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More on dysrhythmias.

February 20, 2013

A couple weeks ago I wrote a post about heart rhythms and dysrhythmias.  Today I encountered a really good set of pages at the Cleveland Clinic website discussing the electrical system of the heart and all types of dysrhythmias.  This link goes to an article about Management of Dysrhythmias.  There is a group of links near the top of the page to articles about all kinds of different rhythm problems.  They also have a nice picture of the electrical system of the heart which I have borrowed because it is very clear and easy to read:Heart-Electrical-System

So what causes irregular heartbeats?  There are many reasons the heart may beat irregularly, too fast, or too slow.  Some of these reasons have to do with damage to the electrical conduction system.  Events or conditions which damage the heart muscle may also damage the conducting fibers.  These include chronic high blood pressure, ischemia (lack of blood flow) from coronary artery disease or myocardial infarction (heart attack), cardiomyopathy (changes in the heart muscle sometimes caused by a virus), problems with heart valves, or surgical scarring.  Other causes of arrhythmias include electrolyte imbalance and certain drugs.

Probably by far the most commonly ingested drug related to abnormal heartbeats is caffeine.  Caffeine is found in many of the foods and drinks we enjoy daily such as coffee, chocolate, tea, and soft drinks such as Coca Cola, Mountain Dew, Dr. Pepper, etc.  Caffeine is also added to various supplements touted for weight loss or alertness.  It is the mainstay of “energy drinks” such as Red Bull or 5 Hour Energy.  Excessive caffeine intake can lead to rapid heartbeat and palpitations (fluttery or thumping feeling in the chest).  These palpitations are usually caused by premature atrial contractions (PAC’s).  These are extra beats that originate from foci in the atria (upper chambers of the heart).  Other supplements or herbs which have stimulant properties can also be pro-arrhythmic (cause arrhythmias).  These include ephedrine (found in Ma Huang), Guarana (contains high levels of caffeine), and Kola Nut (contains caffeine).

Nicotine, found in tobacco products, is another common stimulant drug used by many people.  Tobacco is smoked, chewed, held between lip and gum, or sniffed into the nose.  Ingesting an excessive amount causes increased blood pressure and heart rate due to its vasoconstrictive and stimulant properties.

Drugs such as cocaine, crack, and amphetamines having stimulant properties cause increased blood pressure and heart rate as well.  Note that amphetamines are also the active ingredients of medications such as Adderall and Vyvanse, used to treat ADHD.  Methylphenidate (found in Ritalin and Concerta) has similar properties.

As you can see, there can be many reasons for irregular heartbeats.  I’ve mainly focussed on faster heart rates, but slow heart rates (bradycardias) can be a problem too.  Like other abnormal heart rhythms, bradyarrhythmias can be caused by damage to the heart such as scarring from myocardial infarction (MI), post surgical changes, cardiomyopathy, etc.  Drugs and supplements can also slow heart rate.  We commonly use beta blockers such as metoprolol or carvedilol for this purpose.  Calcium channel blockers such as diltiazem or verapamil slow heart rate to a lesser extent (depending on dose).  Decreased oxygen in the blood, which can be caused by sleep apnea, illness such as pneumonia, or drugs with respiratory depressant effects like opiates (morphine, heroin) may cause lower heart rate.

This is a complicated subject.  I will write more soon!

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