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Abnormal heart rhythms-

How many are there?
Classifying an irregular heart rhythm provides information that may help the cause of the arrhythmia and the reason for its persistence (the so-called “mechanism”).

  • Classified by rate

“Fast” (Tachycardia) vs. “Slow” (Bradycardia)

Normal rate (60-100 beats per minute)



Probably the two most common terms used in discussions of arrhythmia are tachycardia, usually over 100 beats per minute, and bradycardia, usually less than 60 beats per minute. These terms describe only the rate of the heart rhythm, and although important, the rate by itself doesn’t tell you much. Learning which part of the heart is involved in causing arrhythmia is even more valuable.

  • Classified by location

Arrhythmias are easily classified according to their location in the heart. Dividing the heart into three major areas-the top (atria), middle (AV junction), and bottom (ventricular)-makes most arrhythmias understandable.

From the “TOP”

Abnormal heart rhythms from the top of the heart are called “atrial arrhythmias.” They are caused by abnormal electrical impulses from different places on the top of the heart. Because they usually cause the heart muscle to squeeze early, they are referred to as premature atrial contractions (PACs) or beats. These abnormal beats may be single, double, or three or more in sequence. The latter, three or more abnormal beats in sequence may be called PAT (paroxysmal atrial tachycardia), “atrial flutter” or “atrial fib” (atrial fibrillation) depending on the type of problem.

From the “MIDDLE”
Normally, electrical impulses pass from the top of the heart to the bottom of the heart through the middle, or junction (also called AV junction), of the heart. There the impulses may be slowed or even blocked completely. This can be considered a protective mechanism that prevents the major pumping chambers on the bottom of the heart, the ventricles, from beating too fast when the top of the heart has a fast rhythm (tachycardia). Abnormally fast rhythms can result in the ventricles not filling or pumping properly. The overall result can be poor circulation of blood. At times, there is an abnormal slowing or block of the electrical impulses as they pass through the AV junction (called Heart Block or AV Block). These “conduction delays” or blocks almost always result in a slow heart rate. Excessively slow heart rates may cause fatigue, lightheadedness or even fainting that may require a permanent pacemaker.
From the “BOTTOM”
Abnormal heart rhythms from the bottom of the heart are called “ventricular arrhythmias.” These are caused by abnormal electrical impulses from different places in the bottom of the heart. Because they usually cause the heart muscle to contract early, they are referred to as PVCs, or premature ventricular contractions. These abnormal beats may be single, double or three or more in sequence. The latter, three or more abnormal beats in sequence, is usually called VT (ventricular tachycardia). When the rhythm is so chaotic that the muscle can no longer contract, the abnormality is called VF (ventricular fibrillation).
Still interested?

For those who want to know even more (characteristics of specific arrhythmias)

Fast heart rates that are abnormal (Tachycardias)

From the “top” (Atrial arrhythmias)

  • PACs- Premature Atrial Contractions (or beats PABs)

  • PAT- Paroxysmal Atrial Tachycardia

  • “Atrial flutter”

  • “Atrial fib”- Atrial fibrillation

From the “bottom” (Ventricular arrhythmias)

Slow heart rates that are abnormal (Bradycardias)
A “sick starter” (Sick Sinus Syndrome; SSS)

Problems getting through the middle (junctions) of the heart are called “Heart Blocks”

  • Mild (1st degree)

  • Moderate (2nd degree)

  • Severe (3rd degree or “Complete” heart block)

  • Fast heart rates that are abnormal (Tachycardia)

Before we describe the abnormal fast rhythms of the heart, it is useful to review the normal fast rhythm, which is medically called Sinus Tachycardia (See Normal Heart Function). Whenever the natural pacemaker of the heart (sinus or SA node) is caused to increase to greater than 100 beats a minute, it is called a sinus tachycardia. Generally the rate doesn’t exceed 150 beats per minute. If you’re aware that your heart is racing, and many people can feel this change, you are experiencing “palpitations.” As you can see, not all “palpitations” therefore mean there is an abnormal rhythm (arrhythmia) present. It is a normal response of the heart to the bodies needs (such as with exercise, stress or fever associated with illness), certain medications (including cold remedies or stimulants) or certain foods such as coffee, tea, colas, or other caffeinated foods. Generally when we say something is exciting, it’s likely we’re talking about something that can cause our heart rate to increase naturally (that is, produce a sinus tachycardia).

Rx (=treatment) of Sinus Tachycardia. Since this is a normal rhythm, treatment is generally not indicated except as it is focused on identifying the cause and trying to reduce or eliminate it. The heart rate generally will respond as the cause is withdrawn.
PACs (=Premature Atrial Contractions) or Beats (PABs) are early beats that are initiated in the atria by some cause and location other than the natural pacemaker. They can be single (one at a time) or double (two in a row also called a “pair”) and occur before the next expected sinus beat; hence they are early or premature! Many people have PACs and are entirely unaware of them. Others are aware of each PAC as an irregularity or skipping of their heart. Rarely can other symptoms (such as shortness of breath, weakness, or lightheadedness) be clearly attributed to PACs; since these beats do not disturb cardiac function greatly. The causes of PACs are similar to the causes of Sinus tachycardia in one individual and PACs in another.
Rx (=treatment) of PACs, which is harmless though at times very disturbing condition, generally focuses on identifying the possible cause and trying to eliminate or reduce it.

PAT (=Paroxysmal Atrial Tachycardia) or SVT (=Supraventricular Tachycardia) refer to episodes (so-called “paroxysms”) of 3 or more PACs in a row. This is one of the most common types of sudden, rapid, arrhythmias and often very variable in their length, time of occurrence and symptoms. They can occur as only 3 beats and be entirely unnoticed or persist for prolonged episodes (hours and even days if not treated). PAT usually causes sympotoms of “heart racing,” “fluttering” and at times complaints of shortness of breath, tiredness or weakness, and chest comfort. This is rarely a cause of fainting or collapse. A number of patients have reported that they were alarmed to see their chest wall or clothing (in the area of the left nipple) move rapidly in a tapping-like motion. Generally the rate is between 150 and 250 beats a minute and is very noticeable as it starts suddenly. The causes of PAT are similar as the causes of Sinus Tachycardia but the mechanisms (that is how they actually stimulate the heart to beat rapidly) are entirely different. There are several different mechanisms of PAT resulting from different locations in the atria or junctional area. These can at times be suspected from the ECG but at other times require additional testing.

Rx (=treatment) of PAT (SVT) can take many forms. Medications may be used occasionally in patients with rare episodes as a kind of “medication cocktail” to stop an episode already in progress. For patients with more frequent bouts of PAT, medications may be prescribed for daily use to prevent the episodes from occurring. Medications used to treat PAT include digoxin, beta blockers, calcium channel blockers (such as verapamil or diltiazem), and less frequently Class I or III antiarrhythmic agents (See Prescription Medications).
The newest treatment for PAT is not a medication but rather involves studying the patient in a specialized hospital laboratory test called an “EP” Test (ElectroPhysiologic test). In this testing procedure described in (Specialized Tests- Electrophysiologic Study), the electrical pathways in the heart used by the PAT mechanism are identified. After identifying the specific pathway with a wire catheter that gets to the heart through the blood stream, the wire catheter is placed next to it and a small dose of radiofrequency energy can be sent through the wire to damage the pathway and prevent the PAT from ever occurring again. This procedure can eliminate the need for mediation entirely in most cases.

Flutter (or more correctly Atrial Flutter) is an arrhythmia in which the electrical activity of the top of the heart is very fast but also very chaotic and disorganized. As a result, the actual pumping action of the upper heart chambers which helps blood “to load” into the lower chambers is lost. The upper chambers act only to hold blood for the next beat rather than push it forward into the major lower pumping chambers (or ventricles). It is often easily recognized on the standard ECG because of its distinctive changing and “irregular pattern – which distinguishes it from atrial fibrillation and atrial flutter are many. It is unclear why some individuals in response to a particular problem will develop atrial flutter where as another person will develop atrial fibrillation.

Atrial flutter and atrial fibrillation may be caused by:

    • Heart diseases (valve problems, muscle damage from heart attack, virus or alcohol, heart failure, following heart surgery).

    • Lung diseases (chronic bronchitis, emphysema, pneumonia)

    • Overactive thyroid gland

    • Excesses of alcohol, caffeine or other stimulants

    • Low blood potassium or magnesium (sometimes resulting from use of water pills [diuretics] without adequate supplements, chronic diarrhea or laxative use).

Rx (=treatment) The goals in treating Atrial Fib or Flutter include slowing the heart rate so the heart will function better, stop the irregularity and reduce the chance of it reoccurring. Digoxin, beta blockers and two of the calcium channel blockers (verapamil and diltiazem) can be used to slow the heart rate if it is fast. Other drugs can be used to correct the problem (see Medications for the bottom of the heart). These medications are often used in combination and require careful monitoring by your doctor. In addition to drug treatment a carefully controlled electric shock can be used to “convert” (change) either Atrial Fib or Flutter back to normal (sinus) rhythm (see Hospital treatments Cardioversion).

  • Bradycardias (=Slow heart rates)

A slow heart rate (bradycardia pronounced brad’-ee-card-ee-a) can be normal or abnormal. It may occur normally because our natural pacemaker (the sinus or SA node) is firing slowly in response to the reduced needs of the body for added circulation. An appropriately slow heart rate may occur while we are at rest, sleeping or relaxing (see Palpitations are not always caused by arrhythmias; Sinus bradycardia).

If the sinus or SA node is damaged or has problems forming electrical impulses, the heart rate may be abnormally slow, irregular, or show gaps or pauses between beats. These gaps between impulses are referred to as “sinus pauses generally if they occur for only one beat and as “sinus arrest” if more prolonged.

Sinus Pause or Arrest

A slow heart rate may also result from an inability of the electrical impulse produced by the sinus node to travel though the upper chambers and AV junction to the lower chambers of the heart. This block in the electrical impulses pathway almost always occurs in the middle of the heart in the area of the AV junction and is almost always abnormal. It is referred to as “heart block” and may vary in severity.

Junctional problems including Heart Blocks

“Heart block” is a scary term that often confuses people who immediately worry that the “block” that’s being discussed is in a coronary artery and can lead to a heart attack. In fact, “heart block” has nothing to do with the arteries or blood supply of the heart and is not a cause of the common heart attack. Heart block refers to the slowing or complete stopping of electrical impulses as they travel though the middle (junction) of the heart. It can be present in different degrees:


Medical Term

Explanation and Treatment


1st degree heart block

Is a trivial problem that is really no problem at all and requires no treatment. It represents a slowing of the electrical impulse as it travels though the middle (junction) of the heart.


2nd degree heart block

Is rarely a normal finding. This always causes a slowing of the heart beat and may require a pacemaker to be implanted if symptoms of lightheadedness, dizziness or a faint result.


3rd degree heart block

This is also known as complete heart block. It represents complete blockage of all electrical impulses from the top of the heart as they travel though the middle (junction) of the heart. This requires the placement of a permanent pacemaker as a guarantee that there will always be a heart beat.

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