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Arrythmia
Surgery
Pacemakers
The electrical system of the heart is quite complex and very amazing.
A normal pulse is generated by an initial electrical charge that
originates in the sino-atrial (SA) node.
This structure is located near the junction between a patient's superior
vena cava and the right atrium. The pulse then passes through the right
and left atria causing these chambers to contract and then collects at the
atrio-ventricular (AV) node. The
AV node is located at the very top of the septum separating the left and
right ventricular (pumping) chambers. The AV node then fires electrical
pulses through specialized microscopic wiring known as the
bundle of His which then divides into
separate electrical branches to the left ventricle and right ventricle
simultaneously causing these pumping chambers to contract. There are a
variety of electrical problems that can occur due to aging, heart attacks,
and even congenital heart disease. The two most common indications for
permanent pacemakers in adults are sick sinus
syndrome and
heart block. Sick sinus syndrome
results from malfunction of the SA node and heart block occurs when there
is malfunction of the AV node. |
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History of Pacemakers It
has been known for a long time that external electrical stimulation of
the heart can cause the heart to contract. Indeed, in 1804, John
Aldini in London successfully stimulated hearts to contract on
decapitated criminals!
In 1952, Dr. Zoll presented in the New England Journal of Medicine
that he was able to pace patients' hearts with external skin electrodes.
One of the most famous heart surgeons who ever lived, Dr. Walter
Lillehei in Minneapolis, asked a television engineer named Earl Bakken
to help him develop a small portble pacemaker. Mr. Baakken later
became the founder of Medtronics Corporation, now a major supplier of
pacemakers and other heart related devices.
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In 1959, Elmquist and Senning, in Stockhom, placed the first totally
implantable pacemaker. Now, pacemaker insertion is a very common
procedure, usually done under local anesthesia, using tiny electrodes
inside the heart, attached to a small generator (battery) placed under
the skin.
Pacemakers are very effective and very safe. The batteries
usually last 7-10 years and are easy to replace during a second minor
operation.
Unfortunately for me, whereas the majority of pacemakers were
historically placed by cardiac surgeons in the 1970's, 80's, and most of
the 90's, currently nearly all pacemakers are placed by cardiologists.
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Cardiac Pacemaker
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Cardiologists do a fine job with pacemaker insertions, though I
personally wish that the procedure stayed in the surgical arena.
This is a common dilemma in modern medicine. That is, the overlap
of disciplines vying for the same procedures. Unfortunately,
surgeons are "at the bottom of the food chain" and so the referring
doctor (cardiologist, internist) would need to send the patient to the
surgeon to have a pacemaker done by a surgeon. That simply isn't
going to happen if the cardiologists wants to do the procedure
themselves.
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ICD Implants
ICD stands for Internal Cardioverter
Defibrillator. Modern ICDs look very similar to
pacemakers, but they do an additional function. If the heart goes
into a very irregular, life-threatening arrhythmia, the devices sends an
electrical charge to the heart and zaps it back into normal rhythm!
It's like carrying around your own personal defibrillation paddles! |
| The technology is so advanced today,
largely because of our ability to make smaller and smaller computer
chips. These devices can actually sense your rhythm, record it,
analyze it, and then send shock waves to your heart to correct the
rhythm problem. Many of these devices can also serve as a
pacemaker as well.
When I was in training, the ICDs were put in by surgeons. But
just like the pacemakers (see discussion above) most ICDs are put in by
cardiologists, specifically cardiology
electrophysioloigists (EP).
EP cardiologists are in great demand. This is one of the most
rapidly expanding fields in medicine. In addition, studies clearly
show that ICDs should be placed in almost all patients who survive a
potentially lethal arrhythmia (known as sudden
death syndrome) as well as most patients with
cardiomyopathies (diseased heart muscle) whose ejection fractions (EF)
are less than 30% (normal being 60%).
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Combined Cardiac Pacemaker, Cardiac
Resynchronization, and Defibrillation System
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The Maze Procedure
Atrial fibrillation is the most
common cardiac arrhythmia. Indeed, over 2 million people in the
United States have atrial fibrillation.
Atrial fibrillation is a complicated arrhythmia for which the cause is
not completely understood. The most common theory is that
multiple circuit reentry causes the
electric charges in the atrial chambers to go in all different
directions. Thus, the atrial chambers "fibrillate" instead of
contracting in a uniform fashion.
Atrial fibrillation adversely effects the overall function of the heart
and is associated with increase complications and increase risk of
death. For example, blood clots can form in the atrium because the
atrial fibrillation just swirls the blood around in the chamber instead
of ejecting it in a uniform manner. These blood clots can break
loose and travel to the brain causing a stroke. Most patients with
atrial fibrillation therefore require life-long anticoagulation with
blood thinners such as Coumadin ®.
The Maze procedure was designed to interrupt the
multiple reentrant circuits that causes the atrial chambers to
fibrillate.
Dr. James L. Cox,
the now retired Professor and
Chairman, Department of Thoracic and Cardiovascular Surgery at
Georgetown University Medical center is the father of surgery for
atrial fibrillation. Dr. Cox began developing operations to
treat atrial fibrillation in the early 1980's. |
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The basic concept of
the Cox-Maze procedure for atrial fibrillation was to create
multiple incisions in the left and right atrium and then sew them
back up immediately causing a full-thickness scar in the pattern of
a maze. The maze would interrupt the reentry circuit and force
all of the electricity to go in one direction, just as if you were
walking through a maze. |
Conceptual Design of the Maze Procedure
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Incisions and Suturing for the original
Cox-Maze Procedure
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Radio-Frequency Maze Procedure A
recent advance in the Maze Procedure has been the use of a
variety of energy sources to create scars in the atria without the
need to make incisions. Radio-frequency energy is the most
popular, but other energy sources include microwave, laser, and even
freezing the tissue (cryo-ablation).
Eliminating all of the cutting and sewing in the atria greatly
shortens and simplifies the operation and greatly reduces the risk.
Now, a complete Maze procedure using the radio-frequency technique
can take as little as 20 minutes (not including the time to open and
close the chest).
The most common indication for radio-frequency Maze procedure is
during mitral valve repair, since many patients with mitral valve
disease have developed atrial fibrillation.
Below is the equipment I use when I perform radio-frequency Maze
procedure. The machine generates the radio-frequency energy
which is transmitted to a variety of instruments that are placed
both inside and outside of the atria to create the Maze lesions.
Our experience with the Maze procedure is growing. Minimally
invasive approaches are being investigated as well as new
instruments and energy sources. This is certainly one of the
most interesting and most exciting new areas of cardiac surgery. |
Last Modified
Tuesday, October 11, 2005
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