Medical Devices Lectures Notes 3: Defibrillators & ICD PDF

# Medical Devices ## Lectures Notes 3: Defibrillators & ICD ### Prof. Awad Al-Zaben - Biomedical Systems and Medical Informatics Department - HIJJAWI Faculty for Engineering Technology - Yarmouk University - First Term 2023-2024 # Defibrillators - An image of a defibrillator and an x-ray of a per...

# Medical Devices ## Lectures Notes 3: Defibrillators & ICD ### Prof. Awad Al-Zaben - Biomedical Systems and Medical Informatics Department - HIJJAWI Faculty for Engineering Technology - Yarmouk University - First Term 2023-2024 # Defibrillators - An image of a defibrillator and an x-ray of a person with a device embedded in their chest. # Introduction ## Ventricular Arrhythmias - Arrhythmias are caused by variable impulse generation or conduction interruption. - Arrhythmias result in impairment of the coordination of the myocardial fibers, suspended coordination or even plunged into chaos (fibrillation). ## Life-threatening Arrhythmias - **Ventricular fibrillation:** is uncoordinated myocardial fibrillation with no ejection from the ventricles, being characterized on an electrocardiogram (ECG) by irregular and disorganized depolarizations with high frequency - **Pulseless ventricular tachycardia:** is characterized by a regular and rapid sequence of broad QRS complexes, and as with ventricular fibrillation, there is no ejection. # Arrhythmias Examples - An image of several ECG waveforms with labels as follows: - Sinus arrhythmia - Atrioventricular block - Sinus Tachycardia - Ventricular fibrillation - Sinus Bradycardia - Ventricular tachycardia - Atrial fibrillation - Atrial flutter # Ventricular Tachycardia - An image of an ECG with numbered readings from V1 to V6 # Defibrillation - Defibrillation is the definitive treatment for the life-threatening cardiac arrhythmias, ventricular fibrillation, and pulseless ventricular tachycardia by delivering electrical energy to the heart intended to bring simultaneous depolarization of all the myocardial fiber. - Defibrillators are electrotherapeutic high-voltage devices which are used within the course of resuscitation and to terminate tachycardic ventricular and supraventricular arrhythmias. - The device main parts: the charging circuit for the capacitor (duration of charging,is on average 10 – 8 s, and a discharge circuit which delivers the current pulse at different, preselectable energy levels (e.g., 2 – 360 J). - The DC pulse stimulation ranges between 3 and 8 ms at current of 10 - 27 A(internally) and 22 - 60 A (externally). - Automatic safety discharge should occur when no shock is triggered (after ≈ 10 s), and when a new energy level is preselected, as well as in the event of technical malfunction. # Energy Waveform - It is time-based sequence of energy output, with optimal value that produce least mycardial damage. Energy Waveform indicates two important information: - The shape of the wave dictates firstly how much energy is supplied to the patient. - Over what period this energy is administered. # Waveform Types - **Monophasic Waveform:** current is delivered in one polarity and can be categorized by the rate at which the current pulse decreases to zero. If the monophasic waveform falls to zero gradually, the term damped sinusoidal is used. If the waveform falls instantaneously, the term truncated exponential is used. - **Biphasic waveform:** The delivered current flows in a positive direction for a specified time and then reverses and flows in a negative direction for the remaining duration of the electrical discharge. - **Triphasic waveform:** There are no human studies to support the use of multiphasic waveforms over biphasic. - **3 Images:** - A monophasic waveform with voltage on the y-axis and milliseconds on the x-axis. The graph shows a steep rise in voltage and quick decline to zero. - A biphasic waveform with voltage on the y-axis and milliseconds on the x-axis. The graph shows a steep rise in voltage, a decline, and a return to negative voltage. - A triphasic waveform with voltage on the y-axis and milliseconds on the x-axis. The graph shows a steep rise in voltage, a decline, and two peaks with a negative voltage. # Current Flow - Two images of a person with arrows representing electrical current flow: - Biphasic Waveform - Monophasic waveform # Transthoracic Impedance (TTI) - It refers to the impedance between the two paddles. It also refers to the dissipation of energy in the lungs, thoracic cage and the other anatomic structures of the chest. In an animal study, only 4% of the energy supplied reached the heart. - The average adult human TTI is around 70 – 80 Ω and is determined by multiple factors including energy level, electrode size, interelectrode distance, interface skin-electrode, electrode pressure, phase of ventilation, myocardial tissue and blood conductive properties. - When TTI is too high, a low-energy shock will not generate sufficient current to achieve defibrillation. To reduce TTI, the defibrillator operator should use conductive materials. This is accomplished with the use of gel pads or electrode paste with paddles or through the use of self-adhesive pads. # Defibrillators Types - **Transthoracic Devices:** - Manual Defibrillators - Semiautomatic Defibrillators (AED) - Automatic Defibrillators (AED) - Semiautomatic defibrillator: the user is shown a defibrillation recommendation and the administration of the pulse is triggered by the user, whereas this is done automatically with a fully automated defibrillator. - **Intracorporeal Devices:** implantable cardioverter defibrillator (ICD) - Single-chamber system - Dual-chamber system - Triple-chamber system - Atrial defibrillator # Technical Safety Aspects ## Use - Avoid direct contact with the electrodes (safe distance). - There should be no moisture on the patient's skin (electrical bridge), and the patient should also be positioned such that he is electrically isolated. - All additional devices which are connected to the patient must be defibrillation proof; otherwise, they must be disconnected from the patient during cardioversion/defibrillation. - Caution should be exercised with patients with energized implants ## Device - Defibrillators belong to class IIb. - Defibrillators must only be used in an explosion proof atmosphere . - Maximum energy 360 J. - Trigger buttons only on both paddles (connected in series). - Protective circuits, which ensure a reduced power setting when the defibrillator is switched off and ensure energy recovery no later than 1 min after defibrillator charging. - Defib. should always be connected to mains electricity at their device base locations so that they are operational and ready for use. - Automatic safety discharge should occur when no shock is triggered (after ≈ 10 s), and when a new energy level is preselected, as well as in the event of technical malfunction.