Download figure 1. - (canvas.brown.edu).

Electrical Stimulation of the Heart
Utah.edu
Reasons for having a
pacemaker
 Sick sinus syndrome
 Heart block
 Over ride bradycardia
 Control tachycardia
 Pace ventricles during atrial fibrillation
 Coordinate signaling between atria and ventricles
 Coordinate signaling between ventricles
 Cardiac resynchronization therapy devices
 Prevent arrhythmias caused by long QT syndrome
 Monitor and record electrical activity, monitor blood temperature,
breathing rate, adjust heart rate to changes in daily activity
Sick Sinus Syndrome
AAFP.org
FIGURE 1.
Electrocardiogram exhibiting alternating
patterns of bradycardia and tachycardia as
seen in patients with sick sinus syndrome.
Heart Block
Mykentuckyeart.com
http://www.medmovie.com/mmdatabase/Me
diaPlayer.aspx?ClientID=13&TopicID=875
Long Q-T Syndrome
BSCI.com
Atrial Fibrillation
http://www.medmovie.com/mmdatabase/Me
diaPlayer.aspx?ClientID=13&TopicID=837
A-fib.com
Risk Factors
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Coronary artery disease
High blood pressure
Diabetes
Smoking
High cholesterol
Obesity/overweight
A high-fat diet
Excessive use of alcohol (more than 2 drinks per day)
Drug abuse
Stress
Family history of heart disease
Advancing age
Certain over-the-counter and prescription medications, dietary supplements,
and herbal remedies
Patient Presentations
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Fainting (syncope)
Feeling tired all the time (fatigue)
Weakness
Shortness of breath (dyspnea)
Chest pain (angina)
Disturbed sleep
Confusion
Heart palpitations (feeling like your heart is racing,
pounding, or fluttering)
Pacemaker
Clevelandclinic.org
Pacemaker Systems
Mayoclinicproc
FIGURE 1. Schematic of commonly used pacemaker systems. A, Single-chamber ventricular
pacemaker; B, Single-chamber atrial pacemaker; C, Dual-chamber pacemaker; D, Triplechamber (biventricular) pacemaker.
Pacemaker Circuit
Figure 1. Diagram showing how the components of a cardiac pacemaker are connected. Signals from the heart are picked
up by the electrodes and travel up the leads to the sensing unit. The amplified signal from the sensing unit then goes to the
control unit. At the time the control unit determines a pulse is needed, a signal is sent to the pacing unit which sends a
pacing pulse down the leads, through the electrodes, and into the myocardium.
Power Source
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Pacemakers draw a very low amount of power, and their
power output has dropped significantly over the years.
The average continuous power demand of pacemakers
has dropped from 30μW in 1995 to 1μW in 2012 [6].
Chemical batteries are the most practical power source
for pacemakers and usually lithium ion batteries are used.
Two 2.8V lithium batteries are connected in series to
produce 5.6V of potential, and these batteries generally
last 5-10 years before they have to be replaced.
When pacemakers batteries need to be replaced, the
entire device is removed from the leads and taken out.
A new device is then implanted and attached to the
leads.
Nuclear batteries have been created with plutonium, but plutonium is extremely toxic.
Only 1μL in the bloodstream can be fatal; however, radiation exposure increase by the
plutonium batteries is negligible and if the chance of plutonium leakage into the blood
vessels can be decreased enough, this battery can be very practical [1].
J. Webster, Design of Cardiac Pacemakers, New York: Institute of Electrical and
Electronic Engineers, 1995
Housing is Ti
Wires can be
covered with
silicone
An artificial pacemaker with electrode
for transvenous insertion. The body of
the device is about 3-4 centimeters long,
the electrode measures between 50 and
60 centimeters (20 to 24 inches).
Pacemaker electrodes
materials
 Titanium or titanium alloys, iridium or iridium
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alloys, platinum or platinum alloys, or carbon
and metallic activated glass
Steroids are often eluted from the electrode
Electrodes must be designed so that the power
output of the pacemaker is minimized while
being able to effectively stimulate the
myocardium.
Decreasing the geometric size of the electrode
decreases the amount of charge leaked out into
tissue that does not need to be stimulated.
Therefore, less charge is needed for the same
effect.
Having a geometrically small electrode
decreases power output. Currently electrode
tips have surface areas of less than 1.2mm2
J. Webster, Design of Cardiac Pacemakers, New York: Institute of Electrical
and Electronic Engineers, 1995
Illinois.edu
Pacemaker Circuit
Figure 1. Diagram showing how the components of a cardiac pacemaker are connected. Signals from the heart are picked
up by the electrodes and travel up the leads to the sensing unit. The amplified signal from the sensing unit then goes to the
control unit. At the time the control unit determines a pulse is needed, a signal is sent to the pacing unit which sends a
pacing pulse down the leads, through the electrodes, and into the myocardium.
Sensing Unit
Control Unit
An intracardiac electrogram is received by the
pacemaker electrodes.
An intracardiac electrogram shows the
signals from a small amount of cardiac
tissue in close proximity to the
electrodes.
Operational amplifiers are used to amplify the
signal from the heart, and a bandpass filter is
used to reduce noise and DC voltage.
The amplified and filtered signal is then
passed to the control unit which processes the
data.
The control logic of the unit determines
when to send pulses based on data from
the sensing unit.
Pulses need to be sent at very specific
times to correctly pace the heart;
therefore, the timing logic of the control
unit is crucial
Remote programming of the pacemaker
Data can be transferred remotely for
diagnostic purposes.
Pacing Unit
The pacing unit is responsible for generating an electric field of adequate intensity to create
a wave of action potentials and stimulate the myocardium.
The stimulation threshold is the minimum amount of energy required to create the action
potential waveforms.
The pulse generator unit charges a capacitor and the capacitor is discharged whenever the
control unit determines a pulse is needed. J. Webster, Design of Cardiac Pacemakers, New York: Institute of Electrical
and Electronic Engineers, 1995
Surgical Approaches
Cleveland Clinic.org
Surgical Approaches
 Epicardial approach is a less common
method in adults
 More common in children
 General anesthesia
 Surgeon attaches the lead tip to the heart
muscle, while the other end of the lead
(attached to the pulse generator) is placed in
a pocket created under the skin in the
abdomen.
Surgical Approaches
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Endocardial (transvenous) approach
Most common method.
Local anesthetic
An incision is made in the chest where the leads and
pacemaker are inserted.
 The lead(s) is inserted through the incision and into a
vein, then guided to the heart with the aid of the
fluoroscopy machine.
 The lead tip attaches to the heart muscle, while the
other end of the lead (attached to the pulse
generator) is placed in a pocket created under the
skin in the upper chest.
https://www.youtube.com/watch?v=WNN4Fw
2EWxI
Programming
 Electrodes will be placed on the chest and
connected via wires to a computer.
 A small device, programmer, is placed directly
over the pacemaker.
 The programmer allows control of the
pacemaker settings and checking of the
pacemaker and lead functions.
 Results of device check are reported to the
doctor, who then determines the appropriate
settings for the pacemaker.
.
Implantable Cardioverter
Device (ICD)
QueensUniversity.org
ICD
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The ICD wires connected to the heart pick up the electrical signal
coming from the heart as it beats and feeds that signal into the ICD
generator.
The ICD generator contains a battery and computer circuits that help it
recognize when the heart is beating slowly or rapidly and dangerously.
If and when the heart suddenly starts racing dangerously, the ICD
detects this and the computers inside will tell the ICD to automatically
give a shock to correct the heart rhythm or alternatively, deliver smaller
electrical impulses to pace your heart gently out of the dangerous racing
and back to normal.
The ICD successfully corrects the heart rhythm in virtually all
circumstances, but it does not affect why the event happened nor will it
prevent it from happening again.
Recurrences can only be prevented by heart medications or other
procedures.
Approximately one third of patients with an ICD take a medication to try
to prevent the heart from racing.
Rev Esp Cardiol. 2012;65:671-3. - Vol. 65 Num.07 DOI:
10.1016/j.rec.2011.09.025
Host Responses
 Leads
 Lead displacement
 Lead corrosion (with older
leads)
 Scarring at lead/cardiac
tissue interface
 Heating of cardiac tissue
 Pacemaker housing
 Fibrosis
 Twiddler’s Syndrome
Wireless Pacemaker
WICS: In the new pacemaker called the
Wireless Cardiac Stimulation (WiCS) system, a
wireless electrode replaces one or more leads.
A conventional pacemaker is implanted just
below the collarbone in the left side of the
chest and sends out a signal through a lead
running into the heart's right side. The WiCS
unit, implanted near the heart, wirelessly
senses the pacemaker's pulse via this lead; it
then sends an ultrasonic signal to the wireless
electrode on the left side, which converts the
sonic energy into electrical energy to pace the
left ventricle synchronously with the
right.Image: Courtesy of Cambridge Consultants
Scientificamerican.org