A-Fib patients sometimes use consumer ‘DIY” Heart Rate Monitors (HRM) when exercising or performing physically demanding activities (For specific models and options, see our article, DIY Heart Rate Monitors & Handheld ECG Monitors Part I.)
How Do DIY Heart Rate Monitors Work?
Basic HRMs use a chest strap to pick up the electrical signals from the heart. However, due to the inherent design of the chest strap, the accuracy is somewhat limited and is no replacement for the signals recorded by a Holter or Event Monitor.
A HRM keeps track of your heart’s R-R interval or the time between R peaks. Without getting too technical, the R peak on a generic ECG waveform (see the diagram) corresponds to the ventricle beat (depolarization) and has the largest amplitude (height) of the complete waveform.
When the amplitude (picked up as a voltage differential) exceeds a certain threshold, a “beat” is picked up by the chest strap and transmitted wirelessly to the HRM. It is the time between these R peak “beats” that is used by the HRM to determine instantaneous heart rate. It is only going to pick up episodes of arrhythmia as are manifested in ventricle beats (the R on the waveform).
Learn more about the EKG signal, see Steve’s article: “Understanding the EKG (ECG) Signal“.
Learn more about the EKG signal, see Steve’s article: “Understanding the EKG (ECG) Signal“.
This is one of the fundamental differences in how data is recorded by HRMs (R-R interval) versus Holter/Event Monitors (actual waveform).
In fact, this is what Polar has to say:
Polar products are not designed to detect arrhythmia or irregular rhythms and will interpret them as noise or interference. The computer in the wrist unit will make error corrections, so that arrhythmia beats are not included in the averaged beats per minute. The blinking heart symbol in the face of the unit, however, will continue to show all heart beats received.
In most cases the Polar products will work fine for persons with arrhythmia.
HRM Recording Capability
Most HRMs provide some internal storage recording capability. While lower cost HRMs simply record low, high and average heart rate, upper end models allow you to download heart rate data to your PC.
App-enabled smartphones are changing how this data is viewed, collected and saved for future review.
How To Setup and Use an HRM
On most of the HRMs, you can set a heart rate zone, and the watch monitor (or app-enabled smartphone) will record how long you stayed in that zone.
You could then program a high heart rate zone which you might only enter if you were in A-Fib. That way you could record how long you stayed in A-Fib and what your max heart rate was. This data could be reviewed on the watch monitor (or app-enabled smartphone) without having to download it to a PC.
On HRMs with PC interface capability, you can view data in a graphic form (on some watches/smartphones you can view the graphic data but with lower resolution.) This analyses could tell you when you were at a higher heart rate—A-Fib—and how long you stayed there. Of course these kinds of features require some PC skills, but typically the programs are pretty user friendly. (See the above graphic example of a Polar PC program).
For more, see our article, DIY Heart Rate Monitors & Handheld ECG Monitors.
Return to Index of Articles: Diagnostic Testing
Last updated: Tuesday, April 14, 2015
2014 Boston AF Symposium
How ECGI (Non-Invasive Electrocardiographic Imaging) Works
Report by Dr. Steve S. Ryan, PhD
Dr. Michel Haissaguerre of the LIRYC Institute in Bordeaux, France gave a presentation entitled “Mechanistic Insights From Noninvasive Mapping of AF—Implications for Catheter Ablation.”
Dr, Haissaguerre began by discussing the concept of voltage vs. noise in reading an ECG. High accuracy can be obtained with a EGM (electrogram signal) of >0.15mV. Body Filtering (ECGI) can miss small local A-Fib signals, but does not affect global patterns.
He found that when mapping Focal A-Fib signals from both inside and outside the heart, they may differ in location by 3.1mm. (This is a relatively small difference and isn’t enough to affect the overall accuracy of the mapping and ablation.)
How ECGI (Body Mapping) Works
He described how the ECGI system works. A patient lies down on his/her back and a technician places a vest-like device with 256 electrodes over his/her chest and stomach. These electrodes combine with rapid CT (Computed Tomography) scans to produce a very detailed 3D color map of the heart. (For a detailed description and discussion of the ECGI system, see 2013 BAFS: Non-Invasive Electrocardiographic Imaging [ECG])
The system automatically detects rotors and foci and computes them into a “Cumulative Map” or movie. These driver regions are ranked, based on statistical prevalence. Dr. Haissaguerre showed slides of these drivers originating from PVs in Paroxysmal A-Fib.
In persistent A-Fib he found multiple interplaying driver regions (median 4, 1 to 7) found in the Left Atrium, PVs and Right Atrium (“driver regions” include both focal sources and rotors). The rotors were temporally and spatially unstable. They were not sustained. Most had 2-3 rotations with a mean of 448ms. They required a statistical analysis of their core trajectory/density. Patients in Persistent Long-Lasting A-Fib for more than six months had the most driver regions and the least success in A-Fib termination after six months.
…ECGI ablation significantly reduced the amount of burns needed to terminate A-Fib.
Compared to the traditional Bordeaux step-wise ablation for persistent A-Fib, ECGI ablation significantly reduced the amount of burns needed to terminate A-Fib.
Dr. Haissaguerre uses a Multielectrode circular catheter not yet approved for use in the US. This catheter can more easily capture and isolate regional targets like rotors that do move a little.
Dr. Haissaguerre’s Conclusions
- Regional clusters of A-Fib drivers can be mapped non-invasively
- ECGI mapping before a procedure identifies critical regions to ablate. This reduces targeted atrial areas and RF delivery. The optimal timing is in the early months of persistent A-Fib.
- There is a need for appropriate ablation tools (such as circular or multielectrode catheters) as rotor targets are not so limited (they tend to move slightly).
Back in 2013 I predicted that “the ECGI system, barring unforeseen circumstances, will rapidly supersede all other mapping systems and will become the standard of care in the treatment of A-Fib patients.”
Not only does the ECGI system produce a complete, precise, 3D, color video of each spot in a patient’s heart producing A-Fib signals, but also an ECGI can be done by a technician before the procedure rather than by a doctor during an ablation. And the ECGI map is a better, more accurate, more complete map than an EP can produce by using a conventional mapping catheter inside the heart.
From a patient’s perspective, ECGI reduces both the time it takes to do an ablation and the number of burns a patient receives.
The only caveat that Dr. Haissaguerre found (which relate to all mapping strategies, not just to ECGI) is that rotors move slightly and are somewhat unstable. A computer has to be used to statistically analyze their core trajectory. But circular catheters can be used to contain and isolate them.
Addendum: April 2015
Jeffrey Patten asked, “I’ve heard that the new mapping and ablation vest system ECGI (CardioInsight), though very detailed with 256 electrodes, doesn’t directly map the septum area. Is that correct?”
It’s correct to say the ECGI does not directly map the septum area. But, that doesn’t mean the septal activity can’t be mapped with the ECGI.
I posed your question to the world-reknown cardiologist, Dr. Pierre Jais of the Bordeaux group. He explained that “the septal activity projects at the anterior and posterior attachments of the septum on both atria.” He added that mapping the septum with the ECGI system “…requires some experience, but is at the end easy.”
So don’t be reluctant to seek out the new mapping and ablation vest system ECGI (by CardioInsight). Just be sure you have a top-notch, experienced operator.
Return to Index of Articles: AF Symposium: Steve’s Summary Reports
Last updated: Wednesday, September 2, 2015
An electrocardiogram, ECG (EKG), is a test used to measure the rate and regularity of heartbeats, as well as the size and position of the chambers, the presence of any damage to the heart, and the effects of drugs or devices used to regulate the heart.
The ECG signal strip is a graphic tracing of the electrical activity of the heart. It measures the length of time it takes for the initial impulse to fire at the Sinus Node and then ends in the contracting of the Ventricles.
The first upward pulse of the EKG signal, the P wave, is formed when the atria (the two upper chambers of the heart) contract to pump blood into the ventricles. In A-Fib you will see many “fibrillation” beats instead of one P wave.
The next large upward spike segment, the QRS Complex, is formed when the ventricles (the two lower chambers of the heart) are contracting to pump out blood.
The next section, the ST segment, measures the end of the contraction of the ventricles to the beginning of the rest period before the ventricles begin to contract for the next beat.
The next slight rising section, the T wave, measures the resting period of the ventricles.
ECG (EKG) Strip: Atrial Fibrillation
In the case of Atrial Fibrillation, the consistent P waves are replaced by fibrillatory waves, which vary in amplitude, shape, and timing (compare the two illustrations below).
ECG recorder: special graph Paper
The output of an ECG recorder is a graph (or sometimes several graphs, representing each of the leads) with time represented on the x-axis and voltage represented on the y-axis. A dedicated ECG machine would usually print onto graph paper which has a background pattern of 1mm squares (often in red or green), with bold divisions every 5 mm in both vertical and horizontal directions.
Interpreting a ECG strip involves counting the squares of the tracing. For example, by counting the squares of a heart in Normal Sinus Rhythm, you can calculate the heart rate.
To learn more about reading an ECG strip, see an excellent handout from the St. Petersburg College, School of Nursing, ‘EKG Interpretation: The Easy Rs‘.