What if you woke up in a hospital and found out your mortal enemy had surgically removed your face and glued it onto his own and now he was out in the world pretending to be you? Living your life, hanging with all your friends, doing all your drugs, having all your fun?
You’d probably be pretty upset. Maybe even attack him with a spear gun.
What if you woke up in a hospital with a pacemaker implanted in your chest? You’d probably just want to know a little bit more about how they work.
First, what's the difference between a pacemaker and an Implantable Cardio-Defibrillator (ICD)
A pacemaker is an implanted device that provides electrical impulse to the heart when intrinsic heart pacing is too slow or inadequate. Leads are typically placed in the right atrium and right ventricle, however pacemakers can be bi-ventricular. A rhythm paced from the right ventricle will appear as a left bundle branch block on ECG (as the left ventricle is depolarized after the right).
Indications for pacemaker are typically symptomatic bradycardia or AV block, among others. An ICD (or AICD) provides cardioversion or defibrillation when tachyarrythmias are detected. Indications for ICD placement include previous ventricular fibrillation (VF), unstable ventricular tachycardia, structural heart disease or advanced heart failure. Both devices appear similar on X-ray, however ICDs tend to have thicker leads.
How are pacemakers categorized?
There is a five letter code, and the first three are the most important. The first letter indicates chamber(s) paced: A=atrium, V=ventricle, D=dual (atrium + ventricle). The second letter indicates chamber sensed, using the same A, V, D description. The third letter indicates the response to a sensed signal: T = if an intrinsic complex is sensed it will trigger a paced impulse, I = if an intrinsic complex is sensed it will not trigger (or it will inhibit) a paced impulse, D = pacemaker can both trigger and inhibit paced impulses depending on what is sensed or not sensed. For example, if a native atrial complex and ventricular complex are sensed, it will inhibit both the atrial and ventricular pacemaker impulses. If an atrial complex is sensed but no ventricular complex, it will not pace the atrium but will trigger the ventricle. If the pacemaker senses no atrial or ventricular native rhythm it will pace both. Most devices are designed or programmed VVI or DDD.
What are some complications arising from pacemakers?
Problems with pacemaker site: Infection, hematoma, pneumothorax, thrombosis may occur soon after placement, but these complications are rare.
Problems with pacemaker function can be identified with ECG:
1. Failure to pace – Pacemaker does not trigger any impulses at all; no pacemaker spikes are seen on ECG
2. Failure to capture – Pacemaker triggers but does not cause myocardial depolarization; spikes are seen on ECG but not immediately followed by atrial or ventricular complex
3. Failure to sense – Pacemaker triggers despite intrinsic cardiac activity; pacemaker spikes during or directly after intrinsic cardiac activity
4. Pacemaker-mediated tachycardia – Pacemaker acts as one arm of a re-entry circuit in which a ventricular impulse travels retrograde through AV node, triggers the atrial sensing lead in the pacemaker, which then triggers another ventricular complex. The heart rate will be limited by the upper limit of normal in the pacemaker’s settings.
What can be done in the ED for questionable pacemaker malfunction?
Examine the pacemaker pocket itself, chest x-ray to determine lead placement/integrity and to see which device is in place, electrolytes and cardiac enzymes, device interrogation. Placing a device-specific magnet on top of a pacemaker will temporarily disable sensing to generate a fixed-rate (asynchronous) pacing. This means it will pace at its preset rhythm (typically 70 bpm) no matter what intrinsic electrical activity is occurring in the heart. This may be dangerous as it can result in deadly dysrhythmias if the pacemaker triggers a ventricular beat during repolarization from an intrinsic cardiac cycle (R on T phenomenon). However, in an unstable patient with possible pacemaker-mediated tachycardia, placing a magnet can be attempted along with typical ACLS resuscitation.
In conclusion, pacemakers and ICDs are relatively straightforward once you understand their basic functions. Trouble shooting will require a good physical exam, ECG, chest X-ray, and possibly pacemaker interrogation by the device manufacturer or cardiology. Trouble shooting how to get your face back from your mortal enemy will typically require more.
Piktel JS. Chapter 22. Cardiac Rhythm Disturbances. In: Tintinalli JE, Stapczynski J, Ma O, Cline DM, Cydulka RK, Meckler GD, T. eds. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7e New York, NY: McGraw-Hill; 2011. http://accessmedicine.mhmedical.com.newproxy.downstate.edu/Content.aspx?bookid=348§ionid=40381483. Accessed June 12, 2017.
Beyerbach, Daniel. Pacemakers and Implantable Cardioverter-Defibrillators. E-Medicine, Medscape. http://emedicine.medscape.com/article/162245
Bernstein AD, Daubert JC, Fletcher RD, et al. The revised NASPE/BPEG generic code for antibradycardia, adaptive-rate, and multisite pacing. North American Society of Pacing and Electrophysiology/British Pacing and Electrophysiology Group. Pacing Clin Electrophysiol 2002;25:260–264
Martindale, J and deSouza, IS. Managing Pacemaker-Related Complications and Malfunctions In The Emergency Department. Emergency Medicine Practice
ECG obtained from: https://lifeinthefastlane.com/table/ecg-database
X-Rays obtained from: https://radiopaedia.org
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