Download Pacemaker Therapy and the Conducting System of the Heart

Pacemaker Therapy and the
Conducting System of the Heart
By: Tom Kerrigan
Conducting System of the Heart
• Consists of the sinoatrial node (SA node),
atrioventicular node (AV node), the bundle
of His, the bundle branches and the
Purkinje fibers.
Sinoatrial node
• The natural pacemaker of the heart.
• Small mass of specialized cells in the right
atrium of the heart.
• Creates electrical impulses and conducts
them through the myocardium until it
reaches the atrioventricular node (~0.03
seconds)
Atrioventricular Node
• Cluster of cells situated on interatrial septum
close to the tricuspid valve.
• Receive impulses from the SA node and
conducts them to the bundle of HIS.
• Must be conducted though the AV node because
the atria and ventricles are separated by a
fibrous connective tissue septum that has poor
conductivity.
• AV node slows down electrical current to insure
that the atria have fully contracted before
ventricles are stimulated.
Bundle of HIS
• Emerges from the AV node to begin the
conduction to the ventricles.
• located in the proximal interventricular
septum
• Branches into three bundle branches.
Bundle Branches
• Runs along the interventricular septum
• Three bundle branches: the right, left
anteriosuperior and left postrioinferior
bundle branches.
• Known as the trifascular system.
• Bundles give rise to thin filaments known
as Purkinje fibers
Purkinje Fibers
• Distribute impulse to ventricular muscle, causing
the myocardium to contract at a paced interval.
• The bundle branches and purkinje network
comprises the ventricular conduction system.
• It takes ~ 0.03-0.04s for the impulse to travel
from the bundle of His to the ventricular muscle.
Normal Conduction
Dysfunctions of Conduction System
•
SA node
• The signal starts in the SA node but may be slow or delayed in progressing
to the atria, causing a very slow or irregular heart beat. (bradycardia)
•
AV node
• Atrioventricular block occurs when atrial impulses fail to reach the ventricles
or when atrial impulses are conducted with a delay, leading to partial or
complete heart failure.
•
SA/AV node
• SA node sends out electrical impulses too slowly and impulses are partially
or fully blocked between the atria and the ventricles. The combination of SA
and AV node defects cause uncoordinated contraction of atria and ventricles.
Treatment
• Implantation of artificial pacemaker to
monitor the electrical activity of the heart
and respond appropriately.
History of Pacemaker
• The first artificial pacemaker was designed and
built in 1950 by the Canadian electrical engineer,
John Hopps.
• It was not implanted into the body and relied on
external electrodes that had to be plugged into a
wall outlet.
• Patient could go only as far as the extension
cord and a power blackout was of constant
concern.
• In 1958 the first pacemaker was implanted into
the body which had a battery life of ~12 to 18
months.
Parts of Pacemaker
• Pulse generator
• Has a depth of ½” and a width of about 1 ½”.
• Produces impulses and houses the electrical
circuitry.
• Constructed of titanium and contains a lithium
battery with a life of ~5 to 10 years
• The battery will provide a low warning months
before it has fatigued.
• Generator sends out electrical impulses through
leads that are attached to the myocardium.
Parts of Pacemaker
• Lead(s)
• Insulated wires that not only receive impulses, but
carry signals back from the heart to the generator.
• Lead(s) are steroid eluting to decrease the
inflammation of the interface between the distal tip
of the lead and myocardium.
Parts of Pacemaker
Pacing Systems
• Fixed Rate
• Emits electrical stimuli at a constant frequency
regardless of the hearts rhythm.
• Used if heart is able to increase its rate according
to the person’s needs.
• The pulse rate is set and programmed by the
physician.
Pacing systems
• Rate-Responsive
• Has capability to interpret the body’s changes and
increase or decrease the heart rhythm at an
appropriate rate.
• Used when the heart cannot increase its rate with
activity.
• Most pacemakers today are rate-responsive.
Single-Chamber Pacemaker for SA
Node Dysfunction
• Has one lead that is placed into the right atrium.
• Must have a normal conduction of the AV node.
• Can only send and receive signals from
right atrium.
• Candidates for this type of pacing usually have
symptomatic bradycardia.
• Disadvantage of this pacing method is that AV
block develops in 0.6 to 5.0% of patients with
symptomatic bradycardia every year.
Single-Chamber Pacemaker for SA
Node Dysfunction
Single-Chamber Pacemaker for AV
Node dysfunction
• Has one lead placed into right ventricle to be effective.
• Must have a normal SA node conduction.
• Patients with this type of pacing typically have atrial
impulses that delay or fail to reach the ventricles.
• Ventricular pacing can be associated with pacemaker
syndrome. This occurs when the right ventricle
sacrifices the atrial contribution to the ventricle output.
This is due to atrial contraction against closed
atrioventricular valves.
• The ultimate treatment involves an upgrade to a dualchamber pacemaker.
Single-Chamber Pacemaker for AV
Node Dysfunction
Dual-Chamber Pacemaker for SA
and AV Node Dysfunction
• More sophisticated and costly than singlechamber pacemaker.
• Has two leads, with one leading into the
right atrium and one in the right ventricle.
• Can pace and sense the both right
chambers of the heart.
• Beneficial for patients that have acquired
symtomatic bradycardia and partial or
complete block of the heart.
Dual-Chamber Pacemaker for SA
and AV Node Dysfunction
Implantation procedure
• A small 2 to 3” incision is made parallel to and
just below the clavicle in the deltopectoral
groove.
• Small pocket will be made under skin for
generator and lead(s).
• Under fluoroscopy, lead(s) travel through the
subclavian vein, brachiocephalic vein, superior
vena cava, and finally into the desired chamber.
• Physician will create an arrhythmia to insure the
pacemaker is responding appropriately.
• Hospitalization usually last 1 to 3 days.
Devices That Put Your Pacemaker
at Risk
• MRI and large amounts of radiation can interrupt
the circuitry.
• If an MRI must be done, the pacemaker output
in some models can be reprogrammed.
• If exposed to excessive amounts of radiation, it
should be shielded as much as possible.
• Diagnostic radiology appears to no effect
towards pulse generators. CXR’s are actually
beneficial to evaluate lead position.
The Future of Pacemakers
• There are currently more than 3 million
patients worldwide with an implantable
pacemakers, and indications are
expanding.
• Major advancements of pacemaker
technology has enabled patients with life
threatening symptoms to increase their
survival and live a higher quality of life.