CARDIAC MONITORING & RHYTHM RECOGNITION

How to monitor the ECG (1): Monitoring leads 3-lead system approximates to I, II, III3-lead system approximates to I, II, III Colour codedColour coded Remove hairRemove hair Apply over boneApply over bone Lead setting (II)Lead setting (II) GainGain

How to monitor the ECG (2): Defibrillator paddles Suitable for “quick-look”Suitable for “quick-look” Movement artefactMovement artefact Risk of spurious asystoleRisk of spurious asystole

How to monitor the ECG (3): Adhesive monitoring electrodes “Hands-free” monitoring and defibrillation“Hands-free” monitoring and defibrillation

Depolarisation initiated in SA nodeDepolarisation initiated in SA node Slow conduction through AV nodeSlow conduction through AV node Rapid conduction through Purkinje fibresRapid conduction through Purkinje fibres Basic electrocardiography (1)

Basic electrocardiography (2) P wave = atrial depolarisationP wave = atrial depolarisation QRS = ventricular depolarisation (< 0.12 s)QRS = ventricular depolarisation (< 0.12 s) T wave = ventricular repolarisationT wave = ventricular repolarisation

Cardiac arrest rhythms Ventricular fibrillationVentricular fibrillation Pulseless ventricular tachycardiaPulseless ventricular tachycardia AsystoleAsystole Pulseless Electrical Activity (PEA)Pulseless Electrical Activity (PEA)

Ventricular fibrillation Bizarre irregular waveformBizarre irregular waveform No recognisable QRS complexesNo recognisable QRS complexes Random frequency and amplitudeRandom frequency and amplitude Unco-ordinated electrical activityUnco-ordinated electrical activity Exclude artifactExclude artifact –movement –electrical interference

Pulseless ventricular tachycardia Broad regular complex rhythmBroad regular complex rhythm Rapid rate per minRapid rate per min Constant QRS morphologyConstant QRS morphology Atrial activity continues independentlyAtrial activity continues independently

Asystole Absent ventricular (QRS) activityAbsent ventricular (QRS) activity Atrial activity (P waves) may persistAtrial activity (P waves) may persist Rarely a straight line traceRarely a straight line trace

Pulseless Electrical Activity Clinical absence of cardiac output despite electrical activityClinical absence of cardiac output despite electrical activity ECG is normal or near normalECG is normal or near normal

DEFIBRILLATION

Mechanism of defibrillation DefinitionDefinition “The termination of fibrillation or absence of VF/VT at 5 seconds after shock delivery” Critical mass of myocardium depolarisedCritical mass of myocardium depolarised Natural pacemaker tissue resumes controlNatural pacemaker tissue resumes control

Defibrillation Success depends on delivery of current to the myocardium Current flow depends upon: Electrode position Electrode position Transthoracic impedance Transthoracic impedance Energy delivered Energy delivered Body size Body size

Transthoracic Impedance Dependent upon: Electrode sizeElectrode size Electrode/skin interfaceElectrode/skin interface Contact pressureContact pressure Phase of respirationPhase of respiration Sequential shocksSequential shocks

Defibrillators DesignDesign –Power source –Capacitor –Electrodes TypesTypes –Manual (monophasic or Biphasic waveform) –Automated

Defibrillator waveforms Damped Monophasic Truncated Biphasic

Biphasic Defibrillators Require less energy for defibrillationRequire less energy for defibrillation – smaller capacitors and batteries – lighter and more transportable Repeated < 200 J biphasic shocks have higher success rate for terminating VF/VT than escalating monophasic shocksRepeated < 200 J biphasic shocks have higher success rate for terminating VF/VT than escalating monophasic shocks

Automated external defibrillators Analyse cardiac rhythmAnalyse cardiac rhythm Prepare for shock deliveryPrepare for shock delivery Specificity for recognition of shockable rhythm close to 100%Specificity for recognition of shockable rhythm close to 100%

Automated external defibrillators Advantages: Less training requiredLess training required –no need for ECG interpretation Suitable for “first-responder” defibrillationSuitable for “first-responder” defibrillation Public access defibrillation (PAD) programsPublic access defibrillation (PAD) programs

SWITCH ON AED Some AEDs will automatically switch themselves on when the lid is opened ATTACH PADS TO CASUALTY’S BARE CHEST

ANALYSING RHYTHM DO NOT TOUCH VICTIM SHOCK INDICATED Stand clear Deliver shock STOP !!! DEFIBRILLATION Approach safely

SHOCK DELIVERED FOLLOW AED INSTRUCTIONS Deliver CPR 30:2 !! NO SHOCK ADVISED FOLLOW AED INSTRUCTIONS or IF VICTIM STARTS TO BREATHE NORMALLY PLACE IN RECOVERY POSITION

CPR IN CHILDREN Adult CPR techniques can be used on children Compressions 1/3 of the depth of the chest

AED IN CHILDREN Age > 8 years use adult AED Age 1-8 years use paediatric pads / settings if available (otherwise use adult mode) Age < 1 year use only if manufacturer instructions indicate it is safe

Manual Defibrillation Relies upon: Operator recognition of ECG rhythmOperator recognition of ECG rhythm Operator charging machine and delivering shockOperator charging machine and delivering shock Can be used for synchronised cardioversionCan be used for synchronised cardioversion

Defibrillator Safety Never hold both paddles in one handNever hold both paddles in one hand Charge only with paddles on casualty’s chestCharge only with paddles on casualty’s chest Avoid direct or indirect contactAvoid direct or indirect contact Wipe any water from the patient’s chestWipe any water from the patient’s chest Remove high-flow oxygen from zone of defibrillationRemove high-flow oxygen from zone of defibrillation

Shock Energy MONOPHASIC Initial and subsequent shocks energy 360 J*, repeat once if unsuccessfulInitial and subsequent shocks energy 360 J*, repeat once if unsuccessful Deliver shocks singlyDeliver shocks singlyBIPHASIC Initial shock JInitial shock J Subsequent shocks JSubsequent shocks J If defibrillation restores the patient’s circulation and VF/VT recurs, start again at 150J*If defibrillation restores the patient’s circulation and VF/VT recurs, start again at 150J*

Manual Defibrillation Diagnose VF/VT from ECG and signs of cardiac arrestDiagnose VF/VT from ECG and signs of cardiac arrest Select correct energy levelSelect correct energy level Charge paddles on patientCharge paddles on patient Shout “stand clear”Shout “stand clear” Visual check of areaVisual check of area Check monitorCheck monitor Deliver shockDeliver shock

CPR 30:2 Until defibrillator / monitor attached Assess Rhythm Shockable (VF/ Pulsless VT) Non-shockable (PEA / Asystole) 1 Shock J biphasic lub 360 J monophasic Immediately resume: CPR 30:2 For 2 min Call Resuscitation Team Immediately resume: CPR 30:2 For 2 min Open Airway Look for signs of life Unresponsive ?

Pulseless VT is treated with an unsynchronised shock using unsynchronised shock using the VF protocol the VF protocol

Summary Defibrillation is the only effective means of restoring cardiac output for the patient in VF or pulseless VTDefibrillation is the only effective means of restoring cardiac output for the patient in VF or pulseless VT Defibrillation must be performed promptly, efficiently and safelyDefibrillation must be performed promptly, efficiently and safely New technology has improved machine performance and simplified useNew technology has improved machine performance and simplified use