Keeping Pace - An Introduction to Abnormal Heart Rhythms

The heart has a built-in electrical system, which consists of a pacemaker and a set of specialized structures that distribute the electrical signal to the heart muscle. Each time the pacemaker fires, the electrical signal is sent to every cell in the heart and tells them to beat in a precise sequence. The heart’s pacemaker continuously monitors the body’s activity level, and adjusts the heart rate according to the body’s needs. While we are sleeping, the heart rate can slow to as slow as 40-50 beats a minute, and with exercise, can go as fast 180 to 200 beats a minute. Most of the time, we are hardly aware of this amazing organ pumping away in our chests, keeping us alive and monitoring us continuously. However, in some cases, the electrical system in the heart can act up. Instead of our usual, regular heartbeat, the heart can beat too slowly, too quickly or in a different sequence than usual. This is what cardiologists refer to as an arrhythmia. Fortunately, most arrhythmias are not dangerous; some, however may be dangerous or even life threatening. Electrophysiologists are cardiology specialists who deal with heart rhythm disorders. If you are diagnosed with an arrhythmia or experience palpitations, you may be referred to an electrophysiologist for evaluation and treatment. 

There are many different types of arrhythmias. Some may be completely asymptomatic, whereas others can manifest with palpitations, lightheadedness, shortness of breath, and rarely, loss of consciousness or even sudden death. SVT: Supraventricular Tachycardia 

SVT: or supraventricular tachycardia, is a medical term for a fast heart rhythm that originates in the heart’s upper chambers, or atria (hence supraventricular because the arrhythmia comes from above the ventricles). No one knows exactly why some people get SVT and others do not, but we know that there are a few types of SVT. 

AVNRT and AVRT: extra loops of electrical circuitry in the heart AVNRT, or A-V Node Reentrant Tachycardia, and AVRT, or atrioventricular reciprocating tachycardia, are two common types of SVT. Both are caused by an electrical “short circuit” when the electrical signal starts spreading to the heart, but then ends up going around and around in a loop, making the heart beat quickly. People often experience palpitations because of the rapid heart rate and the irregular sequence of contraction of the atria and ventricles. The episodes usually last from one to several minutes. The episodes can come on at any time, and patients often find that they can break the episodes on their own by holding their breath or bearing down. AVNRT and AVRT are not dangerous rhythms, but can cause very bothersome symptoms such as palpitations, lightheadedness and weakness. Fortunately, this rhythm can be easily treated with either medications or using a catheter-based procedure that is extremely effective in eliminating this rhythm. 

AT: An alternate pacemaker takes over AT, or atrial tachycardia, is caused by a different area of the atria taking over the hearts pacemaker function and beating very quickly. There is no loop of electrical activity, but a different focus in the heart starts acting up. The symptoms can be very similar to AVNRT or AVRT, and again, either medication or catheter ablation can be very effective. 

Atrial Fibrillation: A growing epidemic 

Atrial fibrillation is one of the most common arrhythmias that cardiologists treat. There are more than two million people in the United States with this condition, and that number is expected to double over the coming decades as the population ages. In atrial fibrillation, the atria have no single pacemaker. Their electrical activity is completely chaotic, beating almost 600 times a minute. As a result, the rate of the ventricles can be very rapid. People with atrial fibrillation may be symptomatic, but many people experience palpitations from the rapid rate, or shortness of breath, fatigue, or passing out. Some people experience short bursts of fibrillation (called paroxysmal atrial fibrillation), and others have it for longer periods of time (called persistent or permanent atrial fibrillation). The longer your atrial fibrillation is untreated, the greater the odds that your fibrillation will become persistent or permanent. 

Atrial fibrillation is important not only because of the symptoms it causes, but also because when the atria are fibrillating, blood flow through them can be sluggish and non-uniform. This is a risk factor for forming clots in the atrium, which can dislodge and cause a stroke. Your physician can determine how high that risk is, and whether you should go on a blood thinner. In addition, you may need to take a medication to control your heart rate, or an antiarrhytmic medication to prevent the atrial fibrillation. If you cannot take an antiarrhythmic, or the atrial fibrillation is very bothersome to you, your electrophysiologist can do a procedure called a pulmonary vein isolation (PVI) to control your atrial fibrillation. At McKay-Dee, cardiologists use both traditional catheter ablation to perform this procedure, as well as a novel technique called cryoballoon isolation, a proven technique that makes the procedure shorter. 

The more we learn about atrial fibrillation, the more we learn that it is related to other medical conditions. Diabetes, high blood pressure, thyroid problems, obesity and sleep apnea are all associated with an increased incidence of atrial fibrillation. Your cardiologist or electrophysiologist will discuss managing these important medical conditions with you. 

Ventricular Rhythms 

Unlike SVT, which originates in the upper chambers of the heart, there are abnormal rhythms that originate in the lower chambers, the ventricles. Most common are PVCs, or premature ventricular contractions. These are extra heart beats that come from the lower chambers. They are commonly felt as “skipped beats” or “extra heart beats.” PVCs for the most part are not dangerous, however, too many PVCs can actually weaken the heart. If you have very bothersome PVCs, or if you have a lot of them, you may need to be evaluated more thoroughly. As with other arrhythmias, you can be managed with either a catheter-based procedure or with medications. 

Ventricular tachycardia is a continuous series of ventricular beats. This rhythm can be dangerous, since in some patients the heart does not pump blood to the brain and other organs; in this case the patient will lose consciousness, or can even die. Fortunately, ventricular tachycardia is not a common arrhythmia. It occurs most often in patients with preexisting heart disease. If you have had ventricular tachycardia, or if you have a history of heart disease, you may be referred to an electrophysiologist. Ventricular tachycardia can be treated using catheter ablation. In some cases where the risk of recurrent ventricular tachycardia is high, your electrophysiologist may discuss implanting an Implantable Cardiac Defibrillator (ICD) device. This device is implanted under the skin near your shoulder, and it monitors your hearts rhythm. If it detects a dangerous rhythm like ventricular tachycardia, it can shock your heart into normal rhythm. 

Ventricular fibrillation is a completely chaotic rhythm with no organized electrical activity or organized contraction of the heart. Because the ventricles are the main pumping chambers of the heart, ventricular fibrillation results in immediate loss of blood flow. Patients with ventricular fibrillation will suddenly lose consciousness and require immediate CPR and an electric shock delivered through a defibrillator to survive. Ventricular fibrillation can be caused by heart attack, among other causes. When someone “drops dead” of a heart attack, it’s often because of ventricular fibrillation. This is why when you see someone collapse suddenly, it’s so important to start CPR right away and get an external defibrillator, since the only way to treat ventricular fibrillation is using an electric shock, or cardioversion, to convert the heart to a normal rhythm. 

The vast majority of all heart arrhythmias can be easily and effectively treated. With new advances and technology in the field of electrophysiology, you can now start with medications or opt for a catheter-based procedure to treat your arrhythmia in most cases. 

Hopefully, you never have a heart rhythm problem, but if you do, you can rest assured that the providers at McKay-Dee Heart Rhythm Specialists are trained in the latest techniques, technologies and procedures in electrophysiology, and we are always willing and able to help you.