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The
Human Heart in Motion
A Half Century
of Progress
Types of Arrhythmias
The Power of
Electricity to Help the Heart
New Devices
to Save Lives
Controlling
Arrhythmias with Medications
Mondays
can be rough—especially for one’s heart.
Hearts,
like people, know how hard it is to shift gears at the
start of the work week, and that’s why people who have
an irregular heartbeat—what doctors call a cardiac
arrhythmia—are most likely to have problems on
a Monday.
Surprisingly,
this pattern holds even among retired people. In a 1996
study, researchers from the University of Maryland and
the University of Kentucky found that almost twice as
many arrhythmias occur on Monday as on weekends; Friday
brings a second, smaller peak.
The
Human Heart in Motion
"Maintaining a normal heartbeat billions of times
is a real feat," said Douglas Zipes, MD, Distinguished
Professor of Medicine, Pharmacology, and Toxicology
and director of the cardiology division at Krannert
Institute of Cardiology at Indiana University School
of Medicine in Indianapolis. "The heart is not
a Swiss watch, but a complex biologic system that suffers
from occasional hiccups."
The
heart is powered by an electrical impulse that signals
the heart’s four chambers to contract, each at the proper
time. The heart works in an endless contract-relax/contract-relax
cycle. An average heart beats 100,000 times a day, pumping
some 2,000 gallons of blood through its chambers to
the rest of the body and then back to the heart. Over
a 70-year life span, that adds up to more than 2.5 billion
heartbeats.
But
many forms of heart disease can interrupt the normal
contract-relax cycle and cause abnormally fast or unusually
slow heart rates. Called cardiac arrhythmias, these
conditions make the heart pump less effectively, so
that not enough blood reaches the brain and other vital
organs. When the body’s blood flow is inadequate, the
person can faint or suffer chest pain. Even sudden
death can occur.
A
Half Century of Progress
Today, most arrhythmias are treatable, but just 50 years
ago, doctors knew little about why the heart’s rhythm
sometimes goes wrong. Back then, an abnormal heartbeat
was, for most people, an incurable condition. When a
patient complained of excessive fatigue, fainting, and
dizziness in 1949, the physician may have suspected
an abnormal rhythm after listening to the patient’s
heart with a stethoscope, taking a chest X-ray, and
performing an electrocardiogram
(ECG), but the doctor’s suspicions couldn’t always be
confirmed. The arrhythmia usually remained undetected
by the technology of the day. Even when the tests did
detect a problem, the doctor had few tools to deal with
arrhythmias. Only a couple of drugs—digitalis to
slow a fast heartbeat and quinidine to return an irregular
beat to normal—were available at the time.
A
steady pace of new technology and research over the
past 50 years has broadened doctors’ understanding of
arrhythmias. Today’s heart specialist can offer patients
many life-saving treatments.
"The
most notable advance in the therapy of arrhythmias was
the harnessing of electricity," said Leonard A.
Cobb, MD, University of Washington Professor Emeritus
of Medicine. "Resuscitation from cardiac arrest
was almost unheard of before the 1960s, when cardiopulmonary
resuscitation (CPR) and external defibrillation started
to become tools that could be used almost anywhere.
The ability to stop abnormal heart rhythms simply and
effectively with an electrical jolt surely must rank
among the most significant advances in medical history."
Commenting
on how far medical research has progressed since 1949,
Dr. Cobb observed, "The prevention of sudden cardiac
death due to arrhythmia has become a reality."
Types
of Arrhythmias
Arrhythmias stem from several causes. The heart’s natural
timekeeper—a small mass of special cells called
the sinus node—can malfunction and develop an abnormal
electrical impulse rate. Or, because all heart tissue
is capable of starting a beat, any part of the heart
muscle also can interrupt the electrical rhythm or even
take over as the heart’s pacemaker, setting off an abnormal
heartbeat. When one of these events interrupts the heart’s
normal beat, arrhythmias can occur. Doctors frequently
see these five types of arrhythmias—
- Premature
beats. The most common arrhythmia, premature beats—which
affect a large number of people, especially older
Americans—are benign and are often described
as "flip-flops." Caffeine and stress increase
the occurrence of premature beats.
- Atrial
fibrillation. Doctors estimate that 3 to 5 percent
of Americans have atrial fibrillation, making it the
most common type of problematic cardiac arrhythmia.
Atrial fibrillation, which is found most often in
people over 65, develops when a disturbance in the
electrical signals causes the two upper atrial chambers
of the heart to quiver rather than pump correctly.
When this quivering occurs, not all the blood is forced
out of the heart’s chambers. The blood pools inside
the atrium and sometimes clots. Blood clots can cause
a stroke if they break off, travel through the body,
and block an artery in the brain.
- Bradycardia.
A slowed heartbeat, or bradycardia, causes a person
to feel fatigued, dizzy, and lightheaded and may trigger
fainting spells.
- Tachycardia.
Rapid heartbeat, or tachycardia, can also cause inefficient
blood circulation. During an episode of tachycardia,
a person may feel palpitations, rapid heart action,
dizziness, lightheadedness, and may faint.
- Ventricular
arrhythmias. The most severe and life-threatening
arrhythmias affect the beating of the ventricles,
the main pumping chambers of the heart. Ventricular
tachycardia is a rapid heartbeat arising in the ventricles.
Ventricular fibrillation occurs when the ventricles
go out of control, quivering and beating ineffectively,
stopping the pumping action. If a more normal rhythm
is not restored promptly—within three to five
minutes—the patient will suffer brain and heart
damage and die.
The
Power of Electricity to Help the Heart
Since the 1800s, pioneering researchers have pondered
the use of electricity to stimulate a too-slow heartbeat
and worked to find methods to deliver an electrical
charge to stop fibrillation.
A
New York cardiologist, Albert Hyman, MD, invented the
first artificial cardiac pacemaker in the 1930s, but
its power supply lasted only a few minutes. By 1960,
researchers had developed temporary cardiac pacemakers
that could be used in hospitals. Those early models
had an external battery; wires were inserted through
an incision in the patient’s skin and attached to the
heart.
Today’s
smaller permanent cardiac pacemakers are widely used.
The battery is placed just beneath the skin on the chest,
and the wires are guided through neck veins into both
the atrial and the ventricular heart chambers. Modern
pacemakers can regulate a heartbeat for 10 to 15 years
on one battery. Most contain a sensing device that turns
the pacemaker off when the heartbeat is normal but turns
it on and sends an electrical charge when the heartbeat
becomes too slow.
Patients
with more serious, potentially lethal rapid heartbeat
abnormalities have a similar option that has dramatically
improved their chances of survival—an implantable
cardioverter/defibrillator (ICD). An ICD is inserted
surgically, just as a pacemaker is. The ICD constantly
monitors heart rhythm, and when it senses that the rhythm
is abnormal, the ICD gives the heart a small shock to
return the rhythm to normal.
"It
is like having an emergency room implanted in your chest,"
Dr. Zipes remarked.
New
Devices to Save Lives
In addition to pacemakers and ICDs, other significant
breakthroughs in diagnosing and treating arrhythmias
came during the late 1970s and 1980s. The Holter recorder,
one of the tools developed during this period, turned
the ECG into a portable monitor. A patient wears the
Holter monitor all day, and the device records heartbeats
and notes when an irregular rhythm occurs.
Although
more invasive, an electrophysiologic
study (EPS) also measures and studies the heart’s
electrical impulses. Using electrodes attached to catheters
inserted through veins and into the heart, the EPS can
detect almost all types of life-threatening arrhythmias
and lead cardiologists to appropriate treatments.
A
third tool is catheter
ablation. This device returns rapid, irregular heartbeats
to normal by using a catheter to deliver radiofrequency
energy that destroys a small number of heart-muscle
cells. The resulting scar cuts off the route of the
extra impulses. This technique has enabled many patients
to live a life free of both medicines and recurrent
bouts of arrhythmia caused by paroxysmal atrial tachycardia
(PAT) or Wolff-Parkinson-White (WPW) syndrome.
Controlling
Arrhythmias with Medications
Introduced in England in 1785, digitalis (its modern-day
derivative is digoxin) still remains a treatment for
fast heart rates caused by atrial fibrillation. Several
new compounds developed since the 1950s are used to
stabilize the heartbeat or as preventive therapy to
avert complications:
- warfarin,
an anticoagulant, is used in atrial fibrillation patients
to prevent stroke-inducing blood clots;
- antiarrhythmic
agents such as amiodarone and sotalol help maintain
the heart’s normal rhythm;
- beta
blockers such as metoprolol and atenolol limit the
stimulating effects of adrenaline on the heart, and
slow the heart rate in atrial fibrillation; and
- calcium
channel blockers such as verapamil and diltiazem help
slow the heart rate and suppress tachycardias.
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