While pathologic bradyarrhythmias occur for a variety of reasons, clear indications exist for the use of external, or transcutaneous, pacing. This article will discuss not only those indications but also, other modalities that can be used alongside external pacing as potentially life-saving treatment. Technical details of external pacing and a comprehensive review of studies examining external pacing are also included in the discussion.
Normal electrical conduction through the heart originates in the sinoatrial node. This is located in the superior aspect of the right atrium. Conduction then spreads through the atrium to the atrioventricular node at the inferior portion of the right atria. From there, it travels down the Bundle of His. Followed by, the right and left bundle branches located in the interventricular septum. Lastly, it spreads across the ventricles via the Purkinje fibers.
In comparison, external cardiac pacing, pacer pads activate a focal point in the left ventricle. Electricity then spreads to the rest of the ventricular myocardium from that focal point. Direct capture of the atria is very difficult to obtain regardless of pad placement. Indirect capture can occasionally be obtained via retrograde conduction through the atrioventricular node.
Bradycardia is defined as a heart rate less than 60 beats per minute. However, not all cases of bradycardia require pacing. Rather, transcutaneous pacing should only be applied in situations of extremis. These include systolic blood pressure less than 90, heart rate less than 40, or if an arrhythmia is compromising organ perfusion. Prior to initiation of pacing, atropine can be given as a means of improving or reversing the bradycardia. Standard dosing is 0.5 milligrams intravenously. However, larger doses can be given in a patient who shows no improvement with the standard dose.
Patients who have had an acute myocardial infarction that has predisposed them to be atrioventricular (AV) block or sinus pauses are also candidates for pacing. As are cases of bradycardia caused by electrolyte disturbances, metabolic abnormalities or drugs (such as beta-blockers). Even patients who have unstable bradycardia secondary to sepsis may be candidates for external pacing. It is important to emphasize that external pacing is never a replacement for permanent invasive transvenous pacing. Third-degree heart block, a particular type of AV block characterized by an unstable rhythm with a high risk of degeneration to ventricular tachycardia or ventricular fibrillation, is also an indication for transcutaneous pacing.
Cases of ventricular tachycardia may also be improved with external pacing after all other options have been exhausted. Recurrence of the arrhythmia was prevented from recurring in 14 of 16 cases using transcutaneous overdrive pacing.
No definitive contraindications exist for external pacing when clinically indicated. Some negative sequelae associated with cardioversion have been seen. These outcomes include failure of an implanted ventricular lead and failure of an implanted atrial lead. While these adverse reactions are from a very limited number of cases secondary to cardioversion, it is possible to extrapolate that external pacing may result in the same complications.
Only trained healthcare providers should perform external pacing.
If possible, the skin should be prepared prior to placement of the pacer pads. Hair should be removed, but not shaved as this can create a nidus for infection. The skin should be cleansed with an alcohol wipe to remove any dirt, debris, or sweat whenever possible to ensure maximum conduction between the pads and the skin.
Multiple variations of pacer pad placement have been shown to be equally effective. "Negative electrode in the left parasternal region, the positive electrode in right subscapular region; a negative electrode in the left parasternal region, a positive electrode in the left subscapular region; or negative electrode at cardiac apex, a positive electrode in the right parasternal region." As long as the apical/anterior pad is negative, precise electrode placement is not essential.
The rate should be set between 60 to 90 beats per minute with the electrical output, also known as the current, set to its lowest setting. The rate should be slowly increased until a pacer spike is seen on the monitor. Continue to increase the rate until a QRS complex follows each spike. This indicates electrical capture. Confirmation of mechanical capture should be done by feeling for a pulse. Additionally, mechanical capture can be confirmed using ultrasound and by observing ventricular contraction.
In subjects with normal left ventricular function, pacing may reduce stroke volume by approximately 24%. This change was also seen in patients with heart failure. Both external and internal pacing caused a reduction in ejection fraction. There were no significant differences between the reduction that external pacing caused and the internal reduction pacing caused. To maintain approximate cardiac output, the rate of pacing can be increased.
Side effects of transcutaneous pacing include cutaneous burns and muscle contractions. Superficial injury from the pacing pads resembles mild folliculitis. It is well known that the muscle contractions can be extremely painful. To the point that sedation/anesthesia may be required. While the muscle contractions can be painful, no skeletal or myocardial muscle injury (as measured by CK, CK-MB, and troponin blood levels) developed after 30 minutes of pacing at 38 to 70mA with rates 10-20% above resting heart rate. Most cases of cutaneous burns are mild. However, there is a case report of an 86-year old female who sustained 3rd-degree burns. She was externally paced for 2 hours while waiting for an internal pacemaker to be placed. Third-degree burns have also occurred in neonates and children. Risk of burns likely increases when pacer pads are used against manufacture instructions and are reapplied for multiple uses.
Two promising new ways of non-invasive pacing are currently being studied to mitigate the side effects of current transcutaneous pacing techniques. The first uses high-intensity frequency ultrasound to stimulate pacing. The second uses iron microparticles injected intravenously and a generated magnetic field to pace in a concept known as mechano-electrical feedback.
External pacing is one of the quickest and easiest methods for treating multiple types of conduction abnormalities. Everything from bradycardia to ventricular tachycardia can be managed with external pacing until definitive treatment can be implemented. Furthermore, it can be used under a variety of circumstances, ranging from drug-induced electrical disturbances to conduction system inhibition secondary to myocardial infarct. It can be applied in the hospital setting or used by emergency medical service (EMS) providers when transporting critically ill patients.
External pacing is a procedure that is sometimes required on the medical and surgical floors. While the physician may actually initiate the pacing, it is the nurse who is primarily responsible for monitoring of the patient. Hence, nurses have to be familiar with external pacing and its indications. Before the pacing is initiated, the patient should be educated about the potential complications such as burns or failure to capture. The patient should also be informed about the potential discomfort of tingling or small shock like nerve impulses. The nurse has to be fully aware that transcutaneous pacing may not always work and must be prepared to have a transvenous pacer system kit and atropine at the bedside. Finally, the nurse should make sure that no person may use their mobile phones or other electronic devices near the patient as this may interfere with the pacing unit. An appropriate warning sign needs to be placed on the door.
Studies have shown that the hemodynamic effects are similar between external pacing and internal right ventricular pacing. However, currently available studies do not show that transcutaneous pacing improves patient outcomes. Data available is very limited. Most studies available have sample sizes less than 150 patients and the time to application of the pacing was greater than 20 minutes. Larger studies with earlier application times are needed to confirm the effect of transcutaneous pacing on patient outcomes.
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