This lab is the initial contact point for noninvasive diagnostic testing of the heart. The heart beats 60 – 80 times per minute, on average, and continues without stopping for a person’s lifetime. The heart consists of electrical cells and mechanical cells. The electrical cells are responsible for impulse formation and conduction whereas the mechanical cells are responsible for muscular contraction. The electrical activity of the heart is transmitted to the surface of the body where it can be picked up by electrodes and recorded on an electrocardiograph (EKG).
During an EKG, a trained technician will place an electrode (small sticky pads) on each of the patient’s arms and legs. An additional six electrodes will be placed in specific locations on the chest. These electrodes are connected by cable to a recording device that will record the heart’s electrical activity. The EKG takes less than five minutes from beginning to end. The electrical wave forms generated are then reviewed by a cardiologist and the results, in conjunction with the patient’s history, signs and symptoms will guide the physician in planning the patient’s further testing.
Holter monitoring (also called ambulatory electrocardiography) provides a continuous recording of heart rhythm during normal activity for a specific period of time – usually 24 hours – to detect any abnormalities in the beating pattern. It can also be used to monitor the effects of a cardiac medication, to monitor heart function following a heart attack or to help diagnose an abnormal heart rhythm.
Electrodes are placed on the patient’s chest and attached by wires to a small battery-operated recording monitor that the patient carries in a pocket or small pouch. The monitor records the heart’s electrical activity similar to an EKG while the patient keeps a diary of his/her activity. The recording is analyzed and irregular heart activity is correlated with the activity noted in the diary for that period. Consequently, it is important that the diary record be accurate and thorough.
The T-wave alternans test measures extremely subtle beat-to-beat changes in a person’s heartbeat. A routine electrocardiogram (EKG) cannot detect these tiny variations – measured at one millionth of a volt – and thus this test requires specialized sensors to detect the changes and computers to evaluate the results. T-wave alternans is a test that necessitates gradual elevation of the heart rate to above 100 beats per minute. The test can be performed in conjunction with an exercise tolerance stress test.
Extensive clinical research has shown that patients with symptoms of, or who are at risk of, life threatening arrhythmias that test positive for T-wave alternans are at significant risk for subsequent cardiac events including sudden death, while those who test negative are at minimal risk. This test can be an important predictor in determining which patients should have an implanted defibrillator (ICD).