A Basic Overview of How to Interpret 12 Lead EKGs and Treat a Cardiac PatientRegion IV Pre-Hospital Systems Coordination Committee12 Lead EKG 101

The purpose of this course is to provide pre-hospital clinicians with the tools necessary to identify the basic A&P of the heart, interpret 12 Lead EKGs, localize and treat AMIs as well as recognize imposters and potential complications.Purpose:

Basic Cardiac Anatomy & PhysiologyMuscular pump about the size of your fist primary function is to pump oxygenated blood to the rest of the body. Made up of four chambers, right and left atriaright and left ventriclesThe septum is a thin muscular wall that separates the right and left sides of the heart. Each contraction of the heart occurs in response to an electrical impulse that starts in the upper portion of the heart. Blood is moved in a closed circuit through the body by the pumping of the heart.

The heart contracts and pumps blood out to the body (systole) and relaxes to fill with more blood (diastole).

The heart muscle itself is like all other organs in the body and requires oxygen to function.

The oxygen-rich blood is circulated to the heart muscle through the coronary arteries.There are two main arteries: Right coronary arteryLeft main coronary arteryboth start at the aorta

These vessels then branch off into smaller and smaller vessels along the surface of the heart.

Basic Cardiac Anatomy & Physiology

In order to perform work, the heart needs oxygen and nutrients.

There are two main arteries:

Right coronary artery (RCA) Left coronary artery (LCA).

The left coronary artery divides into: Left anterior descending (LAD) branch Left circumflex branch(LCX)The right coronary artery and the branches of the left coronary artery provide numerous smaller branches which penetrate the heart muscle, supplying it with blood.Both coronary arteries originate from the aorta and run along the surface of the heart.In the majority of human hearts, coronary circulation follows a predictable pattern.

Left Main Coronary ArteryBranches quickly into the LAD & LCX. Involves almost 2/3 of the heart muscle

Right Coronary Artery (RCA) The RCA supplies blood to the bottom (inferior) portion and part of the back (posterior) portion of the left ventricle. The posterior portion of the septum is also supplied with blood from the RCA.SA Node 55%AV Node 90%AV Blocks Left Anterior Descending Branch (LAD) The LAD supplies blood to the front (anterior) portion of the left ventricle, apical including most of the anterior portion of the septum separating the ventricles.Bundle Branch Block, AMI, CHFLeft Circumflux Branch (LCX) The LCX supplies blood to the left side (lateral) portion and the back (posterior) portion of the left ventricle.SA Node 45% AV Node 10%Lateral & posterior MI

Sino-Atrial (SA) Node: natural cardiac pacemaker. The heartbeat starts here and spreads throughout the network of conduction fibers in the two atria causing them to contract.

Normally, the heartbeat can only reach the ventricles (the two lower chambers), after it has passed through the atrioventricular (AV) node.

Atrioventricular (AV) Node: slows down the electrical signal so that the atrial contractions can finish filling the ventricles completely. The AV node also prevents the lower chambers from beating too fast if the atria develops a fast rhythm (tachyarrhythmia).

His Bundle, bundle branches, and the Purkinje system : The electrical signal finally passes to the ventricles causing the ventricles to contract

Anatomy of an EKGThe EKG, or a measure of this electrical activity of the heart, is comprised of 3 primary parts...1. P wave---electrical depolarization of the atria...contraction follows...2. QRS COMPLEX---electrical depolarization of the ventricles...contraction follows...3. T wave---electrical repolarization of the ventricles...and thus, relaxation...

P wave: Represents positive and negative deflections of atrial contraction and relaxation

PR Interval: Distance between the P wave and the R wave. Should be consistent

QRS ComplexQ wave: First negative deflectionNormal in I, aVL, V1, V6Significant or pathologic is one box wide and/or 1/3 the height of the R wave

R Wave: First positive deflection

S Wave: Next negative deflection

ST Segment: Essentially isoelectric, slopes gentely upward

J point: the point at which the ST Segment takes off from the QRS complex

T Wave: Upright always in leads I, II, V2-V6. aVR is always negative. Leads III, aVL, aVF, and V1 can be positive or negative

U Wave: Seen best in V3, same polarity as T wave, sign of hypokalemia

QT Interval: One complete ventricular cycle. None are > the preceding R-R

Putting the A&P with the EKG

Einthovens Triangle

This is an example a 12-lead EKG. Anatomy of a 12-Lead EKG

At the bottom of this 12-lead are rhythm strips (highlighted). Any of the 12-leads can be shown as rhythm strips.You can configure the device to show you any of the six limb leads on the rhythm strip (I, II, III, aVR, aVL or aVF).Anatomy of a 12-Lead EKG (cont.)

The format of the 12-lead EKG is very standard. While there are a few exceptions, the format you see here is typical of what you will see in most 12-lead EKGs done in North America.Anatomy of a 12 Lead EKG (cont.)

Anatomy of a 12-Lead EKG (cont.)The 12-lead can provide a computer generated interpretation. When you see ACUTE MI SUSPECTED the machine is right about 98% of the time.In order to attain specificity, if the computer isnt absolutely sure that an AMI is present, it will not say anything about it. In other words YOU are the primary interpreter, the computer is your backup.

The 12-Lead is very good at measuring intervals and durations. It is better at measuring the PR-interval and the QRS width.We express these intervals and durations in seconds 12-lead expresses them in milliseconds. It is simple to convert milliseconds to seconds.Anatomy of a 12-Lead EKG (cont.)

When you use an EKG to determine the cardiac rate and rhythm, certain sampling time is required. 12-lead interpretation: Only one beat from each lead is needed to make an interpretation. Anatomy of a 12-Lead EKG (cont.)

Each lead has one positive electrode.Positive electrode is a camera. view is from the positive electrode toward the negative electrode.The portion of the left ventricle that each leads sees is determined by the location of that positive electrode.Different placements of the electrodes will yield different viewpoints.Anatomy of a 12-Lead EKG (cont.)There are six positive electrodes on the chest, yielding six leads.There are four electrodes on the limbs from which the EKG machine makes another six leads.

Anatomy of a 12-Lead EKG (cont.)Types of Leads

Anatomy of a 12-Lead EKG (cont.)View of Posterior Heart WallLeads V1 & V2Tall R ST DepressionUpright T-Wave

Leads II, III, aVFLooks at inferior heart wallAnatomy of a 12-Lead EKG (cont.)View of Inferior Heart WallLooks from the left leg up

Leads I and aVLLooks at lateral heart wall Looks from the left arm toward heartAnatomy of a 12-Lead EKG (cont.)View of Lateral Heart Wall*Sometimes known as High Lateral*

Leads V5 & V6Looks at lateral heart wallLooks from the left lateral chest toward heartAnatomy of a 12-Lead EKG (cont.)View of Lateral Heart Wall*Sometimes referred to as Low Lateral or Apical view*

Leads I, aVL, V5, V6- Looks at the lateral wall of the heart from two different perspectivesAnatomy of a 12-Lead EKG (cont.)View of Entire Lateral Heart Wall

Leads V3, V4Looks at anterior heart wallLooks from the left anterior chestAnatomy of a 12-Lead EKG (cont.)View of Anterior Heart Wall

Leads V1, V2Looks at septal heart wallLooks along sternal bordersAnatomy of a 12-Lead EKG (cont.)View of Septal Heart Wall

Anatomy of a 12-Lead EKG (cont.)

The ST segment is normally iso-electric (baseline) neither elevated or depressed. May slope upward toward a relatively tall T waveAnatomy of a 12-Lead EKG - ST SegmentThe ST segment is probably the single most important element to identify on the ECG when looking for evidence of AMI.

The Three IsIschemia lack of oxygenation ST depression or T inversionInjury prolonged ischemia ST elevationInfarct death of tissuemay or may not show in Q wave

Cardiac ischemia is a situation in which the blood flow within a coronary artery is limited to the point where the oxygen needs of the heart muscle cannot be met (hypoxia).( Myocardial ischemia, Ischemic heart disease, Ischemia, Myocardium ischemia, Silent ischemia )CARDIAC ISCHEMIA

CARDIAC ISCHEMIAMinor episodes of cardiac ischemia tend to cause little long-term damage to the heart, but these episodes can sometimes cause serious effects in some patients: They can cause arrhythmias, which can lead to either syncope or cardiac arrest and sudden cardiac death. Severe or lengthy episodes can trigger a result in myocardial infarction. The collective effects of minor episodes of cardiac ischemia can potentially lead to cardiomyopathy.

Symptoms of Cardiac Ischemia May be painful symptoms of cardiac ischemia, Pain, pressure or discomfort from cardiac ischemia is angina. Angina may feel like a squeezing vise or crushing pressure deep in the chest behind the sternum. May also be felt in the shoulders, arms, back, neck or jaw.

EKG in Acute IschemiaTracing taken during an episode of anginal pain that occurred while the patient was at rest. Marked ST elevation in leads V25 with some ST depression in aVF.

EKG after Acute IschemiaThis tracing was taken 30 minutes after the initial. The patient was painfree and asymptomatic. The ST segments are isoelectric, and the ECG is normal

Evaluation after Acute IschemiaSubsequent clinical evaluationserial ECGsenzyme determinations, revealed no evidence of acute myocardial infarction. Disappearance of the ST elevation and the absence of clinical and electrocardiographic evidence of infarction on subsequent examinations indicate that initial ECG is representative of severe, acute, and reversible ischemia.

Epicardial Coronary ArteryLateral Wall of LVPositive ElectrodeSeptumLeft Ventricular CavityInterior Wall of LVWell Perfused Myocardium

Normal ECG

Epicardial Coronary ArteryLateral Wall of LVPositive ElectrodeSeptumLeft Ventricular CavityInterior Wall of LVIschemia

IschemiaInadequate oxygen to tissueSubendocardialRepresented by ST depression or T inversionMay or may not result in infarct

ST depression

InjuryProlonged ischemiaTransmuralRepresented by ST elevationUsually results in infarct

ST elevation

ThrombusIschemiaInjury

InfarctDeath of tissueRepresented by Q waveNot all infarcts develop Q waves

Infarcted AreaElectrically SilentDepolarizationMany infarcts do not develop Q wavesInfarction

Q Waves

Infarcted Area Electrically SilentThrombusDepolarizationIschemia

SummaryA normal ECG does NOT rule out ACSST segment depression represents ischemiaPossible infarctST segment elevation is evidence of AMIQ wave MI may follow ST elevation or depression

Pathophysiology of the AMIChronic accumulation of atherosclerotic plaque in coronary vessels around the heartFibrous plaque prone to rupture, lead to thrombytic blockageClots form due to damaged tissue and plateletsBoth release chemicals causing a clot to formForms a substance called fibren that traps cells and platelets eventually blocking and narrowing Tissue damage in AMI results from rupture of plaque on vessel walls creating a chain reaction that forms a clot in the coronary artery.

Process of an AMIImpaired blood flow:Produces varying degrees of myocardial injuryDamage dependent on flow reduction and durationTissue death progress quickly in a wave patternBegins with endocardiumEnds with epicardiumInfarction becomes larger toward the surface of the heart.Ischemia Shortage of oxygen at cellular levelInjury Diminishing supply of oxygenInfarct cardiac cells die of anoxia.

EKG Changes from InfarctionFirst Detectable Change in EKGTall T-wavesincrease in heightmore symmetricmay occur in the first few minutes*Known as hyper acute phase*

EKG Changes from Infarction The Acute PhaseSigns of Myocardial InjuryST Segment ElevationPrimary indication of injuryOccurs in first hour to hoursST Segment Elevation in Leads1mm or greater in limb leads2 mm or greater in chest leadsHallmark indication of AMI*Known as Acute Phase*

EKG Changes of InfarctionReciprocal ChangesST elevation in contiguous leads most often represents acute infarctionST 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.

Acute ST segment elevationReciprocal ST segment depression

EKG Changes from Infarction T Wave InversionSigns of Myocardial Injury T wave inversion presence of ischemia May precede ST elevation

Prominent in precordial chest leads Inversion in limb leads is pathologic T wave inversion can be caused by other things than ischemia

EKG Changes from Infarction The Indeterminate PhaseSigns of Myocardial Infarction

Pathologic Q-waveFirst indication of tissue deathFirst few to several hoursQ-wave size of QRS suggests infarctRepresent current or past eventsDetermine timing through ST elevation and T-wave inversion

Natural Progression of EKG in Infarction

Over time:T-wave regains normal contourST-segment returns to isometric lineQ-wave remains as evidence of infarctIndicates presence of previous MI*ST segment elevation provides the strongest evidence of early recognition of AMI*

EKG Changes from Infarction (cont.) All of the changes in the previous slides are: Indicative Changes ST segment elevation is helpful in detecting an MI in its early stages Hyperacute (Tall) T-waves alone are specific enough to diagnose an MI T-wave inversion can occur with simple angina and is therefore not specific Pathological Q-wave is the most accurate recognition of an MI Not in the first few hours ST segment elevation provides the strongest evidence for early recognition of an MI

ECG Variants Coronary Spasm: Printzmetals anginaInjury pattern that resolves w/ rest, NTG,O2 etc.

Early Repolarization: elevated J point seen best in V3,4. Key to Dx pts are usually young & asymptomatic

Pericarditis: ST elevation usually global associated w/ fever, pleuritic c/p.

ECG Variants due to Drugs or Electrolytes ImbalancesHypokalemia: lg U waves ( usually taller than T) seen best in precordial leads. 6.0PR prolongs, QRS widensP waves disappear > 8.0Hypocalcemia:Prolonged QT intervalHypercalcemia:Shortened QT intervalDigitalis effect:ST depression- downsloping, curved ST segments.scooping, sagging, flat or inverted Ts in lateral leadsPR prolongedQT shortened

Bundle Branch BlocksTurn Signal RuleThis is a simple method for differentiating right bundle branch block from left bundle branch block. V1 will be the only lead you need to view1. Locate the terminal (last) force of the QRS complex2. Determine if it is pointing up or down.3. Compare to the turn signal in your car:Up is for a right turn & RBBBDown is for a left turn and LBBB

Clinical significance: Bundle branch is a significant complication of infarction. Since the left anterior descending artery is the primary supplier of the bundle branches, BBB is considered a complication of anterior septal infarcts.When BBB is the result of MI, the incidence of pump failure is 65-70% and the in-hospital mortality rate is 40%-60%. The BBB itself is not dangerous, but the high mortality rate is due to the extensive amount of tissue death occurring when an infarct is serious enough to cause a BBB. Another manifestation of BBB is in the form of AV Block. This is why infranodal AV blocks are more serious and have wide QRS complexes.

Localizing the Area of InfarctionIndicative changes are not found in every leadOnly present in leads looking at the infarctIndicative changes in two or more leads looking at the same portion of the heart are anatomically contiguous leadsSuspect AMIST segment elevation in two or more leads that are not contiguousAMI not the suspected cause

Recognizing infarct: Know which part of the heart each lead looks atLocalizing Infarct: Note which lead is displaying evidence and which portions of heart they are looking at*Simply knowing the changes to look for and which part of the heart each lead looks at*Recognition & Localization

Leads Displaying Indicative ChangesII, III, aVFV1 & V2V3 & V4V5, V6, I, and aVL

Location of Infarct SiteInferiorSeptalAnteriorLateral

Anterior Wall MIAnterior 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 IICHB

Anterior Wall MI

Inferior Wall MIInferior 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 Idoventricular rhythmComplications:Bradyarrhythmias protective mechanism, 90% of blood supply for SA & AV nodes from the RCAHypotension treated with fluids, consider right side involvement

Inferior Wall MI

Lateral Wall MILateral 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 V1 Sometimes an extension of an Anterior or Inferior MIConduction defects are rare

Anterior/Lateral Wall MI

Posterior Wall MIPosterior Wall MI: Occlusion of the Right Coronary Artery (RCA) or the Posterior Descending ArteryNo leads that look at the posterior wallLeads 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 disturbances*

Posterior Wall MI

Right Ventricular MIRight Ventricular MI: caused by proximal occlusion of the Right Coronary Artery (RCA)

Associated with Inferior Wall MI Can happen independently Standard 12-Lead does not assess right side of heart Infarction is significant Indicates large infarction Indicates involvement of both ventricles If the possibility of RVI exists a set of chest leads can be applied to the right side of the chest V1-6R leads look at right ventricle Lead V4R most accurate

Right Ventricular MI

Septal Wall MISeptal Wall MI: caused by septal perforation involving the LAD or the Posterior DescendingMost often in the setting of an Anterior MI Loss of R-wave in leads V1, V2 or V3May have ST segment elevation in V1 & V2 No reciprocal changes

Overview of Infarcts

Location of InfarctArterial SupplyIndicative ChangesReciprocal ChangesAnteriorLADV1-V4II, III, aVFInferiorRCAII, III, aVFI, aVLLateralCircumflexI, aVL, V5, V6V1PosteriorPosterior Descending (RCA)NoneV1, V2SeptalSeptal Perforating (LAD)Posterior Descending (RCALoss of R wave in V1, V2, or V3None

Overview of Infarcts Suspect infarction when there are indicative changes in at least two anatomically contiguous leads Indicative changes in many leads suggests larger infarct With Inferior Wall MI suspect Right Ventricular Wall Infarct Signs of possible Right Ventricular Wall Infarct: Hypotension JVD Clear lung sounds Causes of ST segment depression include digitalis, ischemia and reciprocal changes Suspect Posterior Wall Infarctions when an Inferior Wall Infarction has ST depression in Leads V1-V3

Complications of Myocardial InfarctionChest Pain: Most common complication Treatment: Oxygen and ASA (162 to 325)mgNTG initially with Morphine if pain persists Usually very effectiveRight Ventricular Wall Infarct: Reduces output of right ventricle decreasing left ventricular filling (decreased preload) NTG and Morphine can worsen conditions Decrease in blood pressure will worsen area of injury Presence of Inferior Wall Infarction with no EKG or clinical evidence of right side infarct does not merit any extra caution when using NTG and Morphine

Complications of Myocardial InfarctionAV Block Location: indicates electrical impulse from atrium is blocked from depolarizing the ventricles Most common block is in the AV Node (nodal block) Second most common block is in the Bundle Branches (infranodal) Infarct frequently produces AV Block due to increase in parasympathetic tone Local ischemia around node can produce the block Less serious than block caused by tissue injury or death Blocks in AV node produce narrow QRS complex Bundle Branches produce wide complexes

Complications of Myocardial InfarctionDetermining the type of QRS presented with is a useful tool in determining the location of the block

Nodal BlockInfranodal BlockCoronary SupplyRight Coronary ArteryLeft Coronary ArteryQR WidthNarrowWideStabilityGenerally StableOften UnstableAtropine ResponseUsually improvesOften does not respond

Complications of Myocardial InfarctionHypotension: A common treatment for hypotension which is secondary to the infarct is to administer fluid boluses and inotropic drugs (dopamine)Hypotension in the setting of an inferior wall infarction is most likely secondary to right ventricular involvement.Although RV Infarcts may require significant boluses to offset loss of preload, continuously monitor the patient for signs and symptoms of developing left sided failure.Hypotension in the setting of an anterior wall infarction may not tolerate fluid boluses and may require a dopamine infusion.

Complications of Myocardial Infarction

Left Coronary Artery OcclusionsRight Coronary Artery OcclusionsLeads Showing Indicative ChangesV1-V6, I, aVLII, III, aVF, V4R-V6RLocalizationSeptal, Anterior, Lateral, PosteriorInferior, Posterior, Right VentricularPain ControlNTG & Morphine as appropriateNTG & Morphine used with caution if RVI presentAV BlockInfrequent, usually wide ORS, often unstable, Atropine may be ineffective, use standby pacingFrequent, usually narrow QRS, Generally stable, Atropine often effective, May not require treatmentHypotension200-250 cc fluid bolus, inotropic medicationsVigorous fluid therapy if RVI present, inotropic medications

Clinical Pearls Suspect infarction when there are indicative changes in at least two anatomically contiguous leads Indicative changes in a greater number of contiguous leads suggests a more extensive infarction RV or Posterior infarcts should be considered in setting of Inferior Wall MIRV: ST segment elevation in rV4Posterior: ST depression +/or Tall Rwave in V1 & V2 Other clinical signs of RV Infarct may include: Hypotension and JVD in the setting of clear lung sounds Other causes of ST segment depression besides ischemia include digitalis effects and ventricular hypertrophy Suspect Posterior Wall Infarctions when an Inferior Wall Infarction has ST depression in Leads V1-V3

Questions

Tall R Wave and ST Depression are hallmarks of Posterior Wall MIThis 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.

Point out the epicardial artery and its branches reaching toward the endocardium.

The endocardium is less well perfused and has higher oxygen demand than epicardial tissue. Illustrate higher demand with glass of water.

When the myocardium is well perfused, the ST segments are isoelectric (equal to the T-P segment).

ST segments are iso-electric.The vessel lumen is now narrowed by a clot. If the clot is incomplete or collateral circulation is good, only the hardworking, poorly perfused sub-endocardial tissue will become ischemic.

This is represented on the ECG by ST depression or T wave inversion.Define ischemia.

Inadequate oxygen to tissue. Represented by ST depression or T inversion. May or may not result in infarct (duration of clot and demand). If infarct develops, may or may not display Q wave. The direction of ST deviation is a poor predictor of Q wave development.Note widespread ST depression and T waves inverted in several leads.Define injury. Ischemia affecting the epicardium represented by ST elevation.

Lack of oxygenation to tissue Represented by ST elevation. Refereed to as the injury pattern. Usually results in infarct (presumptive evidence of MI) If infarct develops, may or may not develop Q wave

The direction of ST deviation is a poor predictor of Q wave development.

Ask group to look for ST elevation.

The ST elevation implied epicardia ischemia (injury pattern).If the clot is complete or the collateral circulation is poor, the ischemia will be transmural (through to wall). This is seen on the ECG as ST segment elevation.

Most often this occurs due to a complete and persistent clot. Spontaneous lysis at this point is rare and the tissue is expected to infarct unless acute reperfusion therapy can be rapidly initiated.

ST segment elevation is presumptive evidence of ACUTE MI.Death of tissue.

Traditionally represented by wide (equal to or greater than 40ms) Q wave.

Not all infarcts develop Q waves.

The direction of ST deviation (elevation or depression) is a poor predictor of Q wave development.

Death of myocardial tissue may result in the development of a pathologic Q wave.

Q wave development can not be predicted by the direction of ST segment deviation.

It does not occur with all infarcts.Pathologic Q waves present in II, III and aVF suggest necrosis has occurred in the inferior region of the left ventricle.During the evolution of an infarct, Q waves, ST elevation, and T inversion may occur together.

ST elevation is the most important finding to the emergency care provider. It is presumptive evidence of acute myocardial infarction.A normal ECG does NOT rule out any Acute Coronary Syndrome.

ST segment depression represents ischemia, infarction is possible.

ST segment elevation represents epicardial ischemia, and is presumptive evidence of AMI.

Since necrosis may occur under all the these situations, a Q wave MI may follow ST elevation, ST depression or even a normal ECG.

Evidence of a Right Ventricular MI are present in Lead V4R only for the first four (4) hours of an MIMaybe just some discussion of reciprocal changes? Debate of significance? Not all MIs have reciprocal changes, that 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.Should also stress that NTG should be given cautiously to patients with borderline blood pressure when evidence of RV Infarct exists.Slide may be confusing. Better stated that if the QRS is narrow, then the block lies at the junction of the AV Node. If the QRS is wide, then the block lies below the level of the AV NodeInferior Wall MIs with RV involvement and hypotension may respond to fluid challenges of up to 2 liters. Boluses should be administered in 250 ml increments while assessing left ventricular function. Anterior Wall MIs may not tolerate even small amounts of fluid and may require pressor intervention in the setting of hypotension.