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Cardiac arrhythmias

Definition of arrhythmia

An arrhythmia is any abnormal way for the heart to be excited i.e. not from the sinus node at a rate appropriate for the needs of the body. In general, there are two classes of arrhythmias: bradycardias and tachycardias. Bradycardias that produce symptoms are not reversible usually require a permanent pacemaker. These will not be considered further. Tachycardias, however, may be treated without a permanent pacemaker.

Etiology of arrhythmias

Arrhythmias may be caused in several ways. First of all would be failure of the normal heart electrical system (i.e. failure of the sinus node, the AV node, the bundle of His and the bundle branches) to function normally. The second major cause would be irritable spots usurping control of normal heart rhythm producing a tachycardia. The third cause would be a short circuit allowing continuous excitation of the heart producing a tachycardia. Some arrhythmias are likely to recur over time, since they are the result of fixed electrical abnormalities in the person’s heart. Other arrhythmias may not recur since they are caused by reversible extra-cardia influences such as medications, hormone abnormalities, electrolyte abnormalities etc. Once these abnormalities are corrected, the heart rhythm returns to normal. Some arrhythmias are genetic and can be transmitted from parent to children. Others, although present from birth, are a sort of heart electrical birth defect and are not heritable. Still others are not present from birth but develop as the person ages.

Prognosis of arrhythmias

Arrhythmias may involve the top (supraventricular arrhythmias) or the bottom of the heart (ventricular arrhythmias). In general, supraventricular arrhythmias are not serious or life threatening. In contrast, ventricular arrhythmias may be life threatening. Secondly, arrhythmias occurring in structurally normal hearts are seldom life-threatening. In contrast, arrhythmias occurring in patients who structural heart disease particularly involving the ventricles may be life threatening. Lastly, patients who have had one or more family members die suddenly or at home “from a heart attack” (these are seldom actual myocardial infarctions but fatal ventricular arrhythmias) may have life-threatening arrhythmias.

Non-threatening arrhythmias may, however, have serious long-term consequences. For example, atrial arrhythmias that are present for at least 90% of the day resulting in an average daily heart rate of at least 130 may lead to left ventricular cardiomyopathy and congestive heart failure. Atrial fibrillation, in certain patients, may lead to a stroke if not treated with coumadin/warfarin.

Presentation of arrhythmias

Some patients truly are asymptomatic – the arrhythmia is usually discovered during a routine physical examination. However, most patients are symptomatic in some way when an arrhythmia occurs. Patients having paroxysms of arrhythmia may have symptoms of palpitations or out-right heart racing. Other symptoms may include chest pain, pulsations in the neck, dyspnea, light-headedness, fatigue, sweating etc. After a spell of arrhythmia, the patient may have frequent urination (due to release of atrial naturetic factor, a polypeptide released from the atria that stimulates diuresis) or feel fatigued for hours to days. Other arrhythmias may cause syncope with the attendant risk of injury. More serious arrhythmias may result in a cardiac arrest or death. In the United States alone, about 400,000 sudden cardiac deaths occur annually, which approaches the total number of deaths from all forms of cancer.