Arrhythmia means an irregular heartbeat that sometimes causes sudden collapse.  There are several types of arrhythmias each with their own causes and risk factors. 

The general causes of arrhythmia mentioned on the program include:

• Coronary artery disease: a history of heart attack, high blood pressure, narrowed heart arteries and other problems can cause arrhythmia
• Drugs: some prescription medicines; over-the-counter diet pills and cold remedies; "street" drugs (illegal or misused) such as cocaine and amphetamine; and the herbal supplement ephedra (ma-huang), can lead to arrhythmia
• Thyroid problems: when your thyroid gland releases too many hormones, your metabolism speeds up, which can cause a fast (tachycardia) or irregular heartbeat (atrial fibrillation); when your thyroid releases too few hormones, your metabolism slows down, which can cause a slower heart rate (bradycardia.)
• Imbalances of body chemicals, especially potassium deficiency, calcium and/or magnesium deficiency, or imbalances in other chemicals such as sodium, adrenalin, oxygen, and bicarbonate.
• Dehydration increases the susceptibility to arrhythmia, as can caffeine.

Other risk factors include:

• Smoking and drinking: caffeine, alcohol and nicotine can lead to a variety of health problems, including damage to the heart and arrhythmia
• Genetics: some people are born with an irregular heartbeat or susceptibility to arrhythmia under certain circumstances or exposures.
• Age: the conduction of electrical impulses through the heart can slow with aging, leading to symptomatic rhythm disturbances.  Individuals over the age of 70 have a 25% chance of having an arrhythmia.
• Diabetes: diabetes increases the risk of developing coronary artery disease and hypertension, both of which can lead to an arrhythmia, and the less controlled the diabetes the faster the cardiovascular problems tend to progress

Arrhythmias can be diagnosed through a variety of tests, including:

• Electrocardiogram (EKG or ECG): an EKG machine (attached to the chest with wires) measures and records the heart's electrical impulses and any arrhythmias
• Portable EKG (also known as ambulatory EKG): if an EKG does not give conclusive results, your doctor may give you a portable EKG machine (called a Holter monitor) to wear for a day or more; it records your heart rate and any arrhythmias
• Stress EKG (stress test): an EKG is attached and heart rate readings are taken while you exercise, usually by jogging on a treadmill or riding a stationary bike
• Electrophysiologic study (EPS): in this more invasive test, the doctor inserts a small tube through a blood vessel, running it to the heart, to more closely discover the source of the arrhythmia
   
  You can find detailed information about these and other diagnostic techniques on the American Heart Association's web site.