Palpitations (cont.)

How are palpitations evaluated?

The first step in the evaluation of patients with palpitations is to determine whether their symptoms are actually due to arrhythmias. Because the treatment of varying types of arrhythmias can differ, it is also important to determine the type of arrhythmias involved. Since arrhythmias can be related to underlying disease of the heart valves, heart muscle, and coronary arteries; tests are often performed to exclude heart abnormalities. Blood tests are also obtained to measure blood sodium, potassium, calcium, magnesium, thyroid hormone levels, and medication levels (such as digoxin levels).

Tests for arrhythmias include resting electrocardiogram (EKG), 24-hour rhythm monitoring (Holter), and a treadmill exercise test.

A resting EKG is a short recording of the heart's electrical activity, usually performed in the doctor's office. An EKG is useful only if the arrhythmia causing the palpitations is occurring when the EKG is being recorded. Often, the resting EKG cannot catch the arrhythmias, and a 24 hour Holter monitor is required. The 24 hour Holter is a cassette tape worn by the patient continuously while carrying out his/her usual activities. The patient simultaneously keeps a diary of palpitations or other symptoms during the recording period. Symptoms of palpitations can later be correlated with the presence or absence of arrhythmias on the Holter tape. If suspected arrhythmias causing palpitations still cannot be captured by the 24 hour Holter, a small patient-activated event monitor is worn by the patient for 1 to 2 weeks. When the patient experiences palpitation, he/she presses a button to record the heart rhythm prior to, during, and after the episode. The recordings can be analyzed by a doctor at a later date.

In some patients, exercise treadmill is used to detect arrhythmias that occur only with exertion. Exercise treadmill is a continuous EKG recording of the heart as the patient performs increasing levels of exercise. In addition to detecting arrhythmias, exercise treadmill is a useful screening test for the presence of narrowed coronary arteries that can limit supply of oxygenated blood to the heart muscle during exercise.

Echocardiography uses ultrasound waves to obtain images of the heart chambers, valves and surrounding structures. Echocardiography is useful in detecting diseases of the heart valves, such as mitral valve prolapse, mitral stenosis, and aortic stenosis (examples of valve diseases that can cause arrhythmias and palpitations). Echocardiography is also useful in evaluating the size of heart chambers, as well as the health and contractions of the muscle of the ventricles. Combining echocardiography with exercise stress testing (stress echocardiography) is an accurate screening test for significant coronary artery disease. The portion of the ventricles supplied by the narrowed arteries does not contract as well as the rest of the ventricles during exercise.

Occasionally, cardiac catheterization with angiography is performed to detect disease in the coronary arteries or in the heart valves which is triggering an arrhythmia. Coronary arteries supply oxygenated blood from the aorta to the heart muscle. During this procedure, a small hollow plastic tube is advanced under x-ray guidance from an artery in the groin to the openings of the two main coronary arteries located above the aortic valve. A contrast agent, made of iodine, is then injected into the arteries while x-ray pictures are recorded. It is an accurate test in detecting, mapping, and assessing the extent and severity of coronary artery disease. For further information, please read the Angina, and Angioplasty articles.

Blood tests are performed to measure the levels of thyroid hormone, potassium, magnesium, and medications, such as digoxin. Excess thyroid hormone can lead to rapid arrhythmias, such as atrial fibrillation. Low blood levels of potassium and magnesium can lead to other arrhythmias. Digoxin (Lanoxin) toxicity can cause serious arrhythmias, such as bradycardia, and ventricular tachycardias. Digoxin toxicity can be enhanced by low blood levels of potassium and magnesium.

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