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Page 1: Introduction to Cardiac Pacemakers

• Course: BME 312 Biomedical Instrumentation II

• Institution: Near East University, Faculty of Engineering, Department of Biomedical Engineering

• Subject Matter: Cardiac Pacemakers

Page 2: St. Jude Medical

• Location: Sylmar, CA, USA

• Model: Victory SR 5610, Serial Number: 1723182

• Components: Cardiac Pacemakers, Electrodes in heart, Pacemaker overview

Page 3: General Overview

• Sources: SCIENCEphotoLIBRARY

Page 4: Function of Cardiac Pacemakers

• Definition: An electric simulator that produces periodic electric pulses.

• Purpose: Conducts stimuli to electrodes in the heart, causing it to contract.

• Application: Used during disease states when the heart does not stimulate at the proper rate.

Page 5: Asynchronous Pacemakers

• Definition: Free-running pacemakers that emit electric stimulus at a uniform rate regardless of the heart’s condition.

Page 6: Mechanism of Asynchronous Pacemakers

• Control Mechanism: The oscillator sets the pulse rate.

• Output: Pulse rate regulates the stimulating pulse to the heart via lead wires to cardiac electrodes.

Page 7: Requirements for Pacemakers

• Reliability: Blocks must be highly reliable.

• Compatibility: Must be biocompatible and tolerable by body.

• Protection: Essential to safeguard circuit components for reliable operation.

• Environment: Designed to work in the corrosive environment of the body.

• Size: Should occupy minimal volume or mass.

Page 8: Packaging of Pacemakers

• Hermetically sealed metal packages for protection.

• Materials: Titanium, Stainless Steel.

• Sealing Techniques: Electron beam or laser welding to avoid damage during sealing.

• Reliability: Metal packages are more compact and reliable than polymer-based alternatives.

Page 9: Power Supply of Pacemakers

• Historical Context: Primary cell batteries used in the 1970s; required replacement every two years.

• Current Battery: Lithium Iodide batteries.

• Characteristics: Increased lifespan, open-circuit voltage of 2.8 V, high reliability, but has high source resistance limitation.

Page 10: Timing Circuit

• Mechanism: Implemented via free-running oscillators.

• Functionality: Advanced pacemakers utilize timer circuits with complex logic, quartz crystal control, and microprocessor-based circuits.

Page 11: Output Circuit

• Purpose: Generates electrical stimulus for the heart.

• Types: Produces constant-voltage or constant-current amplitude pulses optimal for myocardium stimulation.

Page 12: Specifications of Output Circuit

• Constant-voltage pulses: Range from 5.0 to 5.5 V with durations of 500-600 µs.

• Constant-current pulses: Ranges from 8 to 10 mA, with pulse durations of 1.0 to 2.0 ms.

• Typical pulse rate: 70 to 90 beats per minute.

Page 13: Lead Wires & Electrodes Requirements

• Durability: Must be mechanically strong and able to withstand constant heart motion.

• Electrical Insulation: Essential to prevent shunting of stimulating current.

Page 14: Construction of Lead Wires & Electrodes

• Design: Interwound helical coils made from spring-wire alloy, housed in silicone-rubber or polyurethane.

• Features: Coiling minimizes stress, while multiple strands provide redundancy against failure.

• Benefits: Encapsulation maintains flexibility, insulation, and biocompatibility.

Page 15: Bipolar & Unipolar Electrodes

• Unipolar Electrodes: One electrode in contact with the heart with a large indifferent electrode elsewhere.

• Bipolar Electrodes: Two electrodes placed in or on the heart.

Page 16: Types of Electrode Placement

• Epicardial Electrodes: Placed on the heart's surface.

• Intramyocardial Electrodes: Buried within the heart wall.

• Endocardial Electrodes: Pressed against the inner heart's surface.

Page 17: Electrode Material Considerations

• Requirements: Materials must not dissolve, irritate heart tissue, or undergo electrolytic reactions.

• Material Unity: Same materials as lead wires to avoid junctional problems.

• Biological Interaction: Formation of a dense capsule around electrodes reduces interaction and increases stimulation threshold.

Page 18: Electrode Materials

• Common Materials: Platinum, Platinum-based alloys (with stainless steel, carbon, titanium, etc.).

Pages 19-20: Bipolar Intraluminal & Intramyocardial Electrodes

• Structure: Flexible electrodes coiled, providing good contact with heart wall.

• Functionality: Stimulates heart wall through conducting bands; secured in place by silicone rubber.

Page 21: Mechanical Matching

• Flexibility: Back support provides mechanical compliance between the electrode and heart wall.

• Bipolar Stimulation: Involves pairs of electrodes for effective stimulation.

Page 22: Demand-type Synchronous Pacemaker Components

• Components: Includes timing circuit, output circuit, electrodes, reset circuit, and amplifier.

Page 23: Functionality of Demand-Type Synchronous Pacemaker

• Feedback Loop: Resets after each stimulus, awaiting a natural heartbeat.

• Purpose: Amplifies natural beats to reset timer if they occur during the interval.

Page 24: Rate-Responsive Pacemaker

• Components: Controlled by a sensor, controller circuit, pulse generator, control algorithm, lead wire & electrode system.

Page 25: Control Mechanism

• Sensor Role: Converts physiological variable into an electric signal as input to the controller circuit.

• Responsiveness: Allows pacemaker to adjust pacing according to patient’s needs, remaining dormant when natural pacing is functional.

Page 26: Sensor Location

• Placement: Can be inside the pacemaker or at another body site, connected by lead wires.

Page 27: Physiological Variables for Rate-Responsive Pacemakers

• Variables:

  • Right Ventricle blood temperature (Thermistor)

  • ECG Signals (Stimulus-to-T wave interval, R-wave area)

  • Blood pH (Electrochemical pH Electrode)

  • Right ventricular pressure changes (Semiconductor strain gauge)

  • Venous blood oxygen saturation (Optical oximeter)

  • Intracardiac volume changes (Electric-impedance)

  • Respiratory parameters (Thoracic electric-impedance plethysmography)

  • Body vibration (Accelerometer)