| | Ablation | Ablation is a surgical technique in which radio frequency or microwave energy produces thermal energy to destroy tissues. Ablation used in cardiac device patients increases the risk of induced ventricular tachyarrhythmia, device over sensing, unintended tissue damage, device damage, or device malfunction. The Micra VR is designed to withstand exposure to ablation energy.
Medtronic recommends the following to mitigate these risks:
(i) Ensure that temporary pacing and defibrillation equipment is available.
(ii) Avoid the direct contact between the ablation catheter and the Micra VR
(iii) Position the return electrode patch, so that the electrical energy path does not pass through or near device.
(iv) Monitor the patient during ablation with at least 2 separate methods, such as arterial pressure, ECG, taking patient’s pulse, pulse oximetry, or Doppler pulse detection.
To prevent the effects of over sensing, program the Micra VR to the asynchronous pacing mode (e.g., VOO) if patient appropriate. After ablation, restore device parameters. |
| | Diagnostic radiology | Diagnostic radiology includes the following:
(i) Computerized axial tomography (CT or CAT scan)
(ii) Fluoroscopy
(iii) Mammograms
(iv) X-rays
Diagnostic radiology even at accumulated doses is not enough to damage the Micra VR.
Precautions should be taken if the device is directly in the beam of radiation for CT scans. Similar interference may be observed in high-intensity fluoroscopy. Oversensing may occur for the duration of time the device is in the beam. Medtronic recommends placing the Micra VR into the asynchronous pacing mode (e.g., VOO), if patient appropriate, when the device will be directly in the CT scan beam for longer than 4 seconds. This is to avoid or mitigate the effects of oversensing. Restore device parameters upon completion of scan. |
| | Diagnostic ultrasound | Diagnostic ultrasound is a noninvasive imaging method to visualize internal anatomy and measure heart rates or blood flow. Echocardiogram, a form of diagnostic ultrasound, which is directed at cardiac tissue, poses no risk of electromagnetic interference. |
| | Electrosurgery | Electrosurgery (including electrocautery, electrosurgical cautery, Medtronic Advanced Energy surgical incision technology, and Hyfrecator) is a process in which electric energy generated by a probe is used to control bleeding and cut tissue. Electrosurgery used on cardiac device patients increases the risk of device oversensing, unintended tissue damage, tachyarrhythmias, device damage, or device malfunction.
Medtronic provides the following recommendations when electrosurgery cannot be avoided:
(i) Have temporary pacing and defibrillation equipment available on standby.
(ii) Use a bipolar electrosurgery system or Medtronic Advanced Energy surgical incision technology or Hyfrecator, if possible before considering the use of monopolar electrosurgery.
If a monopolar electrosurgery is used, position the return electrode patch, so that the electrical current pathway does not pass through or within 15 cm of the Micra VR.
(i) Do not apply monopolar electrosurgery on tissues within 15 cm of the device.
(ii) Use short, intermittent, and irregular bursts at the lowest clinically appropriate energy levels possible
(iii) Monitor the patient during ablation with at least 2 separate methods, such as arterial pressure, ECG, taking patient’s pulse, pulse oximetry, or Doppler pulse detection.
To prevent the effects of over sensing, program the Micra VR to the asynchronous pacing mode (e.g., VOO) if patient appropriate. After surgery, restore device parameters and interrogate device function. |
| | External defibrillation and cardioversion | External defibrillation and cardioversion deliver an electrical shock to the heart to convert abnormal heart rhythms to a sinus rhythm. The Micra VR is designed to withstand exposure to external defibrillation and cardioversion. Damage to Micra VR by external shock is still possible, especially with increasing energy levels. Device interrogation is recommended following external defibrillation or cardioversion. |
| | Magnetic resonance imaging (MRI) | The Micra VR is 1.5 T and 3 T MR conditional when specific criteria are met.
The following criteria are from the Micra MRI Technician Manual:
Cardiology requirements
(i) No abandoned leads can be present
(ii) Pacing amplitude is ≤ 4.5 V at the programmed pulse width.
(iii) No diaphragmatic stimulation is observed when MRI SureScan is programmed to on.
(iv) The SureScan device that is beyond its projected service life is programmed to device off.
Radiology requirements
(i) The MRI has a maximum spatial gradient of ≤25 T/m (2500 gauss/cm)
(ii) Gradient systems with maximum gradient slew rate performance per axis of ≤ 200 Tesla per meter per second (T/m/s)
(iii) The whole body averaged specific absorption rate (SAR) must be ≤ 4.0 W per kilogram (W/kg). The head SAR must be ≤ 3.2 W/kg.
Continuously monitor the patient’s hemodynamic status and have an external defibrillator available.
Potential adverse outcomes in the MR environment:
(i) Potential for VT/VF induction when the patient is programmed to an asynchronous pacing mode during MRI SureScan
(ii) Damage to the device causing the device to fail to detect or treat irregular heartbeats or causing the device to treat the patient’s condition incorrectly |
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