Tests for Detecting Arrhythmias

Electrocardiogram (ECG or EKG). Records the electrical activity of the heart. Each time the heart beats, it sends out an electric-like signal. An ECG machine can record this activity. To record the ECG, small patches or stickers called electrodes are placed on different parts of the body. One is put on each arm and leg and six across the chest.

With various combinations of these electrodes, different tracings of the heart's electrical activity can be made and permanently recorded on paper or in a computer. The types of ECGs are:

Resting ECG. The patient lies down for a few minutes while a record is made. In this type of ECG, disks are attached to the patient's arms and legs as well as to the chest. Records about 12 seconds of heart electrical activity.

Exercise ECG (stress test). The patient exercises either on a treadmill machine or bicycle while connected to the ECG machine. This test tells whether exercise causes arrhythmias or makes them worse or whether there is evidence of inadequate blood flow to the heart muscle ("ischemia"). Records electrical activity for duration of exercise (10 to 20 minutes).

24-hour ECG (Holter) monitoring. The patient goes about his or her usual daily activities while wearing a small, portable recorder that connects to the disks on the patient's chest. Over time, this test shows changes in rhythm (or "ischemia") that may not be detected during a resting or exercise ECG. Can record continuously for 24 to 48 hours.

Transtelephonic monitoring. The patient wears the recorder and disks over a period of a few days to several weeks. When the patient feels an arrhythmia, he or she telephones a monitoring station where the record is made. If access to a telephone is not possible, the patient has the option of activating the monitor's memory function. Later, when a telephone is accessible, the patient can transmit the recorded information from the memory to the monitoring station. Transtelephonic monitoring can reveal arrhythmias that occur only once every few days or weeks.

Intracardiac Electrophysiologic Procedure. Sometimes it's necessary to study the heart's electrical system with an intracardiac (within the heart) electrophysiologic procedure. In this, one or more long, thin tubes (catheters) are placed into the large blood vessels in the legs, arms or both. Then the tips of the catheters are moved into the heart. Once in the heart, the catheters can record electrical signals from the normal electrical system. This gives much more precise information than an ordinary ECG. During these studies, the heart can be stimulated to beat rapidly or irregularly. The heart's response to this - and the way electricity moves around the heart during a tachycardia - helps the cardiologist diagnose the nature of an arrhythmia. Sometimes abnormal tissue causing an arrhythmia is then destroyed by heating it with a probe (called radioablation therapy).

Esophageal Electrophysiologic Procedure. In some situations, your cardiologist may recommend that an esophageal electrophysiologic procedure be done. This is used to diagnose or treat the type of tachycardia you have. In this procedure, a thin, soft, flexible plastic tube is inserted into your nostril and positioned in the esophagus. (The esophagus is the tube that connects the mouth and stomach.) Since the esophagus is close to the upper chambers (atria) of the heart, an ECG recording there gives more precise information than a regular ECG. An electrical stimulator may be used to make the heart beat faster to try to restart your arrhythmia. This helps your doctor make the right diagnosis.

During this procedure certain medications may be tested to find the one that will be most effective. The esophageal electrophysiologic procedure also may be performed to temporarily stop certain types of arrhythmias. This procedure is similar, but less invasive than an intracardiac procedure. Ablation therapy (directly destroying abnormal heart conduction tissue) cannot be performed with the esophageal procedure.

Arrhythmia Types

Originating in the Atria

• Sinus arrhythmia
  Normal cyclic changes in the heart rate during breathing. Common in children and often found in adults.
  
  
• Sinus tachycardia
  The sinus node sends out electrical signals faster than usual, speeding up the heart rate. A heart rate greater than 100 beats per minute.
  
  
• Sick sinus syndrome
  Sometimes the sinus node, as well as the AV node, doesn't work properly. Different combinations of supraventricular arrhythmias, both slow and fast, are produced on an intermittent basis. This condition almost always indicates disease of multiple areas of the heart conduction system. Symptoms of sick sinus syndrome are caused by either too fast or slow heart rate and include near syncope or syncope (passing out due to not enough blood reaching the brain), chest pain, shortness of breath, palpitations and stroke.
  
  Holter monitoring (a device continuously recording heart electrical activity for 1-2 days) is often needed to diagnose sick sinus syndrome. A routine EKG often does not show intermittent arrhythmias common in this syndrome.
  
  Bradycardias causing symptoms usually require a pacemaker. Tachycardias are usually treated with medication to slow the heart rate down. Medications are usually started after pacemaker insertion because they can make bradycardias worse.

• Premature Atrial Contraction (PAC)
  Irregular heart rhythms are most often caused by premature beats or extra beats. These originate in the upper chambers (premature atrial contraction, PAC). When we feel our heart "skip a beat," it usually results from this type of arrhythmia.

  The heart does not skip a beat. Instead an extra beat comes sooner than normal. This is followed by a pause that causes the next beat to be more forceful. The person feels this more-forceful beat.

  Premature beats are common in healthy people of all ages- most people have them at some time. Caffeine, alcohol, stress and fatigue may cause PAC's to occur more frequently. Usually no special treatment is needed and no cause can be found. The premature beats may disappear, and even if they continue, most people tolerate them well.

• Supraventricular tachycardia (SVT)
  A series of early beats in the atria speed up the heart rate (the number of times a heart beats per minute). In paroxysmal tachycardia, repeated periods of very fast heartbeats begin and end suddenly.
  
  The most common abnormal tachycardia in children (and common in adults as well) is reentrant supraventricular tachycardia (SVT). It's also known as paroxysmal atrial tachycardia (PAT) or paroxysmal supraventricular tachycardia (PSVT). The fast heart rate involves both the heart's upper and lower chambers. This isn't a lifethreatening problem for most people. For many, it doesn't require medical therapy. Treatment is considered if episodes are prolonged or frequent. There are several subgroups of SVT, including Wolf-Parkinson-White syndrome (WPW). The heart rate is generally between 160-200 beats per minute which can be tolerated by most people for an extended period of time.
  
  
• Wolff-Parkinson-White syndrome.
  A specific type of SVT this condition is caused by abnormal pathways between the atria and ventricles, causing the electrical signal to arrive at the ventricles too soon and to be transmitted back into the atria. Very fast heart rates may develop as the electrical signal ricochets between the atria and ventricles. Sometimes the heart rate can be very high (200-300 beats per minute). Some medications used to slow regular SVT down can actually make the heart beat even faster in a particular type of WPW.
  
  
• Atrial flutter
  Rapidly fired signals cause the muscles in the atria to contract quickly, leading to a very fast (250-350 atrial beats per minute) and regular heartbeat. There is normally a conduction block at the AV node. That is for any given number of atrial beats reaching the AV node a certain number are blocked. Usually one ventricular beat occurs for every two atrial impulses reaching the AV node. Sometimes 3:1 or even higher block occurs ( that is for every three atrial impulses reaching the AV node one is conducted through to the ventricles).

  Atrial flutter almost always occurs in patients with underlying heart disease. Atrial flutter is sometimes seen as a transition rhythm between atrial fibrillation and normal sinus rhythm.

• Atrial fibrillation.
  Electrical signals in the atria are fired in a very fast and uncontrolled manner. Atrial signals are rapid and chaotic beating upto 400 beats per minute. Instead of a single electrical signal followed by coordinated atrial contraction there is quivering of the atrial muscle. Not all signals are conducted through the AV node. Heart rates may vary from 100 to 180. Irregular beats (unevenly spaced) heart beats always occur with atrial fibrillation. (Heart beats are very fast but regular in PSVT). Atrial fibrillation can occur in a sustained manner or may occur episodically.

  The atria do not effectively pump blood. Because most of the blood filling the ventricles does not require atrial pumping (blood flows passively into the ventricles from the atria during the heart's rest cycle) most people still have enough blood flow to the body's organs. Atrial fibrillation is usually due to atrial dilatation and associated with four conditions :

  • overactive thyroid (Hyperthyroidism)
  • rheumatic heart disease
  • prolonged high blood pressure
  • ischemic heart disease (coronary artery disease)
  • It may infrequently occur in young to middle aged healthy people.
  
  It is important for your doctor to know is you have atrial fibrillation because of increased risk of stroke. Small emboli ( blood clots) are more likely to form in the atria because blood does not move as well. When these emboli break loose they may travel to the brain or other organs.

Originating in the Ventricles

• Premature ventricular complexes (PVC) An electrical signal from the ventricles causes an early heart beat that generally goes unnoticed. The heart then seems to pause until the next beat of the ventricle occurs in a regular fashion. Premature beats are common in healthy people of all ages- most people have them at some time. Usually no special treatment is needed and no cause can be found. The premature beats may disappear, and even if they continue, most people tolerate them well. Occasionally PVC's may be caused by disease or injury to the heart.
  
  
• Ventricular tachycardia (VT) .
  The heart beats fast due to electrical signals arising from the ventricles (rather than from the atria). It's a potentially serious condition that could threaten a person's life. Heart rate ranges from 150 to 200 beats per minute. Certain medications can make this condition worse.

  VT almost always results from serious heart disease such as coronary artery disease and acute heart attacks; it usually requires prompt treatment. Ventricular tachycardia, rare in children, occurs more frequently as people age. Often specialized tests, including an intracardiac electrophysiologic procedure (see Special Tests), may be needed to evaluate the tachycardia and the effect of drug treatment. Some forms of VT may not need treatment.

• Ventricular fibrillation.
  Electrical signals in the ventricles are fired in a very fast and uncontrolled manner, causing the heart to quiver rather than beat and pump blood. This is the rhythm responsible for "shocking" unconscious people on television shows. The ventricle "quivers" with no effective pumping of blood. The heart has not actually stopped. Because the heart does not pump blood to the body a person in ventricular fibrillation loses consciousness immediately.

  VF is almost always seen in patients with severe coronary artery disease. Much less commonly it may occur in younger people with normal coronary arteries who have certain inherited heart conditions and in people who have had the heart muscle or conduction system injured by infection (myocarditis). VF may also occur with a very hard blow to the chest, abnormal concentrations of certain minerals in the body, too low a body temperature (hypothermia), and when the amount of certain medications in the body is too high.

  Electrical cardioversion, using DC current, is always the first treatment. With an electrical shock, it immediately disrupts a deadly arrhythmia. To have any chance of recovery cardioversion must be done quickly. CPR is started if cardioversion unsuccessful after 3 consecutive attempts.

Cardiac Standstill (Asystole)

Is the complete absence of heart electrical activity. This is often a terminal arrhythmia usually causing death. That is other arrhythmias, such as ventricular fibrillation, progress to asystole if not treated. The heart does not pump or even quiver.