BACKGROUND: A pacemaker is a device that is placed in the chest to help control abnormal heart beats. It uses electrical pulses to prompt the heart to beat normally. Usually, pacemakers are used to treat arrhythmias (problems with the heart rate or rhythm of the heartbeat). During arrhythmias the heart may not be able to pump enough blood to the body causing other symptoms like fatigue, fainting, or shortness of breath. Severe arrhythmias can attack the body's vital organs and can result in loss of consciousness or even death. A pacemaker may relieve some arrhythmia symptoms and can also help people with abnormal heartbeats resume an active lifestyle.
UNDERSTANDING THE HEART'S ELECTRICAL SYSTEM: The heart has its own internal electrical system that controls the rhythm and rate of the heartbeat. When the heart beats, an electrical signal spreads from the top to the bottom of the heart. When the signal travels, it causes the heart to contract and pump blood. Each electrical signal normally begins in the sinus node (a group of cells). As the signal spreads, it coordinates the timing of heart cell activity. First, the heart's two upper chambers (the atria) contract, then the ventricles contract and pump blood throughout the body. The combination of the contraction between the atria and the ventricles is called a heartbeat. When the electrical signaling fails in the heart, it causes arrhythmias .(Source: www.nhlbi.nih.gov).
DANGER OF PACEMAKERS AND MRIs: MRI systems expose patients to very strong magnetic fields that can disrupt electronic pulses generated by a pacemaker. A study performed in 2009 found that the magnetic field can also increase the temperature at the tip of the pacemaker lead within the heart and can cause heart tissue to burn. FDA researchers also found that when the pacemaker is exposed to strong magnetic fields it could drastically alter the pulse and may not stimulate the heart properly. According to the National Council of Aging, a person's chance of needing an MRI doubles after the age of 65 and 50% to 75% of patients with pacemakers will need an MRI over their lifetime. (Source: www.eldercareteam.com).
NEW MRI SAFE PACEMAKER: To help solve this problem, a new pacemaker has been developed. The FDA recently approved a new device, the Medtronic's Revo MRI SureScan pacemaker. It will allow people with a pacemaker to safely use an MRI machine. The SureScan is the first and only pacemaker in the U.S. approved as MRI safe. The device can set itself into MRI mode that allows modifications to both the device and the leads that can reduce hazards associated with MRIs. Since the Medtronic's pacemakers are designed to treat bradycardia (a slow, irregular heartbeat that is interrupted), patients are a population that could benefit from MRI scans. The best part about the new pacemaker is that it costs the same as a traditional pacemaker and is usually covered by insurance (Source: www.medtronic.com).
Dr. Marc Silver, a Cardiologist at Wake Med in North Carolina, talks about a new technology that is bringing MRI's and pacemakers together.
What do pacemakers do?
Dr. Silver: Pacemakers are basically fancy computers with batteries that are attached to the heart and prevent the heart from going slow. Sometimes it's because of heart block where the hearts' upper and lower chambers don't communicate together correctly, and sometimes it's because the hearts' own little pacemaker in the upper chamber of the heartis asleep and it doesn't like to fire on time.
What is the drawback?
Dr. Silver: Pacemakers have become incredibly sophisticated. They're extremely small and they don't bother people much. The great thing about a pacemaker is we can say to a patient ‘you're going to feel better when you get this device and it's not going to limit anything you can do in your life except for one thing and that is patients with pacemakers generally can't have an MRI scan.' MRI scans have become the cornerstone of imaging for virtually every part of the body, brain, the spinal cord, muscles, bones and joints. The lung is the only part of the body that we don't use an MRI as the best imaging tool. The other great thing about MRI scans is that there's no radiation. Everytime you get a CAT scan or a nuclear stress test or an x-ray, you're exposed to radiation. It increases your risk of cancer as you get older. With an MRI there is not that risk so the ONLY limitation for a pacemaker patient is, except under very special circumstances, they're not allowed to have MRI scans.
What does an MRI do to a tradional pacemaker and what's the risk?
Dr. Silver: There's basically 3 problems with an MRI scan. Most people look at it kind of simpistically: Pacemaker looks like a little metal device and the MRI is a big magnet. There are 3 problems that the MRI can do to a pacemaker and the patient that has the pacemaker. Number one, it can either temporarily or permanently damage the function of the device. If it's temporary, it's not a big deal, you reprogram it and you're back to normal afterwards. If it's permanent and the device has to be removed and a new one put in, that has risks obviously. Number two, the pacemaker wire that's attached to the pacemaker goes down into the patients' heart. It acts as an antenna and someof the incoming energy from the radiofrequency that the MRI scanner puts into the body gets concentrated at the tip of the lead where it touches the heart muscle. That is dissapated as heat, so the heart tissue heats up in a really small little area. Although this doesn't generally kill people, it causes scar tissue on the muscle, so the pacemaker has a harder time working. The final problem with an MRI scan, and this is the one that can kill people, is that when the energy comes in and gets coupled to the lead, that's acting like an antenna. Not all the energy goes down to the heart, some of it goes back up into the device and pacemakers are designed to re-channel that energy and get it out of the device so it doesn't damage the device, then it goes back down the lead tip. Unfortunately in the way pacemakers have reformatted that energy, it can allow the heart to actually start contracting very rapidly in sync with the the energy coming from the MRI scan, and that can be fatal.
How can patients with a pacemaker benefit from a MRI?
Dr. Silver: A patient who gets a pacemaker today has anywhere from a 50 to 75% chance of needing an MRI in the remainder of their lifetime. If you think in an average group of 50 people, how many of those people have had an MRI's its always at least half. When you're committing someone to a lifetime where they can't have their body imaged in the way everyone else does, it's a big deal for them. If it were me, I would certainly want to have a pacemaker that would allow me to have an MRI. It's a big deal, it changes management, and if we now have technology where patients can have a pacemaker just like every other pacemaker but know that their safe when they have and MRI, that's a big deal if you're that patient.
Do we know how many people get pacemakers today?
Dr. Silver: Hundreds of thousands of patients per year get a pacemaker. There's well between a million and two million patients in the United States who have implantable devices like pacemakers and defribillators in them today.
FOR MORE INFORMATION, PLEASE CONTACT:
J Marc Silver, MD
Cardiologist
WakeMed, NC
msilver@wakemed.org