Infection
Most commonly S. aureus or S. epidermidis
2% local wound infection; 1% sepsis/bacteremia
Hematoma
Typically occurs shortly after placement
Most commonly S. aureus or S. epidermidis
2% local wound infection; 1% sepsis/bacteremia
Typically occurs shortly after placement
Dislodgment
Perforation (most commonly at RV apex)
Infection can cause severe sepsis
Tricuspid regurgitation
Coiling (ie: Twiddler's Syndrome)  Twiddler Syndrome after large pocket and defibrillator wires coiled around the generator
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)
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
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
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
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
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
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
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<unk> 
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
Pacemaker complication
Infection
Implantable Cardioverter-Defibrillator complication
Most commonly S. aureus or S. epidermidis
Acute coronary syndrome 
2% local wound infection; 1% sepsis/bacteremia
Myocardial rupture
Hematoma