ECG & Holter Machine PDF

Medical Instrumentation Technology / Grade 3 Assistant Lecturer: Noor A. Waleed ECG and Holter Machine Introduction to ECG and Cardiac Electricity Electrocardiography (ECG) is a pivotal diagnostic tool in cardiology, providing a visual representation of the heart's el...

Medical Instrumentation Technology / Grade 3 Assistant Lecturer: Noor A. Waleed ECG and Holter Machine Introduction to ECG and Cardiac Electricity Electrocardiography (ECG) is a pivotal diagnostic tool in cardiology, providing a visual representation of the heart's electrical activity. Each heartbeat originates from an electrical impulse generated by specialized cells in the heart. The ECG machine captures these impulses, offering insights into heart rhythm, speed, and health. Principle of ECG Operation Working Principle: The ECG machine operates by detecting and amplifying the tiny electrical changes on the skin that occur during the cardiac cycle due to the depolarization and repolarization of the heart muscle. These changes are captured by electrodes attached to the skin at specific locations. Signal Processing: After capturing the electrical signals, the ECG machine amplifies them to a readable level without distorting the information. The amplified signal is converted from analog to digital form in modern systems. Advanced filtering techniques remove noise, and algorithms interpret the signals to produce a waveform displayed on the ECG monitor or printed on paper. Page 1 Medical Instrumentation Technology / Grade 3 Assistant Lecturer: Noor A. Waleed Components of an ECG Machine Main Parts: Input Module (Electrodes): Essential for initial signal capture, electrodes are typically coated with a conductive gel and attached to specific body parts to detect electrical activity. Amplifier: Enhances the electrical signals to levels suitable for detailed examination and analysis. Filter: Integrated to refine the signal quality by eliminating unwanted noise and interference, thus ensuring that the signals are as clear and accurate as possible. Filters can include high-pass, low-pass, and notch filters to target specific types of noise. Processor: A critical component that converts analog signals to digital, analyzes the waveform, and ensures accurate representation of the heart's electrical activity. Display and Output: Processes signals are displayed in real-time on monitors or printed out for diagnostic purposes. Data can also be stored digitally for record- keeping or further analysis. Page 2 Medical Instrumentation Technology / Grade 3 Assistant Lecturer: Noor A. Waleed Pre-Amplifier Circuit in ECG The pre-amplifier circuit in ECG devices is an essential part of the system, as it amplifies the weak electrical signals from the body before processing and analyzing them. These signals, recorded from the skin's surface, are very small (usually in the microvolt range), so they need to be amplified before being sent for accurate analysis. Components of the Pre-Amplifier Circuit in ECG: Inputs: The signal comes from the body through electrodes (such as Lead I, Lead II, and Lead III) and enters the pre-amplifier circuit. Operational Amplifier (Op-Amp): The operational amplifier is mainly used in the pre- amplifier circuit because it provides high amplification and can handle very weak signals. Filter: Filters are used to remove electrical interference and noise (like 50/60 Hz signals from the power supply). Feedback Network: This is used to adjust the gain of the circuit. Basic Equations in the Pre-Amplifier Circuit: Gain Equation: The gain in the pre-amplifier circuit is determined by the feedback resistor. The basic equation for the gain of the operational amplifier is: Gain=1+Rin/Rf Where: Rf: Feedback resistor. Rin: Input resistor. Output Voltage Equation: The output of the pre-amplifier depends on the gain and the input signal: Vout=Gain×Vin Where Vin is the signal coming from the electrodes. Low-pass Filter: To reduce noise, a low-pass filter can be used to remove high- frequency unwanted signals. The cut-off frequency is calculated as: Page 3 Medical Instrumentation Technology / Grade 3 Assistant Lecturer: Noor A. Waleed fc=1/2πRC Where: R: Resistor. C: Capacitor. Isolated Circuit in ECG An isolated circuit in an ECG device is crucial for protecting both the patient and the device from electrical hazards. It ensures that the patient is electrically isolated from the ECG machine, preventing any dangerous currents from flowing through the patient’s body. Isolation circuits are typically implemented using components like transformers or opto- couplers, providing a barrier between the input signals and the rest of the electronic system. Purpose of an Isolated Circuit: 1. Patient Safety: The primary goal is to protect the patient from electrical shocks, especially since the ECG device is directly connected to the body. 2. Signal Integrity: Isolation helps prevent interference from other electrical devices or power line noise, improving the quality of the ECG signal. 3. Device Protection: It shields the sensitive components of the ECG machine from high-voltage surges or faults. Basic Equations: Isolation Barrier Impedance: The isolation barrier is designed to have a very high impedance, effectively blocking any significant current from flowing between the ECG machine and the patient: Z= V/I Where: o Z: Isolation impedance. o V: Voltage across the isolation barrier. o I: Current through the isolation barrier. Signal Transfer Efficiency: The signal must be transferred with minimal loss across the isolation barrier, and this is typically defined as the ratio of output signal to input signal: Page 4 Medical Instrumentation Technology / Grade 3 Assistant Lecturer: Noor A. Waleed Efficiency= Vout / Vin Band-Pass Filter in ECG A band-pass filter in an ECG system is a crucial component that allows only a specific range of frequencies to pass through, while blocking frequencies outside that range. This is essential for removing unwanted noise and focusing on the frequency range where the most important ECG signal components are located. Components of a Band-Pass Filter: 1. Low-Pass Filter: This filter allows frequencies below a certain threshold to pass while blocking higher frequencies (e.g., above 150 Hz). It helps to remove high-frequency noise, such as muscle interference or external electrical noise. 2. High-Pass Filter: This filter allows frequencies above a certain threshold to pass while blocking lower frequencies (e.g., below 0.05 Hz). It helps eliminate low- frequency noise such as baseline drift caused by patient movement or respiration. Band-Reject Filter in ECG A band-reject filter (also known as a notch filter) in ECG systems is used to remove a specific range of unwanted frequencies while allowing other frequencies to pass. This is particularly useful in ECG systems to eliminate power line interference at 50 Hz or 60 Hz, which is a common source of noise. Purpose of a Band-Reject Filter in ECG: 1. Removing Power Line Interference: One of the most important uses of a band-reject filter in ECG is to eliminate the 50 Hz (or 60 Hz in some regions) interference caused by power lines. This interference can distort the ECG signal, making it difficult to interpret accurately. 2. Preserving ECG Signal Quality: By removing specific unwanted frequencies, the band-reject filter ensures that the ECG signal remains clean without affecting other important frequencies related to heart activity. 3. Reducing Noise without Impacting Signal: Unlike a band-pass filter, which removes all frequencies outside a certain range, a band-reject filter removes only a narrow band, leaving the rest of the signal intact. Page 5 Medical Instrumentation Technology / Grade 3 Assistant Lecturer: Noor A. Waleed Electrodes and Lead Placement Electrode Names and Types: Standard Limb Leads (I, II, III): Provide a frontal plane view and are crucial for basic cardiac diagnostics. Augmented Limb Leads (aVR, aVL, aVF): Offer additional details about the heart's electrical axis. Precordial Leads (V1 to V6): Critical for assessing the heart’s horizontal plane, particularly useful in detecting conditions affecting the ventricles. Electrode Placement for a 12-Lead ECG: 1. Limb Electrodes: o RA (Right Arm) o LA (Left Arm) o RL (Right Leg) o LL (Left Leg) These four electrodes are placed on the limbs (not actually on the arms and legs, but close to the wrists and ankles) and are used to record the limb leads. 2. Chest (Precordial) Electrodes: o V1, V2, V3, V4, V5, V6 These six electrodes are placed in specific positions across the chest: o V1: 4th intercostal space (between ribs), right of the sternum. o V2: 4th intercostal space, left of the sternum. o V3: Between V2 and V4. o V4: 5th intercostal space at the midclavicular line. o V5: Level with V4 at the left anterior axillary line. o V6: Level with V5 at the left midaxillary line. Page 6 Medical Instrumentation Technology / Grade 3 Assistant Lecturer: Noor A. Waleed Calculating Heart Rate from an ECG: The heart rate can be calculated from the ECG strip using several methods, with the most common being: Counting the Number of QRS Complexes: o Measure the time interval over which the ECG was recorded (usually this is a standard 10-second strip). o Count the number of QRS complexes (the spikes representing ventricular depolarization) present in this interval. o Multiply this number by 6 to get the heart rate per minute (since 10 seconds x 6 = 1 minute). Page 7 Medical Instrumentation Technology / Grade 3 Assistant Lecturer: Noor A. Waleed Holter Monitoring Principle Holter monitoring is used to record the electrical activity of the heart over extended periods, typically 24 to 48 hours. This device is crucial for observing the heart's electrical patterns during daily activities and rest. Application Holter monitoring is particularly useful for detecting and diagnosing arrhythmias that may not appear during short-term ECG tests. It tracks the electrical changes in the heart that occur irregularly and might be missed during a routine ECG. Procedure Electrodes are attached to the patient’s body and connected to a small, portable device that the patient carries. The patient wears this device throughout the recording period, allowing for continuous documentation of the heart's electrical activity without significantly interfering with their daily routine. To download this Lecture scan the QR Code : Page 8