Pace Yourself

     You shake your head in disbelief as you look at the cardiac monitor. Your patient, a 67-year-old female, was supposed to be a routine transfer. Although she has a history of angina and asthma, she was in good spirits and comfortable while you took the report at the sending hospital. During your transport to a regional cardiac center for a routine workup, things changed for the worse. Following a simple complaint of weakness, your patient's vitals quickly changed to a heart rate of 32, a blood pressure of 70/42, a respiratory rate of 20 with clear lung sounds, and an SpO₂ of 87%. Her appearance became pale and diaphoretic, and she is now unresponsive to painful stimuli. You're glad you placed a larger-bore IV before transporting, because as you look at the cardiac monitor, you see an ominous third-degree AV block...

     The ability of the heart to pump effectively depends on an intact and normally functioning electrical system. Any alteration to the pathways, strength or presence of this electrical signal will result in dramatic vital sign changes, generally for the worse. The good clinician must consider all options when facing this electrical problem. In this article, we will focus on the use of the cardiac pacemaker to treat a slow cardiac rhythm.

Pacemaker 101
     The term pacemaker can be generically applied to four types of devices: implanted, transvenous, transthoracic and transcutaneous. Implanted pacemakers may be noticed by a small protrusion under the patient's skin, often near the lower left rib cage or upper anterior chest. Visible pacer spikes found upon examining EKG tracings are indicative of implanted pacemakers (although modern technology has significantly reduced their size, and they may be difficult to see).

     Transvenous pacemakers are temporary in nature and are "floated" through the jugular vein in emergent hospital settings. Transthoracic pacemakers are surgically implanted and leave small wires outside the chest wall that are connected to a control box that controls the pacemaker's function. Transcutaneous pacemakers-the type with which EMS providers will be most familiar-are attached to the chest wall through use of multifunction electrode (MFE) pads attached to a portable cardiac monitor/defibrillator/pacer. We will focus on this type of pacemaker.

How They Work
     The pacemaker, regardless of type, is designed to introduce an electrical stimulus to produce a heartbeat. By generating an electrical signal of sufficient strength, we basically fool the heart into thinking this external signal is the inherent rate of the heart itself, and as a result, hopefully the muscle and strength of contraction respond accordingly. Because of this, pacemakers are flexible in both the rate at which they generate impulses and the strength of these impulses. Although surgically implanted pacemakers may control both the atria and the ventricles, prehospital pacemakers generally affect the rate of the ventricles and ignore the atria. The MFE pads are not able to specify which heart chamber is stimulated. The ventricles are generally more responsive to outside stimuli, and the depolarization and contraction of the ventricles will result in more benefit to the patient than atrial contraction alone. A person can survive on functioning ventricles alone, but not solely on atria.

Indications
     Although state and local protocols may vary, the basic consideration for application of a pacemaker is a heart rate that is too slow (generally below 60 bpm) to allow for effective circulation and is causing symptoms. Current recommendations from the American Heart Association are to use pacemakers for "treatment of symptomatic bradycardia" and that "immediate pacing is indicated if the patient is severely symptomatic." These symptoms of poor perfusion generally include "hypotension, acute altered mental status, chest pain, congestive heart failure, seizures, syncope or other signs of shock related to bradycardia." AHA no longer recommends the use of pacemakers for asystolic patients, and encourages providers instead to provide effective CPR.

Using a Pacemaker
     The use of prehospital pacemakers is fairly simple, but a few missteps can lead to frustration and poor results. Ensure the basics are taken care of: complete patient assessment, ensuring a secure airway, providing high-flow oxygen and effective IV access. For proper pacemaker use, the limb leads must be applied-this is probably the biggest error providers make. Although some models allow for pacing without use of limb leads, that means it's being done completely blind (i.e., you have no idea of the underlying heart rhythm). This is equivalent to defibrillating someone who is unconscious about whom you know nothing else. Again, attach the limb leads. Put them on the extremities, not the chest wall and abdomen. The limitation of the MFE pads is that they are a one-way street: You can read Lead II or deliver electricity, but not at the same time.

     Correct pacing depends on the underlying EKG, but if MFE pads were used alone, electricity being delivered for the pacing would prevent seeing the underlying EKG. Obviously, MFE pads must be applied to the chest, so a completely bare chest is critical. Remove any chains or necklaces that may come into contact with the pads, or at least ensure they are moved out of the way. The pads are most commonly applied in one of the two locations used for AED pads:

• Sternal-apical (anterolateral), the standard placement at the right of the sternum and near the lower left border of the rib cage;
• Anterior-posterior, on the front of the chest and on the right or left back.

     The goal should always be to provide a direct line from each pad to pass electricity directly through the heart, so careful placement is important. As mentioned, pacers are generally used on the sickest of patients, and these patients may be extremely diaphoretic. Drying the chest will help with adhesion. If the patient has significant chest hair, providers may need to shave the area. Apply the MFE pads and smooth any wrinkles out, as wrinkles may cause arcing. If an existing pacemaker or implanted defibrillator is found in the normal MFE pad location, adjust the pads slightly so they are not directly over the implanted device.

How to Begin
     Once the pads are correctly placed, the provider must set the rate and strength. The rate is generally set first, often between 60-80 beats per minute, and then the strength is determined. The rate you set determines the pulse you would like the patient to have, so remember that the higher you set the rate, the more you increase myocardial oxygen demand once mechanical capture is obtained. The rate you set will also determine the number of visible pacer spikes you see on the EKG (e.g., at a rate of 60, you will see 10 pacer spikes in a six-second EKG strip).

     The next step is to set the strength, or electricity delivered, in milliamps (mA). The milliamps needed will vary from patient to patient, but use the lowest setting possible to gain capture. Most cardiac pacemakers will increase strength in 5mA increments. Electrical capture will often occur at settings of 50-90 mA, but again, this may vary. As milliamps are increased, you'll begin to see more QRS complexes follow each pacer spike. Be cautious, as too high of a rate or too strong of a milliamp setting will cause you to lose mechanical capture (as you overtax the heart with speed and strength) as well as electrical capture.

What Is Capture?
     The goal with the strength of the electricity is to deliver just a little more than it takes to gain capture of the myocardial rate, and no more. Capture is determined by the appearance of a pacemaker spike on the EKG, followed by a wide and bizarre-looking QRS. If some pacemaker spikes are followed by QRS complexes and some are not, then the provider does not truly have capture. Complete capture needs to have a QRS complex after every pacer spike. Electricity causes pain (so consider analgesia as your protocols allow) and some damage during its use, so any excess electricity provides no additional clinical benefit. Many clinicians will adjust both rate and strength to gain capture, and then go a little higher as a safety net. Just as no two patients are the same, pacing a patient is different each time. The provider must fine-tune both rate and strength to obtain effective capture and benefit. This is a bit of a balancing act, and the balance cannot be assumed to remain the same throughout your patient care, so be vigilant about monitoring the EKG.

     Merely obtaining capture does not solve all the issues. Remember that the pacemaker controls electrical capture, but not necessarily mechanical capture. If the heart is damaged, electrical rate changes may not equate to effective pumping. Additionally, if there's not enough blood to fill the vessels, even effective pumping may not produce clinical benefits. The only way to ensure that a pacemaker is performing in a beneficial way is to see capture on the EKG strip, palpate a perfusing pulse, and ensure that your indications for using it are resolving (or at least not worsening). Fluid and/or pharmacological interventions (such as atropine, dopamine and epinephrine drips) may also be needed to help with hypotension.

Street Tips

• Although medications such as atropine may help with bradycardic rates, high-degree AV blocks will rarely benefit from this medication due to the disassociation of the atrial and ventricular electrical pathways. Additionally, atropine significantly increases myocardial oxygen demand.
• You can still touch the patient, and even perform CPR, as the electricity delivered during pacing is not enough to harm the provider. However, it is still electricity, and providers should use common sense. Evaluate your location-would you use a hair dryer there? If not, don't use the pacemaker!
• Once you've obtained capture with the pacemaker, don't disconnect the leads or MFE or shut the machine off. Providers will sometimes disconnect the EKG monitor to facilitate moving the patient. This is risky, as you may not be able to obtain capture a second time, and the patient may deteriorate as a result.
• When arriving at an ED, make sure the resuscitation team is immediately told that pacing is being performed so that no one removes any leads or pads while moving the patient to a hospital bed.
• Check MFE pads for an expiration date. If the gel dries up, their use could result in burns to the patient's chest wall.
• At high-milliamp settings, you may see chest wall trembling. This is normal (provided you have electrical and mechanical capture) and will not hurt you during patient care.

What About Pain?
     The use of the cardiac pacemaker may cause significant patient discomfort; consider pain-control options. It is a delicate balance between making the patient as comfortable as possible and the risk of hypotension from many forms of analgesia. EMS options for pain control generally include morphine sulfate (2-10 mg), fentanyl (25-100 mcg) and nitrous oxide (50% mix). Of these choices, fentanyl is probably the safest, with rapid onset, short duration of action if discontinued, and less risk of hypotension, nausea and vomiting. Another option is Versed/midazolam (1-5 mg) to help as a sedative and amnesiac. Regardless of choice, the provider must ensure that administration of analgesia will not worsen the clinical condition of the patient.

Conclusion
     Remember that bradycardia may or not be symptomatic. In the case of poor perfusion associated with bradycardia, EMS providers must be swift in their assessments and with critical interventions such as oxygen, IV therapy and, in some cases, an external cardiac pacemaker. The goal of the cardiac pacemaker is to speed the heart rate up and, as a result, increase blood pressure and therefore improve overall perfusion. With its use, and successful electrical and mechanical capture, patients will have better chances at recovery.

Bibliography
American Heart Association. Advanced Cardiovascular Life Support. South Deerfield, MA: Channing Bete Company, 2006.
American Heart Association. Part 5: Electrical therapies. Circulation 112:67-77, 2005.
American Heart Association. Part 7.3: Management of symptomatic bradycardia and tachycardia. Circulation 112:35-46, 2005.
Zoll Medical. Section 8, Noninvasive Temporary Pacing. Zoll E-Series Operators Guide, pp. 8-1-8-4, Oct 2006.

Marc A. Minkler, NREMT-P, CCEMT-P, is a paramedic/firefighter with the Portland (ME) Fire Department and a faculty member at York County Community College in Wells, ME. He is the author of several internationally published EMS instructor programs. Reach him at mam@portlandmaine.gov.