Ohm, Sweet Ohm: The Role of Ohm’s Law in Cardiac Devices
- Mary Smith, MS, CCDS
- 2 minutes ago
- 4 min read
In the world of cardiac devices, there’s a little law doing some heavy lifting → Ohm’s Law.
When working with cardiac devices, this simple formula shows up more often than you think. It's the behind-the-scenes rule that helps us deliver effective, efficient pacing without wasting energy or guessing our way through lead issues. Without it, we’d be left to guess whether devices are delivering the right jolt to make the heart beat, rather than having a clear electrical roadmap. But thanks to this foundational principle, devices know precisely how much energy to deliver, and when.
Let’s break it down: useful, not overwhelming.
Ohm’s Law: A Quick Refresher
At its core, Ohm’s Law is a simple equation with a BIG impact: V = I × R, where:
V is voltage — the push behind the pulse. Think of it like a helpful shove to get things going.
I is current — the flow of electricity that gets the job done. It’s the movement of charge that stimulates the tissue.
R is resistance — the bouncer at the door. It controls how easy (or not) it is for current to get through, and voltage has to push harder when resistance plays tough.
Picture water flowing through a pipe. Voltage is the pressure, current is the flow, and resistance is the diameter of the pipe. Smaller pipe? More pressure is needed to get the same flow.
In other words, if resistance goes up and you still want the same flow, you’ll need more voltage. If resistance decreases, you might be able to get by with less effort. It’s all a balancing act, and the equation tells us exactly how to maintain that balance. The same applies to electricity.
From Formula to Function
In cardiac devices, every delivered pulse is built on this equation. Whether it’s pacing, defibrillation, or sensing, Ohm’s Law guides how energy moves through the lead and into heart tissue.
Let’s break it down further:
Voltage (V): This is the device’s push; the programmed output that initiates the impulse. If it’s too low, there’s no effect. Too high, and you risk draining the battery or damaging tissue. Balance is key.
Current (I): This is what actually flows into the tissue. It's what gets the job done. Current depends on both voltage and resistance, so changes in tissue or lead conditions can affect how much current flows, even at the same voltage.
Resistance (R): The variable in the equation. It depends on factors like lead placement, tissue characteristics, scar formation, and more. As resistance changes over time, so must the device’s response to maintain effectiveness.
Ohm’s Law is fundamental in cardiac devices because it describes how voltage, current, and resistance interact within the heart’s electrical system. Understanding this relationship helps clinicians optimize device settings—such as output voltage and pulse width—to ensure effective pacing, reliable sensing, and safe energy delivery to the heart tissue.
📚Read more in this blog: Pacing with Purpose: Optimizing CIEDs
Why It Matters
Ohm’s Law isn’t just a formula we learned once for that "one" exam; it’s the foundation for how we test, program, and troubleshoot cardiac devices. We monitor impedance (the clinical version of resistance) to ensure everything’s working as expected. A sudden jump or drop in impedance can be an early sign of a lead issue, insulation breach, or change in tissue contact.
And when we’re trying to conserve battery life? Ohm’s Law helps us find the lowest possible output that still gets consistent capture, maximizing longevity without compromising performance.
When impedance drops and voltage stays the same, current increases—that’s straight from Ohm’s Law (V = IR). More current means the device is working harder to deliver each pulse, which drains the battery faster. Monitoring impedance trends helps catch these changes early and protect battery longevity. Just as importantly, tracking voltage and threshold trends can reveal rising capture needs or early signs of lead issues, helping ensure reliable pacing and long-term device performance.
📚Read more in this blog: Keeping the Pace using PBL-STOP
Wrapping It Up: The Rhythm Behind the Rhythm
Ohm’s Law may not get much attention during device checks, but it’s behind every decision we make, whether we’re adjusting thresholds, evaluating lead performance, or optimizing output settings. Balancing voltage, current, and resistance ensures each device pulse is delivered just right.
So, the next time you're looking at an output setting or impedance trend, remember there's a quiet little law in the background, keeping the beat on track.
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Mary Smith
MS, FHRS, CCDS, RCES, RCIS
Chart Certified Coach and IBHRE Ambassador