Palpitations (cont.)

Arrhythmias are pattern and/or speed changes from the normal heart rhythm. Some patients are totally unaware of their arrhythmias. Others may report symptoms including palpitations, skipping or fluttering sensations, dizziness, fainting, shortness of breath, or chest pain.

In both tachycardias and bradycardias, lack of blood flow to the brain, the coronary arteries, or the rest of the body can occur. Lack of blood flow to the brain can cause dizziness or loss of consciousness (syncope). Lack of blood supply to the coronary arteries can cause chest pain or pressure (angina). Inadequate blood supply to the rest of the body can cause weakness and shortness of breath.

In some patients, arrhythmias are caused by diseases of the heart muscle, valves, or coronary arteries. In others, arrhythmias can reflect disease of the electrical system of the heart only, while the rest of the heart is healthy. Other causes of arrhythmias include medications, alcohol excess, excessive levels of thyroid hormone, low blood oxygen levels, stress, and smoking.

Atrial tachycardias

Examples of atrial tachycardias include atrial fibrillation, atrial flutter, and paroxysmal atrial tachycardia (PAT). These arrhythmias occur because of electrical disturbances in the atria and/or the AV node, leading to fast heart beats.

• Atrial fibrillation is a common atrial tachycardia. In atrial fibrillation, multiple, rapid, and chaotic electrical signals fire rapidly from different areas in the atria rather than from one single area pacemaker at the SA node. These signals, in turn, cause rapid irregular contractions of the ventricles. Causes of atrial fibrillation include heart attack, high blood pressure, heart failure, mitral valve diseases (such as mitral valve prolapse), overactive thyroid, blood clots in the lung (pulmonary embolism), alcohol excess, emphysema, and inflammation of heart lining (pericarditis). For further information, please refer to the Atrial Fibrillation article.
• Atrial flutter is a more regular (less chaotic) version of atrial fibrillation as the electrical signal initiates in the atria. Conditions that cause atrial fibrillation can also cause atrial flutter. Treatment of atrial flutter and atrial fibrillation are also similar (see below).
• Paroxysmal atrial tachycardia (PAT) represents bouts of rapid, regular heart beating originating in the atrium. Patients with PAT are believed to have abnormalities in the AV node "relay station" that lead to rapid firing of the electrical impulses from the atrium which bypass the AV node under certain conditions. These conditions include alcohol excess, stress, caffeine, overactive thyroid or excessive thyroid hormone intake, and certain drugs. PAT is an example of an arrhythmia where the abnormality is in the electrical system of the heart, while the heart muscle and valves may be normal.

Ventricular Arrhythmias

Ventricular arrhythmias are rapid arrhythmias that originate in the lower chambers of the heart (the ventricles). Ventricular arrhythmias include ventricular tachycardia and ventricular fibrillation. Ventricular tachycardia is a rapid, regular arrhythmia which originates from an area of the ventricle. Ventricular fibrillation is an irregular arrhythmia that is a result of multiple rapid and chaotic electrical signals firing from many different areas in the ventricles.

Ventricular tachycardias and fibrillation are life-threatening arrhythmias most commonly associated with heart attacks or scarring of the heart muscle from previous heart attack. For further information, please read the Heart Attack article. Less common causes of ventricular arrhythmias include severe heart muscle failure (cardiomyopathy), medication toxicity [such as digoxin (Lanoxin) toxicity], medication side effects, and blood electrolyte disturbances (such as low potassium level). Ironically, some medications used in treating heart arrhythmias can cause ventricular tachycardias (see the treatment section below).

Bradycardias

Diseases of the SA node, the AV node, and the conduction system in the ventricles can lead to slow arrhythmias (bradycardias). Calcium channel blockers, such as verapamil (Calan), beta-blockers, such as propanolol (Inderal), and digoxin (Lanoxin) can cause bradycardias. These medications can also seriously aggravate bradycardias in patients with existing diseases of the SA node, AV node, and other parts of the conduction system. Some patients have no symptoms with a low heart rate. However, severe bradycardias can lead to low blood pressure (shock) and passing out (syncope).

Premature Contractions

Early heartbeats that don't originate from the SA node pacemaker are called premature contractions. Premature atrial contractions (PACs) and premature ventricular contractions (PVCs) can be caused by stress, fear, caffeine, cigarette smoking (and other tobacco or nicotine products), and excessive alcohol intake. Generally, PACs and PVCs, when they are infrequent and isolated, are not associated with significant heart disease and are not dangerous.

Source: MedicineNet.com
http://www.medicinenet.com/palpitations/article.htm