Cardiac arrhythmias (irregular heartbeats) can vary from the totally harmless to the rapidly fatal. The rate at which the heart beats is controlled by a collection of nerve fibers near the top of the heart called the pacemaker. This fires off at regular intervals to produce an electrical charge that causes the upper chambers of the heart (the atria) to contract, and a fraction of a second later, the lower chambers (the ventricles) of the heart are stimulated to contract. Normally the pacemaker sends out its signals 70 times a minute, but at times of exercise or stress this can increase to three or more times this normal rate. In many individuals, particularly in fit athletes, the normal rate is lower, while in others, such as small women, the natural rate may be higher. If the pacemaker does not act at all, the heart muscles will contract anyway, as they have an in-built ability to contract rhythmically. This rate is very slow though… about 40 beats per minute. Many diseases can alter the heart rhythm. Anemia and an overactive thyroid can cause an increase in rate, while an underactive thyroid may cause a decrease.
Occasional dropped beats are very common in older people and are no cause for concern. If the dropped beats are more frequent (say one in every five), then it is necessary for tests such as an electrocardiogram (ECG) to be done to determine the cause. Even in this situation, there may be no serious problem. The occasional extra heartbeat fits into this category also. Stress, alcohol, smoking and exercise are common causes of dropped or extra beats. More serious diseases may also be responsible, such as high blood pressure, rheumatic heart disease and as an after effect of a heart attack.
A totally irregular heartbeat may occur if the upper heart chambers (the atria) are fibrillating (vibrating rapidly) rather than contracting correctly. Atrial fibrillation will cause the patient to be tired and breathless, but often minimal symptoms are present. The condition can be corrected in most cases by using drugs such as digoxin or verapamil. It should not be allowed to persist for long periods unless control is difficult or impossible.
There are many combinations and permutations of heartbeat irregularities, the fine details of which need to be assessed on an individual basis by a doctor.