Chen Bojun, Guangdong Provincial Hospital of Traditional Chinese Medicine, Cai Hirong
With the economic development of China and the change of people’s living and eating habits, the prevalence of cardiovascular diseases such as coronary heart disease, arrhythmia and heart failure is gradually increasing in China. According to statistics, the death rate of cardiovascular diseases in China was 183.7 per 100,000 people in 2006 and 241.0 per 100,000 people in 2008, accounting for 34.8% and 40.27% of deaths in that year respectively. With the in-depth study of these diseases, percutaneous coronary intervention (PCI), pacemaker and defibrillator implantation have become the main treatment methods for cardiovascular diseases, and more and more people are receiving percutaneous coronary intervention (PCI), pacemaker and defibrillator implantation. But while stent, pacemaker, and defibrillator implantation can improve the quality of life and extend the life of patients, it also inevitably brings with it another confusion and dilemma: can patients undergo magnetic resonance imaging (MRI), computed tomography (CT), and positron emission computed tomography (PET-CT) when the need for examination arises? Indeed, the safety of patients implanted with these devices to undergo these examinations is still controversial. Chen Bojun, Cardiovascular Disease Specialist, Guangdong Provincial Hospital of Traditional Chinese Medicine
I. Why MRI, CT, PET-CT?
MRI is widely used for the diagnosis of diseases in the brain, head and neck, heart and kidney, and has an irreplaceable role in disease diagnosis. Epidemiological studies have shown that patients over the age of 65 are twice as likely to need an MRI than younger patients. CT is also widely used in the diagnosis of diseases in the brain, head and neck, chest, heart and abdomen, and its application is becoming more and more common and has become one of the routine clinical examinations. Early detection and diagnosis of major diseases in such areas as tumor, brain and heart. Therefore, MRI, CT and PET-CT have been used more and more commonly in clinical practice.
However, there is currently insufficient awareness of the safety of MRI, CT and PET-CT in patients with stents and pacemaker implants, resulting in two extremes in practice: either patients do not pay enough attention to them, ignore safety screening and blindly perform the above examinations, or all patients with stents and pacemaker implants in their bodies simply refuse the above examinations, resulting in the inability to obtain reasonable and accurate examinations. Therefore, it is necessary to further understand stents, pacemakers, MRI, CT, and PET-CT in order to differentiate them scientifically and reasonably, and to understand whether the above tests can be done and when they are appropriate.
Hazards of MRI on cardiac implant devices
The 1.5T and 3T MR static magnetic field strengths commonly used in clinical practice are about 30,000 and 60,000 times that of the earth’s magnetic field, respectively, and the powerful magnetic field produces a strong suction on ferromagnetic objects entering the field, which may cause the following consequences.
1. MRI generates a strong magnetic field during the scanning process, causing the local temperature of the metal part of implanted devices such as stents and pacemakers to rise, causing the implant to heat up, stretch, turn or shift, resulting in stent dislodgement and causing patients with coronary artery disease to face the risk of recurrent heart attack.
2. Pacemakers may be interfered by electromagnetic fields generated during the scanning process and lose some or all of their functions, such as causing asynchronous pacing, suppressing necessary pacing, giving inappropriate pacing, and other changes, resulting in tissue damage to patients, which may lead to death in severe cases.
III. Ferromagnetic nature of cardiac implants
The above mentioned injuries are only for ferromagnetic implants, but not for non-ferromagnetic implants, which can be examined with <1.5 tmr. Therefore, it is important to know the information provided by the manufacturer regarding the material and ferromagnetic properties of the product in order to determine whether a patient with a cardiac implant can undergo an mri examination. Cardiac implants are generally classified into two categories, ferromagnetic and nonferromagnetic, based on their behavior in a magnetic field, and nonferromagnetic implants are classified as metallic or nonmetallic, as shown in Table 1 below:< span="">
Heart
Implant
Classification
Ferromagnetic
MRI is not indicated. Unless there is information that the ferromagnetic implant has minimal tilt or displacement in the magnetic field.
Non-ferromagnetic
Metallic
MRI can be performed, but it will result in severe metallic artifacts in the images, which may have an impact on the judgment of the examination results
Non-metallic
MRI examination is possible
Table 1 Classification of cardiac implants according to magnetism
Since stent and pacemaker implantation is a surgical treatment, these implants have been firmly fixed to the surrounding tissues during the surgery, plus these cardiac implants have healed together with the tissues around the implantation for 2 to 6 weeks after the surgery and do not pose a risk of displacement.
(i) Cardiac stents
However, at present, cardiac stents are mainly made of stainless steel, titanium and tantalum, and according to statistics, the 1.5 TMRI examination of patients with the above-mentioned stent implantation will not cause stent loosening or significant temperature change, which is not enough to cause harm to human body. safe and feasible. In practice, MRI examination of cardiac stents must meet the following three conditions.
① the cardiac stent is a non-magnetic material made of titanium or tantalum or a weakly magnetic 300 series stainless steel (refer to the information provided by the vendor for specific magnetic properties).
(ii) MRI should preferably be performed 4 to 8 weeks after cardiac stent implantation.
(③ MRI instrument magnetic field strength of 1.5T.
(ii) Cardiac pacemakers and cardioverter-defibrillators
Cardiac pacemakers and defibrillators are different from cardiac stents because they contain complex electromagnetic components, because MRI examination not only poses a risk of displacement of the pacemakers and defibrillators, but also poses a greater risk of displacement of the pulse generators and electrodes of the pacemakers and defibrillators, closure of the reed switch resulting in off-demand pacing and heartbeat competition, which may lead to serious arrhythmias and, in the case of Pacemaker-dependent patients may die, so pacemakers and defibrillators are generally contraindicated for MRI. However, the new generation SureScan pacing system can effectively control the reed switch, prevent electromagnetic interference from causing electrical resetting, reduce the heating of electrode leads due to RF fields (cross-conversion fields). It also reduces the interaction of the electrodes with the gradient magnetic field and RF field of magnetic resonance to reduce the heating of the leads. Therefore, the whole pacing system is able to work properly in the MRI magnetic field environment. Therefore, implantation of MRI-resistant pacing system can be recommended for such patients if the possibility of needing MRI scan after pacemaker implantation is taken into account. Therefore, the following is recommended:
(i) MRI in non-pacemaker-dependent patients should not be ventured and should be considered only in those cases where there is a strong clinical indication and the benefit clearly outweighs the risk.
(ii) MRI should in principle not be performed in pacemaker-dependent patients, except when there are compelling circumstances and the benefits clearly outweigh the risks.
(iii) MRI is not performed in principle in patients with defibrillators unless it is mandatory and the benefit clearly outweighs the risk.
Can CT and PET-CT be performed in patients after cardiac stent, pacemaker and defibrillator implantation?
CT and PET-CT are generally feasible for patients with cardiac stent implantation because they do not affect the cardiac stent, but MRI is absolutely contraindicated in patients with pacemakers and defibrillators, so CT scan is preferred. According to studies, CT scans have not been found to cause abnormal defibrillation, device resetting, or other serious clinical events in patients with pacemaker and defibrillator implantation in clinical practice. Therefore, CT and PET-CT are generally feasible in patients after pacemaker and defibrillator implantation.
In practice, we strictly grasp the indications for MRI, CT, and PET-CT in patients with cardiac stents, pacemakers, and repeat defibrillators in order to avoid the harm caused by inappropriate examinations on the one hand, and to perform relevant examinations in a timely manner when necessary examinations are needed in order not to miss or misdiagnose.