Overview of abnormal heart rhythms

[Tanya Shivari]

Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart.

Heart disorders are the most common cause of an abnormal heart rhythm.
Sometimes people are aware of abnormal heart rhythms, but many times they feel only their consequences, such as weakness or fainting.
The diagnosis is based on electrocardiography.
Treatment involves restoring the heart to a normal rhythm and preventing further episodes.

The heart is a muscular organ with four chambers designed to work efficiently, reliably, and continuously over a lifetime. The muscular walls of each chamber contract in a regulated sequence, pumping blood as required by the body while expending as little energy as possible during each heartbeat.
Contraction of the muscle fibers in the heart is controlled by electricity that flows through the heart in a precise manner along distinct pathways at a controlled speed. The electrical current that begins each heartbeat originates in the heart’s pacemaker (called the sinus node or sinoatrial node), located in the top of the upper right heart chamber (right atrium). The rate at which the pacemaker discharges the electrical current determines the heart rate. This rate is influenced by nerve impulses and by levels of certain hormones in the bloodstream.
The heart rate is regulated automatically by the autonomic nervous system, which consists of the sympathetic and parasympathetic divisions. The sympathetic division increases the heart rate through a network of nerves called the sympathetic plexus. The parasympathetic division decreases the heart rate through a single nerve, the vagus nerve.
Heart rate is also influenced by hormones released into the bloodstream by the sympathetic division:

Epinephrine ( adrenaline )
Norepinephrine (noradrenaline)

Epinephrine and norepinephrine increase the heart rate. Thyroid hormone, which is released into the bloodstream by the thyroid gland, also increases the heart rate.
In an adult at rest, the normal heart rate is usually between 60 and 100 beats per minute. However, lower rates may be normal in young adults, particularly those who are physically fit. A person’s heart rate varies normally in response to exercise and such stimuli as pain and anger. Heart rhythm is considered abnormal only when the heart rate is inappropriately fast (called tachycardia), slow (called bradycardia), or irregular or when electrical impulses travel along abnormal pathways.