2 OBJECTIVESDiscuss the changes in T wave and ST segment morphology with an MIList the criteria for identification of right or left bundle branch blocks.List the anatomically congruent leads associated with an inferior, lateral and anterior wall MIDescribe morphology of Q wave presence
3 Myocyte bundles are what make cardiac cells different from other cells Myofibrils are individual units that slide over one another causing contractionThey pull the sarcomere together causing contractionCa+ is the primary stimulant for the effect of sarcomeresTroponin is inside the sarcomere, this is the only place troponin comes from which is why it is cardiac specific
4 ECG Leads 6 limb leads (frontal plane) 3 bipolar leads 3 unipolar leads6 precordial leads (horizontal plane)V1 – V6Mathematically Constructed6 limb leads6 precordial leadsModified Chest Leads are roughly analogous to the precordial leads in a traditional 12-lead EKG. To obtain them with your three- or four-lead monitor, set the monitor to display Lead III, and move the left leg electrode to mimic the placement of the precordial leads: MCL1 in the fourth ICS, right sternal border; MCL2 in the fourth ICS, left sternal border; MCL4 in the fifth ICS, mid-clavicular line; MCL6 in the fifth ICS, midaxillary line; MCL3 midway between MCL2 and MCL4; and MCL5 midway between MCL4 and MCL6.
5 Einthoven’s Triangle Limb Leads BIPOLAR Lead I RA (-) to LA (+) Lead IIRA (-) to LL (+)Lead IIILA (-) to LL (+)Lead III extends from the left arm to the left footLead I extends from the right to the left armLead II extends from the right arm to the left footForm an equilateral triangle known as Einthoven’s triangleBipolar (requires 2 limbs) and a ground lead (right leg)Depolarization travels from NEGATIVE to POSITIVEThe EKG machine allows each limb electrode to be positive or negativePushing the leads to the center of the triangle creates three intersecting lines of reference
6 AUGMENTED (UNIPOLAR) LEADS Augmented leads combine 2 leads together (the null point) from the center point of the triangle with one positive pole.aVR (Augmented Voltage Right Arm positive) is a combination of bipolar Leads I and IIaVL (Augmented Voltage Left Arm Positive) is a combination of I and IIIaVF (Augmented Voltage Left Foot positive) is a combination of Bipolar Leads II and IIIAugmented Leads are unipolar leadsSingle positive leadaVR – least useful looks primarily at right atriumRight arm (+)aVLLeft arm (+)aVFLeft leg (+)The thought is the negative pole is in the center of the heart and positive pole is on any of the limb leads
7 WHAT ARE THE LEADS LOOKING AT? LIMB and AUGMENTED LEADS II, III & AVFWHAT ARE THE LEADSLOOKING AT?I & AVLWhere the positive electrode is positioned, determines what part of the heart is seen!LIMB and AUGMENTEDLEADS
8 Precordial Lead Placement V1 – 4th intercostal space right of sternumV2 - 4th intercostal space left of sternumV4 – 5th intercostal space midclavicular lineV3 – midway between V2 and V4V6 – 5th intercostal space midaxillary lineV5 – same level as V4 at anterior axillary line between V4 and V6R wave progression negative in V1 and V26 leadsHorizontal planeV1 – V6Each is a + leadV3 isoelectric and/or biphasicV5 and V6 are uprightElectrolyte and BBB defects cause changes in R wave progression
9 Same lead position as left side – RIGHT SIDED EKGV4R, the right-sided chest lead, can reveal ST segment changes that unmask a right ventricular myocardial infarction. RVI is present in percent of inferior wall myocardial infarctions. Many of these patients are highly dependent upon preload to maintain cardiac output, and administration of vasodilators like nitroglycerine may cause a precipitous drop in BP.Right leads “look” directly at Right Ventricle and can show ST elevations in leads II. III. AVF, V4R , V5R and V6RBe sure to label RIGHT SIDE EKG and the R’s after the lead numbersThe machine does not know left from rightThe single most accurate tool used in measuring RVI.90% sensitive and specificSame lead position as left side –looks directly at theRight ventricle
10 Posterior View Posterior leads: V7 – lateral to V6 at posterior axillary lineV8 – level of V7 at the mid-scapular lineV9 – level of V8 at the paravertebral line(left posterior thorax midway from spine to V8)Posterior ViewPosterior Wall MI: Occlusion of the Right Coronary Artery (RCA) or the Posterior Descending ArteryNo leads look at the posterior wall - unless a 15 lead EKG is doneAnterior Leads look at the infarct site from the opposite side (backwards)ST depression in V1 & V2Tall R waves in V1 and/or V2Most often associated with Inferior MI*Associated with dangerous conduction disturbancesV7-V9 electrodes extend in a horizontal line from V6In V7-9 ST elevation of 0.5 mm and QRS amplitude is <10mm = posterior MI
13 Bottom line is continuous strip calibration markerLIMB LEADSAUGUMENTEDLEADSPRECORDIAL LEADSBottom line is continuous strip
14 R – Wave ProgressionV3 is isoeletric or biphasic
15 R – Wave ProgressionV3 is isoeletric or biphasic
16 Myocardial ischemia Myocardial injury Various definitions are used. The term commonly refers to diffuse ST segment depression, usually with associated T wave inversionMyocardial injuryInjury always points outward from the surface that is injured with ST segment elevation
18 ST segment should be electrically neutral Myocardial ischemiaST segment usually isoelectric or less than 1mmT wave – Less than 6 mm high in limb leads, and 12 mm in precordial leads - upright in Leads I, II, V₃ to V₆, negative in aVRReflects ischemia or injuryIschemia – ST depression and T wave opposite of normalInjury – ST elevation with or without T wave changesVarious definitions are used. The term commonly refers to diffuse ST segment depression, usually with associated T wave inversionMyocardial injuryInjury always points outward from the surface that is injured with ST segment elevationST segment should be electrically neutral
19 Visual aid in determining: Ischemia or injury to myocardiumNormal should be at baselineDepressed ST segment - >2 mm below baselineST segment depression is MOST specific for ischemia if the ST segment slopes down from the J point.Horizontal or flat STs are also quite suspicious for ischemia.Upsloping ST depression is only about 60% accurate for diagnosing ischemia.ST segment depressionif transient - almost always due to acute myocardial ischemiathe ECG signs of ischemia may come and go fairly quickly — over a matter of minutes.
22 ST Segment ElevationST segment elevation is attributed to impending infarctionbut can also be due to pericarditis or vasospastic (variant) angina.The height of the ST segment is measured at a point 2 boxes after the end of the QRS complexsignificant if it exceeds 1 mm in a limb lead or 2 mm in a precordial lead.ST elevation is death of cells
24 T Waves T waves are normally positive in leads with a positive QRS T waves are normally asymmetricalT waves are normally not more than 5 mm high in limb leads or 10 mm high in precordial leads or 2/3 the height of the R waveT waves are normally not more than 5 mm high in limb leads or 10 mm high in precordial leads or 2/3 the height of the R waveTall, symmetrical T wavesHyperkalemiaInfarction or ischemiaDigitalisPericarditisBroad, symmetrical, inverted T waves are classic for intracranial bleed or strokeCVAIncreased intracranial pressure
25 T wave Ischemia Ischemia Hyperkalemia Ischemia In some patients with partial thickness ischaemia the T waves show a biphasic pattern. This occurs particularly in the anterior chest leads and is an acute phenomenon. Biphasic T wave changes usually evolve and are often followed by symmetrical T wave inversion. These changes occur in patients with unstable or crescendo angina and strongly suggest myocardial ischaemia.HyperkalemiaIschemiaIschemia
26 Elevated T waves – symmetrical pointed > 2/3 of QRS = hyperkalemia (6.5-7.0) Tall, symmetrical T wavesHyperkalemiaInfarction or ischemiaHyperkalemiaEKG 3
27 ST-T Wave Combination of infarction and often hyperkalemia Called Tombstone ‘T’ because of the shape.Usually a sign of impending cardiac death.ST segment and T wave are combined
30 Localization of ECG Pathology Inferior: Abnormalities that appear in leads II, III, and aVF (called the inferior leads) indicate pathology on the inferior or diaphragmatic surface of the heart.Lateral: Leads I, aVF, and V5-V6 are called lateral leads. Abnormality in these leads indicates pathology on the lateral, upper surface of the heart.Anterior: Anterior pathology is seen in leads V1-V4, and often in lead I.ST elevation in contiguous (congruent) leads most often represents acute infarctionThere must be changes in more than 1 congruent lead for it to mean anythingST depression in contiguous leads may represent acute ischemiaIn acute infarction, ST elevation in contiguous leads coupled with reciprocal ST depression in non-infarcting leads is added evidence of an AMI
31 Overview of Infarcts Anterior Inferior Lateral Posterior Septal Location of InfarctArterial SupplyIndicative ChangesReciprocal ChangesAnteriorLADV1-V4II, III, aVFInferiorRCAI, aVLLateralCircumflexI, aVL, V5, V6V1PosteriorPosterior Descending (RCA)NoneV1, V2SeptalSeptal Perforating (LAD)Posterior Descending (RCALoss of R wave in V1, V2, or V3Not all MI’s have reciprocal changes, their presence may indicate a bigger infarct, more ischemic area. Sometimes reciprocal changes are more evident (stick out more) than ST elevation and help zero in on infarcted region.Reciprocal changesIn addition to the primary changes that occur in the ECG leads facing the infarcted myocardium, "reciprocal changes" may occur in leads opposite to the site of infarction. The changes are just the inverse of the primary changes. Thus, "ST segment elevation and T wave inversion" will appear as "ST segment depression and tall pointed T waves", respectively. The inferior limb leads on the one hand and the precordial leads, together with leads I and aVL, on the other hand are "mutually opposite". Thus, primary changes in one of the above groups will usually be accompanied by reciprocal changes in the other group. It will be safe to assume that if on the ECG there is ST segment elevation in one group (as above) and ST segment depression in the other group, the elevation is the primary change and the ST segment depression is the secondary change.
32 T Wave ElevationTST Segment ElevationSTSTQTPathologicalQ WaveQQTT Wave Inversion
33 EKG Changes from Infarction First Detectable Change in EKGTall T-wavesincrease in heightmore symmetricmay occur in the first few minuteshyperacuteHyper-acute Phase
34 Acute Phase ST Segment Elevation Primary indication of injury Occurs in first hour to hoursST Segment Elevation in Leads1mm or greater in limb leads2 mm or greater in chest leadsHallmark indication of AMI
35 Localization of myocardial injury The different leads monitor different anatomic regions of the heart. Thus, the different leads are used to detect myocardial injury in their corresponding regions of the heart. In an ECG tracing, myocardial injury can be localized to the following anatomic regions of the heart:Lateral wall: Left wall of the left ventricle. Leads I, aVL, V5, and V6 are usedInferior wall: The part of the left ventricle resting on the diaphragm. Leads II, III, and aVF are usedAnterior wall: Ventral (front) wall of the left ventricle. Leads V2, V3, V4, and sometimes V1 and/or V5 are usedPosterior wall: The dorsal (back) part of the left ventricle. Leads V1, V2, V3, and V4 are used to monitor the reciprocal changesSeptal region: The intraventricular septum. Leads V1 and V2 are usedRight ventricle: Lead V4R is used. This lead is not part of the standard ECG leads and is placed in a similar manner as lead V4 but on the right side of the chest. Lead V4R is only placed if the patient is suspected of having a myocardial infarction involving the right ventricle.
36 View of Inferior Heart Wall Leads II, III, aVFLooks at inferior heart wallInferior Wall MI: Occlusion of Right Coronary Artery (RCA)At least 1mm ST segment elevation in leads II, III, aVFReciprocal ST depression in leads I & aVL or precordial leadsConduction defects:Sinus bradycardiaSinus arrest1st degree blockAccelerated Idioventricular rhythmThe ECG changes associated with anterolateral myocardial infarction, including pathologic Q waves and repolarization abnormalities, are best seen in leads V2, V3, V4, V5. The anterior leads, leads I, aVL, V5, and/or V6, or the lateral leads may also be used to detect this type of infarction.Inferior myocardial infarctionThe blood supply of the posterior and inferior regions of the heart is provided by the Ramus Descendens Posterior (RDP), also known as the Posterior Descending Artery (PDA).· • In 85% of cases, the RDP is a branch of the right coronary artery (RCA). When this is the case, the coronary circulation is described as a right-dominant system.· • In 7% of cases, the RDP branches from the Ramus Circumflexus. When this is the case, the coronary circulation is described as a left-dominant system.· • In the remaining 8% of cases, blood supply of the posterior and inferior regions of the heart is provided by both the right coronary artery and the RCx. When this is the case, the coronary circulation is described as a co-dominant system.In most cases, an inferior myocardial infarction results from occlusion of the right coronary artery. In some cases, inferior myocardial infarction results from occlusion of the Ramus Circumflexus. The ECG changes associated with inferior myocardial infarction, including pathologic Q waves and repolarization abnormalities, are best seen in the inferior leads: II, III, and aVF.Complications:Brady arrhythmias – protective mechanism, 90% of blood supply for SA & AV nodes from the RCAHypotension – treated with fluids, consider right side involvementLeads II, III and aVFPredominately Right Coronary ArteryEKG changes1st degree AV block2nd or 3rd degree AV BlocksN/V and/or bradycardia are common
37 InferiorWith Inferior Wall MI suspect Right Ventricular Wall InfarctSigns of possible Right Ventricular Wall Infarct:HypotensionJVDClear lung soundsEKG 5
39 *Sometimes referred to as High Lateral or High Apical view* View of Lateral Heart WallLeads I and aVLLooks at lateral heart wallLooks from the left arm toward heartLateral Wall MI: results from occlusion of the Left Circumflex ArteryAt least 1 mm ST segment elevation in leads I, aVL, V5 & V6 and /or 2 mm ST segment elevation in V5 & V6Reciprocal ST depression in V1Sometimes an extension of an Anterior or Inferior MIConduction defects are rareLeads I, aVL, V5 & V6Left CircumflexUsually in combo with other areas of infarctEKG changesRelative to other areas of involvement*Sometimes referred to as High Lateral or High Apical view*
40 View of Lateral Heart Wall Leads V5 & V6Looks at lateral heart wallLooks from the left lateral chest toward heart*Sometimes referred to as Low Lateral or Low Apical view*
41 View of Entire Lateral Heart Wall Leads I, aVL, V5, V6- Looks at the lateral wall of the heart from two different perspectivesLateral Wall
44 View of Anterior Heart Wall Leads V3, V4Looks at anterior heart wallLooks from the left anterior chestAnterior Wall infarct: Occlusion of the Left Anterior Descending Artery (LAD)2mm ST segment elevation in two or more of leads V1-V4Reciprocal changes in leads II, III, aVFLethal due to large myocardium involvementPossible conduction defects:Bundle Branch Block2nd Degree Block Type IICHBLeads V1 – V4Left Anterior Descending ArteryV1 and V2 indicative of septal involvementEKG ChangesLeft or Right Bundle Branch Blocks2nd or 3rd Degree Heart block
45 AnteriorAnterior Wall infarct: Occlusion of the Left Anterior Descending Artery (LAD)2mm ST segment elevation in two or more of leads V1-V4Reciprocal changes in leads II, III, aVFLethal due to large myocardium involvementPossible conduction defects:Bundle Branch Block2nd Degree Block Type IICHBEKG 9
47 View of Septal Heart Wall Leads V1, V2Looks at septal heart wallLooks along sternal bordersSeptal Wall MI: caused by septal perforation involving the LAD or the Posterior DescendingMost often in the setting of an Anterior MILoss of R-wave in leads V1, V2 or V3May have ST segment elevation in V1 & V2No reciprocal changes
48 Putting it ALL together ANTERIORLATERALSEPTALLATERALLATERALINFERIOR
49 Q Waves Definition Septal depolarization Normally present in I, aVL, V6
50 Two types of Q waves Non-pathologic Pathologic Narrow, shallow Q waves Not visible in all leadsPathologic> 0.04 in duration; at least 1/4 to 1/3 height of R waveRepresent an infarcted area of myocardiumQ waves are significant if they are grater than 1 box in width or are larger than ¼ of the R wave, indicates MI or obstructive septal hypertrophy IHSScauses: septal, infarction, IHSSSeptal, I, L, V5-6 occasionally inferior leadsSignificant Q> ¼ R or Q > 1 box wide and not in lead IIIHIS increased septal Qs, evidence of LVH
51 Part of inferior wall mi/pathological Q’s PATHOLOGICAL Q WAVES
52 If the QRS duration is > .12 Bundle Branch BlocksIf the QRS duration is > .12there is usually an abnormality of conduction of the ventricular impulseThe most common causes for prolonged QRS complexes is a bundle branch blockHowever, other conditions may also prolong the QRS duration.The type of bundle branch block can usually be determined from the examination of three key leads: I, V1 and V6.
53 RBB BlockInterruption of impulse conduction through the right tract of the bundleLead V1 - rSR' & R' (seeing both ventricles depolarizing separately) are the result of the third wave of depolarization traveling back toward lead V1 to depolarize the right ventricle i.e. impulse goes down the LBB then around to the RBBR’ is bigger because right side lead is closer to the impulseIf the complex is greater than 0.10 seconds, it represents an incomplete right bundle branch block. If the complex is greater than 0.12 seconds, it represents a complete right bundle branch block.Most common ventricular conduction defectCan be acute or chronicAcute RBBB is associated with an acute anterior MI
55 Always indicates a diseased heart More common in older adults LBB BlockAlways indicates a diseased heartMore common in older adultsInterruption in conduction of an impulse through the left branch of the bundleMost commonly diagnosed using precordial leadsBundle branch block can be diagnosed by pattern recognition of the QRS complexes in the V1 and V6 leadsthese two leads look at the left ventricleThere is a wide QRS you don’t see the waves separately as in RBB you will see a notchNew LBBB can be diagnostic of myocardial infarction (MI).
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