There are literally dozens of different types of arrhythmias.  Some arrhythmias can kill a patient instantly while others are completely benign.  Some can cause severe symptoms like racing heartbeat and fainting spells while others may produce absolutely no symptoms whatsoever.  Making a specific diagnosis of the type of arrhythmia the patient has, therefore, is of paramount importance.

As a general rule, in order to make a diagnosis of an arrhythmia, some forms of electrocardiographic recording (i.e., EKG, Holter monitor, or event monitor) must be made at the time the arrhythmia is occurring.  Evaluation by symptoms alone is inadequate.  This is because symptoms from different arrhythmias may feel exactly the same to a patient, and the same arrhythmia may feel differently for different patients.  For example, the sensation of palpitation can occur in patients with ventricular tachycardia or with PVCs, two conditions with vastly different prognoses.  The physician, therefore, usually can not diagnose one arrhythmia from another based on symptoms alone.

In addition, in between episodes of arrhythmias, the EKG can be completely normal, making the diagnosis quite challenging.  A very common scenario is a patient with an SVT (a very rapid arrhythmia) who has an episode of attack once a month, lasting 10 minutes each.  Every time this patient runs to the emergency room, the SVT has already stopped and the EKG in the ER is completely normal.  Many such patients have been misdiagnosed as "panic attack" or "anxiety" because of the lack of physical evidence (other than patient's subjective report of symptoms) of an arrhythmia.  Some patients even leave the ER with a diagnosis of "palpitation," which is a symptom, not a diagnosis.  The true diagnosis can be quite elusive until one day when an EKG is finally done at the time an episode is still ongoing. 

If an arrhythmia becomes persistent and is present day-in and day-out, as often is the case for atrial fibrillation or atrial flutter, the diagnosis is quite easy with a routine EKG done in the physician's office.  The challenge is when an arrhythmia occurs intermittently (on and off) or is self-limiting, whereby a EKG performed in between attacks can be completely normal.  To circumvent this problem, one would go to the next level of evaluation with a long-term monitor.

Long-term monitors basically are EKG recorders that patients can take with them.  They fall into two major categories.  A "Holter monitor" records continuously the EKG of a patient, usually for 24 hours.  The advantage of a Holter is that every single heartbeat during that day is recorded and can be analyzed.  The disadvantage is that if an arrhythmia did not happen  on that particular day, the Holter would not be useful.  An "event monitor," on the other hand, is a long-term monitor that can be used for up to 30 days at a time.  The advantage is that the longer the recording period, the better chance of "catching" an intermittent arrhythmia.  The disadvantage is that an event monitor must be activated by the patient and downloaded through a telephone line, a task that requires certain amount of manual dexterity and may be difficult for some patients.

For certain arrhythmias which are so rare that they occur once or twice a year, the diagnosis can be nearly impossible to make with any of these monitors.  In these cases, or in patients who are not capable of handling an event monitor, an implantable monitor is available that can monitor patients' rhythms for up to 2 years, continuously, 24/7.  The major advantage of this monitor is the length of time of monitoring compared to other monitors.  The disadvantage is that it requires a surgery, though a very minor one that takes about 5 minutes to complete.

For many patients, both Holter monitor or event monitors, or even implantable monitors may be necessary because these different monitors have different capabilities and complement each other.  However, if the diagnosis remains elusive after extensive evaluations with these "passive" tests, a "proactive" test may be necessary.

A "passive" test waits for an arrhythmia to occur spontaneously before making a recording.  This can be time consuming and sometimes a diagnosis simply can not be made despite extensive evaluation.  In those cases, a "proactive" approach may be necessary whereby the physician actively "provokes" an arrhythmia in order to make a recording of it for a diagnosis.

This "proactive" approach may involve simply having patient engage in activities which historically have provoked patient's symptoms, while the patient is wearing a monitor.  For example, certain arrhythmias that occur consistently during physical activities or after ingestion of alcohol may be reproduced with these activities during a monitoring period. 

For conditions that occur with exercise, a treadmill stress test supervised by your physician sometimes can reproduce an arrhythmia, helping to clench the diagnosis.  A similar test monitoring the "T waves" of the EKG can help reveal underlying conditions that can cause serious arrhythmias.  For certain conditions that cause fainting spells, a tilt table study can recreate an episode and help reveal a cause.

Lastly, when all else fails and the diagnosis remains uncertain, an electrophysiology study can be done to confirm or exclude certain arrhythmia diagnoses.  This invasive test is also done in conjunction with radiofrequency ablation.

In summary, there is an extensive battery of diagnostic tests for patients with symptoms suspicious for arrhythmias.  These tests range from simple and routine to complex and invasive.  Different tests have different yields for diagnosing an arrhythmia and not all tests are appropriate for every patient.  Your physician can made the decision on which tests are appropriate for your particular condition.

Electrocardiogram (EKG). This is the most basic and standard initial evaluation for patients with a suspected arrhythmia. An EKG is a window into the electrical activities of the heart.  Multiple electrodes (stick patches) are placed on the arms, legs, and over the chest area in order to record electrical activities of the heart from different angles of view.  The heart generates electrical activities with each heartbeat, which can be detected by the voltage difference between pairs of electrodes and translated into graphical display on paper.  Today's standard EKG utilizes 12 electrodes, thus the name "12-Lead EKG."  An EKG is most useful in diagnosing an ongoing arrhythmia at the time the EKG is being performed, but it is not useful if the arrhythmia, or the symptoms suspected to be due to arrhythmia, is no longer present at the time of the evaluation.  Keep in mind that an EKG is a static picture, or a "snap shot," of what is happening in the heart at the time the recording is made.

Holter monitor. This is an EKG recorder that continuously records every heartbeat of a patient for a period of usually 24 hours.  Rather than having 12 leads, most Holter monitors utilizes 3 leads.  Patients are usually "hooked up" with a Holter while in the physician's office, wearing it for 24 hours, then returns the next day to have it removed in the office.  Patient may not shower and should avoid strenuous activities (unless specifically instructed by the physician) during the recording period.  At the end of the 24 hour period, patient may remove the unit on his or her own and bring the unit back to the office for analysis.

The recording of the heart rhythm on a Holter is made in a continuous fashion onto an electronic media, which is then downloaded into a computer and analyzed beat-by-beat.   This test is most useful if an arrhythmia is there all the time, or occurs frequently enough to be "caught on tape" during that 24-hour period of recording. It is therefore very important for the patient to write down in the accompanying diary any symptoms that occurred during the recording period, so the physician can correlate the symptoms to actual arrhythmias found on the recording.

One important limitation of a Holter monitor is that it records only during that 24 hours of time and may miss an infrequent arrhythmia.  In other words, an arrhythmia that occurs only a few times a year is unlikely to be "caught" by chance during any single 24-hour period of recording. In those cases, a long-term event monitor may be the preferred choice of test.

Event monitor. An event monitor is a long-term (usually 30 days) monitoring device that records "patient triggered" events.  Similar to an EKG or a Holter monitor, it records the electrical activities of the heart via electrodes placed on the patient's chest.  The electrodes and wires are attached at all time to patient's chest and can be taken off and replaced as needed for shower and other activities where patients may not wish to have the hardware attached.

Unlike a Holter monitor, which records continuously, the event monitor records only when activated by patients.  In other words, while the monitor continuously keeps a "loop" memory, the actual recording of the heartbeat and writing of the data onto the electronic media occurs only when patient triggers the recording by pressing a button on the unit.  This is so that the physician can correlate patient's symptoms to what is recorded, thus confirming or refuting the cause of patient's symptoms being of arrhythmic origin.  A major advantage of a loop-recorder is that it always keeps the preceding 40-60 seconds of data in the loop memory, such that if a patient was not able to trigger the recording immediately at the time of the symptoms, but does so a short time later, the data may still be useful.