Reviewed by: Joseph Maloney, MDAn irregularity in the normal rhythm of the heart beat is called an arrhythmia. Almost everyone experiences arrhythmias in the form of mild palpitations or skipped heart beats at some point in his or her life. Arrhythmias are more common as we age, and they affect millions of people. Isolated incidences are usually innocuous, but a physician should look at a recurrent arrhythmia or arrhythmias accompanied by symptoms listed below.
Many types of heart disease cause arrhythmia. Coronary artery disease, which can cause a heart attack, produces scar tissue that can disrupt the transmission of electrical signals; this is caused by insufficient blood flow to the heart muscle due to sclerotic obstruction in the coronary artery. Other causes of arrhythmia include congenital heart disease, heart valve disorders, lung disease (smoking, congenital and acquired), thyroid conditions (both over active and under active thyroid), anemia, fever, alcohol, drugs such as cocaine, cigarette smoking and electrolytes abnormalities.
There are many types of arrhythmias: the most common ones are tachycardia, bradycardia and an irregular heartbeat. Tachycardia is defined as a heartbeat of more than 100 beats per minute, and bradycardia is defined as a heartbeat of less than 60 beats per minute. Normally, the heart beats between 60 and 100 times per minute when someone is at rest. However, well-trained athletes achieved heart beats less than 60 beats per minutes when resting and this represents a normal physiological adaptation due to intense training activity like swimming, running, bicycling, etc.
Arrhythmias can begin in the left ventricle (the pumping part of the heart that supplies oxygenated blood to the body’s organ and tissues), right ventricle (the pumping part of the heart that supplies non-oxygenated blood to the lungs) or the left and right atria (the chamber in where the blood enters prior to being pumped into the ventricles.
Most arrhythmias are of the tachycardia type (tachyarrhythmia). Tachyarrhythmia that starts in the ventricle is usually more serious than one that starts in the atria. Ventricular arrhythmias are more serious because the ventricles are reduced to twitching, and almost no pumping takes place, thus the blood cannot get to other parts of the body. Atrial tachyarrhythmia can be serious because again, the atria are reduced to twitching and clots may build up in the atria. If the clot breaks loose from the atria, an embolus (small clot) can be sent to various parts of the body, and may cause an artery occlusion, resulting in a compromised blood supply to tissues and vitals organ such the brain, kidneys, gastrointestinal track as well as fingers, hands, legs or toes. This last phenomenon is defined as ischemia and if the deficiency is in the brain tissue, it is commonly recognized as an embolic stroke. For this reason, atrial fibrillation is usually treated with blood thinners (anticoagulants, among other therapies).
Bradycardias (Bradyarrhythmias) are sometimes caused by problems or defects with the nerves that control the speed your heartbeat (the sinus node, where the electrical impulse that controls the heart beat originates), or the transmission of those impulses through the heart. Atrial bradyarrhythmias occur when the sinus node is not functioning correctly. This can be due to an injury associated with, aging, coronary artery disease secondary to elevated cholesterol or other conditions that can cause problems in the conducting system of the heart.
Ventricular arrhythmias occur when the electrical conducting system (the wiring) from the sinus node to the heart does not function properly. The ventricle itself has its own intrinsic beat of about 45 beats per minute that it generates by itself if the conducting system from the atrium fails. However, if it becomes chaotic due to lack of regulation from the sinus node or conditions that can trigger a catecholamine surge, heart rates of greater than 120 beats per minute can be generated. These conditions are associated with heart muscle injury such as Myocardial Infarction (MI), thyroid diseases, high fever, anemias, and response to toxic substances such cocaine, caffeine or medications.
Irregular heartbeats occur when there is some problem with the electrical system of the heart or when the atria send out too many signals (i.e. other parts of the atrium other than the sinus node send out a signal for the ventricles to contract).
Related is Brugada syndrome, an abnormality in the heart's electrical system that causes arrhythmia. It is most common in young people and Asians, but the cause is unclear. During a Brugada episode, decreased oxygen flows to the brain, causing fainting. Chaotic heart beat and/or death can ensue - unless the heart receives an immediate electrical shock from a defibrillator.
