Cardiac pacing is a potentially life-saving skill to which emergency physicians often have a limited exposure during their careers. Although many modalities of cardiac pacing have been described in the literature, transcutaneous and transvenous pacing have emerged as the preferred methods for use in the emergency department. This article will review the indications, contraindications, benefits, use, and possible complications of these pacing modalities. Transcutaneous Pacing: Indications Since it was originally described in 1952 by Zoll for the treatment of asystole as well as of bradydysrhythmias, transcutaneous pacing has continued to be used in the emergency setting. This noninvasive method of cardiac pacing allows for expedient placement and initiation of therapy without the risks of an invasive procedure. Symptomatic bradydysrhythmias represent the primary indication for the use of transcutaneous pacing. The pathophysiology that results in a slowed ventricular rate may be subdivided into two main etiologic classifications: disorders of impulse formation (such as sinus arrest or sinus bradycardia) and disorders of impulse conduction (such as second- or third-degree AV blocks). Etiologies that are not responsive to medical treatment may require the initiation of cardiac pacing to ensure adequate cardiac output. Transcutaneous pacing may serve as a needed bridge until transvenous or permanent pacemaker placement can occur. Transcutaneous Pacing: Contraindications In the past, cardiac pacing has been used for the treatment of asystolic cardiac arrest. However, randomized controlled trials have failed to demonstrate that it improves mortality. As a result, the 2010 AHA ECC guidelines recommend against the routine use of cardiac pacing for the treatment of asystolic cardiac arrest. In patients with significant hypothermia, bradydysrhythmias are frequently present; however, it is hypothesized that electrical derangements are a direct result of low temperature on the myocardial cells and not of a primary conduction abnormality. The evidence on the effect of cardiac pacing in these patients is mixed, and no recommendations exist regarding the use of pacing in the hypothermic patient. Transcutaneous Pacing: Procedure In the emergency department, most of the equipment needed for transcutaneous pacing is often contained in a predesignated crash cart. Successful initiation of transcutaneous pacing requires: •ECG monitoring equipment with monitor and cables. •ECG patches. •Pulse generator unit. •Pacer pads and cables. •Analgesia and sedation medications. Prior to the initiation of cardiac pacing, all patients should be placed on a continuous ECG monitor. This will aid in the diagnosis of the underlying dysrhythmia, as well as provide evidence of the cardiac response to pacing efforts. Newer pacer/defibrillator units often have pacing functionality in addition to the standard defibrillating setting, obviating the need for a second generator unit for transcutaneous pacing. Current pacing pads often are available with attached pacing cables, as well as adhesive surfaces to optimize contact with the patients skin. There are two placement configurations recommended for maximum cardiac response. One option is to center a pad over the apex of the heart and place the other on the right upper chest. Alternatively, a pad may be placed over the V3 lead position, while the other is placed between the left scapula and the thoracic spine. Transcutaneous pacing can be quite uncomfortable for patients who are conscious, as it requires the discharge of electrical impulses through the skin and chest wall muscles. Therefore, sedation and analgesia should be considered to help reduce this discomfort. Side effects of sedation and analgesia can exacerbate the condition of patients with significant hemodynamic compromise, so extra care should be taken when dosing these patients. The initial pacing rate should be set to 80 bpm with the current set to minimal output. Initially, pacer spikes may be visualized without resultant cardiac depolarization. The current can be increased by 5-10 mA at a time until a definite QRS complex and T wave is demonstrated following each pacer spike. Check the patients pulse at this point to confirm that electrical capture results in physiologic hemodynamic response. This level is defined as the pacing threshold and will be found between 40 and 80 mA for most healthy patients. Final current output should be set to 5-10 mA above the threshold level to ensure continued capture. Transvenous Pacing: Indications The use of transvenous pacing is technically more difficult and invasive than transcutaneous pacing but can provide substantial benefit to the patient. Proper placement requires a knowledgeable practitioner. With appropriate training, emergency physicians can be proficient in this skill. As with transcutaneous pacing, symptomatic bradycardia is the primary indication for transvenous pacemaker placement. Transvenous pacing should also be considered for patients who are unable to tolerate transcutaneous pacing or the hemodynamic effects of sedation, or in whom transcutaneous pacing fails to obtain or maintain electrical capture. In addition, prophylactic placement has been described for conditions that pose a high risk for progressing to symptomatic bradydysrhythmias. These conditions include asymptomatic bradydysrhythmias, new bundle branch/bifascicular block, or following an acute MI. Occlusion resulting in anterior or inferior infarct may involve the conduction system and predispose a patient to dysrhythmias, with a subsequent increase in mortality. Transvenous Pacing:Contraindications Contraindications to transvenous pacing are similar to those mentioned above for transcutaneous pacing. Because of the need to introduce the pacing lead into the central venous system, distortions of anatomy or bleeding dyscrasias remain relative contraindications and must be assessed prior to placement. Cardiac glycoside toxicity, as well as other drug ingestions, can cause myocardial irritability and increase the risk of ventricular fibrillation as the pacing lead is introduced. Therefore, possible drug ingestion should be assessed prior to transvenous placement. Transvenous Pacing:Procedure Transvenous pacing begins with cannulation of the central venous system followed by the introduction of the pacing catheter. The equipment that is necessary for successful transvenous pacing includes: •ECG monitoring equipment with monitor and cables. •ECG patches. •Sterile gown, gloves, drapes. •Sheathed, single-lumen central venous catheter. •Pulse generator unit. •Pacer cables. Several anatomic sites may be used to gain access to the central venous system. The right internal jugular vein and the left subclavian vein are the preferred sites of entry. Once the patient is monitored with routine ECG readings, sterile technique is used to prepare the site for central venous access. A single-lumen catheter may be placed and secured using standard technique. The pacing catheter contains a small balloon at the distal tip that must be checked for leaks prior to insertion. This can be accomplished by filling the balloon with 1.5 mL of air while the balloon rests in a container of saline. The presence of bubbles in the saline indicates a leak in the balloon, and a new catheter will be needed. Once the balloon has been confirmed to be intact, connect the positive and negative electrodes to the external pacemaker unit and advance the catheter through the introducer sheath to roughly 20 cm. Once the catheter is advanced, inflate the balloon with the appropriate volume of air. Recommended volumes may differ based on the specific brand of product used, and practitioners are encouraged to refer to product packaging for the correct volume. The pacer may be turned on at this point with an initial setting of 80 bpm and the maximal current output (usually 20 mA). The sensitivity dial should be adjusted to the asynchronous setting. Multiple methods of advancing the pacer wire have been described. In the blind approach, the catheter is advanced slowly while the ECG monitor is watched for evidence of capture. Pacer spikes will begin to be apparent and will be soon followed by a widened QRS and have a similar appearance to a left bundle branch block as the electrode contacts the wall of the right ventricle. At this time, deflate the balloon and secure the catheter in place. Electrical current settings may be reduced until failure to capture is demonstrated to determine a threshold level. Final settings should be roughly twice the threshold value to ensure continued capture. Ultrasound has now been advocated as an additional method for determining lead placement and capture. Verification of placement is accomplished by chest radiography demonstrating the catheter tip over the inferior border of the cardiac shadow. Another approach uses the sensing function of the pacer to determine appropriate lead placement. The negative electrode of the pacer lead is attached via an alligator clip to any precordial lead on the patients chest. The remainder of the ECG leads should remain in their usual positions. Advance the wire slowly while watching the intracardiac lead for morphology changes consistent with superior vena cava, right atrial, right ventricle, or pulmonary artery waveforms. Engagement of the right ventricle endocardium by the pacer lead is indicated by an injury pattern of ST elevation. The pacer lead is then disconnected from the ECG and placed into the generator, and the generator is turned on using similar settings as above. Finally, fluoroscopy may be used in patient-care settings where it is available. Complications of Cardiac Pacing Transcutaneous pacing is much safer than transvenous pacing but is not without some complications. Discomfort and skin irritation can be seen, especially with higher-current settings. The majority of transvenous complications are related to central venous access. They include but are not limited to infection, pneumothorax, air embolism, arterial puncture, and venous thrombosis. Valvular tears or ruptures and perforations of the ventricular septum, atria, or ventricular free wall have been described and are most commonly seen with rigid catheters. Acute changes in ECG morphology, failure to capture, or sudden decompensation of the patient may be evidence of perforation. Catheter balloon rupture can result in a pulmonary embolism. Conclusion Cardiac pacing has emerged as a life-saving procedure that has found a place in the armamentarium of the emergency physician. Prompt recognition of pacing indications, successful initiation of therapy, and recognition of complications is integral to the successful use of this critical procedure. References •Birkhahn RH, et al. Emergency medicine-trained physicians are proficient in the insertion of transvenous pacemakers. Ann. Emerg. Med. 2004;43:469-74. •Fitzpatrick A, Sutton R. A guide to temporary pacing. BMJ 1992;304:365-9. •Harrigan RA, et al. Temporary transvenous pacemaker placement in the emergency department. J. Emerg. Med. 2007;32:105-11. •Labovitz AJ, Noble VE. Focused cardiac ultrasound in the emergent setting: A consensus statement of the American Society of Echocardiography and American College of Emergency Physicians. J. Am. Soc. Echocardiogr. 2010;23:1225-30. •Link MS, et al. Electrical therapies: Automated external defibrillators, defibrillation, cardioversion, and pacing (Part 6). 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2010;122:S706-19. •Mark J, Hockberger R, Walls R. Rosens emergency medicine, 7th ed. Elsevier, 2010. •Reichman EF, Simon RR. Emergency medicine procedures. McGraw Hill, 2004. •Zoll PM, Linenthal AJ, Norman LR. Treatment of unexpected cardiac arrest by external electric stimulation of the heart. N. Engl. J. Med. 1956;254:541-6.
Posted on: Thu, 03 Jul 2014 11:49:37 +0000
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