ImplantationImplantation & Equipment & Equipment

Department of Thoracic & Cardiovascular SurgerySeoul National University Hospital

Types of PacemakerTypes of Pacemaker

• Temporary Pacemaker

• Permanent Pacemaker

The Pacemaker SystemThe Pacemaker System

• Patient

Lead

Pacemaker

• Programmer

• Lead• Pacemaker

Pacing System AnalysisPacing 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 & SensitivityPacing 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 & ImpedancePacing 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 & ResistanceStimulation 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 & ImpedancePacing 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 ResistancePacing System Resistance

• Lead conductor elements 60-150 ohms

• Body tissues 200-500 ohms

• Polarization resistance 15-35%

( The alignment of oppositely charged

ions at the electrode-tissue interface

during a pacing impulse)

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 MeasurementAcute Threshold Measurement

Factors• Type of lead

• Lead-tissue interface

• Location of lead within the heart

• Length of time after lead fixation

Optimal Placement of LeadsOptimal 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 ComplicationsElectrophysiologic Complications

• Pacemaker syndrome

Ventricle

Atrial

• Pacemaker-mediated tachycardia

Venous Route

Subclavian vein Cephalic vein

External jugular V Internal jugular V

Transvenous Implantation

Atrial Endocardial Placement

VentricleVentricle

AtrialAtrial

Epicardial ImplantationEpicardial 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 ImplantationEpicardial Implantation

A; Subxiphoid approach

B; Anterior thoracotomy

• Ideal electrode distance in bipolar pacing; 0.8-1.2cm

Connection of the leadsto the Pacing System Analyzer (PSA)

Connection to PacemakerConnection to Pacemaker

Insure the leads

are placed behind

the Pacemaker

Temporary Epicardial Pacing 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 PacingBiventricular PacingIndication• 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 PacingBiventricular 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 ComplicationsEarly 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 ComplicationsLate Implantation Complications• Surgical 1. Venous thrombosis

2. Pulmonary embolism

3. Constrictive pericarditis (after asymptomatic perforation)

4. Pulmonary embolism

5. Tricuspid valvular insufficiency

• Wound 1. Infection

2. Generator migration

3. Skin erosion

4. Device manipulation by patient (Twiddler’s syndrome)

Pacemaker Malfunction (Pacing)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)Pacemaker Malfunction (Sensing)1. Skeletal myopotentials Pectoral Abdominal Diaphragmatic2. Cardiac events T-wave Atrial R-wave sensing Ventricular P-wave sensing Concealed extrasystoles3. Generator malfunction Programming error-high sensitivity or output Programming error-short refractory period Microchip malfunction4. Connector malfunction Loose set screw Current leak from header5. Lead malfunction Conductor fracture Insulation break Polarization potentials6. Environmental interference Electromagnetic

Transvenous Lead ExtractionTransvenous Lead Extraction

A. Cook transvenous lead

extraction system

B. Common sites of adhesion