Diagnosing Cardiac Arrhythmias

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If you have a heart rhythm problem, 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, many times 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.

The Initial Evaluation

If your doctor thinks you may be having a cardiac arrhythmias, the first question is whether those arrhythmias are likely to be life-threatening. If you have had spells of unexplained, severe dizziness, or have had syncope (loss of consciousness) - especially if you have underlying cardiac disease - your doctor should 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).

On the other hand, more typical symptoms 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 ECG during an episode of symptoms. This generally can be done using an ambulatory cardiac monitor as you go about your daily routine.

Recording the Heart Rhythm During Symptoms

If your symptoms occur daily or almost daily, the best choice for diagnosing the cause may be to use the Holter monitor, a recording device which continuously records the heart rhythm for a 24 - 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.

If symptoms occur less frequently, the best choice may be a long-term recording device, which you can use for several weeks at a time. Advanced types of ECG recorders are now available that can store very lengthy recordings of your heart rhythm, and some can automatically detect and record any cardiac arrhythmias you may have.

If your symptoms are extremely infrequent, so that even a month’s worth of recordings is unlikely to capture one, there are small implantable heart rhythm recorders that can be used for very prolonged periods of time. It is rarely necessary to resort to such a device, however.

Interpreting the Recording

The purpose of recording the 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 onset of symptoms will coincide with the onset of an arrhythmia, and the symptoms will 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 is likely that the symptoms you are experiencing are NOT due to an arrhythmia, and your doctor should begin considering alternative explanations for your symptoms.

The Electrophysiology Study (EPS)

If your symptoms suggest the possibility of a dangerous cardiac arrhythmia, an outpatient evaluation is not a good idea. In such cases, an electrophysiology study (EPS) may be used to assess the likelihood that a life-threatening arrhythmia is present. If so, the EPS can quickly direct your doctors toward the appropriate therapy.


Crawford MH, Bernstein SJ, Deedwania PC, et al. ACC/AHA guidelines for ambulatory electrocardiography: executive summary and recommendations. A report of the American College of Cardiology/American Heart Association task force on practice guidelines (committee to revise the guidelines for ambulatory electrocardiography). Circulation 1999; 100:886.

Olson JA, Fouts AM, Padanilam BJ, Prystowsky EN. Utility of mobile cardiac outpatient telemetry for the diagnosis of palpitations, presyncope, syncope, and the assessment of therapy efficacy. J Cardiovasc Electrophysiol 2007; 18:473.

Furukawa T, Maggi R, Bertolone C, et al. Additional diagnostic value of very prolonged observation by implantable loop recorder in patients with unexplained syncope. J Cardiovasc Electrophysiol 2012; 23:67.

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