Diagnosing heart rhythm problems can be trivially easy, devilishly difficult, or somewhere in between. Making the diagnosis is easy if you have a chronic or persistent cardiac arrhythmia - then it's just a matter of recording an electrocardiogram (ECG) and documenting the presence and type of arrhythmia the patient is experiencing.
Unfortunately, many times cardiac arrhythmias are episodic in nature - they come and go without warning. In these cases, you may experience episodes of symptoms, often lasting just a few seconds. Recording a simple ECG in these cases is not likely to reveal the arrhythmia, so additional testing is necessary. But the basic principle remains the same: to diagnose a cardiac arrhythmia, the arrhythmia should be "captured" by recording an electrocardiogram while the arrhythmia is present.
Your Initial Evaluation
The first step in figuring out whether a your problems may be caused by an arrhythmia is to find out your symptoms. ( The symptoms of heart arrhythmias are described in this article. ) It's important to know that if you have episodes of loss of consciousness, and if there is a reasonable chance your symptoms are due to an arrhythmia, you should probably be hospitalized and placed on a cardiac monitor until a definite diagnosis is made. This is because if an arrhythmia is causing loss of consciousness, it can also cause cardiac arrest at any moment. People with this problem are usually evaluated using the invasive electrophysiology study (described below).
Assuming that the symptoms do not suggest a life-threatening arrhythmia, the question becomes how to best record the presumptive arrhythmia. Obviously, if you are aving symptoms while seeing the doctor, an ECG should be done right away. More commonly, symptoms occur as occasional episodes, and a decision needs to be made as to which method to use to try to record the heart rhythm during an one of these spontaneous episodes.
Recording the Heart Rhythm During Symptoms
If 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 episodes of symptoms occur less frequently, the best choice may be an event recorder. Event recorders use a circular tape that stores only approximately 30 seconds of a patient's heart rhythm. That is, at any given time while a patient is wearing them, event recorders will have the most recent 30 seconds of the patient's heart rhythm recording. When you patient experiences an episode of symptoms, you press a button that freezes the recording, which is then transmitted by telephone to an interpreting center. A major advantage of event recorders is that they can be used for up to 30 to 60 days, until the transient symptom being looked for occurs.
If episodes of symptoms are so infrequent that even an event monitor is unlikely to capture one, there are small implantable heart rhythm recorders, placed under the skin near the collarbone, 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 the symptoms with a particular arrhythmia. 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, symptoms will be reported when the heart rhythm is 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 have are NOT due to an arrhythmia, and alternative explanations for your symptoms should be considered.
The Electrophysiology Study (EPS)
On occasion, for certain types of arrhythmias and in certain types of patients, prolonged recordings of the heart rhythm and "waiting" for spontaneous symptoms is impractical or inadvisable. In these patients, the electrophysiology study (EPS) sometimes can be used to help determine whether a significant or life threatening arrhythmia may be likely.
In the EPS, specialized catheters are placed into the heart. These catheters can be used to "pace" the heart, and also to record the electrical activity of the heart, from various locations within the heart. Information gained from the EPS can be used to decide whether a you have the propensity to develop either bradycardias, or certain kinds of tachycardias. (Some tachycardias, called the "re-entrant" tachycardias, can be induced with pacing techniques in patients who are likely to experience these arrhythmias spontaneously. "Reentrant" tachycardias include most kinds of ventricular tachycardia and fibrillation, and most kinds of SVT.)
The disadvantages of doing the EPS are that a) it is an invasive study, and b) it generally only reveals whether there is a propensity for an arrhythmia, and does not necessarily "prove" that the arrhythmia has occurred in the past, or is going to occur in the future. For these reasons, the EPS is usually reserved for patients:
- who are thought to be at relatively high risk for cardiac arrest, and so are poor candidates for simply sending the patient home with a recording device and "waiting" for the potentially life-threatening arrhythmia to occur spontaneously; or
- who are thought to have one of the forms of SVT that are potentially "curable" with ablation techniques. Here, the EPS is required to fully characterize the arrhythmia.
