Arrhythmia

Your  heart pumps nearly 5 quarts of blood through your body every minute. Even while  you are sitting still, your heart beats (expands and contracts) 60 to 80 times each minute. These heartbeats are triggered by electrical impulses that begin in your heart's natural pacemaker, called the sinoatrial node (SA node). The SA node  is a group of cells located at the top of  your heart's upper right chamber (the right atrium). 

Any irregularity in your heart's natural rhythm is called an arrhythmia. Almost everyone's  heart skips or flutters at one time or another, and these mild, one-time palpitations are harmless. But there are about 4 million Americans who have recurrent arrhythmias, and these people should be under the care of a doctor. 

Categories of Arrhythmia 

Arrhythmias can be divided into two categories: ventricular and supraventricular. Ventricular arrhythmias happen in the heart's two lower chambers, called the ventricles. Supraventricular arrhythmias happen in the structures above the ventricles, mainly the atria, which are the heart's two upper chambers. 

Arrhythmias are further defined by the speed of the heartbeats. A very slow heart rate, called bradycardia,  means the  heart rate is less than 60  beats per minute. Tachycardia is a very fast heart rate, meaning the heart beats faster than 100  beats per minute. Fibrillation, the most serious form of arrhythmia,  is fast, uncoordinated beats, which are contractions of individual heart-muscle fibers. 

What is heart block? 

Heart block happens when the SA node's electrical signal cannot travel to the heart's lower chambers (the ventricles). 

What causes an arrhythmia? 

Many factors can cause your heart to beat irregularly.  Some people are born with arrhythmias, meaning the condition is congenital. Some medical conditions, including many types of heart disease and high blood pressure,  may be factors. Also, stress, caffeine, smoking, alcohol, and some over-the-counter cough and cold medicines can affect the pattern of your heartbeat. 

What are the symptoms? 

Whether you have symptoms and what those symptoms feel like depend on the health of your heart and the type of arrhythmia you have. Symptoms  also depend on how severe the arrhythmia is, how often it happens, and how long it lasts. Some arrhythmias do not produce any warning signs. Contrary to popular belief, heart palpitations do not always mean that you have an arrhythmia. 

Symptoms of bradycardia 

• You may feel tired, short of breath, dizzy,  or faint. 

Symptoms of tachycardia 

• You may feel a strong pulse in your neck, or a fluttering, racing heartbeat in your chest. 
• You may feel chest discomfort, weak, short  of breath, faint, sweaty, or dizzy. 

How is an arrhythmia diagnosed? 

The following techniques are used to diagnose arrhythmias. 

• A standard electrocardiogram (ECG or EKG) is the best test for diagnosing arrhythmia. This test helps doctors analyze the electrical currents of your heart and determine the type of arrhythmia you have. 
• Holter monitoring gets a non-stop reading of your heart rate and rhythm over a 24-hour period (or longer). You wear a recording device (the Holter monitor), which is connected to small metal disks called electrodes that are placed on your chest. With certain types of monitors, you  can push a "record" button  to capture your heart's rhythm when you feel symptoms. Doctors can then look at a printout of the recording to  find out what causes your arrhythmia. 
• Event monitoring records problems that may not be found within a 24-hour period. The devices used for this type of test are smaller than a Holter monitor. One such device is the size of a beeper, and another is worn like a wristwatch. As with Holter monitoring,  you wear the recording device. When you feel the symptoms of  an arrhythmia, you can telephone a monitoring station, where a record can be made. If you cannot get  to a telephone during your symptoms, you can turn on the device's memory function. Later, you can send the recorded information to  a monitoring station by using  a telephone. These devices also work during episodes of fainting. 
• Electrophysiology studies (EPS) are usually done in a cardiac catheterization laboratory. A long, thin tube called a catheter is inserted into an artery in  your leg and guided to your heart. A map of electrical impulses from your  heart is sent through  the catheter. This map helps doctors find out what kind of arrhythmia you have and where it starts. During the study, doctors can give you controlled  electrical impulses to show how  your heart reacts. Medicines may also be tested at this time to see which will stop the  arrhythmia. Once the electrical pathways causing the arrhythmia are found, radio waves  can be sent through the catheter to destroy them. (See radiofrequency ablation in treatment section below.) 
• A tilt-table exam is a way to evaluate your heart's rhythm in cases of fainting. The test is noninvasive, which means that doctors will not use needles or catheters.  Your heart rate and blood pressure are monitored as you lie flat on a table. The table  is then tilted  to 65 degrees. The angle puts stress  on the area of the nervous system that maintains  your heart rate  and blood pressure. Doctors can see how your heart responds under carefully controlled times of stress. 

How is arrhythmia treated? 

Anti-arrhythmic medicines, including digitalis, beta-blockers,  and calcium channel blockers, are often  the first approach taken for treating arrhythmia. Other treatments include percutaneous (catheter) interventions, implantable devices, and surgery (for severe cases). 

• Ventricular tachycardia and ventricular fibrillation can be treated by an implantable cardioverter defibrillator (ICD).  This is  a device that applies electric impulses or, if needed, a shock to restore a normal heartbeat. The device's power source is implanted  in a pouch beneath the skin of  your chest or the area above  your stomach and connected  to patches placed on your heart. Newer implantable devices are inserted through blood vessels, which means that you do not need open-chest surgery. 
• An electronic pacemaker is used in some cases of slow heart rate. Smaller than a matchbox,  the pacemaker is surgically implanted near  the bone below your neck (the collarbone). The pacemaker's batteries supply  the electrical energy that acts like  your heart's natural pacemaker. 
• Radiofrequency ablation is a procedure that uses a catheter  and a device for mapping the electrical pathways of  the heart. After you are given medicine  to relax you, a catheter is inserted into a vein  and guided to  your heart, where doctors use high-frequency radio waves to destroy (ablate) the pathways causing the arrhythmia. 

In some cases, these treatments may not work or they may not be right for you, and surgery may be needed to destroy the source  of the irregular heartbeat. 

• Surgical ablation is like radiofrequency ablation. Using computerized mapping techniques, surgeons can find out which cells are "misfiring." A technique called cryoablation can then be used  to eliminate tissue with  a cold probe and destroy the "misfiring" cells. 
• Maze surgery may be recommended if you  have atrial fibrillation that has not responded to medicines or electrical shock (cardioversion therapy) or to pulmonary vein ablation (a procedure similar to radiofrequency ablation). Surgeons create  a number of incisions in the atrium to block the erratic electrical impulses that cause atrial fibrillation. 
• Ventricular resection  involves  a surgeon removing the area in the heart's muscle where the arrhythmia starts. 

In other cases, no treatment is needed. Most people with an arrhythmia lead normal, active lifestyles. Often, certain lifestyle changes, such as avoiding caffeine (found in coffee, tea, soft drinks, chocolate, and some over-the-counter pain medicines) or avoiding alcohol,  are enough to stop the arrhythmia.