T Wave Test: for The Prediction of Heart Rhythm Disorders (Arrhythmia) Risk

T Wave Test: for The Prediction of Heart Rhythm Disorders (Arrhythmia) Risk

The heart is a four-chambered pump with two upper chambers and two lower chambers. The upper chambers are called the atria and the lower chambers are called the ventricles. In order for the heart to pump enough blood to meet the body's needs, these chambers need to maintain a healthy rhythm. They need to contract on time, to relax on time, and they need to do this in a coordinated way.

Each heartbeat begins in a specialized area of the right atrium called the sinus node. The sinus node starts each heartbeat by generating a small amount of electricity, which spreads into the muscle cells of the atria. This causes these upper chambers to contract.

Next, the electrical activity moves into the junction between the atria and ventricles. (The ventricles are the heart's main pumping chambers.) This area is called the atrioventricular node or A-V node. The A-V node acts as a relay station. It takes the signal coming from the atria, delays it slightly, then passes it into the ventricles, which causes them to beat. When the ventricles beat, they pump blood throughout the body. This creates a pulse, which can be felt at several places in the body.

In the normal heart these electrical impulses occur in regular intervals. When something goes wrong with the heart’s electrical system, the heart does not beat regularly. The irregular beating results in a rhythm disorder, or arrhythmia.Normally, the heart beats 60-100 times a minute. This state is called "normal sinus rhythm" or "normal rhythm." Depending upon the needs of the body, it may beat faster (sinus tachycardia) due to stress or slower (sinus bradycardia) such as during sleep.

If untreated, this abnormal heart rhythm can lead to dizziness, chest pain, a sensation of fluttering or pounding in the chest (palpitations),shortness of breath, or fainting (syncope). Atrial fibrillation also increases the risk of stroke and sudden death.

A variety of rhythm disorders can be controlled with artificial pacemakers. Slow heart rates (bradycardias) are the most common reasons to use a pacemaker. A pacemaker is a small device (1 to 2 ounces, 1.5" x 1.5" x 0.25") placed inside the body and connected to the heart with one or two thin wires. It sends small painless amounts of electricity to the heart to make it beat.

Patients who have very fast heart rhythms accompanied by serious symptoms, such as fainting, may need an implanted defibrillator (implanted cardioverter-defibrillator, ICD). This device (about 2" x 3" x 0.75") is placed just beneath the collarbone or in the abdomen. It's connected to the heart with one or two thin wires. When a fast heart rhythm develops, the device detects it and shocks the heart to correct the rhythm.

Catheter ablation, an approach that may cure patients who have the most common form of irregular heart rhythm, called atrial fibrillation or AF, and allowed them to return to an active life. The catheter ablation technique doesn't involve surgery, but rather a system of tiny wires that are fed into the heart through a major blood vessel. Patients only need a mild sedative, and go home from the hospital the next day.

If the arrhythmia is life threatening, cardioversion is done without delay or special preparation. For a planned cardioversion, follow any instructions your health care provider may give you.

An implantable cardioverter-defibrillator (ICD) — a pager-sized device implanted in your chest like a pacemaker — may reduce your risk of dying of cardiac arrest by detecting and stopping these dangerous arrhythmias. An ICD continuously monitors your heartbeat and delivers precisely calibrated electrical shocks to restore a normal heart rhythm.The surgery to implant an ICD is usually relatively minor.ICDs have become standard treatment for anyone who has survived cardiac arrest and are used increasingly in individuals who are at high risk of sudden cardiac arrest.

A new study provides more evidence that a special heart test could give cardiologists guidance on which patients need implanted defibrillators.

The research, which looks at patients who have weak heart muscles but no underlying coronary disease, suggests that the test, known as T-wave alternans, can predict which patients are at highest risk of suffering heart rhythm disorders. They can then get the implanted defibrillators, while the others could potentially avoid the procedure.

Still, more research is needed, said Dr. Andrea Russo, an electrophysiologist at the University of Pennsylvania. "We need more studies that are confirmatory before we start excluding patients from implantable defibrillators," she stressed.

A number of conditions, including viral infections and alcoholism, can weaken parts of the heart even when someone doesn't have clogged arteries. In some cases, there's no apparent cause.

People with this condition -- including some young people -- can suffer from abnormal heart rhythms and die. But doctors often try to boost their chances with implanted defibrillators designed to shock their hearts back into a proper rhythm when necessary.

Doctors have been looking for a way to predict which patients need defibrillators and which would be fine without them. Enter the T-wave test, which Russo said is similar to an EKG.

Patients typically undergo the test, which requires electrodes to be placed on the body, while exercising. According to Russo, it detects whether the heart's electrical system has the rough equivalent of a short circuit that could cause a heartbeat so fast that the heart can't handle it.

In the new study, Italian researchers examined what happened after 446 patients with heart failure -- defined here as moderate heart muscle damage -- were given the T-wave test. None of the patients had significant cardiovascular disease.

The findings were to be presented at the American College of Cardiology's annual meeting in New Orleans.

Researchers followed the patients for 18 to 24 months, and found that those with an abnormal T-wave test (65 percent of patients) were four times more likely to suffer from cardiac death or life-threatening disruptions in heart rhythm. The study authors suggest the other patients aren't ill enough to need implanted defibrillators.

"Knowing this, we are able to better treat the two-thirds of patients that really need the device," contributing author Dr. Gaetano De Ferrari, of the San Matteo Hospital in Pavia, Italy, said in a statement.

While there have been other studies supporting the T-wave test, cardiologists haven't embraced it, said Dr. Paul Chan, a fellow in cardiovascular medicine at the University of Michigan Medical School. According to him, some cardiologists are worried about the legal ramifications if the test suggests that someone doesn't need a defibrillator and then the patient dies.

Meanwhile, he said, "the ultimate question that hasn't been answered really well is whether or not those patients who screened as normal [would] have any benefit" from getting a defibrillator.

Cost could be another factor: T-wave machines cost about $25,000. However, implantable defibrillators are hardly cheap themselves: by one estimate, they can cost $90,000 over a lifetime.


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