Cardiac Arrhythmia Surgery
Surgical Treatment of Atrial Fibrillation
What is Artrial Fibrillation?
Artrial fibrillation (AF) is the most common cardiac rhythm disorder. With AF, the atria
have many circuits that send signals. The extra signals make the atria beat very quickly and
unevenly. The atria may beat so fast and unevenly that they stop contracting and begin to
quiver.
The atria stop contracting as they fibrillate and become ineffectual at filling the ventricles.
This significantly creates a negative impact on cardiac output. The ventricular rate becomes
irregular and can range from bradycardic to tachycardic in different patients, but is always
less than the atrial rate. This high atrial rate combined with a rapid ventricular rate can
reduce a patient's cardiac output up to 30 percent.
The risk of stroke also increases because the lack of atrial contraction allows blood to pool
and may lead to thrombus formation.
A patient diagnosed with AF can be placed in one of three classifications:
- Paroxysmal AF--paroxysmal AF terminates spontaneously
- Persistent AF--persistent AF does not terminate spontaneously, but requires
cardioversion.
- Permanent (chronic) AF--over time, a patient's AF will progress from paroxysmal to
chronic. Many patients being surgically treated for AF fall into the chronic AF
category.
Causes of Atrial Fibrillation
AF can occur in the absence of apparent heart disease although it is typically associated
with an underlying cardiovascular problem.
Rheumatic heart disease and hyperthyroidism have historically been the major causative
factors and continue to be in underdeveloped countries. In more developed countries, these
factors have been replaced by hypertension, coronary artery disease and post-cardiopulmonary
bypass.
Cardiac causes of atrial fibrillation:
- Hypertension
- Coronary artery disease
- Ischemic heart disease
- Valvular heart disease
- Congestive heart failure
- Cardiomyopathies
- Others (sinus node disease, tumors, pericarditis, etc.)
Non-cardiac causes of atrial fibrillation:
- Chronic obstructive pulmonary disease
- Pneumonia, pulmonary embolism
- Thyroid disease
- Electrolyte disturbance
- Diabetes
- Alcohol abuse
- Vagal simulation (following meals or exercise)
AF can also occur as a secondary went to other arrhythmias, such as atrial tachycardia or
atrial flutter. These arrhythmias which are often initiated from a single region or either
atrium can subsequently degenerate into AF.
Lastly, another factor affecting the occurrence and significance of AF is the complex nature
of the atrial anatomy. Natural barriers formed by structures such as the tricupid annulus or
inferior vena cava (IVC) can markedly influence the pattern and velocity of electrical
propagation in atria.
Impact on Health
Symptoms occur in 80 percent of patients with AF. They often describe the rapid, irregular
rhythm as palpitations or chest discomfort.
AF increases the incidence of stroke 5-fold in patients without rheumatic heart disease and
17-fold in patients with rheumatic heart disease. The risk of stroke increases with age,
most notably in AF patients over age 70.
Atrial fibrillation also can have a significant negative effect on a patient's quality of
life. In addition to the physical symptoms, there is a strong emotional impact when a
patient's lifestyle and peace of mind is disturbed by chronic symptoms and concerns over
financial burdens.
Atrial Fibrillation Management Methods
Cardioversion, Drug Therapy,
Implantable Devices,
Catheter Ablation, and
Surgery are variety of therapies that enable the physician to treat
AF based on the patient's specific symptoms, heart rhythm, and other medical conditions. With each
method, the objective is to restore and maintain a normal sinus rhythm. If this cannot
be accomplished, the goals are to control the heart rate, prevent stroke, and manage other
symptoms.
Cardioversion
Direct current (DC) cardioversion treatment is highly effective in providing symptom relief
and restoring cardiac function in patients in the early stages of AF. Success rates for
patients in later stages of AF drop over time due to increase duration of AF, artrial
enlargement, and advanced age. Cardioversion can also be accomplished chemically through
medication.
Drug Therapy
Antiarrhythmic drugs are used to maintain sinus rhythm after cardioversion or to provide
ventricular rate control during AF. Drug therapy is often started in the hospital in order
to closely monitor the patient for drug effectiveness and potential dangerous proarrhythmic
adverse effects.
Implantable Devices
AV node ablation with the implantation of a permanent pacemaker provides symptom control
during AF by eliminating the rapid, irregular ventricular rate associated with the disease.
This procedure permantly severs the electrical connection between the fibrillating atria and
the ventricles; and thus requires a pacemaker to supply ventricular stimulation. While an
effective therapy, the procedure is typically limited to highly symptomatic patients due to
its irreversible nature, need for implantation of a permanent pacemaker, and continued higher
risk of stroke.
Implantable devices, such as some pacemakers and ICDs, provide electrical therapies that may
prevent and terminate atrial tachyarrhythmias, as well as provide monitoring capabilities,
but are ineffective for patients in chronic AF.
Catheter Ablation
During catheter ablation, catheters are inserted into the heart to destroy cells in the
heart that are causing the arrhythmias. The cells causing arrhythmia are found. Then,
energy is sent through the wires to destroy some of the electrical cells causing the
arrhythmias.
Surgery
During surgery, the patient is put on cardiopulmonary bypass and the heart is exposed.
The right atrium is opened where an ablation pen is used to create a "maze" of incisions
within the atria that block the re-entry pathways responsible for AF by creating linear
lesions in the atria, while preserving myocardial function.
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