The safety and effectiveness of long-term arrhythmia treatment depend on accurate diagnosis. Sometimes ventricular arrhythmias can be detected by listening to the heart with a stethoscope. The diagnostic tool of choice, though, is the electrocardiogram (ECG or EKG), which shows the relative timing of atrial and ventricular electrical events. ECG's generate telltale spikes, whose characteristic rhythm and shape identify the specific type of arrhythmia.
To make an ECG, a technician attaches several electrodes to the chest and sometimes the limbs. The electrodes detect electrical activity that is recorded on a moving strip of paper or projected on a computer-like screen. The procedure is harmless and painless.
Because of the fleeting nature of many arrhythmias, they may not occur while the ECG is running, and so they may go undetected on the ECG. In these cases, doctors may ask patients to wear a small portable ECG recorder, called a Holter monitor, for 24 hours. This device, about the size of a tape recorder, records continuous electrocardiographic signals or selectively records arrhythmias causing symptoms. Holter monitoring requires patients to wear electrodes continuously on their chests during the 24 hours.
ECG's of arrhythmias with symptoms that occur less frequently than daily can be transmitted via the telephone to a doctor's office or a hospital with a hand-held device called an event monitor. This monitor converts ECG signals into tones that travel over a telephone line and are then converted to paper tracings. If a telephone is not available at the time the arrhythmia occurs, the ECG signals can be recorded and stored in the device's memory for transmission later. For such transtelephonic monitoring, patients place electrodes on their chests only when they are experiencing symptoms.
Another diagnostic option for infrequent arrhythmias is to provoke them purposely through exercise or with electrical devices. For example, a patient whose arrhythmias are thought to be prompted by exercise may undergo a treadmill workout while his or her heart activity is being monitored by an ECG device.
An arrhythmia also may be induced with electrophysiologic testing. In this procedure, electrodes are attached to small tubes known as electrode catheters, which are threaded through arm or leg veins until they reach the heart. There, they are placed at strategic positions in the ventricles, atria or both.
These electrodes record electrical signals and allow doctors to "map" the spread of electrical impulses during each heartbeat. The electrodes also can electrically stimulate the heart at programmed rates to trigger latent ventricular tachycardias. These arrhythmias are then stopped by electrical stimuli transmitted via the electrode catheters. An externally applied shock may be required if the patient loses consciousness during the tachycardia.
Being able to "turn on" tachycardias during electrophysiologic testing allows doctors to test antiarrhythmic drugs quickly for effectiveness. It also can indicate the electrically blocked areas of the heart responsible for triggering a patient's arrhythmia. If these areas are limited in size and number, destruction of them is a treatment option.
Cardiologists usually reserve electrophysiologic testing for patients whose arrhythmias do not occur during ECG monitoring or are not controlled by their current medication. Electrophysiologic testing is considered safe, although rare complications, such as bleeding, infection, perforation of the heart, and fatal arrhythmias, can occur.
