July 26, 2016
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Heart Rhythm Disorders (cont.)

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Every person experiences the occasional palpitation in which the atrium or the ventricle beats early. These premature atrial contractions (PACs) or premature ventricular contractions (PVCs) are normal variants and most people are unaware of their occurrence. However, some patients report a palpitation in the chest and neck, often described as a "thump" or "thud." PACs and PVCs in otherwise healthy individuals do not pose any health risks.

Sinus tachycardia

The heart, its cells, and its electricity may come under many outside influences that may cause it to beat more quickly. Sinus tachycardia (sinus = from the SA node + tachy = rapid + cardia = heart), or a rapid regular heartbeat, is a common rhythm issue. It occurs when the body signals the heart to pump more blood, or when the electrical system is stimulated by chemicals.

The body needs increased cardiac output in times of physiologic stress. Cardiac output is the amount of blood the heart pumps in the course of 1 minute. It can be calculated by the amount of blood that the heart pumps with each beat (stroke volume) multiplied by the heart rate.

Cardiac output = (stroke volume) x (heart rate)

The stroke volume tends to be relatively constant. When the body requires extra oxygen delivery, the heart rate needs to increase to meet that demand. Examples include:

  • exercise, in which the muscles have greater oxygen requirements and the heart rate speeds up to pump more blood to meet that need;
  • dehydration, in which there is less fluid in the body and the heart rate has to speed up to compensate; or
  • in cases of acute bleeding that may occur after trauma.

The electrical system can be stimulated in a variety of ways to make the heart beat faster. In times of stress, the body generates cortisol and adrenaline, causing an increased heart rate in addition to other changes in the body. Think of being frightened and feeling your heart race. Increased thyroid hormone levels in the body can also cause a tachycardia. Ingestion of a variety of drugs can also cause the heart to race, including caffeine, alcohol, and over-the-counter cold medications that include chemicals such as phenylephrine and pseudoephedrine. These compounds are metabolized by the body and act like an adrenaline stimulus to the heart. Illegal drugs such as methamphetamine and cocaine can also cause a sinus tachycardia.

Medically Reviewed by a Doctor on 2/18/2016

Source: MedicineNet.com

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