Presentation on theme: "Introduction to 12 Lead ECGs"— Presentation transcript:
1 Introduction to 12 Lead ECGs Terry White, RN, EMT-P
2 Topics Why 12 Lead ECGs? Critical Concepts in ACS Monitoring vs Diagnostic ECGsAcquisition & Transmission
3 Why 12 Lead ECGs? Demonstrated Advantages Rapid Identification of Infarction/Injurydiagnosis made sooner in many casesDecreased Time to Reperfusion Treatmentspeeds preparation of & time to reperfusion therapiesIncreased Index of SuspicionModification to Therapies
4 Why 12 Lead ECGs? Perceived Disadvantages Increased time spent on scenedemonstrated at 0-4 min increaseCostequipment & trainingNo clinical advantage to patient & “our transport times are short”demonstrated decrease in time to treatmentcompare to early notification for trauma patientsNot helpful in “our system”Possibly true!
5 Why 12 Lead ECGs?“The US National Heart Attack Alert Program recommends that EMS systems provide out-of-hospital 12-lead ECGs to facilitate early identification of AMI and that all advanced lifesaving vehicles be able to transmit a 12-lead ECG to the hospital”American Heart Association in collaboration with International Liaison Committee on Resuscitation. Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care: International Consensus on Science, Part 7: The Era of Reperfusion. Circulation ; 102 (suppl I): I-175.
6 Critical Concepts in ACS Ischemialack of oxygenationST segment depression or T wave inversionInjuryprolonged ischemiaST segment elevationInfarctprolonged injury results in death of tissuemay or may not show Q waveThis information will aid in understanding the ECG subsets in the next section.Define ischemia, injury and infarct.Note that the definitions are correlated with specific ECG criteria.Note that “injury” is also ischemia and does not imply any permanent damage or death to tissue. The term injury simply means ischemia identified by ST segment elevation.
7 Critical Concepts in ACS ST elevation - the key to the acute reperfusion therapy subsetYou can’t see ST elevation without a 12-lead ECGPerform on every patient suspected of ACSObtain earlyRepeat frequentlyWhile it is not always possible to identify which of the ACS a patient is experiencing, it is possible to determine if a patient can benefit from acute reperfusion therapy.The indication for acute reperfusion therapy is ST segment on the 12-lead ECG. For EMS to identify this subset of patients, a diagnostic 12-lead must be obtained .“The 12-lead ECG stands at the center of the decision making pathway in the management of patients with ischemic chest pain, and delays in obtaining the 12-lead ECG must be eliminated.”AHA, ACLS Textbook, 1997, 9-13
8 Critical Concepts in ACS Will Infarct Occur? CollateralCirculationThrombusFormationPlaqueRuptureTissueDeath?Whether tissue necrosis occurs as in AMI or does not occur resulting in unstable angina is determined by the interplay of several factors.This underscores why it is usually impossible to determine which syndrome is present and why we should instead concentrate on identifying the the presence of any ACS.The issue of suspecting ACS will be addressed after a brief explanation of the terms ischemia, injury and infarction.MyocardialOxygen DemandCoronaryVasoconstriction
9 Critical Concepts in ACS Chest pain or anginal equivalent suspicious of ischemiaImmediate assessment and initial general treatmentAssess initial ECGST elevation or new BBBST depression or T inversionNondiagnostic - no ST-T deviationNote treatment continuation for ST elevation or new BBB (a.k.a. acute injury pattern) subset.Prepare and evaluate for reperfusion therapyOur Focus is Here!Fibrinolytics or primary PTCA
10 Critical Concepts in ACS Acute Reperfusion TherapiesFibrinolyticsRetaplase (rPA)Actiplase (tPA)Streptokinase (rarely used today)Percutaneous Transluminal Coronary Angioplasty (PTCA)Balloon angioplastyStent placementAtherectomyThrombolytics are pharmacological agents administered IV that dissolve a coronary thrombus.PTCA is an intervention that utilizes a balloon or other device, inserted through a large artery, to create a larger lumen in the offending coronary artery. Atherectomy procedures remove the occlusion by laser or cutting mechanisims.
11 Critical Concepts in ACS Pain is InjuryPain-Free is the GoalTime is MuscleDoor to Reperfusion Therapy Time is the issue
12 Monitoring vs Diagnostic ECGs Extra wires3 wires vs 10 wiresAre there other differences?
13 Monitoring vs Diagnostic ECGs Monitoring Quality ECGDesigned to provide information needed to determine rate and underlying rhythmDesigned to “filter out” artifactReduces the amount and degree of electrical activity seen by the ECG monitor
14 Monitoring vs Diagnostic ECGs Monitor QualityThe typical “3-lead” ECG was never designed to capture QRS-ST-T waveforms with complete accuracy.The 3-lead was designed to provide enough information for the user to determine cardiac rate and rhythm.Because artifact makes interpretation difficult, the 3-lead is set to “filter out” artifact by reducing the spectrum of cardiac electrical activity that it “sees”.This strategy significantly reduces artifact and still renders waveforms of sufficient quality for rate and rhythm determination.However, in doing so, the QRS-ST-T may not always be accurately represented.Therefore, do not use monitor quality for ST analysis.
15 Monitoring vs Diagnostic ECGs Diagnostic Quality ECGDesigned to accurately reproduce QRS, ST and T waveformsDesigned to look more broadly at the cardiac electrical activityUnfortunately, may result in greater artifact being visible
16 Monitoring vs Diagnostic ECGs Diagnostic QualityThe 12-lead is designed to accurately reproduce the QRS-ST-T waveforms.In order to do so the 12-lead must “look” at a broader spectrum of cardiac electrical activity. This spectrum is referred to as “frequency response”This broader spectrum is referred to as “diagnostic quality”.A diagnostic quality ECG is necessary for accurate ST segment analysis.Unfortunately, when in diagnostic quality, all 12-lead ECGs are more susceptible to more artifact than are 3-lead ECGs.
17 Monitoring vs Diagnostic ECGs Frequency ResponseTerm used to describe the breadth of the electrical spectrum viewed by the ECG monitorDiagnostic quality is usually 0.05 Hz to 150 HzMonitor quality is usually 0.5 Hz to HzUsually printed on the ECG recording strip
18 Monitoring vs Diagnostic ECGs The frequency response is printed on the ECG paper.The frequency response for diagnostic quality is 0.05Hz - 150Hz. There may be some slight variation among manufacturers and ECG models.The low end for monitor quality is often 0.5 Hz (not 0.05Hz), while the high end often is in the range of 20-50Hz.
19 Acquisition & Transmission ECG quality begins with skin preparation and electrodesHair removalSkin preparationAge & Quality of Electrodes & CablesElectrode PlacementBecause of the increased “window” to electrical signals, additional steps must be taken to reduce the amount of artifact produced.Removing excess hair and prepping the skin allows the electrode gel to better penetrate the skin, thus receiving a stronger signal with less artifact.First we will discuss the techniques themselves, later in the module we will look at strategies to accomplish these additional tasks quickly.
20 Acquisition & Transmission Hair RemovalClipper over razorLessens risk of cutsQuickerDisposable blade clippers availableMost EMS systems use razorsExcess hair presents two problems:• First, hair may prevent the electrode from adhering well.• Second, hair may inhibit gel contact and skin penetration.Some thrombolytic manufacturers recommend that clippers be used to remove chest hair. The intent is to minimize the potential for bleed sites in a patient who may receive a thrombolytic.
21 Acquisition & Transmission Read the clipper manufacture’s recommendations. This is one model designed for medical applications and may be used near oxygen. In addition the head is disposable, avoiding de-contamination issues.
22 Acquisition & Transmission Skin PreparationHelps obtain a strong signalWhen measured from skin, heart’s electrical signal about voltsSkin oils reduce adhesion of electrode and hinder penetration of electrode gelDead, dried skin cells do not conduct wellWhen measured from the patient’s skin, the heart’s electrical signal is extremely small, about to volts.That’s as small as one-ten thousandth of a volt. Compare this with energy from a nine volt battery.Good skin prep will make the ECG signal as strong as possible, and make the artifact signals as small as possible.
23 Acquisition & Transmission Rubbing skin with a gauzepad can reduce skin oiland remove some of dead skin cellsSimply rubbing the skin with a gauze pad can have a noticeable effect on ECG clarity by:• Reducing skin oil• Removing part of the stratum corneum
24 Acquisition & Transmission Other causes of artifactPatient movementCable movementVehicle movementElectromagnetic Interference (EMI)Once the skin has been prepped and the electrodes applied, there are still other sources of artifact to consider.
25 Acquisition & Transmission Patient MovementMake patient as comfortable as possibleSupine preferredLook for subtle movementtoe tapping, shiveringLook for muscle tensionhand grasping rail, head raised to “watch”It is important to place the patient in a position of comfort. The reduction in muscle tension will help to prevent artifact.When possible, the patient should be in the supine position for a 12-lead ECG.Sometimes this is not feasible, practical or desirable.If ECG is not recording in supine position, simply note this on ECG.
26 Acquisition & Transmission Cable MovementEnough “slack” in cables to avoid tugging on the electrodesMany cables have clip that can attach to patient’s clothes or bed sheetIt is important to place the patient in a position of comfort. The reduction in muscle tension will help to prevent artifact.When possible, the patient should be in the supine position for a 12-lead ECG.Sometimes this is not feasible, practical or desirable.If ECG is not recording in supine position, simply note this on ECG.
27 Acquisition & Transmission Vehicle MovementAcquisition in a moving vehicle is NOT recommendedMay or may not be successfulTipsPull ambulance over for seconds during acquisitionAcquire ECG while stopped at traffic lightIt is important to place the patient in a position of comfort. The reduction in muscle tension will help to prevent artifact.When possible, the patient should be in the supine position for a 12-lead ECG.Sometimes this is not feasible, practical or desirable.If ECG is not recording in supine position, simply note this on ECG.
28 Acquisition & Transmission Electromagnetic Interference (EMI)Can interfere with electronic equipment60 cycle interference is a type of EMILook for nearby cell phones, radios or electrical devicesNo contact between cables & power cordsTurn off or move away from AC devicesUse shielded cables; inspect for cracksIt is important to place the patient in a position of comfort. The reduction in muscle tension will help to prevent artifact.When possible, the patient should be in the supine position for a 12-lead ECG.Sometimes this is not feasible, practical or desirable.If ECG is not recording in supine position, simply note this on ECG.
29 Acquisition & Transmission Things to look forLittle or no artifactSteady baseline
30 Acquisition & Transmission Note how the baseline straightened out by simply repositioning the patient cables and clipping them onto the sheet.What technique(s) would you consider in order to resolve the muscle artifact?
31 Acquisition & Transmission ECG Accuracy depends uponLead placementFrequency responseCalibrationPaper speedAll of the techniques discussed to this point have related to ECG clarity. We now need to look at what is necessary to ensure ECG accuracy.
32 Traditional Placement Limb Lead PlacementTraditional PlacementAvoid placing on the trunk!!!Limb leads should be placed on the limbs. The traditional placement is near the ankles and wrists.Acceptable Placement
33 Chest Lead Placement V1: fourth intercostal space to right of sternum V2: fourth intercostal space to left of sternumV3: directly between leads V2 and V4V4: fifth intercostal space at left midclavicular lineV5: level with V4 at left anterior axillary lineV6: level with V5 at left midaxillary lineV1 fourth intercostal space to the right of the sternumV2 fourth intercostal space to the left of the sternumV3 directly between leads V2 and V4V4 fifth intercostal space at left midclavicular lineV5 level with lead V4 at left anterior axillary lineV6 level with lead V5 at left midaxillary line
34 Chest Lead PlacementHere is what lead placement looks like on a patient.
35 ECG Accuracy Look for: Negative aVR if aVR upright, look for reversed leadsOne complete cardiac cycle in each leadDiagnostic frequency responseProper calibrationAppropriate speedOnce a clear ECG has been obtained (free of excess artifact and has a steady baseline), it may then quickly be examined to confirm accuracy.Listed here are five items that relate the the accuracy of the ECG.
36 ECG Accuracy Frequency Response Display screen is non-diagnostic Use the printed ECG for ST segment analysisIt is important to note that the display screen in 12-lead monitors is not in diagnostic quality.Usually a 12-lead must be printed out for accurate ST analysis.Check the 12-lead printout and confirm the correct frequency response.
37 ECG Accuracy Calibration Voltage measured vertically Each 1 mm box = 0.1 mV1 mV = 10 mmcalibration standardConfirm calibrationcalibration impulse should be 10 mm (2 big boxes tall)stated calibration should be “x 1.0”It is important to note that the display screen in 12-lead monitors is not in diagnostic quality.Usually a 12-lead must be printed out for accurate ST analysis.Check the 12-lead printout and confirm the correct frequency response.
39 ECG Accuracy Paper Speed Standard is 25 mm/sec Faster paper speed means the rhythm will appear slower and the QRS widerSlower paper speed means the rhythm will appear faster and the QRS narrowerIt is important to note that the display screen in 12-lead monitors is not in diagnostic quality.Usually a 12-lead must be printed out for accurate ST analysis.Check the 12-lead printout and confirm the correct frequency response.
41 When to AcquireNote times and differences in these two ECGs for the same patientThese tracings show how much the ECG can change in a short time.Note the times on these ECGs.
42 When to Acquire Assessment Treatment Vital Signs Oxygen Saturation IV Access12-Lead ECGBrief HistoryTreatmentOxygenAspirinNitroglycerinMorphineThis excerpt from an American Heart Association algorithm shows the initial 12-lead acquisition along with the vital signs. Note treatment is concomitant and is not inordinately delayed.In later modules we will further develop the concepts relating to the dynamic nature of AMI and the 12-lead ECG.At that time it will be very apparent why early ECGs are critical.Accepting that fact necessitates a strategy for QUICK 12-lead acquisitionModified from “The Ischemic Chest Pain Algorithm”, ACLS Textbook, Chapter 9, American Heart Association, 1997.
43 Exposing the Chest Immediately upon suspecting ACS... Remove all clothing above the waistOr, open shirt/blouseReplace with gown (if possible)Allows for complete examMinimizes wire entanglementEnhances quick defib if VF occursExposing the chest before obtaining the 12-lead is probably the single most important factor to reduce time and effort.If a gown is not available a sheet may be used, however, the gown is preferable.
44 Transmission Transmit as soon as possible Coordinate with ED Can use patient’s land-lineMany EMS systems use cell phone enrouteCoordinate with EDCorrelate ECG with a specific patientEarly notification of AMI is key!!!Transmission protocols and strategies very tremendously from system to system. Some systems may not transmit the ECG at all.Receiving facilities may receive two 12-leads in a short period of time. Therefore, some identification mechanism must be in place to correlate the transmitted ECG to a particular EMS unit.