How Cardiac Arrhythmias Are Diagnosed

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If you have an abnormal heart rhythm, the first step in getting it treated is for your doctor to figure out exactly what kind of arrhythmia it is. Diagnosing cardiac arrhythmias can be trivially easy, devilishly difficult, or somewhere in between. Making the diagnosis is easy if you have a chronic or persistent arrhythmia—then it's just a matter of recording an electrocardiogram (ECG) and documenting the presence and type of arrhythmia you are experiencing.

Unfortunately, often cardiac arrhythmias are episodic in nature—they come and go without warning. In these cases, your symptoms may occur as sporadic episodes, often lasting just a few seconds, so recording a random 12-second ECG is not likely to reveal the arrhythmia, and additional testing is necessary. But the basic principle remains the same: To diagnose a cardiac arrhythmia, the arrhythmia itself needs to be "captured" on some type of heart rhythm recording.

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Medical History/Physical Exam

If your doctor deems your symptoms to be non-life-threatening, he or she will likely start with a physical exam and a review of your symptoms and possible conditions that could be causing an arrhythmia. For instance, if he or she suspects that you have a thyroid disorder or heart disease that's causing your arrhythmia, you may be tested for these conditions. Additionally, you may have a heart monitoring test such as an electrocardiogram or an echocardiogram.

Arrhythmia Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

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Labs and Tests

If your doctor thinks you may be having cardiac arrhythmias, the first question is whether those arrhythmias are likely to be life-threatening.

Warning Signs

If you have had spells of unexplained, severe dizziness, or have had syncope (loss of consciousness)—especially if you have an underlying cardiac disease—your doctor will likely consider the possibility that you are having a potentially dangerous arrhythmia, such as ventricular tachycardia or heart block.

If so, you should probably be placed in the hospital on a cardiac monitor until a firm diagnosis can be made and, if necessary, effective treatment is instituted.


More typical symptoms of an arrhythmia such as palpitations, mild fatigue, or mild, transient dizziness, are unlikely to indicate a life-threatening arrhythmia and a more routine cardiac evaluation can be used. Generally, this is accomplished by attempting to record an electrocardiogram (ECG) during an episode of symptoms. With a basic ECG, you have electrodes connected to your chest that record the electrical activity of your heart, including when and for how long your heartbeats occur. It may be necessary to use a portable ECG that you can wear while you go about your daily routine.

Holter Monitor

If your symptoms occur daily or almost daily, the best choice for diagnosing the cause may be to use a Holter monitor, a portable ECG device that continuously records your heart rhythm for a 24- to 48-hour period of time. You may be asked to keep a careful diary, noting the precise times that episodes of symptoms occur. The diary can then be correlated with the rhythm recording to show whether symptoms are associated with a cardiac arrhythmia.

Event Monitor

If your symptoms occur less frequently than every day or every few days or they happen very quickly, the best choice may be an event monitor, another type of portable ECG. You attach it to your body when you're having symptoms and press a button to record your heart's electrical activity during that time. Some smartphones also have a version of this technology.

Patch Monitors

Another option if your symptoms occur less frequently is a patch monitor such as a Zio patch, an adhesive long-term recording device that can store up to two weeks of continuous recordings of your heart rhythm and automatically detect and record any cardiac arrhythmias you may have. There's also the SEEQ MT system, which can record and monitor for up to 30 days. The disadvantages of patch monitors are that they can be expensive since they're not reusable and it may take extra time to get your results, but they are convenient, water-resistant, easy to use, and comfortable.

Implantable Loop Recorder

If your symptoms are extremely infrequent, there are small implantable heart rhythm recorders that can be used for up to three years to continuously record your heart rhythm and pick up arrhythmias that shorter-term heart monitors may miss. This device is implanted under your skin in your chest and may be especially helpful if you've had a stroke to pinpoint what caused it.


An echocardiogram is a type of painless ultrasound that's used to look at the size and structure of your heart, as well as how it beats. You can have an echocardiogram while you're exercising or while you're resting.

Interpreting the ECG

The purpose of recording your heart rhythm during an episode of symptoms is to try to correlate your symptoms with a recording of your ECG at the time the symptoms are occurring.

Ideally, to make the diagnosis, the symptoms will start when the arrhythmia does, and resolve when the arrhythmia stops. If such a pattern is seen, it is almost certain that the arrhythmia is producing the symptoms.

Often, however, people will report symptoms at times when the heart rhythm turns out to be entirely normal; or conversely, an arrhythmia will be recorded at a time when no symptoms are present. Under these circumstances, it's likely that the symptoms you're experiencing are NOT due to an arrhythmia, and your doctor should begin considering alternative explanations for your symptoms.

If your doctor doesn't find an arrhythmia at all on a heart-monitoring test, but still suspects you have one, he or she may try to trigger one using one of these tests:

Stress Test

Since some arrhythmias are triggered or made worse by exercise or exertion, your doctor may do a stress test, monitoring your heart while you work out on a stationary bike or a treadmill. If there's a reason why you can't exercise, you may be given a heart-stimulating drug instead.

Tilt Table Test

If you've had fainting spells or syncope, your doctor may want to do a tilt table test. While you lie flat on a table, your heart activity and blood pressure are monitored. You may also be given an intravenous line (IV) in case you need medication. The table is then tilted so that it's vertical as if you're standing up while your doctor monitors any changes in your blood pressure and/or heart activity.

Electrophysiology Study (EPS)

If your arrhythmia is infrequent or your doctor's having a hard time finding it and thinks it may be life-threatening, he or she may do an electrophysiology study (EPS). This is a special catheterization test in which electrode catheters (flexible, insulated wires with metal electrode tips) are inserted into your heart in order to study the cardiac electrical system.

What to Expect: If your doctor has referred you for an EPS, you will be brought to the electrophysiology laboratory (a specialized catheterization laboratory) where you'll lie down on an examination table. You will be given local anesthesia, and possibly a mild sedative, and then electrode catheters will be inserted into one or more of your blood vessels. The catheters are inserted either through a small incision or by means of a needle-stick, usually in your arm, groin, or neck. Most often two or three catheters are used, and they may be inserted from more than one site. Using fluoroscopy, which is similar to an X-ray, the catheters are advanced through the blood vessels and positioned in specific areas within your heart.

Once they're appropriately positioned, the electrode catheters are used to do two main tasks: to record the electrical signals generated by your heart and to pace your heart. Pacing is accomplished by sending tiny electrical signals through the electrode catheter. By recording and pacing from strategic locations within your heart, most kinds of cardiac arrhythmias can be fully studied. When the procedure is complete, the catheter(s) are removed. Bleeding is controlled by placing pressure on the catheterization site for 30 to 60 minutes.

What It Does: An EPS can help to evaluate both bradycardias (slow heart arrhythmias) and tachycardias (rapid heart arrhythmias). Tachycardias are assessed by using programmed pacing techniques to trigger the tachycardia. If tachycardias can be triggered during the EPS, then by studying the electrical signals recorded from the electrode catheters, the precise cause of the tachycardia can usually be identified. Once this is accomplished, the appropriate therapy usually becomes clear.

Determining Treatment: There are a few ways an EPS can help you and your doctor make treatment decisions. Treatment options that may be considered based on the results of an EPS include: 

  • Insertion of a pacemaker: If the EPS confirms the presence of significant bradycardia, a permanent pacemaker can often be inserted immediately, during the same procedure.
  • Ablation: If supraventricular tachycardia (SVT)—and some forms of ventricular tachycardia (VT)—are found, radiofrequency ablation is often the treatment of choice. The ablation procedure is usually carried out during the same procedure, immediately following the EPS.
  • Insertion of an implantable defibrillator: If rapid forms of VT and/or ventricular fibrillation (VF) are identified during the EPS, most commonly an implantable defibrillator is the treatment of choice. This device can now often be inserted in the EP laboratory, immediately following the EPS. In earlier years, the EPS was used to identify the best anti-arrhythmic drug for patients with VT or VF, but today it's known that no anti-arrhythmic drug is as effective as the implantable defibrillator in preventing sudden death from these arrhythmias.

Risks: The potential risks of having an EPS are similar to those of having a cardiac catheterization. These procedures are relatively safe, but because they are invasive procedures involving the heart, several complications are possible.

You should not have an EPS unless there is a reasonable likelihood that the information gained from the procedure will be of significant benefit.

Minor complications include minor bleeding at the site of catheter insertion, temporary heart rhythm disturbances caused by the catheter irritating the heart muscle, and temporary changes in blood pressure. More significant complications include perforation of the heart wall causing a life-threatening condition called cardiac tamponade, extensive bleeding, or, because potentially lethal arrhythmias are being induced, cardiac arrest. The risk of dying during an EPS is less than one percent.

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