It’s electric

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There are countless diseases that affect the heart.  Sometimes it is easiest to look at heart problems in terms of two simplistic categories: plumbing and electrical.  Plumbing problems include heart attacks, high blood pressure, valve disorders, and congestive heart failure.  Electrical diseases include rhythm disturbances such as atrial fibrillation, fast and slow heart rates, and heart blocks.   

The heart’s electrical system is self-initiating and self-perpetuating.  It beats on average about 80 times a minute.  That amounts to around 115,000 beats each day, 40 million beats a year, and nearly 3 billion beats for an average lifetime.  

The heart’s pacemaker cells are located in the muscle of the right atrium, an area called the sino-atrial (SA, sinus) node.  These specialized cells are responsible for generating the heart’s initial electrical impulse.  Tiny sodium, potassium, and calcium ions are continually moving back and forth across the cell membranes to create an electrical charge and to move the impulse along the heart’s nerve cells.  

Each impulse travels within the heart muscle through a specific pathway to the ventricles of the heart.  When stimulated, the ventricles contract, allowing the heart to pump blood to the rest of the body.  The heart’s electrical activity can be monitored using an EKG machine (electrocardiogram).  If the electricity is flowing normally through the circuit, the heart rhythm is called normal “sinus” rhythm.  

There are many different diseases involving abnormal electric flow through the heart.  These are called arrhythmias or dysrhythmias.  The electrical flow can be blocked to varying degrees or short-circuited.  This in turn causes the heart muscle to pump irregularly.  

One such condition is atrial fibrillation.  In this disease, the atrial chamber of the heart is essentially twitching or fibrillating (sometimes 150-200 beats/min).  This unorganized signal is haphazardly sent through the electrical pathway to the ventricles causing a heart beat that is unusually rapid (tachycardia) and irregular.  

Some individuals are born with short-circuits in their hearts.  These accessory pathways allow the electrical impulse to move too quickly from the SA node through the circuit to the ventricles.  This can also cause a very rapid heart rate.

When the heart is beating too fast, it doesn’t have time to properly relax and fill with blood in between beats.  This compromises the heart’s ability to pump blood both to itself and to rest of the body.  Individuals feel weak and tired, short of breath, and may experience chest pain.  They may feel palpitations, like their heart is flip-flopping in their chest.      

Many arrhythmias such as atrial fibrillation can be the result of previous damage to the heart muscle, for example after a heart attack.  When the muscle is deprived of oxygen it dies and scar tissue replaces it.  Scar tissue is not specialized like the nerve cells or the heart muscle cells; therefore, it cannot conduct the impulses effectively.  When the electrical pathway is damaged, a rhythm disturbance can result.

Some people with untreated high blood pressure can develop an enlarged heart and enlarged atria.  This can lead to atrial fibrillation.  High or low levels of thyroid hormones can cause it as well.  Lung disease, heavy alcohol consumption, and some medications are some other causes.      

The content in this column is for informational purposes only.  Consult your physician for appropriate individual treatment.  Dr. Reynolds practices Family Medicine in Chesterfield.

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