Defibrillation & Cardioversion by DJ

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Defibrillation and Cardioversion

Dr. Dharmendra Joshi (DJ)

Defibrillation & Cardioversion

HistoryCase & CensusDefinitionTypesPrinciplesIndicationsContraindicationsAnaesthesiaEquipmentsPositioningTechniqueSafetyComplicationsTroubleshooting

Topics

History1849: Ludwigg and Hoffa VF induced by electrical stimuli

1849: Written history of fibrillation and defibrillation goes back to the pioneering work of Carl Ludwigs laboratory. In 1849, Ludwigs student M. Hoffa was the first to witness and, most importantly, to document the onset of ventricular fibrillation, which he induced by electrical stimulus. This picture from their paper shows rapid contractions produced by electrical stimulation, which resulted in cardiac arrest.

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History1899: Prevost and Batelli - while a weak stimulus can produce fibrillation, a stimulus of higher strength applied to the heart could arrest ventricular fibrillation and restore normal sinus rhythm.

1899: Further experiments with faradization of the heart were conducted by two physiologists from University of Geneva, Switzerland, J.-L. Prevost and F. Batelli. They discovered that, while a weak stimulus can produce fibrillation, a stimulus of higher strength applied to the heart could arrest ventricular fibrillation and restore normal sinus rhythm. This discovery was made in 1899. Unfortunately, unlike discovery of contemporary electrocardiogram, defibrillation did not enjoy similar attention and success. They did this using dogs! 4

History1947: First defibrillation on humans.

Work of Carl J. Wiggers in the Department of Physiology of Western Reserve University was well known to the thoracic surgeon Claude S. Beck from the University Hospitals in Cleveland, which are adjacent to the Western Reserve University. In 1947, Dr. Beck successfully applied defibrillation therapy and saved the first human life by this method (C.S. Beck, W.H. Pritchard, H.S. Feil, Ventricular fibrillation of long duration abolished by electric shock. Jour. Amer. Med. Assoc. 135: 985, 1947). His success triggered the immediate acceptance of this method by the clinical community and started a wide front of basic and clinical research of fibrillation and defibrillation. 5

History1966: Belfast Ambulance transported physicians performed first pre-hospital defibrillation.1969: First pre-hospital defibrillation by non physicians.1970s: Diack, Wellborn and Rullman developed first AEDs.

Chain of Survival

Early Recognition and Assessment Early Access Early CPR Early Defibrillation Early Advanced Cardiac Life Support

Chain of Survival

Sudden cardiac arrest survival rate: Pre-Hospital: 10% In-Hopsital: 10%

No record found about patient who was treated by defibrillation or cardioversion in KMCTH, Duwakot in last one month!!!Case Scenario & Census

Defibrillation is a non-synchronized delivery of energy during any phase of the cardiac cycle.Cardioversion is the delivery of energy that is synchronized to the large R waves or QRS complex.Definition

Electrical cardioversion has now become a routine procedure and is used electively or emergently to terminate cardiac arrhythmias. The delivered shock in both defibrillation and cardioversion causes electric current to go from the negative to the positive electrode of the defibrillator, passing the heart on its way. It causes all the heart cells to contract simultaneously, thereby interrupting and terminating the abnormal electrical rhythm without damaging the heart, and thus allowing the sinus node to resume normal pacemaker activity.10

11TYPES OF DEFIBRILLATORSInternalExternal

Internal defibrillatorElectrodes placed directly to the heartEg.-PacemakerExternal defibrillator Electrodes placed directly on the heart Eg.-AED

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DEFIBRILLATOR ELECTRODESTypes of Defibrillator electrodes:-

Spoon shaped electrode

Applied directly to the heart.

Paddle type electrode

Applied against the chest wall.

Pad type electrode

Applied directly on chest wall.

DEFIBRILLATOR ELECTRODES

Fig.- Pad electrodeDEFIBRILLATOR ELECTRODES

PRINCIPLE OF DEFIBRILLATIONEnergy storage capacitor is charged at relatively slow rate from AC line.

Energy stored in capacitor is then delivered at a relatively rapid rate to chest of the patient.

Simple arrangement involve the discharge of capacitor energy through the patients own resistance.

PRINCIPLE OF DEFIBRILLATION

PRINCIPLE OF DEFIBRILLATION

The discharge resistance which the patient represents as purely ohmic resistance of 50 to 100 approximately for a typical electrode size of 80 cm2.

This particular waveform Fig 13.9(b) is called Lown waveform. The pulse width of this waveform is generally 10 ms.

External Defibrillator

power supply

energy storage

patient

ECG monitor

timing circuitry

gate

charge

dischargestandbyswitch is under operator control

applies shock about 20 ms after QRS complex, avoids T-wave

energy (joules)charge (coulombs)current (amps)pulse duration

defibrillation occursno defibrillation

Defibrillator Strength Duration Curve

Minimum defibrillation energy occurs for pulse durations of 3 - 10 ms (for most pulse shapes).

Pulse amplitude in tens of amperes (few thousand volts).

Strength Duration Curve

intrinsic characteristics of patient patients disease duration of arrhythmia patients age type of arrhythmia (more energy required for v. fib.)

Operator selects energy delivered: 50-360 joules, depends on:Strength Duration Curve

22THE POWER OF DEFIBRILLATIONHigher voltages are required for external defibrillation than for internal defibrillation.A corrective shock of 750-800 volts is applied within a tenth of a second.That is the same voltage as 500-533 no. of AA batteries!

Normal Cardiac Conduction

ECG tracing

Electrical pattern

Explain the cardiac conduction pathways with the electrical impulse originating in the SA node (right atrium) which travels to the AV node (division of the right and left ventricles), down along the right and left bundle branches to the Purkinje fibers.Intrinsic heart rates at the SA node are 80 bpm, the AV node is 60 bpm, and the ventricular rate (Purkinje fibers) is 40 bpm.

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Cardiac Arrest

Occlusion of the coronary artery leads to ischemiaIschemia leads to infarct which causes interruption of normal cardiac conductionInfarct = VF/VT

Shockable RhythmsVentricular FibrillationVentricular Tachycardia

Indications for synchronized electrical cardioversion:Supraventricular tachycardiaAtrial fibrillationAtrial flutterVentricular tachycardiaReentrant tachycardia with narrow or wide QRS complex.Indications

Any patient with reentrant tachycardia with narrow or wide QRS complex (ventricular rate >150) who is unstable (eg, chest pain,pulmonary edema, hypotension)

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1. Pulse less ventricular tachycardia (VT)2. Ventricular fibrillation(VF)Indications: Defibrillation

3. Cardiac arrest due to or resulting in VF

Ventricular fibrillation is a serious cardiac emergency resulting from asynchronous contraction of the heart muscles.Due to ventricular fibrillation, there is an irregular or rapid heart rhythm.Ventricular fibrillation can be converted into a more efficient rhythm by applying a high energy shock to the heart.This sudden surge across the heart causes all muscle fibres to contract simultaneously. Possibly , the fibres may then respond to normal physiological pacemaking pulses.The instrument for administering the shock is called a DEFIBRILLATOR.

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DysrhythmiasMultifocal atrial tachycardiaContraindications

Dysrhythmias due to enhanced automaticity such as in digitalis toxicity and catecholamine-induced arrhythmia.For dysrhythmias due to enhanced automaticity such as in digitalis toxicity and catecholamine-induced arrhythmia, a homogeneous depolarization state already exists. Therefore, cardioversion is not only ineffective but is also associated with a higher incidence of postshock ventricular tachycardia/ventricular fibrillation (VT/VF).28

Cardioversion:Almost always under induction or sedation. Exceptions: hemodynamic instability or if cardiovascular collapse is imminent. Defibrillation is an emergent maneuver and performed promptly.

Anesthesia

Cardioversion is almost always performed under induction or sedation (short-acting agent such as midazolam). The only exceptions are if the patient is hemodynamically unstable or if cardiovascular collapse is imminent. Defibrillation is an emergent maneuver and when necessary should be promptly performed in conjunction with or prior to administration of induction or sedative agents.29

Defibrillators (automated external defibrillators [AEDs], semi-automated AED, standard defibrillators with monitors)Paddle or adhesive patchConductive gel or pasteECG monitor with recorderOxygen equipmentIntubation kitEmergency pacing equipmentEquipments

The use of hand-held paddle electrodes may be more effective than self-adhesive patch electrodes. The success rates are slightly higher for patients assigned to paddled electrodes because these hand-held electrodes improve electrode-to-skin contact and reduce the transthoracic impedance.30

Antero-lateralAntero-posteriorPositioning

Fig. anterior apex scheme of electrode placement (AED)Anterior electrode padApex electrode pad

Paddle placement on the chest wall has 2 conventional positions: anterolatera