemaker of the heart) fires and the electrical impulse spreads across the atria, resulting in atrial depolarisation and contraction (the P wave).

After arriving at the AV node, the electrical impulse is then conducted down to the ventricles through the bundle of His, right and left bundle branches and Purkinje fibres, causing ventricular depolarisation and contraction (QRS complex).

Indications

Profound bradycardias for example sometimes found in complete heart block that has not responded to pharmacological treatment, such as atropine. Note that if the intrinsic QRS complexes are not associated with a pulse (pulseless electrical activity or PEA), attempts at pacing will be futile.

Ventricular standstill - P waves (atrial contraction) only on the ECG. Note that although pacing is not indicated in asystole, always carefully check the ECG for the presence of P waves (ventricular standstill) as this may respond to pacing (Nolan et al, 2005).

Advantages of trancutaneous pacing:

Can be quickly established;

Easy to undertake, minimal training;

Risks associated with central venous cannulation are avoided;

Can be undertaken by nurses (Resuscitation Council UK, 2000).

Percussion pacing

Percussion pacing is the delivery of gentle blows (from a height of several cm above the chest) over the precordium, lateral to the lower left sternal edge (Resuscitation Council UK, 2000). Trial and error will determine the optimum place for percussion.

Procedure for transcutaneous pacing

If appropriate, explain the procedure to the patient.

Ideally, first remove excess chest hair from the pacing electrode sites by clipping close to the patient’s skin using a pair of scissors. Shaving the skin is not recommended as any nicks in the skin can lead to burns and pain during pacing (Resuscitation Council UK, 2000).

Attach the pacing electrodes following the manufacturer’s instructions.

Pacing-only electrodes: attach the anterior electrode on the left anterior chest, midway between the xiphoid process and the left nipple (V2-V3 ECG electrode position) (Fig 2). Attach the posterior electrode below the left scapula, lateral to the spine and at the same level as the anterior electrode (Fig 3). This anterior/posterior configuration will ensure that the position of the electrodes does not interfere with defibrillation. ECG monitoring will usually need to be established if an older pacing system is being used (Resuscitation Council UK, 2000).

Multifunctional electrodes (pacing and defibrillation): place the anterior electrode below the right clavicle and the lateral electrode in the mid-axillary line lateral to the left nipple (V6 ECG electrode position). This anterior-lateral position (Fig 4) is convenient during CPR as chest compressions do not have to be interrupted (Resuscitation Council UK, 2000).

Check that the pacing electrodes and connecting cables are applied following the manufacturer’s recommendations. If they are reversed, pacing may be ineffective or high capture thresholds may be required (Resuscitation Council UK, 2000).

Adjust the ECG gain (size) accordingly. This will help ensure that the intrinsic QRS complexes are sensed.

Select demand mode on the pacing unit on the defibrillator.

Select an appropriate rate for external pacing, usually 60-90 per minute (Fig 5).

Set the pacing current at the lowest level, turn on the pacemaker unit and while observing both the patient and the ECG, gradually increase the current until electrical capture occurs (QRS complexes following the pacing spike) (Jevon, 2002). Electrical capture usually occurs when the current delivered is in the range of 50-100mA (Resuscitation Council UK, 2000) (Fig 6).

Check the patient’s pulse. If there is a palpable pulse (mechanical capture), request expert help and prepare for transvenous pacing. If there is no pulse, start CPR. If there is good electrical capture, but no mechanical capture, this is indicative of a non-viable myocardium. Note that there is no electrical hazard if in contact with the patient during pacing (Resuscitation Council UK, 2000).

Cautions

If the patient is conscious, analgesia and sedation will usually be required.

If pacing-only electrodes have been applied and defibrillation is subsequently indicated, position the defibrillation paddles least 2-3cm away from the pacing electrodes to avoid arching.

Turn off pacemaker unit during CPR to prevent inappropriate stimulation of the patient (Resuscitation Council UK, 2000).

 

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