Arrhythmia is the term given to an irregular heartbeat.

In healthy hearts, the electrical charge the causes the normal heartbeat, originates from a group of specialized cells referred to as a node. This “pacemaker” site is located in the left upper heart chamber called the left atrium.

This principal node, where the normal conduction impulse starts, is referred to as the SA node which stands for sino-atrial, in reference to its anatomic location. From this node, the electrical current propagates down a circuit or pathway if you will, much like the electrical circuit in our homes to another node, located within the top portion of the ventricles, or lower heart chambers.

Here in the ventricle the node is referred to as the AV node for atrio-ventricular, again in reference to its location. The AV node, essentially acts like a relay station, transforming the single large electrical current into smaller currents and dispersing the electrical charge down through the walls of the ventricular muscle via smaller electrical circuits called Purkinje fibers. This electrical current depolarizes the cells and tissues in its path, and causes a mechanical contraction of the heart chambers. The contraction of these heart chambers in this sequence from the upper chamber to the bottom, forces blood into the circulation. And it is this contraction the causes blood to be pumped out of the heart chamber producing the pulse we feel, and the EKG signal we record.

This is the normal sequence for a heart beat, referred to as a normal sinus rhythm. It is the most efficacious rhythm and is referred to as sinus rhythm.

The pulse we feel should be regular in frequency, and in a normal physiologic state, be between a rate of 60-100 beats per minute, with an average of 80 beats per minute. That means that one electrical impulse is generated in under 1 second, every minute of every hour of every day for a lifetime!

 

As the electrical current travels from the atria through the top portions of the heart on its way to the ventricle, it leaves a trail which we can trace with the use of an electrocardiogram (EKG). The EKG is by far the most common test used by medical personnel.

A heart beat that originates normally from the SA node, that is beating greater than 100 beats per minute is called a tachycardia. A heart beat, beating less than 60 beats per minute is referred to as bradycardia. As these rhythms originate from the normal sinus node, they are not considered an arrhythmia in the true sense of the term. These extremes typically do not require any aggressive management other than going over and reviewing the medicines the person is taking as many blood pressure, heart medications and glaucoma medications especially beta blockers, calcium blockers and digitalis medications can cause bradicardia. Tachycardia on the other hand is usually a reflection of an underlying problem and not typically due to a problem with the heart. In other words, it is a signal that the person could be hypovolemic-dehydrated, anemic-sudden loss of blood, have metabolic problems-thyroid, or a reflection of a multitude of conditions that can cause this condition. One needs to look for and exclude physiologic, metabolic or emotional issues when trying to search for a cause of a sinus tachycardia, which in daily medical practice in hospitalized patients, a common occurrence.

 

Types of Arrhythmias

There are different ways doctors categorize arrhythmias. The most common and simplest way, especially for patients to understand, is to classify them according to they originate. Supraventricular arrhythmias as the name suggests, are any arrhythmias that develop or originate from the heart chambers above the ventricles. All arrhythmias that develop or originate from the lower heart chambers, the ventricles are ventricular arrythmias.

All arrhythmias share in common, the possibility of producing symptoms. The symptoms produced by arrhythmias range from palpitations (heart beat too fast), weakness, dizziness, shortness of breath, tiredness (symptoms produced by both a too fast or too slow heart rate), collapse to heart attacks and sudden death.

These symptoms are typically the result of a reduced volume of blood flow from the heart with each heart beat. Remember that with each heart beat, blood is being ejected from the ventricles. That’s the whole purpose of our heart beat. It depolarizes the tissues causing a mechanical contraction of the heart chambers and it’s the contraction of the ventricles that forces blood out, maintains our blood pressure and keeps us alive. The result of either extreme will be a ventricle the squeezes out less amount of blood (a decreased cardiac output) and we can get symptoms.

Atrial Fibrillation

Atrial Fibrillation (AF), is the most common type of arrhythmia we see in daily practice, as it affects 6% of the population and increases with age.

In AF the electrical impulses originate not in the SA node, but rather from multiple, independent areas of the atrial wall. Since the origin is from the heart chambers above the ventricles, it is categorized as a supraventricular rhythm.

Because these areas, are not true pacemaker sites but rather emergency “backup” sites, we get ineffective contractions from various sites in the atrium. As a result the resulting heart beat is irregular, of varying frequency with a reduced amount of blood ejected from the ventricle. AF in effect, is an inefficient heart rhythm.

Again, the symptoms produced are due to the decreased cardiac output or amount of blood ejected from the ventricle. Whether too fast or too slow, the rhythm is so ineffective and both extremes can produce symptoms. As the ventricle is contracting inefficiently and incompletely, the danger of this arrhythmia is in the possibility of clots forming in the heart chamber. Clots result from stagnant blood that is merely squeezed around in the heart chambers and not ejected. Clots within the heart can eventually find their way into the circulation and produce, pulmonary embolism, arterial occlusion in any artery within the body including the leg arteries, carotid artery which can produce TIA’s, and strokes, arteries of the small intestines producing ischemic bowel, and coronary arteries leading to even heart attacks.

It is for this reason, that AF is treated with a blood thinner or anticoagulation. All AF should be treated with anticoagulation regardless of the patients age. Contraindications are limited to patients with bleeding issues such as active, acute bleeding, recent history of stroke due to a bleed, are prone to falls, or are unwilling to adequately take their meds as indicated.The only oral anticoagulation used in the U.S. is warfarin, trade name: Coumadin. Aspirin, Plavix and persantine are not the same class of medications as blood thinners and are of no use as anticoagulants. These agents are anti-platelets, have a completely different function and should not be confused with anticoagulants. In situations where the heart rate is either to slow and produces symptoms, a pacemaker may be needed. There is a condition called sick sinus syndrome, which is manifest with a combination of fast and slow heart rate, each extreme capable of producing symptoms. Sick sinus syndrome which is a common presentation of AF is treated with a pacemaker to prevent the heart rate from decreasing too much and with medications which prevent the heart rate from beating too fast.

Causes of AF include coronary artery disease, diseases of the heart valves, ischemic heart disease, hypo or hyperthyroidism, any stimulants including drugs like cocaine, drinks like caffeine, cola’s, tea’s, and diseases of the heart muscle just to mention a few of the most common. Treatment in addition to the medications and therapies previously mentioned including a search for treatable causes and correctable factors.

Heart Blocks

Heart blocks occur when the electrical impulses are produced and generated from the normal pacemaker node, but along the way, something happens that prevents or “blocks” their normal conduction through the entire cardiac electrical circuit. What is seen on the EKG is typically more electrical impulses from the atria as the source of stimulation is typically normal, the problem being with the ventricles not receiving all the impulses. Causes include those that cause AF. Symptoms are similar, again due to a reduced cardiac output. Treatment consists of reviewing medications first, as common medications can cause this and most arrhythmias. Some patients may need a pacemaker.

 

 

Ventricular arrhythmias in different section