Changes in cardiac excitability and vulnerability in NMR fields

Area of Science:

• Cardiovascular Physiology
• Biophysics
• Medical Imaging Physics

Background:

• Magnetic Resonance Imaging (MRI) utilizes strong static magnetic fields and radiofrequency pulses.
• The potential effects of these fields on cardiac electrophysiology, specifically ventricular excitability and vulnerability, require thorough investigation.
• Understanding these interactions is crucial for patient safety during MRI procedures.

Purpose of the Study:

• To assess the impact of static magnetic fields and radiofrequency pulsing on ventricular refractoriness.
• To evaluate alterations in ventricular vulnerability under MRI conditions.
• To determine the safety of MRI-related electromagnetic fields for cardiac electrical activity.

Main Methods:

• Isolated perfused rabbit hearts were used to measure ventricular refractoriness via strength-interval curves.
• Measurements were taken both inside and outside a 4.7-tesla static magnetic field with 5-gauss radiofrequency pulsing.
• Ventricular vulnerability was assessed by determining the repetitive response and ventricular fibrillation thresholds.

Main Results:

• No significant differences were observed in ventricular refractory periods at various stimulation thresholds (threshold, midpoint, 10 mA) inside versus outside the magnetic field.
• The repetitive response threshold showed a statistically significant increase inside the magnet (P=0.04).
• The ventricular fibrillation threshold did not show a significant change between conditions.

Conclusions:

• Static magnetic fields combined with radiofrequency pulsing do not alter the strength-interval relationship, a measure of ventricular refractoriness.
• The study found no evidence of increased ventricular vulnerability under the tested MRI conditions.
• These findings suggest that MRI electromagnetic fields do not adversely affect cardiac electrophysiological stability.