Download Pacing Concepts

Implantation & Equipment
Department of Thoracic & Cardiovascular Surgery
Seoul National University Hospital
Types of Pacemaker
• Temporary
Pacemaker
• Permanent
Pacemaker
The Pacemaker System
• Patient
• Lead
• Pacemaker
• Programmer
Lead
Pacemaker
Pacing System Analysis
• Ohm’s law ; R=E/I
R; resistance in ohms
E; potential in volts
I ; current in amps
• Unipolar system: the negative alligator clip of the cable
is attached to the electrode(anode) and the positive clip
to an indifferent electrode(12-15cm2, stainless steel)
• Bipolar system: the cathode(tip electrode) is usually the
most proximal(pin) terminal and anode(ring electrode)
is connected to the less proximal(ring) terminal of the
lead
Pacing Threshold & Sensitivity
• Current threshold(mA) is the quantity of electron/ion
flow across the electrode that is required to initiate
depolarization of the myocardium.
This may also be expressed in terms of current density
or current per unit of electrode surface area, usually
milliamps per square millimeter
• The voltage threshold(V) is the amount of potential
drop required to maintain this current flow
• Lead impedance is a measure of the total resistance to
current flow along the lead conductors, across the
electrode-tissue interface, and across the body tissues
Pacing Threshold & Impedance
• Pulse generator and lead along the body provide a
continuous circuit for current flow and the total pacing
system resistance is comprised of three part
• Lead conductor and tissue resistance are relatively
constant, while polarization resistance increases
throughout the period during which current is flowing
• Largely as a result of polarization resistance, lead
impedance varies directly with pulse duration and
current amplitude and inversely with electrode surface
area
Stimulation Threshold & Resistance
• With time, a layer of fibrosis forms around the electrode
tip, causing separation of the electrode surface and
viable tissue
• The stimulation threshold at implant will provide a basis
for estimating the expected rise in thresholds that results
from this fibrotic buildup
• Threshold may rise transiently to levels of 4 to 5 times
those at implant but generally decline after 14-21 days
to levels of 2 or 3 times the acute values
• Newer electrode materials and configuration may lessen
the development of the fibrous capsule, thus decreasing
both transient & permanent rises in threshold
Pacing Threshold & Impedance
• Pulse generator and lead along the body provide a
continuous circuit for current flow and the total pacing
system resistance is comprised of three part
• Lead conductor and tissue resistance are relatively
constant, while polarization resistance increases
throughout the period during which current is flowing
• Largely as a result of polarization resistance, lead
impedance varies directly with pulse duration and
current amplitude and inversely with electrode surface
area
Pacing System Resistance
• Lead conductor elements
• Body tissues
• Polarization resistance
( The alignment of oppositely charged
ions at the electrode-tissue interface
during a pacing impulse)
60-150 ohms
200-500 ohms
15-35%
Acceptable Threshold Limit
(Acute)
• Acute implant stimulation threshold
– Atrium
• Less than 1.0-1.5 Volts
• Less than 1.5-2.0mA(current)
– Ventricular
• Less than 1.0 Volts
• Less than 2.0mA(current)
• Acute implant sensing thresholds
– Atrium
• Greater than 1.5-2.0 mV
– Ventricular
• Greater than 5.0 mV
• Acute implant lead impedance
. Both chamber within 300-1000 ohms
Acceptable Threshold Limit
(Chronic)
• Chronic voltage stimulation threshold
Less than 50% of nominal voltage output of pulse
generator at pulse width <1.0
• Chronic current stimulation threshold
– Atrium ; less than 3.0-3.5mA
– Ventricular; less than 3.0-3.5mA
• Chronic sensing thresholds
– Atrium ; greater than 1.0 mV
– Ventricular ; greater than 4.0 mV
• Chronic lead impedance
– Atrium ; 300-1000 ohms
– Ventricular ; 500-1000 ohms
Acute Threshold Measurement
Factors
•
•
•
•
Type of lead
Lead-tissue interface
Location of lead within the heart
Length of time after lead fixation
Optimal Placement of Leads
• Acceptable eletrophysiologic values
• Visual assessment on fluoroscopic
examination
• Adequate securing of the lead and
is in good contact with viable tissue
Electrophysiologic Complications
• Pacemaker syndrome
Ventricle
Atrial
• Pacemaker-mediated tachycardia
Transvenous Implantation
Venous Route
Subclavian vein
Cephalic vein
External jugular V
Internal jugular V
Atrial Endocardial Placement
Atrial
Ventricle
Epicardial Implantation
Indications
•
•
•
•
•
Multiple endocardial lead failure
Abnormalities of thoracic venous anatomy
Presence of congenital heart disease
Presence of tricuspid valve prosthesis
Repeated development of exit block of
endocardial lead
• Small infants and occasionally in children
Epicardial Implantation
A; Subxiphoid approach
B; Anterior thoracotomy
• Ideal electrode distance in bipolar pacing; 0.8-1.2cm
Connection of the leads
to the Pacing System
Analyzer (PSA)
Connection to Pacemaker
Insure the leads
are placed behind
the Pacemaker
Temporary Epicardial Pacing
• Temporary pacing leads are invaluable in the diagnosis
and treatment of arrhythmia after cardiac surgery.
• Bipolar leads have been shown to have better pacing
and sensing function compared with unipolar leads
• Atrial leads were implanted directly into the lateral
muscular part of right atrium near interatrial groove.
• Temporary epicardial atrial leads are more effective
when placed in the atrial body of right atrium than
wrapped within the right atrial appendage
• Ventricular leads were implanted into the myocardium
on the anterior surface of the right ventricle.
Biventricular Pacing
Indication
• Adjuvant treatment for patients with heart failure and
intraventricular conduction delay
• Acute hemodynamic improvement is most likely to be
observed when QRS duration is greater than 150 ms in
patients with left bundle-branch block.
Techniques
• Usually, left ventricular lead implant is accomplished
percutaneously through coronary sinus cannulation,
advancing the lead into a major cardiac vein.
• Epicardial lead placement is often a rescue procedure,
so it offers advantages related to its safety and shorter
implant time.
Biventricular Epicardial Pacing
Selection of implantation site
• Selection of the best implantation site was made by
echocardiography with tissue Doppler imaging in
combination with intraoperative electrophysiologic
measurements.
• Leads were positioned, but not fixed, on several spots
of the left ventricular epicardial surface.
• The final site was chosen on the basis of the longest
atrioventricular delay in activation. The target was
the posterolateral wall of the left ventricle in most of
the patients
Early Implantation Complications
1. Surgical
Pneumothorax
Arterial or venous vascular injury
Air embolism
Cardiac chamber perforation
Lead dislodgment due to inadequate fixation
Neural (brachial plexus) injury
2. Wound
Hematoma
Infection
Drainage
Late Implantation Complications
• Surgical
1.
2.
3.
4.
5.
Venous thrombosis
Pulmonary embolism
Constrictive pericarditis (after asymptomatic perforation)
Pulmonary embolism
Tricuspid valvular insufficiency
• Wound
1.
2.
3.
4.
Infection
Generator migration
Skin erosion
Device manipulation by patient (Twiddler’s syndrome)
Pacemaker Malfunction (Pacing)
1. Lead position
Displacement
Microdislodgment
Perforation
Poor placement at implantation
2. Inadequate device output
Power source failure (end of life)
Programming error below safety factor
Microchip component failure
3. Increased pacing threshold
Acute postimplant rise
Late fibrotic exit block
Myocardial infarction
Metabolic, toxic, or electrical influence
4. High resistance in lead system
Lead fracture
Pacemaker Malfunction (Sensing)
1.
2.
3.
4.
5.
6.
Skeletal myopotentials
Pectoral
Abdominal
Diaphragmatic
Cardiac events
T-wave
Atrial R-wave sensing
Ventricular P-wave sensing
Concealed extrasystoles
Generator malfunction
Programming error-high sensitivity or output
Programming error-short refractory period
Microchip malfunction
Connector malfunction
Loose set screw
Current leak from header
Lead malfunction
Conductor fracture
Insulation break
Polarization potentials
Environmental interference
Electromagnetic
Transvenous Lead Extraction
A. Cook transvenous lead
extraction system
B. Common sites of adhesion