Ver el código de «Pacemaker complication»

==Background==
*All [[ICD]]s are also pacemakers (i.e. have pacing functionality), but not all pacemakers are ICDs (i.e. do not have shocking functionality)

===Nomenclature===
[[File:paced.gif|thumb|Paced rhythm with characteristic wide LBBB and pacer spikes]]
[[File:xray-pacemaker.jpg|thumb|PA Xray with pacemaker]]
[[File:a-sense-v-pace-ecg.jpg|thumb|Atrial Sensed Ventricular Paced ECG]]
[[File:pacer.jpg|thumb|Pacer type based on Xray]]
{| class="wikitable" 
! I || II || III || IV || V 
|-
|+Generic code for pacing modes<ref>Bernstein AD. 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 Feb; 25(2) 260-4. lmid:11916002</ref>
| Chamber(s) paced  || Chamber(s) sensed || Response to sensing || Rate modulation || Multisite pacing
|-
| O = None || O = None || O = None || O = None || O = None
|-
| A = Atrium || A = Atrium || T = Triggered || R = Rate modulation || A = Atrium
|- 
| V = Ventricle || V = Ventricle || I = Inhibited || || V = Ventricle
|-
| D = Dual (A+V) || D = Dual (A+V) || D = Dual (T+I) || || D = Dual (A+V)
|-
|}

===Indications===
*Sinus Node Dysfunction-sinus bradycardia/arrest, sinoatrial block, chronotropic incompetence, a-fib. 
*Acquired AV block- 3rd degree block and 2nd degree type II
*Chronic Bifascicular or Trifascicular block
*After Acute MI-high mortality with persistent AV block post MI
*Cardiac Resynchronization Therapy- Conduction delay (>150msec with mortality benefit) in chronic systolic heart failure further decreases EF, increases remodeling and increased MR.
*Neurocardiogenic Syncope and Carotid Sinus Syndrome

===Lead Location===
*Atrial
**Right Atrial Appendage
**Lateral RA wall
*Right Ventricle
**Apex
**Septum
*Left Ventricle (most commonly placed for cardiomyopathy or CHF)
**Coronary veins along external LV wall via coronary sinus
**Rarely, externally placed electrode during open surgical procedure

===Additional Pacemaker Functions===
*Can record rhythm strips of AF, VT, and VF episodes for later review
*Keeps track of % of paced vs intrinsic beats
*Keeps a rate histogram, as well as % of time spent in AF

===Methods to Identify Manufacturer===
*Patient most often has a pocket card indicating manufacturer
*Manufacturer Hotline has patient database
**Medtronic Inc. (1-800-328-2518)
**St. Jude Medical Inc. (recently acquired by Abbott, Inc.) (1-800-722-3774)
**Boston Scientific Inc. (1-800-227-3422)
*Magnet mode - with placement of a magnet over the device, the mode changes to asynchronous (i.e. DOO or VOO). Each brand has slightly different rates
**Medtronic Inc.: 85 bpm; 65 bpm when battery is ready for replacement
**St. Jude Medical Inc.: 98.6 bpm; 86.3 bpm when battery is ready for replacement
**Boston Scientific Inc.: 100 bpm; 85 bpm when battery is ready for replacement
*Manufacturer code on pulse generator is visible on Chest Xray

===Electromagnetic Interference===
*Nonmedical
**Cell phones: do not interact with device
**Airport security: may trigger alarm, no alteration of activity
*Medical Sources
**[[MRI contraindications|MRI]]: mostly safe, consult cards on device specific recs
**Cardioversion: Use AP pads >8cm from device to minimize adverse effects
**Unipolar Cautery - can cause sensing and pacing malfunction as well as reprogramming

==Differential Diagnosis==
===Pacemaker Malfunction===
====Problems with pocket====
*Infection
**Most commonly S. aureus or S. epidermidis
**2% local wound infection; 1% sepsis/bacteremia
*Hematoma
**Typically occurs shortly after placement

====Problems with leads==== 
*Dislodgment
*Perforation (most commonly at RV apex)
*Infection can cause severe sepsis
*Tricuspid regurgitation
*Coiling (ie: [[Twiddler's Syndrome]]) [[File:Twiddler Syndrome.png|thumb|Twiddler Syndrome after large pocket and defibrillator wires coiled around the generator]]

===Failure to Capture===
*Delivery of pacing stimulus without depolarization
**Functional - refractory myocardium, desensitized local tissue around the lead
**Medical - drugs, myocardial disease, electrolytes
**Technical - insufficient device output, lead dislodgment, fracture, insulation defect, ventricular wall perforation
*Battery of End of Life (EOL)

===Failure to Pace===
*Failure to deliver a stimulus to the heart
**Oversensing - most common cause: retrograde P’s, T’s, skeletal muscle myopotentials, 
**Crosstalk - type of oversensing where the ventricular lead senses atrial pacing stimulus, and ventilator output inhibited

===Failure to Sense===
*Normal function: a sensed myocardial depolarization greater than the programmed threshold causes inhibition of pacing
*Failure to sense results in a paced beat on top of an intrinsic beat (as the device is "unaware" of the intrinsic beat")
**Voltages of patient's intrinsic QRS complex is too low to be detected
**New intrinsic arrhythmia (AF has a smaller depolarization than sinus beat), AMI, electrolyte abnormalities, lead separation, battery depletion

===Runaway Pacing===
*Physiologic electrical activity (T waves, muscle potentials)
*External electromagnetic interference
*Signals generated by interaction of different portions of the pacing system
*Potentially life-threatening as it can cause V-Fib or (paradoxically) bradycardia due to failure to capture

===Pacemaker Mediated Tachycardia===
*Also known as Endless Loop Tachycardia
*Formation of a re-entrant circuit causing inappropriate tachycardia
**Most commonly: paced ventricular beat ->  retrograde AV node conduction -> intrinsic P wave -> device reacts to intrinsic P wave by looking for intrinsic QRS, but since AV node is now refractory it delivers a paced beat at the programmed P-R interval (typically ~200-250ms), starting the process anew
*Tachycardia does not exceed programmed upper limit rate on pacemaker

==Evaluation==
===Work-Up===
*BMP and Mg
*[[CXR]]
*[[ECG]]
*[[Troponin]]
*Interrogation
**Each company has on-call representatives who will come interrogate a device 24/7 (phone numbers above)
**Most cath labs will have machines capable of interrogating each brand

===Expected ECG Patterns===
*Absence of pacer artifact indicates intrinsic depolarization
**With newer pacemakers, pacer spikes may not appear on some or all paced beats, depending on EKG machine
*Pacing artifacts preceding depolarizations indicate successful pacing and capture
*Leads in RV apex produce LBBB pattern with appropriate discordance
*New RBBB pattern may indicate lead in LV
* Bi-ventricular devices can produce paced QRS complexes that are either narrow or wide and bizarre, depending on device programming
*Simultaneous depolarization of ventricles produces dominant R wave in V1

===Plain Film Findings===
*Obtain PA/Lateral Films to confirm pulse generator, manufacturer, lead placement/number/integrity
*R atrial lead J shaped(tip medially on AP) entering right atrial appendage
*RV leads point downward with tip between left spine and cardiac apex--lateral XR shows inferior and anterior
*Coronary sinus lead- courses posteriorly on lateral XR
*Extra leads may be appropriately abandoned and capped
*ICD component appears as thickened shock coil

==Management==
*Pacemaker Mediated Tachycardia
**Break with [[adenosine]] or magnet.<ref>EB Medicine- Sept 2014- Managing Pacemaker-Related Complications and Malfunctions in the Emergency Department </ref>
***Magnet placement will stop the sensing of the retrograde-conducted P waves driving PMT; this will immediately terminate the rhythm. 
***Recurrence of PMT after earlier termination means that the pacemaker settings need to be changed
**Consider chest wall stimulation techniques<ref>Barold SS, Falkoff MD, Ong LS, Heinle RA. Pacemaker endless loop tachycardia: termination by simple techniques other than magnet application. Am J Med. 1988;85(6):817-22.</ref> - transcutaneous pacing, isometric muscular exercise, precordial thump
*Electrophysiology or cardiology consult is often needed
*Contact a device representative for a full interrogation

==Disposition==
*Resolved Pacemaker-mediated Tachycardia without recurrence - discharge
*Infection - admission with [[MRSA]] coverage antibiotics, consult to cardiology, with likely replacement of pacemaker after 4-6 weeks of IV antibiotics
*Pacing/sensing/capture issue - likely admit

==See Also==
*[[Medical device complications]]
*[[In-Training Exam Review]]
*[[Implantable Cardioverter-Defibrillator complication]]

==References==
<references/>
[[Category:Cardiology]]
[[Category:Surgery]]