Palpitations
Medical Author: John P. Cunha, DO
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
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Hyperthyroidism and Heart Palpitations
Medical Author: Ruchi
Mathur, MD
Medical Editor:
William C. Shiel, Jr, MD, FACP, FACR
 I see a number of patients with
hyperthyroidism. Very frequently, their
symptoms involve the heart. The most
common symptoms are a feeling of palpitations and
a sensation of a racing heart beat. These symptoms are due to a physiologic
effect of thyroid hormone on the heart. I thought I'd take a moment to explain
more about what impact thyroid
hormone can have on the heart and why these symptoms result.
Many of the signs and symptoms
patients experience when they are diagnosed with hyperthyroidism result from the
direct effect of thyroid hormones on the heart.
While heart effects are also
seen in hypothyroidism, they are usually much more
obvious in hyperthyroidism.
Excess
thyroid hormone causes palpitations and some degree of exercise intolerance that
is due to an increased heart rate and fatigue.
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What are palpitations?
Palpitations are unpleasant sensations of irregular and/or forceful beating of the heart. Some persons with palpitations have no heart disease or abnormal heart rhythms and the reasons for their palpitations are unknown. In others, palpitations result from
abnormal heart rhythms (arrhythmias).
- Arrhythmias refer to heartbeats that are too slow, too rapid, irregular, or too early.
- Rapid arrhythmias (greater than 100 beats per minute) are called tachycardias.
- Slow arrhythmias (slower than 60 beats per minute) are called bradycardias.
- Irregular heart rhythms are called fibrillations (as in
atrial fibrillation).
- When a single heartbeat occurs earlier than normal, it is called a premature contraction, and this can cause the sensation of a forceful heartbeat.
- Abnormalities in the atria, the ventricles, and the electrical conducting system [the Sino-atrial (SA) node, and the Atrio-ventricular (AV) node] of the heart can lead to arrhythmias that cause palpitations.
The atria (right atrium and left atrium) are the upper chambers of the heart.
- The right atrium receives venous blood from the body and pumps it into the right ventricle.
- The left atrium receives oxygenated blood from the lung and pumps it to the left ventricle.
- The ventricles are lower chambers of the heart.
- Each heart has two ventricles (right and left ventricles).
- The right ventricle pumps venous blood to the lung and the left ventricle pumps oxygenated blood to the rest of the body.
The SA node is the pacemaker of the heart and is located in the right
atrium. The electrical signals initiated in the SA node are transmitted to
the atria and the ventricles to stimulate heart muscle contractions
(heartbeats). The AV node is specialized heart tissue which acts as an
electrical relay station between the atria and the ventricles. Electrical
signals from the SA node and the atria must pass through the AV node to
reach the ventricles.
When rapid arrhythmias (tachycardias) and premature contractions occur
because of abnormal electrical activity of the atria, they are called
atrial tachycardias and premature atrial contractions (PACs). When
tachycardias and premature contractions occur because of abnormal
electrical activity of the ventricles, they are called ventricular
tachycardias and premature ventricular contractions (PVCs).
Slow arrhythmias (bradycardias) can occur because of slowing of the
electrical signals initiated by the SA node, a condition called sinus
bradycardia. Bradycardias can also result from varying degrees of "heart
block," wherein certain medications or diseases in the electrical
conduction system of the heart impede the transmission of signals from
the atria to the ventricles (see the "Bradycardias" section
below).
Premature contractions are isolated heartbeats that occur earlier than
expected. The premature contraction is followed by a pause, as the heart
electrical system "resets" itself. The contraction following the
pause is usually more forceful than normal contractions. The patients
frequently perceive these more forceful contractions as palpitations.
For more, please read the
Abnormal Heart Rhythms article.
Next: What is the normal heartbeat? »
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