STEMI vs. STE-Mimic Thompson 2 Electrode placement V1 – 4th Intercostal space, right parasternal V2 – 4th Intercostal space, left parasternal V3 – Directly between V2 & V4 V4 – 5th Intercostal space, left mid clavicular V5 – Anterior axillary line, lateral to V4 V6 – Mid axillary line, lateral to V5 * Electrodes should be placed on a bare torso, with points of contact free of hair or moisture.
STEMI vs. STE-Mimic Thompson 3 The Culprit Electrode Leads with artifact Electrode Precordial Leads Check the associated electrode Leads I & II Check the Right Shoulder electrode Leads I & III Check the Left Shoulder electrode Leads II & III Check the Left Leg electrodeThe presence of artifact makes it very difficult to appropriately interpret a 12-lead ECG.While it may be nearly impossible to mitigate all artifacts, steps should be taken to assurethe cleanest tracing possible. Above is a table that describes which electrode is causingthe problem.
STEMI vs. STE-Mimic Thompson 4 Contiguous Leads Precordial Leads Limb Leads Right Left I aVR V1 V4 High Lateral Septal Anterior II aVL V2 V5 Inferior High Lateral Septal Low Lateral III aVF V3 V6 Inferior Inferior Anterior Low Lateral
STEMI vs. STE-Mimic Thompson 24ECG – 1 & ECG – 2These are both examples of Left Ventricular Hypertrophy with a typical Left Ventricular Strain Pattern. Because there is limitedspace on prehospital 12-lead print outs, the monitor actually cuts the depth and height of complexes short. This is to keep extra tall ordeep complexes from interfering with other leads. The ST-Elevation present in the right precordial leads (V1, V2, V3) is entirely dueto the LV-Strain pattern. With LV-Strain, you will typically see ST-Elevation in the right precordial leads, and ST-Depression in theleft precordial leads (V4, V5, V6)."Strain" is a pattern of asymmetric ST segment depression and T wave inversion. LV strain is most commonly seen in one or moreleads that look at the left ventricle (leads I, aVL, V4, V5, V6); less commonly it can be seen in inferior leads.Some clues to identifying LVH & LV-Strain:When the left ventricle enlarges (LVH), the leftatrium often follows suit, and becomes larger aswell. Left atrial enlargement can present as analtered p-wave morphology, known as P-Mitrale.A p-wave with the characteristic “double hump” isindicative of P-Mitrale. Left atrial enlargement canalso be identified in V1. If the P-wave in lead V1is biphasic, it may be due to left atrial enlargement.If it is deeper, than it is tall, LAE is likely. T-Wave Discordance With LVH, paced rhythms, ventricular rhythms, and Bundle Branch Blocks, T- wave discordance is a normal finding. T-wave discordance is present when the terminal deflection of the QRS-complex is opposite of the direction of the following T-wave. If you look at the image to the left, you will see that with both complexes, the last wave of the complex, and the T-wave are deflected in opposite directions. When this is present, and the terminal deflection of the QRS is negative (S-wave), ST- elevation is normal. This can usually be seen on a normal 12-Lead in V1, V2, V3.
STEMI vs. STE-Mimic Thompson 27ECG – 3, ECG – 4, ECG – 5, & ECG – 6These are various examples of Left Bundle Branch Block (LBBB). LBBB is most commonly identified by a supraventricular rhythm(p-waves are present), that is wide (greater than 3 small boxes, 120ms), and has a terminal S-wave in V1. This means that if the 12-lead shows a sinus or atrial rhythm wider than 3 small boxes, with a negative last wave of the QRS-complex in V1, it is probablyLBBB. Usually the terminal wave is the biggest wave in V1, so with LBBB, the QRS-complex typically presents as almost entirelynegative (down).It is important to remember that the width of a QRS-complex in a monomorphic rhythm (doesn’t change) can be determined in anylead. Sometimes the QRS complex may appear of normal width in one lead, while looking wide in others. Always go with the width ofthe QRS-complex where it looks the widest.Because Bundle Branch Blocks have T-wave discordance. STEMI is not generally determined in the presence of a LBBB. This isbecause LBBB has deep S-waves in the right precordial leads, causing the presence of ST-elevation without any myocardial damage.Sgarbossa’s CriteriaThis is an advanced skill used to determine the presence of an MI with a LBBB. Since this is not widely understood by most medicalprofessionals, it CAN’T be used to call a STEMI alert. The rule: If the ST-Elevation is greater than 25% of the preceding S-wave, orif concordant ST-elevation is present, an MI is almost 100% likely to be present.Non-Specific Intraventricular Conduction Delay (IVCD)A LBBB is a type of IVCD. To be a true LBBB, in addition to the V1 criteria, leadsI and V6 should have monomorphic R-wave QRS-complexes. If a 12-lead presentswith a LBBB pattern in V1, but has negative complexes in leads I & V6, it is actuallyconsidered a Non-Specific IVCD. This, however, is not of great importance in theemergency setting.STE-MimicThe important thing to remember is that a LBBB can look a lot like a STEMI. Do notinadvertently call STEMI alert on a patient with a LBBB, unless the LBBBspontaneously occurred right before your eyes.
STEMI vs. STE-Mimic Thompson 29ECG – 9ECG – 10
STEMI vs. STE-Mimic Thompson 30ECG – 7, ECG – 8, ECG – 9, & ECG – 10These are all examples of Benign Early Repolarization (BER), “Early Repol”. BER is one of the most common reasons formisdiagnosed STEMI. BER is caused by an elevation of the J-Point due to premature repolarization (recharging) of the ventricles. “Early Repol” Clues - No reciprocal changes – because an MI often causes st-depression in leads opposite to those with elevation - Asymmetrical T-waves – because an early infarction has hyperactute T-waves (tall, broad, & symmetrical) - Concave ST-elevation – because the presence of convex ST-elevation is almost always an MI - Notched J-points – not always present with early repol, but a GREAT indicator that it is NOT an MI - Normal R-wave progression – because a MI often causes poor R-wave progression (clockwise rotation)Remember, these clues don’t rule out a MI just because of their presence. For instance, if you have notched j-points, but reciprocalchanges are present, it is most likely a STEMI. These clues should be used together with patient presentation. If all clues are present,it is almost certainly NOT a STEMI.The chart above outlines reciprocal areas of the 12-lead. The imageto the right illustrates the difference between concave & convexST-elevation. Draw a line from the J-Point to the top of the T-wave, if the ST-segment falls below that line it is concave. If it is above the line, it is convex. Convex is worse!
STEMI vs. STE-Mimic Thompson 31ECG – 11ECG – 12
STEMI vs. STE-Mimic Thompson 32ECG – 13ECG – 11, ECG – 12, & ECG – 13These are all examples of Acute Pericarditis. Note the widespread ST-Elevation amongst the many leads. PR-depression is also acommon finding with pericarditis. The patient’s symptoms may be the biggest clue; positional pain relief is common.ST-Elevation that occurs simultaneously in leads I and II should always be very suspicious. The most common cause of this is acutepericarditis. Another cause would be an Apical MI (infarct of the apex). An apical Mi is just a fancy way to say that the entire bottomof the heart is infracted. This is very rare, yet very severe.All three of these examples were identified by the ECG monitor’s 12-lead interpretive algorhythm. All three of these patients weretreated as STEMI alerts, incorrectly. Sometimes the printout diagnosis is right! In fact, with a clean tracing, the 12-lead software isvery accurate at determining a STEMI, bundle branch block, LVH, and even early repolarization.
STEMI vs. STE-Mimic Thompson 33ECG – 14ECG – 15
STEMI vs. STE-Mimic Thompson 34ECG – 14 & ECG – 15These are both examples of Hyperkalemia. Hyperkalemia is an elevated serum potassium level, and may lead to lethal cardiacarrhythmias. The patients most susceptible to hyperkalemia are renal failure patients that require dialysis.ECG – 14: This 12-lead presents as a LBBB vs. Sine-wave. The patient’s history, and presentation should be used come to a soliddetermination. A Sine-wave is a sign of significant hyperkalemia, and may only last for minutes before degrading into a lethalarrythmia. A Sine-wave is present when there is a straight line from the tip of the S-wave (nadir) to the peak of the T-wave.ECG – 15: This 12-lead has a great example of peaked T-waves, indicating hyperkalemia. Note the tall, narrow T-waves in nearlyevery lead. The T-waves are actually larger than most of the QRS-complexes. This is a sign of increased potassium.
STEMI vs. STE-Mimic Thompson 35ECG – 16ECG – 16This is most likely an early Inferior Wall MI with lateral, and posterior wall extension. If you recall how the coronary anatomy works,the right coronary artery (RCA) is usually the producer of the posterior descending artery (85% of the time). The right coronary arterymay supply the inferior, posterior, and part of the lateral wall of the heart.ST- Elevation: minimal, but present in leads II & III, V5 & V6 (remember to compare against the following TP-Segment)ST- Depression: leads V1 & V2 have some ST-Depression, probably reciprocal to a posterior wall injuryT-Wave Inversion: lead aVL has a very indicative look of an inferior wall injury (aVL is the most reciprocal lead to lead III)Hyperacute T-Waves: the tall, symmetrical, broad-based t-waves in leads II & aVF are the easiest to identifyWith the combination of these findings, this patient should certainly be transported emergently to a PCI facility. Remember, 1mm ofSTE in two contiguous leads is all that is needed to call STEMI; we almost have that with leads II & III. This patient should bemonitored diligently for any changes.
STEMI vs. STE-Mimic Thompson 36ECG – 17ECG – 17This is an example of an Antero-Septal MI, with some lateral wall extension. This is likely due to a proximal occlusion of the LeftAnterior Descending coronary artery (LAD). The LAD, termed “Widow Maker”, supplies predominately the left ventricle.ST-Elevation: extensive, note the convex STE in V1 to V4.ST-Depression: There appears to be reciprocal changes in III & aVF, probably opposite to lateral wall injury.Notice how the amount of ST-Elevation present is not dependant on the size of the QRS-complex. This is damning evidence, in favorof an MI. With a benign cause of ST-elevation (STE), you have more STE with bigger QRS-complexes. If you look at this 12-leadthough, V3 has smaller QRS-complex than V1, but has much more STE.Also worth mentioning is V4. Note the size of the QRS-complexes in V4. When you have a very small QRS-complex, the degree ofSTE will be less. So a QRS-complex as small as the one in V4 with STE of 1mm is just as significant as the presence of“tombstones”.
STEMI vs. STE-Mimic Thompson 37ECG – 18ECG – 18This is an example of an extensive Inferior Wall MI (IWMI), with posterior & lateral wall extension. Just like ECG-16, this isprobably due to a proximal RCA occlusion.Something worth noting on this ECG is that lead III has more STE than lead II. This is an indication of possible right ventricular (RV)infarction. A RV MI can effectively turn the right side of the heart into a conduit system, making cardiac output very dependent onpreload. These patients often present with hypotension, and are very sensitive to preload reducers like nitroglycerine. Fluidadministration goes a long way to increase cardiac output for these patients. V4R is the most sensitive lead for identifying a RVinfarct. Move V3 & V4 to a mirrored placement on the right side of the patient’s chest to obtain V3R & V4R.Posterior Wall MI (PMI)With ST-depression in V1, V2, or V3 with or without T-wave inversion, a PWMI should be suspected; especially when an IWMI ispresent. Posterior leads (V7, V8, V9) may be used to conclude the presence of a PWMI.
STEMI vs. STE-Mimic Thompson 38ECG – 19ECG – 19This is another example of an Antero-Septal MI. Often, multiple sides of the heart are affected simultaneously. The anterior wall, andseptum are commonly infarcted together.The image to the right outlines the contiguous leads. Remember, STE must be present in 2or more contiguous leads for a STEMI Alert.
STEMI vs. STE-Mimic Thompson 39ECG - 20ECG – 20This is a rare example of an isolated Lateral Wall Infarct. This injury pattern is nearly always due to an occlusion to the LeftCircumflex (LCx). Since the LCx is a sharp-turned branch of the Left Main coronary artery, it is the least likely to develop asusceptible lesion.This 12-lead is difficult to interpret though, due to its PR-depression & concave STE.STEMI vs. STE-Mimic: There are some clues on this ECG to help us determine that it is an AMI. - The STE is in the left precordial leads. Usually with “early repol”, the benign STE is present mostly in V2 to V4. - No Global STE. All of the STE present is in contiguous leads, even minimally in aVR. - Reciprocal change. Lead III shows minimal, but present ST-depression. - The STE is concordant. This means that the STE is in the same direction as the terminal wave of the preceding R-wave. - Hyperacute T-waves. The T-waves in the leads with STE are tall, symmetrical, and broad-based.
STEMI vs. STE-Mimic Thompson 40ECG – 21ECG – 21This is an example of an Inferior Wall MI, with probable posterior wall extension.Its important to note that since aVR is the most reciprocal lead to Lead III, it almostalways has some form of reciprocal change present with an IWMI. The most commonchange is downwardly sloping ST-depression.Once again, like ECG – 16 & ECG – 18, we see possible posterior wall changes in thepresence of an IWMI. To obtain V7, V8, & V9, move leads V4, V5, & V6 just below thepatient’s left scapula. See the image to the right.
STEMI vs. STE-Mimic Thompson 41ECG – 22ECG – 22This is an example of Wellen’s Phenomenon. Sometimes called Wellen’s warning, syndrome, or sign, this phenomenon is anindication of an impending anterior infarction. This phenomenon does NOT always occur. There is no rhyme or reason as to whichpatients will present with Wellen’s prior to his or her anterior MI, but its presence is an ominous finding.Wellen’s Syndrome can present as it does above, with symmetrical inverted T-waves in theseptal and/or anterior leads (V2/V3 most common). It may also present as biphasic(positive & negative) T-waves, also most commonly seen in V2 & V3.In the absence of ST-elevation, these patients are not STEMI alerts, but should be transported toa STEMI facility, and monitored for the impending MI. Some literature states that an infarctionhas already begun when Wellen’s is present. It would be appropriate to treat these patients as ifthey are having a STEMI, notify the receiving facility of your concern, and call STEMI Alert ifSTE becomes present. Nitrates may impede STE from occurring.
STEMI vs. STE-Mimic Thompson 42ECG – 23ECG – 23This is another Antero-Septal Infarct with lateral wall extension (seen best in aVL). A 12-lead with this many ST-elevated leads maycreate concern about possible acute pericarditis. The reciprocal changes found in the inferior leads should erase any doubt, confirmingthat this is, in fact a STEMI.Remember that leads aVL & III are the most reciprocal to each other. If you seeST-segment changes in one of these leads, immediately look for inverse changesin the other. As you can see on this ECG, there is STE in aVL, and ST-depressionin lead III.This is true because of lead III & aVL’s placements. Look at the hexaxial referencesystem to the right. You can see that lead III’s positive pole is at 120 degrees, andaVL is at -30 degrees.
STEMI vs. STE-Mimic Thompson 43ECG – 24ECG – 25
STEMI vs. STE-Mimic Thompson 44ECG – 24 & ECG – 25These are both examples of Inferior Wall Infarction, with probable posterior wall extension. Note that both ECGs have reciprocalchanges present in aVL.Hyperacute T-WavesThe inferior leads in ECG – 24, and the low lateral leads (V5 & V6) in ECG – 25 both have examples of hyperacute T-waves. TheseT-waves are usually present for the first 30 minutes of an MI, and they are symmetrical, broad-based (wider than hyperkalemic T-waves), and tall.A symmetrical T-wave is always a result of some sort of pathology. They don’t necessarily have to be a result of an AMI, but mayindicate hyperkalemia (tall & narrow), or some other disease process. Conditions like LVH with left ventricular strain should alwayshave asymmetrical T-waves. Keep in mind; a person may still be having an MI with asymmetrical T-waves.
STEMI vs. STE-Mimic Thompson 45ECG – 26ECG – 26This ECG is an example of Right Bundle Branch Block (RBBB). RBBB is presentwhen a wide supraventricular rhythm presents with a positive terminal deflection in V1.Other findings include appropriate T-wave discordance, and a slurred S-wave in Lead Iand V6. The absence of the slurred S-wave in Leads I and V6 would indicate a non-specific intraventricular conduction delay (IVCD). This is of little importance in theprehospital arena though. For matters of simplicity, a wide supraventricular rhythm witha terminal R-wave in V1 is a RBBB.This ECG does not have any STE. Often, STE is misdiagnosed on 12-leads with RBBBbecause the J-point is inaccurately identified. Remember that the QRS-complexes aboveand below any lead in question will have J-points in the exact same spot. If you areunsure of the presence of ST-elevation, compare your J-points to the other leads in thesame vertical plane by drawing a straight line.
STEMI vs. STE-Mimic Thompson 46ECG – 27ECG – 27This is an early Antero-Septal Infarct. This ECG does not meetSTEMI Alert criteria yet, since V1 is the only lead with STE.The concavity of the STE in V1 is a significant sign of myocardialinjury. Other factors that help in determining that this ECGindicates an early AMI are the hyperacute T-waves in V2 to V4,and the reciprocal ST-depression in the inferior leads. Remember,when trying to determine if STE is present, compare the J-point tothe following TP-segment.
STEMI vs. STE-Mimic Thompson 47ECG – 28ECG – 28This is an example of Atrial Bigeminy with an Anterior Infarct.The extra-systole is probably occurring because of the severe 1st degree AV block found in the underlined rhythm. If you look at theECG from afar, it appears to have a pattern. This coupling of complexes is caused by the premature beat, persistently occurring inthe same position. This is the heart’s own electrical backup system taking effect. ST-elevation can be seen with both morphologies, inV3 through V5, indicating some lateral extension. The convex STE in V4 & V5 leaves no question, this IS an AMI. STEMI Alertshould be called for this patient.Side note: Premature complexes, whether ventricular or not, should not be treated if the underlined rhythm is very slow. The cardiacconduction system has a magnificent way of compensating for itself, and if this compensation is blocked by medications, the patient’scondition may decline rapidly. Not everything abnormal is bad!
STEMI vs. STE-Mimic Thompson 48ECG – 29ECG - 29ECG – 29This ECG is that of a Right Bundle Branch Block with Antero-Septal Infarction, and lateral extension.T-wave discordance is normal with a RBBB, however, it is not excessive enough to cause benign STE.STEMI Alert may still be called in the presence of a RBBB. This ECG has enough evidence to callSTEMI Alert. Massive STE in V2 through V6, with reciprocal changes in the inferior leads (II, III, aVF).Whenever you see a QRS-complex in V1 & V2 that is more positive than it is negative, RBBB should beconsidered. Right Ventricular Hypertrophy (RVH) may cause an R:S ratio in V1/V2 greater that 1 as well.RVH presents with narrow QRS-complexes, and RBBB presents with wide QRS-complexes. Even thoughthese QRS-complexes don’t appear excessively wide, they are greater than 120 ms, concluding thepresence of RBBB. Tall R-waves in V1/V2 may also be present with a posterior wall infarct; this is theequivalent of the Q-waves found with an older infarction.
STEMI vs. STE-Mimic Thompson 49ECG – 30ECG – 30This is an example of Global Ischemia. The ST-depression, found in most of the leads, indicates ischemia. This is a much moreinteresting ECG than that, however. This particular 12-lead tracing indicates a significant lesion in the Left Main Coronary Artery(LMCA); that’s the big one.This is one of the very few times that aVR can be used for more than just assuring correct limb lead placement. The rule states that ifyou have STE in aVR greater than the STE in V1, a LMCA lesion is very likely. The likeliness only improves in the presence ofglobal ST-depression. This is NOT an indication of occlusion; an occluded LMCA is present mostly on dead people only. This is nota STEMI Alert, but this patient should be transported to a PCI facility because of their risk of morbidity & mortality.* ST-Elevation in aVR may also be indicative of “Three Vessel Disease”, occlusions of the RCA, LAD, & LCx.** Isolated ST-Elevation in V1 may also be indicative of a Right Ventricular Infarct. Consider performing a right-sided 12-lead whenSTE is present in V1, hypotension exists, and/or inferior changes exist.
STEMI vs. STE-Mimic Thompson 50ECG – 31ECG – 31This is an Anterior Wall Infarct. This is not an obvious STEMI, but the tracings taken after this one were. Although V3 looks to haveST-elevation on this printout, it does not. If you compare the J-point in V3 to the TP-segment that follows, you will find that there isno STE; this is why we don’t compare the J-point to the PR-segment. The presence of hyperacute T-waves help to conclude thepresence of myocardial injury. The T-wave inversion in V1 & V2 is likely due to the zone of ischemia surrounding the area of injury.This ECG is an example of poor data quality. The limb leads have obscuring artifact, and the entire tracing has a wanderingbaseline—making interpretation more difficult. It is possible that a cleaner tracing may have had more clear cut STEMI criteriapresent. Fortunately, the 12-leads that followed had obvious STEMI criteria, and the patient was transported to a PCI facility.Worth Noting: Those tall, peaked P-waves, seen most obviously in the limb leads, are a sign of Right Atrial Enlargement. Thisfinding is called P-pulmonale. Right atrial enlargement is often a result of RVH; usually caused by pulmonary hypertension, resultingfrom a chronic respiratory pathology (COPD, Asthma, etc.). P-pulmonale & P-mitrale combined is known as biatrial enlargement.
STEMI vs. STE-Mimic Thompson 51ECG – 32ECG – 32This is an example of Reversed Limb Leads. While at first glance the inverted T-waves on this ECG look concerning, the problemwith this tracing are misplaced electrodes. Lead I should almost always be predominately positive, although a left posterior fascicularblock may cause Right Axis Deviation. aVR should always be mostly negative outside of paced or ventricular arrhythmias. Thecombination of a narrow QRS-complex, negatively deflected Lead I, and positively deflected aVR will almost always be due tomisplaced limb leads.Dextrocardia Situs Inversus (reversed heart) is a very uncommon congenital pathology that could also cause these findings.
STEMI vs. STE-Mimic Thompson 52ECG – 33ECG – 33This ECG shows a Sinus Tachycardia With Trigeminy. This is a more difficult 12-lead to interpret, but if you take a close look, youwill see that there is a regularly occurring aberrant complex, every third beat. If you look at the underlined complex, there appears tobe some form of an intraventricular conduction delay, similar to a LBBB. There is also ST-elevation present in V1 & V2. ST-depression appears in V5 & V6. The ST-segments are very diffuse in the inferior, and anterior leads. Due to the LBBB pattern in V1,we cannot call this a STEMI Alert.
STEMI vs. STE-Mimic Thompson 53ECG – 34ECG – 34This is an excellent example of Left Bundle Branch Block. Notice the presence of P-waves, the wide QRS-complex, and the terminalS-wave in V1. This ECG also displays how LBBB can alter ST-segments & T-waves without the presence of myocardial damage.