Heart rhythm problems (“arrhythmias”) are very common, and they cause a wide variety of symptoms. Some people feel their heart beating rapidly, or irregularly, or may notice a flutter or a “skipped” beat. Others have more subtle symptoms like shortness of breath with exercise, lightheadedness, or a feeling of anxiety. At times, serious heart rhythm problems can even cause sudden fainting spells. There are about 20 different types of heart rhythm disturbances, so it’s important for doctors to correctly diagnose the nature of the abnormal rhythm before making any recommendations since the prognosis and treatment for your particular problem depend on the exact nature of the arrhythmia. Unfortunately, arrhythmias can come and go, and they usually leave no telltale signs of their existence once the heart rhythm goes back to normal. Therefore, people sometimes have to wear a heart monitor to be able to record the problem at the time of the symptoms to see what’s actually happening.
How Is The Heart Rhythm Controlled?
The heart rhythm is controlled by the electrical system of the heart. All arrhythmias are due to electrical disturbances. The electrical signals produced by the heart can be picked up from the skin, amplified, and printed out on paper. This is the basis of the electrocardiogram (ECG or EKG). The ECG has a very characteristic appearance that was first described by William Einthoven, a Dutch physician, who was awarded the Nobel Prize in Medicine for his publications regarding the electrocardiogram. His described specific waves produced by the heart and labeled them as “P-Q-R-S-T,” which are the letters we still use today to describe the ECG signals of the normal heartbeat.The electrical signal that controls the heartbeat arises from a specialized structure in the top of the right atrium. This electrical structure is known as the sinus node or sinoatrial node. The signal generated by the sinus node stimulates the top chambers (atria) to contract. On the ECG the activation of the atrial muscle produces a small bump called a “P-wave.” The atrial signal then enters another electrical structure called the AV (atrioventricular) node, which serves as the “main wire” connecting the top and bottom chambers. The AV node delays the signal for a fraction of a second and then passes it down to the ventricles. The activation of the ventricles produces a sharp spikey signal on the ECG referred to as the “QRS Complex.” After a fraction of a second, the ventricles electrically “reset” themselves and a broad, smooth “T-wave” is produced.
If a patient is having an arrhythmia, the ECG will show disturbances in the timing of the P-wave and the QRS complexes, allowing the doctor to diagnose the rhythm disturbance. However, patients often complain of palpitations but are not having the symptom in the office. It’s like going to the auto mechanic and telling him, “My car made a funny noise yesterday… what could it be?” Of course, if the car isn’t making the noise right at that time, the problem is anybody’s guess. Likewise, if the ECG is normal in the doctor’s office, it just means that we have to try harder to record the ECG at the time of the symptoms. That’s where a monitor becomes useful. Monitors are like miniature ECG machines that can record your heartbeat at the time of the symptoms so the proper diagnosis can be made.
A Brief History of Monitors
ECG machines were originally quite large — as large as a table — and they needed to be plugged into work. As time went on they became smaller and smaller, but the basic principle stayed the same… they would generate a strip of paper with the ECG printed on it.
The trouble is that people cannot walk around plugged into the wall. However, that problem was overcome by an American biophysicist named Norman Holter. The original Holter monitor was developed at the Holter Research Laboratory in Helena, Montana in 1949. He and his team created an ECG machine that was battery operated and could transmit the ECG via radio waves to a receiving station, thus allowing a patient to walk around unattached to any power supply. Ironically, the original Holter monitor weighed 75 pounds and had to be carried in a backpack! In the 1950s, Holter and his team developed a wearable cardiac monitoring device that would record the ECG onto a reel of magnetic tape. The tape could be scanned at high speed by a technician, who could then print out the relevant parts for the doctor to review. The Holter monitor was released for commercial use in 1962.
Beyond The Holter Monitor
Even today, doctors will often order a Holter Monitor as a first step in diagnosing an arrhythmia. Modern Holters do not use analog tape any longer but have computerized memory chips that hold the data. They are completely digital and small enough to not be very noticeable. The problem is that the standard Holter only runs for about 24 hours, so unless the patient is having symptoms virtually every day, nothing may show up. Some Holters can run for up to 48 hours, but the technology was not available to record more data than that, and so other solutions were needed.
In the 1980s, the cardiac “Event Monitor” was invented to allow for longer monitoring periods. These monitors were designed to record the ECGs digitally only when needed… when the patient was having an “event” or a symptom. The original design was a pocket-sized box with small metal electrodes on the bottom surface. If the patient had a symptom, they could pull out this box, press it to their chest, and press a button to record the heartbeat right at that time.
The box would store the rhythm digitally, and the patient could then call a receiving station on the phone and “playback” the recording directly over the phone so that the arrhythmia could be analyzed by the technician and sent to the doctor. As technology improved, wearable event monitors would be connected to the chest with wires and sticky electrodes and the patient could record their heartbeat any time they wanted. The problem was that fleeting symptoms could still be missed unless the patient had their finger on the button all day long.
That’s when event monitors began to incorporate a memory “buffer” that stored a period of the ECG all the time. Thus, when the patient pressed the button the monitor would actually save a recording that began 5 or 10 seconds BEFORE they pressed the button, allowing doctors to see what caused a symptom that only lasted a second or two. The memory in these monitors was called “looping” because of the way the digital information was stored in the memory chip, so these became known as “Loop Recorders.”Nowadays, loop event monitors are still used, but they all have automatic detection circuits that will save a recording even if the patient does not press the button. That allows for diagnosing arrhythmias that have more subtle symptoms that the patient may not notice. Advanced units can transmit the recordings through a cell phone connection to the monitoring company, so the doctor can get to see the recording very quickly if a patient has an arrhythmia.
However, it is still annoying for the patients to hook up wires to their chest, especially considering that they have to take the monitor off to shower and then put it back on. It can also be uncomfortable to sleep with. In response to this problem, several companies developed a “patch” style event monitor. Patch monitors incorporate the circuitry, electrodes, push button, and communication abilities into a single flat gadget that looks like a giant Band-Aid. The patient peels off a strip to reveal an adhesive and applies the patch to the skin on their chest wall. The patch then stays there for a week or so, monitoring the rhythm and even transmitting abnormal recordings automatically, yet the patient can shower, exercise, and carry on a normal lifestyle all while the patch is working.
Implantable Cardiac Monitors
Unfortunately, some arrhythmias occur so rarely that wearing an event monitor for a week or two can still miss it. Some event monitor services will let a patient keep the monitor for 30 days, but if the symptoms only occur every month or two then you could still miss the problem. That’s why Implantable Cardiac Monitors or Implantable Loop Recorders (ILRs) were invented. Implantable monitors have been around for a couple of decades and were surgically implanted to provide about 3 years of heart monitoring.They had sophisticated detection capabilities and patients were also able to manually record their heartbeat with a 5-minute looping memory. In 2015, a miniaturized version (Reveal® LINQ, Medtronic, Inc.) was released that could literally be injected under the skin in a 5 minute procedure. This new ILR featured improved detection circuitry that could even diagnose arrhythmias like atrial fibrillation that were not associated with symptoms. It even sends daily reports to the central station automatically when the patient is sleeping, so the doctor can be made aware of arrhythmias that may have occurred within just a day or two. The LINQ has been revolutionary, given that it’s only the size of a paperclip, yet it allows doctors to rapidly detect arrhythmias that were never able to be diagnosed before.
Which Monitor Is Right For You?
The choice of which monitor you should wear has mostly to do with how often your symptoms occur. In patients with daily symptoms, a Holter monitor should be adequate. However, someone with infrequent fainting spells would not likely benefit from a Holter unless they happened to faint on the day they were wearing it. The other important factor is how long the symptom lasts. In people with fleeting sensations that only last a few seconds, you are limited to using a monitor that is worn continuously or implanted.
However, there is another option for people who have palpitations or symptoms that last for a minute or longer. Several companies now market a device used with a “smartphone” that can allow you to record your own rudimentary ECG. These pocket-sized recorders pick up your ECG from your fingers – you just start the phone application, place your fingers on the device, and you can record your own ECG any time you need. These devices are especially useful for tech-savvy individuals who don’t want to wear a monitor long term, and it actually winds up being very economical since the device costs less than $100 (no prescription necessary).
Regardless of your symptoms, you should have an open discussion with your doctor about which type of monitor is right for you, given the nature of your symptoms. When long-term monitoring becomes necessary, you should see a heart rhythm specialist or Cardiac Electrophysiologist, since they would most likely be able to offer you expert advice and could implant an ILR if necessary.