Normal Rhythm & Arrhythmias
Your Heart's Normal Rhythm
The heart is a remarkable muscle that beats by way of an electrical conduction
system. Disease and abnormality in the electrical pathways may cause normal
rhythm (called sinus rhythm) to be disrupted, prompting the heart to beat too
slowly (bradyarrhythmia
or bradycardia), too quickly (tachyarrhythmia,
tachycardia, or fibrillation) or erratically. Physicians use several methods to
diagnose cardiac arrhythmias, and they use several therapy options for rhythm
management, including cardiac
ablation, pacemaker
implantation or ICD
Implantation.
An arrhythmia occurs when the sinoatrial, or SA, node (the heart's natural
pacemaker) becomes diseased (sick
sinus syndrome), or when the atrioventricular, or AV, node that sits at
the base of the heart's upper chambers fails to pass an impulse along the
heart's electrical pathway, or when there is blockage anywhere in the heart's
conduction system.
An arrhythmia affects the heart's pumping ability by either speeding up or
slowing down the electrical impulses responsible for each heartbeat. If the
heart beats too slowly (bradyarrhythmia),
it will not pump enough blood to meet the body's demands. If the heart beats
too quickly (tachyarrhythmia),
it will not have enough time between contractions to fill completely and will
fail to pump enough blood to the body. Sometimes a tachycardia will progress
into fibrillation, which is a quivering of either the heart's atria (atrial
fibrillation) or ventricles (ventricular
fibrillation) and an inability to pump at all.
Fibrillation, which can also occur spontaneously, causes a serious disruption in
the rhythm and function of the heart.
Atrial fibrillation is the number one contributor to stroke, and
ventricular fibrillation, which if not treated immediately, results in
sudden cardiac arrest.
Arrhythmias are further classified according to where they originate: atrial or
supraventricular (above the ventricles) arrhythmias and ventricular (in the
ventricles) arrhythmias.
Arrhythmias that progress to fibrillation can be serious, or even fatal if not
interrupted, as in the case of ventricular fibrillation; however, others are
not serious and do not necessarily indicate heart disease. Things such as
caffeine, medications, or stress cause some arrhythmias. They are most common
among middle-aged adults. People are more likely to experience arrhythmias as
they age.
Arrhythmia
There are several types of arrhythmias. Select a link below to jump down the
page:
Bradycardia
Bradycardia means that the heart is beating too slowly (less than 60 beats per
minute). The two most common causes of bradycardia are diseases of the
sinoatrial (SA) node, which is the heart's natural pacemaker, or other problems
with the heart's electrical conduction system. These diseases can cause the
heart to beat too slowly occasionally or all the time. In either case, the
heart may not pump enough blood to meet the body's needs. As a result, patients
may feel tired, weak, sluggish, dizzy or light-headed, or short of breath. Some
bradycardias produce no symptoms (are asymptomatic); others warrant treatment,
usually with a pacemaker. To learn more, go to
pacemaker implantation.
Premature Contractions
Premature atrial contractions (PACs or PABs for premature atrial beats) are
atrial beats that occur too early due to an abnormal electrical signal. Often,
things such as caffeine, alcohol, medications (especially decongestants),
certain medical conditions such as hyperthyroidism, anemia, and hypertension,
and stress can trigger PACs. Some people may feel a fluttering in their hearts
when experiencing PACs, whereas others have no symptoms. PACs are benign and
may require no treatment.
Premature ventricular contractions (PVCs or PVBs for premature ventricular
beats) are early ventricular contractions that occur when the ventricles (lower
chambers of the heart) contract out of sequence with normal heart rhythm.
Though they are generally benign and usually do not require treatment, PVCs may
result in more serious arrhythmias in those with heart disease or a history of
ventricular tachycardia. For these people, antiarrhythmic drugs and an
implantable cardioverter defibrillator (ICD) may be prescribed. To learn more,
go to ICD implantation.
PVCs most often occur spontaneously; however, like PACs, they can also be
triggered by caffeine, alcohol, medications (especially decongestants), certain
medical conditions such as hyperthyroidism, anemia, and hypertension, and
stress.
Tachycardia
The average heart beats between 60 and 100 times per minute. Tachycardia is a
fast heart rate, or rhythm, caused by disease or injury, or it is part of a
normal response to increased activity or oxygen demands. A heart rate in excess
of 100 beats per minute is called a tachycardia. When the tachycardia is due to
disease or injury, it usually requires treatment. Tachycardias may begin in the
atria or ventricles; some are harmless, but others are life threatening.
Several therapy options exist for tachycardias, including implantation of an
ICD. To learn more, go to
ICD implantation.
Sinus tachycardia results when the sinoatrial (SA) node sends electrical
impulses faster than usual, thus raising the heart rate to meet the increased
needs of the body, such as fever or exercise. This is a normal response and, as
such, it is considered a normal rhythm.
Supraventricular Tachycardia
Paroxysmal (starting and stopping suddenly) supraventricular (originating above
the ventricles) tachycardia (PSVT) is a series of fast atrial contractions that
can cause the heart to beat up to 250 times per minute. Though it is rarely
serious, PSVT can be frightening. The type of treatment depends on whether the
electrical impulses reenter the atria through the atrioventricular (AV) node or
via a bypass tract.
Wolff-Parkinson-White (WPW) syndrome is an example of impulses using a bypass
tract. With WPW syndrome, the heart rate may exceed 220 beats per minute. This
condition can be treated, most often with cardiac ablation. In other cases
medication or surgery may be used.
Ventricular Tachycardia
Ventricular tachycardia occurs when the ventricles produce impulses that make
the heart beat too quickly. With this disorder, the heart tries to beat 200 or
more times a minute. It can't contract completely and just quivers. The heart
then doesn't fill with enough blood between beats to meet the body's needs.
Symptoms include a pounding sensation, dizziness, and sometimes fainting.
Ventricular tachycardia is treated with an ICD. To learn more, go to
ICD implantation.
Ventricular tachycardia or ventricular fibrillation syndrome refers to a
condition in which some patients have ventricular tachycardia that quickly
accelerates to ventricular
fibrillation. Ventricular fibrillation is a life-threatening arrhythmia
that necessitates immediate treatment with an external defibrillator, an ICD,
antiarrhythmic drugs, or VT ablation.
Fibrillation
Fibrillation is caused when the heart muscle begins to quiver, or fibrillate,
continually and cannot contract normally. When a heart is in a state of
fibrillation, there is no synchronization between the atria and the ventricles.
This may cause the patient to experience a racing sensation–and sometimes
discomfort in the chest–and/or to feel light-headed or faint.
Atrial fibrillation
(AF or A Fib) is a very fast, uncontrolled atrial heart rate caused by rapidly
fired signals. During an episode of AF, the atrial heart rate may exceed 350
beats per minute. Not all of these beats reach the ventricles, so the
ventricular rate is not this high. However, the ventricular rate is often
higher than normal and an also be erratic, exceeding 100 beats per minute.
Sometimes an impulse will circle the atria, triggering atrial flutter, which is
similar to AF. Alone, AF is rarely serious, but if a patient has high blood
pressure, valvular disease, or heart muscle damage, AF can increase the risk of
stroke or heart failure.
There are several treatments for AF, including medication, ablation and an
electrical therapy called cardioversion. Electrical cardioversion converts the
heart rate back to normal sinus rhythm through the use of a controlled
electrical shock that excites all the heart cells at once, allowing the SA node
to resume its role as the heart's natural pacemaker. If medication and
electrical cardioversion do not improve the AF, the physician may recommend
cardiac ablation to prevent conduction of abnormal electrical impulses from the
atria to the ventricles, with implantation of a permanent pacemaker to control
heart rate. To learn more, go to
pacemaker implantation.
Ventricular
fibrillation (VF) is a chaotic heart rate resulting from multiple areas
of the ventricles attempting to control the heart's rhythm. Ventricular
fibrillation can occur spontaneously (generally caused by heart disease) or
when ventricular
tachycardia has persisted too long. When the ventricles fibrillate,
they cannot contract normally, hence, they cannot effectively pump blood. The
instant VF begins, effective blood pumping stops. VF quickly becomes more
erratic, resulting in
sudden cardiac arrest or sudden cardiac death. This arrhythmia must be
corrected immediately via a shock from an external defibrillator or an ICD. The
defibrillator can stop the chaotic electrical activity and restores normal
rhythm.
Select a link below to jump to another page in the Learn More About section:
Related Web Site
- Inside Cardiac Arrest
-
This site—created by St. Jude Medical—is an educational resource providing
information about sudden cardiac arrest and a review of the heart's anatomy.
Watch the “Am I at Risk?” video and commentary provided by Charles Machell, MD.
-
[ www.insidecardiacarrest.com
]
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