Signal-Average Electrocardiogram

Overview

The normal conduction of the electrical stimulus through the pathways may be disrupted by several factors, including the following:

• altered chemical levels in the blood (levels of substances such as potassium, magnesium, or calcium are too high or too low, or a pH level is too high or too low)
  
  
• inflammation at or near the conduction pathways (may be caused by infection of the heart tissue)
  
  
• swelling at or near the conduction pathways (may be caused by tissue manipulation during heart surgery or chest trauma from an automobile accident or other source of trauma)
  
  
• the effects of medications (this may be accidental or intentional)
  
  
• the effect of too much caffeine, stress, exercise, or tobacco

When the electrical stimulus is disrupted, a condition known as “arrhythmia” (also called dysrhythmia; terms may be used interchangeably) may develop. In arrhythmia, the heart may beat too fast, too slow, with an irregular rhythm, or with extra beats. Often, arrhythmias cause few, if any, problems. However, symptoms such as lightheadedness, dizziness, fainting, prolonged fatigue, low blood pressure, a feeling of fluttering in the chest or even chest pain may occur as a result of arrhythmias. When this occurs, your physician will perform any of a number of diagnostic tests to determine the cause and treatment of the arrhythmia. Treatment options for arrhythmias may include:

• medication
  
  
• lifestyle changes (to decrease stress and eliminate caffeine, alcohol, tobacco, etc.)
  
  
• catheter ablation - an invasive procedure performed in a manner similar to a cardiac catheterization; the conduction pathways that are misfiring are eliminated with direct application of radiofrequencies through a catheter (a small tube) inserted through the groin and passed through the blood circulation into the heart.
  
  
• cardioversion - a procedure that is similar to defibrillation (shocking the heart with electrical currents to restore normal EKG activity) with paddles, but one that uses lower voltage.
  
  
• implantation of a pacemaker or pacemaker-like device called an implantable cardioverter-defibrillator (ICD) - a device that is pre-programmed to deliver low-energy electrical shocks to the heart if a certain heart rate is exceeded.

Signal-average EKG is one of several procedures used to diagnose arrhythmias. For additional information regarding other procedures used to diagnose arrhythmias, please refer to the following sections in this Online Guide:

• Holter monitor
• Electrophysiological studies
• Tilt testing
• Exercise EKG

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