Cardiac Devices on Imaging

Open up a chest X-ray of an older patient and there's a decent chance you'll find some hardware staring back at you: a little metal hockey-puck under the skin, a couple of wires snaking toward the heart, maybe a row of staples. Your job isn't to be intimidated by the gadgetry — it's to read it like a transit map. Every device has a station it's supposed to stop at, and once you know the stops, the whole thing turns from "mystery robot parts" into "oh, that's a dual-chamber pacemaker, the leads are fine, moving on."

This is a reference page: a field guide to the cardiac hardware you'll actually meet, and how to tell them apart without a manual.

The generator: that hockey puck in the upper chest

Most rhythm devices — pacemakers and defibrillators — have a pulse generator, the battery-and-brains box. On a frontal chest radiograph it shows up as a dense, rounded rectangle, usually tucked in a pocket below the left collarbone (sometimes the right, occasionally deeper if it's been hidden under muscle for cosmetic reasons). Wires (the leads) emerge from it and dive toward the heart.

The single most useful habit: count the leads. It tells you what the device is for before you've read a single chart note.

That third lead is the sneaky one. It doesn't sit inside the left ventricle — it rides along a vein on the outside of the heart to pace the left ventricle from the surface. On the X-ray it curves up and out to the left rather than plunging straight down, which is your tip-off that you're looking at a resynchronization device.

Figure · CXR

Pacemaker vs. defibrillator: hunt for the shock coil

People mix these up constantly, and the visual giveaway is wonderfully simple. A plain pacemaker lead is a thin, uniform wire from box to tip — like a single strand of cooked spaghetti. An implantable cardioverter-defibrillator (ICD) has the same job plus the ability to deliver a life-saving jolt, and to do that its lead carries one or two shock coils: short segments that look noticeably thicker and denser, almost shaggy, compared to the rest of the wire.

Why care? Because an ICD is a clue to the patient's risk, it behaves very differently in the MRI scanner and the operating room, and "the patient has a pacemaker" written in a note is wrong surprisingly often when the films actually show an ICD.

There's also a sleeker cousin: the leadless pacemaker, a tiny capsule planted directly inside the right ventricle with no generator pocket and no wires at all. On imaging it looks like a small metallic bullet sitting in the cardiac silhouette — easy to overlook, easy to mistake for an artifact if you're not expecting it.

Following the wires (and catching the trouble)

For any lead, do the boring, reliable thing: trace it from generator to tip. A normal right ventricular lead ends near the cardiac apex; a right atrial lead usually curls into the atrial appendage. While you're tracing, you're really asking two questions — is the tip in the right neighborhood, and is the wire whole?

These overlap heavily with the bedside skills covered in lines, tubes, and devices — same discipline of "find the tip, judge the position," just applied to permanent hardware.

The rest of the hardware zoo

Cardiac patients collect devices over time, and a few more deserve recognition:

• Prosthetic heart valves — mechanical valves are densely metallic with a recognizable ring (and often tilting disc/leaflets); bioprosthetic valves usually show only a faint metallic ring or stent frame, because the leaflets are tissue and invisible on X-ray. Position over the expected valve plane tells you which valve was replaced.
• TAVR (transcatheter aortic valve replacement) — a stent-like metallic cage perched at the aortic root, placed without open surgery; increasingly common and easy to spot once you know to look at the aortic valve plane.
• Left atrial appendage occluders — a small umbrella/plug device parked in the left atrial appendage to keep clots from forming there.
• Sternotomy wires — that vertical row of wire "staples" down the breastbone, the calling card of prior open-heart surgery (and a handy reminder to look for bypass clips and valve prostheses on the same film).

Figure · CXR

One safety rule worth tattooing on your brain

Before anyone with cardiac hardware goes into an MRI, the device's MRI status has to be checked. Many modern devices are "MR conditional" — scannable only under specific conditions (field strength, programming, monitoring) — which is emphatically not the same as "MR safe." Older or unknown devices can be a genuine hazard. When in doubt, the scan waits until the device is identified and cleared.

The takeaway is friendlier than the hardware looks: count the leads, find the shock coil, trace each wire to its tip, and check the MRI status. Do those four things and you've read the device.