We all know that the heart’s main job is to pump blood.Your heart’s upper chambers (atria) take in the blood fromyour lungs and body. They pass that blood on to yourlower chambers (ventricles) through your heart’s first setof valves. Your second set of valves then open and yourventricles push your blood out to your lungs and body.But all of this action is coordinated by another importantset of structures—your heart’s electrical system. Thissummary will describe the heart’s electrical system andcommon problems that occur. It will also describe thesymptoms and treatments of heart rhythm problems.

Your Heart’s Wiring:To begin pumping, your heart muscle has to contract in auniform way. Contraction starts when an electricalmessage goes out to your individual heart muscle cells.Your heart’s electrical system has a very intricate networkof connections that uses special tissue to carry thismessage through the heart. Although it can operateindependently, your heart responds to many factors in yourbody. These factors include arousal, stress, fear, fever,anxiety, thirst, exercise, blood chemistry, and your overallwell-being. There are a number of feedback systemsbetween your heart, your brain, and other organ systemsthat help maintain a normal heart rate and rhythm.

Your heartbeat starts in the top of your heart in the sinusnode. The sinus node sends the impulse that makes thetop of your heart contract. The impulse then travels to themiddle of the heart to the atrioventricular (AV) node. TheAV node then sends the message out to your ventricles.The ventricles contract and pump blood to the lungs andthe body. The sinus node sets the pace for your heart. It isvery responsive to factors like stress or fright. It also tellsyour heart to slow down when you are at rest. In an adultwith a normal sinus node, the heart rate will range from 50to 100 beats per minute (bpm) during periods of relativeinactivity. The heart rate can go as high as 170 to 200 bpmduring exercise. During sound sleep, it can slow to thelow-to-mid 40s.

“Slow” Heart Rhythm Problems (Bradycardia):In some congenital heart defects (CHDs) the sinus node ismissing or does not work well. The sinus node can also bedamaged during heart surgery. This is especially commonin operations that place sutures or patches in the sinusnode area. This includes the Fontan, Senning, or Mustardprocedures. Occasionally tubing for the bypass machinecan damage the sinus node or its blood supply.Regard-less of the reason, if your sinus node is notworking well your cardiologist may prescribe medicationsor pacemaker therapy to help increase your heart rate.

The second major part of the electrical system in the heartis the AV node. The AV node is located in the middle of theheart between the upper and lower chambers. Its main jobis to help manage the electrical activity as it travels fromthe atrium to the ventricles. The AV node slows down theelectrical message slightly. This delay allows time for yourheart’s valves to open and let blood travel into theventricles. This blood is then pushed into your lungs andbody when the ventricles contract. The AV node can alsoindependently fire and contract the lower chambers of theheart without an impulse from the sinus node. This allowsthe AV node to function as a “backup” pacemaker whenthere are problems with the sinus node.

Like the sinus node, the AV node can be abnormal incertain heart defects. These include correctedtransposition of the great arteries (CTGA), some singleventricle defects, and in babies born to mothers withlupus. Because the AV node is the center of the heart, it isvery vulnerable to surgical damage. Such damage canoccur when holes in the heart are closed or when artificialvalves are placed. It can also be damaged during surgeryto correct narrowing under the aortic valve.

©The Adult Congenital Heart Association. Reprinted from the winter 2008 issue of Heart Matters.

HEART MATTERS A P U B L I C AT I ON O F T H E ADU L T CONGEN I TA L H E A R T A S SOC I AT I ON

The Heart and Its Electrical System

If your AV node is not working well, you may develop acondition known as heart block. First-degree heart block iswhen it takes too long for your heartbeat to travel from thetop to the bottom of your heart. Third degree heart block iswhen the electrical impulse no longer travels through theAV node at all. Patients with advanced forms of heart blockfrequently require pacemaker therapy.

“Fast” Heart Rhythm Problems (Tachycardia):So far, we have discussed problems with your sinus andAV node that can cause your heart to go too slowly(Bradycardia). But congenital heart patients also canexperience problems with the heart rate going too fast(Tachycardia). This can happen due to in-born problemswith your heart’s anatomy. It can also be caused byproblems with your heart function such as heart failure orleaky heart valves. Sometimes surgical intervention canalso bring on this kind of problem. If these rhythmdisturbances come from the upper chambers of the heart,they are called atrial arrhythmias (abnormal rhythms of theheartbeat). Problems that begin in the lower chambers ofthe heart are known as ventricular arrhythmias. Sometimesthe heart develops new electrical pathways from top tobottom that bypass the AV node. This allows abnormalrhythms to develop called atrioventricular reentryarrhythmias.

Medications are often used to treat these rhythm problems.There are also pacemakers that have been developed toprovide therapy for abnormally fast heart rhythms. Theycan be programmed to detect abnormal heart rhythmsfrom the upper or lower chambers of the heart. They theneither pace the heart out of the fast rhythm or deliver anelectrical shock to convert the rhythm back to normal.Patients with these special pacers usually also continue onmedications to help prevent rhythm problems from starting.

Heart Rhythm Symptoms:Whatever their cause, heart rhythm problems can cause arange of symptoms. If you have a heart defect, it isimportant that you know how to tell if you might be havinga heart rhythm problem. Occasional skipped beats arecommon in everyone with or without heart defects. Theyare usually more of a nuisance than a danger. But if youhave sustained skipped beats or racing heart, you shouldcheck in immediately with your cardiologist. You shouldalso let them know right away if you feel dizzy or pass out.Heart rhythm problems can occur at any time including at

rest and during exercise. They can be fatal, so it is veryimportant that you do not ignore symptoms. In general,atrial rhythm problems are less dangerous than ventricularproblems. But all rhythm problems should be evaluated tohelp protect your heart function and health. Sometimesheart rhythm problems can start without any symptoms.Be sure to continue with recommended cardiology visits soyour heart’s rhythm is checked regularly.

If you report heart rhythm symptoms, your cardiologist willlook for possible cause. This might include any or all of thefollowing: an electrocardiogram (ECG), 24-hour Holtermonitor, 30-day event monitoring, exercise testing, or anintracardiac electrophysiology study. If there is a questionabout whether a change in your heart function is causingthe problem, imaging testing such as an echocardiogramor a cardiac MRI might also be ordered.

Special Care for Special Beats:There are many cardiologists trained to take care of heartrhythm problems. But if you have a congenital heart defect,it is important that you see someone with special trainingin congenital heart disease. Although congenital heartpatients get similar heart rhythm problems as everyoneelse, they often need different treatments. Rhythmproblems can sometimes be caused by new problems withunderlying defects and/or previous re-operations. Heartrhythm problems should always be treated in the contextof the “whole picture” of the defect and heart history.This will help ensure that your cardiologist recommendsa treatment plan that takes into account your uniquecongenital heart anatomy. You can find an online directoryof adult congenital heart programs at www.achaheart.org,or by calling the Adult Congenital Heart Association(ACHA) at (888) 921-ACHA.

Although some people have rhythm problems as a child,many heart defect patients develop new rhythm problemsas they age. Heart rhythm disorders are the most commonnew heart problem in adults living with heart defects. Thegood news is that there are now many new medications,devices, and other treatments to help control heart rhythmproblems. By working as a team with your health careproviders, and reporting any new problems promptly, youcan help protect your heart health. �

Larry A. Rhodes, MD, is a pediatric cardiologist with special trainingin the management of patients with abnormal rhythms. He nowspends a significant portion of his time taking care of adults withcongenital heart disease in a rural state. He is very interested in theongoing care of adults with congenital heart disease, especiallythose that live in areas remote from major centers that offer care forthese patients.

©The Adult Congenital Heart Association. Reprinted from the winter 2008 issue of Heart Matters.

Heart rhythm problems should always be

treated in the context of the “whole picture”

of the defect and heart history.