Extracorporeal shock wave lithotripsy (ESWL)
-Safe if shock is given synchronously with the R wave on ECG and safety pacing is enabled
-Dependent patients should be reprogrammed to asynchronous mode to avoid ventricular inhibition
-ICDs should have magnet applied to disable tachy therapies
-Could damage a pacemaker using an older activity sensing PPM using a piezoelectric crystal
Transcutaneous electrical nerve stimulation (TENS)
-Probably safe in most bipolar pacemakers
-Reasonable to monitor patients during initial TENS application
-Best avoided in ICD patients as it could create EMI misinterpreted as a tachyarrhythmia
Impedance plethysmography
-Is used to document the patient’s respiratory rate and to detect ECG lead disconnection
-Can cause interference with minute ventilation pacemakers because it also functions by detecting a change in intrathoracic impedance
-The current injected by the monitor may result in inappropriate sensor-driven pacing
Electroconvulsive therapy (ECT)
-Generally safe as only a minimal amount of electricity reaches the heart
-ICD patients should be placed on continuous monitoring and turn of tachyarrhythmia detection until ECT is completed
Welding
-Significant EMI unlikely to occur if using welding equipment in the 100-150 A range
Patient recommendations:
-Limit welding to 130 A
-Work only in dry areas with gloves and shoes
-Keep welding cables close together and far from the ICD as possible
-Keep the welding arc at least 2 feet away from the implanted device
Metal detectors
-Asynchronous pacing might occur for 1 or 2 beats without ill effect to the patient
Radiation therapy
-Radiation therapy to any part of the body away from the site of the pulse generator shouldn’t cause a problem with the generator but it should be shielded to avoid scatter
-Can result in inappropriate ICD shock
-Can result in ICD “reset”
-Can cause changes in sensitivity, amplitude, or pulse width, loss of telemetry, failure of output, or runaway rates
-If dysfunction occurs, replacement is required as the long term reliability of the device is suspect
-Most common is breast cancer on the ipsilateral side of the device. Device must be moved to the contralateral side
Potential sources of electromagnetic interference that should maintain at least a 12 inch distance from the device
-Ignition system components of car/motorcycle
-Electric fence
-Transformer box
Potential sources of electromagnetic interference that should maintain at least a 24 inch distance from the device
-Metal detector search head (ex: beach comber)
-Induction cooktop stove
Potential sources of electromagnetic interference that are not recommended for device patients
-Ab stimulator
-Electric body-fat scale
-Magnetic mattress pad/pillow
Potential sources of electromagnetic interference that should maintain at least a 6 inch distance from the device
-Cordless telephone
-Electric cart (grocery or golf)
-Hand held electric kitchen appliances
-Corded electric shaver
-Electric toothbrush charging base
-Hair dryer
-Magnetic therapy products
-Sewing machine motor
-Speakers
-Motorized treadmill
-Motorized vacuum
Diathermy / Electrocautery
-Most instances of EMI occur when electrocautery is performed within 8 cm of the device
-Magnet application or reprogramming to asynchronous mode for surgeries above the umbilicus / iliac crest
-Magnet/reprogramming likely unnecessary for surgeries below the umbilicus
Zener diode
-Electrically regulates the voltage entering the pacemaker circuit and prevents high currents from being conducted by the lead to the myocardium
-What helps protect the device from external defibrillation damage
Defibrillation
May result in:
-Reprogramming to the backup or reset mode
-Transient increase in pacing or sensing threshold
-Damage to pacemaker circuitry
Precautions:
-Place pads in A/P position
-Interrogate device post defibrillation and compare to pre defibrillation settings
MRI-safe
-Device in which there are no known hazards in any MRI environment
-(No MRI-safe CIED systems approved at this time)
MRI-conditional
-Device with no known hazards in a specific MRI environment
Abbott magnet rate
BOL = 100 bpm
ERI = 85 bpm (older devices 86.3 bpm)
EOL = 80.7 bpm
Medtronic magnet rate
100 bpm x 3 beats —> decreases to 85 bpm
EOL = 65 bpm
Boston magnet rate
Battery > 1 year = 100 bpm
ERI within 1 year = 90 bpm
ERT = 85 bpm
EOL = <85 bpm
Biotronik magnet rate
Asynchronous magnet response modes:
-Paces at 90 bpm
-ERI = 80 bpm
Synchronous magnet response modes:
-Paces at lower rate limit
-EOL = 11% lower than lower rate limit
Auto magnet response modes:
-Paces at 90 bpm x 10 cycles then paces at lower rate limit
-ERI = 80 bpm x 10 cycles then paces at lower rate limit
External interference
-Filtered by narrow band pass filters to exclude non cardiac signals
-Signals in the 5-100 Hz range are not filtered because they overlap the cardiac signal range (PVCs and R waves)
-T wave range 0-8 Hz
-PVC range 3-32 Hz
-R wave range 15-120 Hz
-Potential sources of external interference often fall within the 30-300 Hz range
Noise sampling period (NSP)
Back up mode / reset mode
-Indicates that the pacemaker has been affected by interference (powerful EMI) or has reached battery depletion
-Usually VVI (rate varies between manufacturer) and unipolar
