Tiny Pacemaker Can Be Installed Via Catheter

the_newsbeagle writes "About four million people around the world have pacemakers implanted in their bodies, and those devices all got there the same way: surgeons sliced open their patients' shoulders and inserted the pulse-generating devices in the flesh near the heart, then attached tiny wires to the heart muscle. ... A device that just received approval in the EU seems to solve those problems. This tiny pacemaker is the first that doesn't require wires to bring the electrical signal to the heart muscle, because it's implanted inside the heart itself, and is hooked onto the inner wall of one of the heart's chambers. This is possible because the cylindrical device can be inserted and attached using a steerable catheter that's snaked up through the femoral artery."

Comments

Whew!

[DaTroof]

Ah, through the femoral artery. My imagination went to a much more horrifying place when I read "catheter."

Quickest way

[The_Star_Child]

The quickest way to a man's heart is through his catheter.

Technical correction and comment by a cardiologist

[cecst]

The leadless pacemaker is indeed a real advance, but the summary needs a few corrections, and a comment can be made. I would not want a reader who needs a standard pacemaker to be frightened unnecessarily by the summary as written.
"surgeons sliced open their patients' shoulders and inserted the pulse-generating devices in the flesh near the heart, then attached tiny wires to the heart muscle ... through the femoral artery."

• 1. The incision is made in the skin, not a joint. The implant location is usually the left or right prepectoral region, which is an inch or two lower than the collar bone on the stated side. The pacemaker itself is placed in a "pocket" formed by separating the skin and its attached fat from the underlying muscle. If you have ever eaten chicken, you know that the skin and fat can be separated from muscle. In the uncooked human, of course, separation requires a bit of effort but not much, and a good surgeon will have the area complete numbed up so the patient doesn't feel anything. Thus, the pacemaker is not near the heart: it's outside the rib cage. There are variations on the implant location, but none of them is inside the rib cage.
• 2. The tiny wires (well, pretty tiny) are long, and extend from the area where the pacemaker is through a vein (not an artery, hopefully!) to the heart. The method by which the wires are put in the vein is simple but outside the scope of this post.
• 3. The access is always through a vein (femoral vein, in the case of the new device), not an artery. Blood clots (thrombi, when inside the body) will form on most foreign bodies. From the veins, they can spread only into the lungs, which is relatively safe. From the arteries, even tiny thrombi can cause trouble when they go the brain (strokes), heart (heart attack), gut (ischemic gut), limbs (ischemic arm, leg, etc). Not good.
• 4. The new device can still get infected and still can run out of battery power. What I haven't yet understood is how it can easily be extracted if it gets infected, which is necessary because life-threatening infection can (and usually does) result if an infected foreign body remains in the patient. I guess it's small enough that a new one can be inserted without removing the old one when the battery runs out. There are more technical limitations too that will likely be overcome as the technology improves.

Re:MRI

[ChumpusRex2003]

Probably a lot less susceptible.

The main concern with MRI and pacemakers is not so much the magnetic field but the RF field. The magnetic field is not without problems as most pacemakers contain a reed switch which is used to activate "safe mode", where the pacemaker enters a special diagnostic mode. This is largely for historical purposes, as early pacemakers used this for battery level testing. The doctor would hold a magnet to the patient's chest. The pacemaker would enter diagnostic mode and would stimulate the heart to beat a rate dependent on battery voltage. The doc would feel the patient's pulse and could look up the estimated battery level in a table.

Modern pacemakers contain rather more sophisticated NFC capability, so much more useful readouts are available with a proper scan tool (battery voltage, stimulation mode, inputs from various sensors, lead impedances, stimulation voltages and currents, etc.) as well the ability to reconfigure various modes (e.g. vibration response - where the pacemaker increases rate in response to exercise induced vibration), whether the pacemaker can sense other heart parameters (so that different chambers of the heart contract synchronously), etc. In general, however, a magnet will switch the pacemaker into a basic mode of operation. (Defibrillators are different, as basic stimulation can be very dangerous in people with severe heart disease, as it can trigger ventricular fibrillation; therefore magnet mode in implantable defibrillators usually only just tweaks some parameters, rather than anything more dramatic).

The major issue with MRI is the RF field. MRI requires a very powerful RF pulse. A typical MRI power amplifier will take up 6U of rack space, and about 5 gallons per minute of cooling water and need a 3phase 480V power supply, while providing a peak RF power output of 35-70 kW.

A modern pacemaker will typically sense the ECG as well as stimulating. It will include a watchdog timer, and if a beat is not detected before the timer expires, it will trigger a stimulation pulse. One risk with the MRI environment is that the capability of the pacemaker to sense the 1 mV ECG signal may be degraded by the pulsed transmission from the 70 kW RF transmitter 6 inches away.

There are other issues with conventional pacemakers. Being implanted near the shoulder, the pacemaker connects to the heart muscle via leads approx 8-12 inches long. These typically form an arc in shape due to the anatomy. It just so happens that this wire loop forms quite a nice 1/4 wave loop antenna tuned to the scanner's RF frequency; it can absorb the RF energy and channel RF into the tissues around the pacemaker "box" and at the electrode tips. In minor cases, the RF pulses can act as pacemaker pulses on the cardiac muscle. Fine at 1 Hz scan rate. Not so good at 5 Hz scan rate. In extreme cases, the voltage build up across the pacemaker leads can cause RF burns to the cardiac muscle or damage the pacemaker circuitry. (There are MRI compatible pacemakers around which use various tricks - upgrading from normal coax cables to coax with heavy copper screens so rigid that they actually have to be articulated in order to bend + a liberal helping of ferrite beads; or dividing the leads up into 1" segments interconnected by small ferrite transformers)

The nanostim device doesn't have any exposed leads, so it is likely to be much less susceptible to RF problems. Due to size and location, it's also likely that it doesn't feature a conventional magnet mode, relying instead completely on NFC for control and communication. It also has the option of being completely removable. Conventional pacemakers often aren't, as the leads are generally not retrievable from where they screw into the heart muscle. Because it is RF pick-up in the leads that is the No 1 hazard with MRI, simply removing the pacemaker device, but leaving the leads isn't a safe option (it may actually make it worse, as the pacemaker itself often contains clamping and termination circuits to protect itself from EMI, and