If you have an arrhythmia that causes your heart to beat too fast or
too slow, you may feel lightheaded or dizzy. This happens because your heart
cannot pump blood effectively during excessively fast or slow heart rates. The
ineffective pumping action decreases your blood pressure, reducing the amount
of blood that reaches your brain.
The sensation of lightheadedness is a result of this lack of blood
flow to the brain. If your blood pressure drops too low, you may feel that you
are about to pass out. This sensation is called presyncope. Syncope is the
medical term for a temporary loss of consciousness (passing out).
When is lightheadedness not caused by an arrhythmia?
Dizziness can be caused by conditions other than arrhythmia. For
this reason, your doctor will try to find out whether your
dizziness is caused by a heart condition, medicine, or other things.
Other causes of lightheadedness include hyperventilation, panic or anxiety attacks, prolonged standing, and excessive fluid loss caused by problems such as vomiting or diarrhea.
Many of the medicines used to treat heart conditions, such as
beta-blockers, calcium channel blockers, angiotensin-converting enzyme (ACE)
inhibitors, and diuretics, can lower the blood pressure excessively and result
in lightheadedness. In general, medicine-induced lightheadedness frequently
occurs soon after you stand up because of a drop in blood pressure that happens
when you stand (orthostatic hypotension). In contrast, lightheadedness due to
an arrhythmia can occur even when you are sitting or reclining.
Syncope (say "SING-kuh-pee") refers to a sudden loss of
consciousness that doesn't last long. Syncope may be the first sign that you
have an arrhythmia. And it is a very worrisome symptom for several
- Fainting can result in a serious injury (for
example, if you faint while climbing stairs or driving).
- You faint
because your brain did not get enough oxygen to function, which may be a
warning sign that you have a serious medical condition.
An arrhythmia can cause syncope in the same way that it causes
lightheadedness (presyncope). Your heart cannot pump blood effectively during
excessively fast or slow heart rates, reducing the amount of blood that reaches
your brain. With syncope, though, the arrhythmia causes such a dramatic drop
in the blood pressure that the brain doesn't receive enough blood to keep you
awake. So you lose consciousness. For an arrhythmia to
cause syncope, your heart rate must be extremely fast or extremely slow, or you
must also have some other heart condition.