12-Lead EKG MEPN Level IV

OBJECTIVES Discuss the changes in T wave and ST segment morphology with an MI List the criteria for identification of right or left bundle branch blocks. List the anatomically congruent leads associated with an inferior, lateral and anterior wall MI Describe morphology of Q wave presence

Myocyte bundles are what make cardiac cells different from other cells Myofibrils are individual units that slide over one another causing contraction They pull the sarcomere together causing contraction Ca+ is the primary stimulant for the effect of sarcomeres Troponin is inside the sarcomere, this is the only place troponin comes from which is why it is cardiac specific

ECG Leads 6 limb leads (frontal plane) 3 bipolar leads 3 unipolar leads 6 precordial leads (horizontal plane) V1 – V6 Mathematically Constructed 6 limb leads 6 precordial leads Modified 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.

Einthoven’s Triangle Limb Leads BIPOLAR Lead I RA (-) to LA (+) Lead II RA (-) to LL (+) Lead III LA (-) to LL (+) Lead III extends from the left arm to the left foot Lead I extends from the right to the left arm Lead II extends from the right arm to the left foot Form an equilateral triangle known as Einthoven’s triangle Bipolar (requires 2 limbs) and a ground lead (right leg) Depolarization travels from NEGATIVE to POSITIVE The EKG machine allows each limb electrode to be positive or negative Pushing the leads to the center of the triangle creates three intersecting lines of reference

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 II aVL (Augmented Voltage Left Arm Positive) is a combination of I and III aVF (Augmented Voltage Left Foot positive) is a combination of Bipolar Leads II and III Augmented Leads are unipolar leads Single positive lead aVR – least useful looks primarily at right atrium Right arm (+) aVL Left arm (+) aVF Left leg (+) The thought is the negative pole is in the center of the heart and positive pole is on any of the limb leads

WHAT ARE THE LEADS LOOKING AT? LIMB and AUGMENTED LEADS II, III & AVF WHAT ARE THE LEADS LOOKING AT? I & AVL Where the positive electrode is positioned, determines what part of the heart is seen! LIMB and AUGMENTED LEADS

Precordial Lead Placement V1 – 4th intercostal space right of sternum V2 - 4th intercostal space left of sternum V4 – 5th intercostal space midclavicular line V3 – midway between V2 and V4 V6 – 5th intercostal space midaxillary line V5 – same level as V4 at anterior axillary line between V4 and V6 R wave progression negative in V1 and V2 6 leads Horizontal plane V1 – V6 Each is a + lead V3 isoelectric and/or biphasic V5 and V6 are upright Electrolyte and BBB defects cause changes in R wave progression

Same lead position as left side – RIGHT SIDED EKG V4R, the right-sided chest lead, can reveal ST segment changes that unmask a right ventricular myocardial infarction. RVI is present in 30-50 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 V6R Be sure to label RIGHT SIDE EKG and the R’s after the lead numbers The machine does not know left from right The single most accurate tool used in measuring RVI. 90% sensitive and specific Same lead position as left side – looks directly at the Right ventricle

Posterior View Posterior leads: V7 – lateral to V6 at posterior axillary line V8 – level of V7 at the mid-scapular line V9 – level of V8 at the paravertebral line (left posterior thorax midway from spine to V8) Posterior View Posterior Wall MI: Occlusion of the Right Coronary Artery (RCA) or the Posterior Descending Artery No leads look at the posterior wall - unless a 15 lead EKG is done Anterior Leads look at the infarct site from the opposite side (backwards) ST depression in V1 & V2 Tall R waves in V1 and/or V2 Most often associated with Inferior MI *Associated with dangerous conduction disturbances V7-V9 electrodes extend in a horizontal line from V6 In V7-9 ST elevation of 0.5 mm and QRS amplitude is <10mm = posterior MI

PRECORDIAL LEADS V1 & V2 V3 & V4 V5 & V6

Bottom line is continuous strip calibration marker LIMB LEADS AUGUMENTED LEADS PRECORDIAL LEADS Bottom line is continuous strip

R – Wave Progression V3 is isoeletric or biphasic

R – Wave Progression V3 is isoeletric or biphasic

Myocardial ischemia Myocardial injury Various definitions are used. The term commonly refers to diffuse ST segment depression, usually with associated T wave inversion Myocardial injury Injury always points outward from the surface that is injured with ST segment elevation

Ischemia, Injury, Infarction Waveforms

ST segment should be electrically neutral Myocardial ischemia ST segment usually isoelectric or less than 1mm T 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 aVR Reflects ischemia or injury Ischemia – ST depression and T wave opposite of normal Injury – ST elevation with or without T wave changes Various definitions are used. The term commonly refers to diffuse ST segment depression, usually with associated T wave inversion Myocardial injury Injury always points outward from the surface that is injured with ST segment elevation ST segment should be electrically neutral

Visual aid in determining: Ischemia or injury to myocardium Normal should be at baseline Depressed ST segment - >2 mm below baseline ST 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 depression if transient - almost always due to acute myocardial ischemia the ECG signs of ischemia may come and go fairly quickly — over a matter of minutes.

EKG 1

ST Segment Elevation ST segment elevation is attributed to impending infarction but 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 complex significant if it exceeds 1 mm in a limb lead or 2 mm in a precordial lead. ST elevation is death of cells

EKG 2

T Waves T waves are normally positive in leads with a positive QRS T waves are normally asymmetrical T 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 wave T 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 wave Tall, symmetrical T waves Hyperkalemia Infarction or ischemia Digitalis Pericarditis Broad, symmetrical, inverted T waves are classic for intracranial bleed or stroke CVA Increased intracranial pressure

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. Hyperkalemia Ischemia Ischemia

Elevated T waves – symmetrical pointed > 2/3 of QRS = hyperkalemia (6.5-7.0) Tall, symmetrical T waves Hyperkalemia Infarction or ischemia Hyperkalemia EKG 3

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

EKG 4

Pathology of an MI

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 infarction There must be changes in more than 1 congruent lead for it to mean anything ST depression in contiguous leads may represent acute ischemia In acute infarction, ST elevation in contiguous leads coupled with reciprocal ST depression in non-infarcting leads is added evidence of an AMI

Overview of Infarcts Anterior Inferior Lateral Posterior Septal Location of Infarct Arterial Supply Indicative Changes Reciprocal Changes Anterior LAD V1-V4 II, III, aVF Inferior RCA I, aVL Lateral Circumflex I, aVL, V5, V6 V1 Posterior Posterior Descending (RCA) None V1, V2 Septal Septal Perforating (LAD) Posterior Descending (RCA Loss of R wave in V1, V2, or V3 Not 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 changes In 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.

T Wave Elevation T ST Segment Elevation ST ST Q T Pathological Q Wave Q Q T T Wave Inversion

EKG Changes from Infarction First Detectable Change in EKG Tall T-waves increase in height more symmetric may occur in the first few minutes hyperacute Hyper-acute Phase

Acute Phase ST Segment Elevation Primary indication of injury Occurs in first hour to hours ST Segment Elevation in Leads 1mm or greater in limb leads 2 mm or greater in chest leads Hallmark indication of AMI

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 used Inferior wall: The part of the left ventricle resting on the diaphragm. Leads II, III, and aVF are used Anterior wall: Ventral (front) wall of the left ventricle. Leads V2, V3, V4, and sometimes V1 and/or V5 are used Posterior wall: The dorsal (back) part of the left ventricle. Leads V1, V2, V3, and V4 are used to monitor the reciprocal changes Septal region: The intraventricular septum. Leads V1 and V2 are used Right 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.

View of Inferior Heart Wall Leads II, III, aVF Looks at inferior heart wall Inferior Wall MI: Occlusion of Right Coronary Artery (RCA) At least 1mm ST segment elevation in leads II, III, aVF Reciprocal ST depression in leads I & aVL or precordial leads Conduction defects: Sinus bradycardia Sinus arrest 1st degree block Accelerated Idioventricular rhythm The 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 infarction The 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 RCA Hypotension – treated with fluids, consider right side involvement Leads II, III and aVF Predominately Right Coronary Artery EKG changes 1st degree AV block 2nd or 3rd degree AV Blocks N/V and/or bradycardia are common

Inferior With Inferior Wall MI suspect Right Ventricular Wall Infarct Signs of possible Right Ventricular Wall Infarct: Hypotension JVD Clear lung sounds EKG 5

Inferior EKG 6

*Sometimes referred to as High Lateral or High Apical view* View of Lateral Heart Wall Leads I and aVL Looks at lateral heart wall Looks from the left arm toward heart Lateral Wall MI: results from occlusion of the Left Circumflex Artery At least 1 mm ST segment elevation in leads I, aVL, V5 & V6 and /or 2 mm ST segment elevation in V5 & V6 Reciprocal ST depression in V1 Sometimes an extension of an Anterior or Inferior MI Conduction defects are rare Leads I, aVL, V5 & V6 Left Circumflex Usually in combo with other areas of infarct EKG changes Relative to other areas of involvement *Sometimes referred to as High Lateral or High Apical view*

View of Lateral Heart Wall Leads V5 & V6 Looks at lateral heart wall Looks from the left lateral chest toward heart *Sometimes referred to as Low Lateral or Low Apical view*

View of Entire Lateral Heart Wall Leads I, aVL, V5, V6 - Looks at the lateral wall of the heart from two different perspectives Lateral Wall

Lateral EKG 7

Lateral EKG 8

View of Anterior Heart Wall Leads V3, V4 Looks at anterior heart wall Looks from the left anterior chest Anterior Wall infarct: Occlusion of the Left Anterior Descending Artery (LAD) 2mm ST segment elevation in two or more of leads V1-V4 Reciprocal changes in leads II, III, aVF Lethal due to large myocardium involvement Possible conduction defects: Bundle Branch Block 2nd Degree Block Type II CHB Leads V1 – V4 Left Anterior Descending Artery V1 and V2 indicative of septal involvement EKG Changes Left or Right Bundle Branch Blocks 2nd or 3rd Degree Heart block

Anterior Anterior Wall infarct: Occlusion of the Left Anterior Descending Artery (LAD) 2mm ST segment elevation in two or more of leads V1-V4 Reciprocal changes in leads II, III, aVF Lethal due to large myocardium involvement Possible conduction defects: Bundle Branch Block 2nd Degree Block Type II CHB EKG 9

Anterior EKG 10

View of Septal Heart Wall Leads V1, V2 Looks at septal heart wall Looks along sternal borders Septal Wall MI: caused by septal perforation involving the LAD or the Posterior Descending Most often in the setting of an Anterior MI Loss of R-wave in leads V1, V2 or V3 May have ST segment elevation in V1 & V2 No reciprocal changes

Putting it ALL together ANTERIOR LATERAL S E P T A L LATERAL LATERAL INFERIOR

Q Waves Definition Septal depolarization Normally present in I, aVL, V6

Two types of Q waves Non-pathologic Pathologic Narrow, shallow Q waves Not visible in all leads Pathologic > 0.04 in duration; at least 1/4 to 1/3 height of R wave Represent an infarcted area of myocardium Q 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 IHSS causes: septal, infarction, IHSS Septal, I, L, V5-6 occasionally inferior leads Significant Q> ¼ R or Q > 1 box wide and not in lead III HIS increased septal Qs, evidence of LVH

Part of inferior wall mi/pathological Q’s PATHOLOGICAL Q WAVES

If the QRS duration is > .12 Bundle Branch Blocks If the QRS duration is > .12 there is usually an abnormality of conduction of the ventricular impulse The most common causes for prolonged QRS complexes is a bundle branch block However, 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.

RBB Block Interruption of impulse conduction through the right tract of the bundle Lead 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 RBB R’ is bigger because right side lead is closer to the impulse If 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 defect Can be acute or chronic Acute RBBB is associated with an acute anterior MI

EKG 11 RBBB

Always indicates a diseased heart More common in older adults LBB Block Always indicates a diseased heart More common in older adults Interruption in conduction of an impulse through the left branch of the bundle Most commonly diagnosed using precordial leads Bundle branch block can be diagnosed by pattern recognition of the QRS complexes in the V1 and V6 leads these two leads look at the left ventricle There is a wide QRS you don’t see the waves separately as in RBB you will see a notch New LBBB can be diagnostic of myocardial infarction (MI).

EKG 12 LBBB