Diagnostics

Acute myocardial infarction with Left bundle-branch block: disproportional anterior ST elevation due to right ventricular myocardial infarction in the

presence of left bundle-branch block

Stephen W. Smith MD^a,b,?, William Heegaard MD^a,b, Fouad A. Bachour MD^b,c,

William J. Brady MD^d

^aDepartment of Emergency Medicine, Hennepin County Medical Center, Minneapolis, MN 55415

^bDepartment of Internal Medicine/Cardiology, University of Minnesota School of Medicine, Minneapolis, MN 55415 ^cDepartment of Internal Medicine/Interventional Cardiology, Hennepin County Medical Center, Minneapolis, MN 55415 ^dDepartment of Emergency Medicine, University of Virginia School of Medicine, Charlottesville, VA 22908

Received 22 May 2007; accepted 25 May 2007

Abstract A case of inferior and right ventricular acute myocardial infarction in the presence of left bundle-branch block is presented. The electrocardiogram manifests disproportional, discordant ST elevation in leads II, III, and aVF and in leads V₁ through V₄.

(C) 2008

A 55-year-old woman presented to the emergency department after 22 minutes of Chest tightness with gradual onset that began while gardening; it was 10/10 in severity at presentation, radiated down the left arm, and was associated with nausea, diaphoresis, and dizziness. The patient had no history of coronary disease but did have known left bundle- branch block (LBBB). She also had hypertension, hyperch- olesterolemia, and a remote smoking history; both of her parents had myocardial infarction (MI) in their 50s. She had a history of an equivocal adenosine sestamibi stress test several months previously. In addition, the patient had a history of asthma, gastroesophageal reflux, and hypothyr- oidism. Her medications were levothyroxine, 81 mg/d

* Corresponding author. HCMC Emergency Medicine, Minneapolis, MN 55415. Tel.: +1 612 873 3963.

E-mail address: [email protected] (S.W. Smith).

aspirin, fluticasone and albuterol inhalers, and simvastatin. On examination, she was pale and diaphoretic, with triage blood pressure of 150/80, pulse rate of 76, and pulse oximetry reading of 97%. The remainder of the examination was unremarkable.

An electrocardiogram (ECG) was recorded 14 minutes after presentation (Fig. 1). It showed discordant ST-segment elevation in leads III and aVF and in precordial leads V₁ through V₄, as well as minimal (b1 mm) concordant ST elevation in lead II. In both areas the discordant STE is out of proportion to the depth of the preceding S waves. The ST elevation at the J point in both of leads V₃ and V₄ is equal to 25% of the depth of the S wave, suggestive of ST-segment elevation myocardial infarction [1]. A previous ECG (Fig. 2) confirmed that this disproportional STE in inferior and anterior leads was increased from 4 months previous, at which time the ST elevation was only 8% of the

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Fig. 1 Presenting standard 12-lead ECG. This ECG is diagnostic of inferior MI by the Sgarbossa criteria (at least 1 lead with >=1 mm of concordant ST elevation [lead II]). There is also disproportionate discordant ST elevation in leads III and aVF. More importantly, there is disproportionate (ST/S ratio = 0.25) discordant ST elevation in lead V₄, which is a result of concurrent RV infarction.

S wave’s negative amplitude. A Right-sided ECG recorded 13 minutes later (Fig. 3) also showed discordant STE in right- sided leads V₃R through V₇R (V₁R and V₂R correspond to left-sided leads V₂ and V₁, respectively). The inferior and anterior excessively discordant ST elevation was noticed by the emergency physicians and diagnosed as inferior and right ventricular (RV) infarction. The physicians activated the coronary intervention team immediately.

The patient’s systolic blood pressure dropped to 100 mm Hg after sublingual nitroglycerine. Five hundred milliliters of normal saline was administered, and the systolic blood pressure returned to 120 mm Hg. Initial troponin I level was 0.1 ng/mL (Dade Stratus; 99% reference, b0.1 ng/mL). All other laboratory values were within normal limits. The patient was administered aspirin, heparin, metoprolol,

morphine, and eptifibatide and taken for coronary angio- gram and percutaneous coronary intervention. At angio- gram, the right coronary artery had a proximal occlusion, obstructing flow to the RV marginal branch (Fig. 4). Thrombolysis in Myocardial Infarction -3 flow was restored with angioplasty and stenting, and all ST elevation resolved. The first subsequent ECG was identical to the patient’s baseline 4 months before (Fig. 2). The second subsequent ECG 1 hour after percutaneous coronary intervention revealed concordant T-wave inversion in all limb leads and in precordial leads V₅ and V₆ (Fig. 5). The maximum troponin I level was 25 ng/mL. An echocardio- gram 2 days later showed inferoposterior wall motion abnormality of the Left ventricle and mildly decreased LV function.

Fig. 2 Baseline ECG with ST/S ratio of normal proportion (ST/S ratio = 0.08) and no concordant ST elevation.

Fig. 3 Right-sided ECG showing limb leads diagnostic of inferior MI, as in Fig. 1, but also with disproportional ST elevation in leads V₃R through V₆R.

The patient recovered fully.

In LBBB without acute myocardial infarction (AMI), repolarization (the ST segment and T wave, or ST-T complex) is in the opposite direction from depolarization (the major, terminal portion of the QRS complex); thus they are located on opposite sides of the isoelectric line. This relationship is described using the term discordant, which refers to the opposing positions of the major, terminal portion of the QRS complex and the ST-T complex. QRS complexes which are predominantly positive (eg, the qR, R, or Rs complex) are associated with discordant ST-segment depres- sion (Fig. 6A). Leads with predominantly negative QRS complexes (eg, the QS or rS complex) will demonstrate discordant ST elevation (Fig. 6B). This relationship is described as the rule of appropriate discordance. According to this rule, leads with either QS or rS complexes (predominantly negative QRS, mostly leads V₁ through V₄) may have nonpathologic markedly elevated ST seg- ments. Leads with a large monophasic R wave (predomi- nantly positive QRS) demonstrate nonpathologic ST- segment depression. A concordant ST segment is defined as an ST-T complex in the same direction as the QRS and is generally pathologic, as described below.

In an attempt to assist the clinician in this challenging presentation, Sgarbossa et al [2] have developed a clinical prediction rule to assist in the ECG diagnosis of AMI in the setting of LBBB using specific ECG findings. These investigators analyzed numerous abnormalities previously reported to be suggestive of AMI and found 3 specific ECG criteria that were independent predictors of AMI super- imposed on LBBB; furthermore, they devised a probability score for the diagnosis of AMI in the patient with LBBB. The ECG criteria suggestive of AMI with probability score include STE of greater than 1 mm in at least 1 lead, concordant with the QRS complex (score of 5, Fig. 7A) [1]; ST-segment depression of greater than 1 mm in leads with predominantly negative QRS, limited to leads V₁, V₂, or V₃

(score of 3, Fig. 7B) [2]; and STE of at least 5 mm, discordant with the QRS complex (score of 2, Fig. 7C) [3]. The authors suggested that a total score of 3 or more suggests that the patient is likely experiencing AMI based on the ECG criteria; with a score of less than 3, the ECG diagnosis is less assured, requiring additional confirmatory evidence. How- ever, even a score of 2 points, generated by concordant STE of at least 5 mm in leads V₁ through V₃, had a specificity of 89%.

Importantly, these criteria were developed using creatine kinase (CK)-MB as the reference standard, not coronary occlusion. Furthermore, ST elevation criteria were absolute, not proportional to the preceding QRS amplitude.

Fig. 4 Angiogram showing proximal RCA occlusion before the takeoff of the RV marginal branch that supplies the RV.

Fig. 5 “Reperfusion” T waves are inverted in leads III, aVF, V₅, and V₆. In leads II and aVF, only the later part of the T wave is inverted (“terminal T-wave inversion,” analogous to Wellens’ type A T waves as Wellens’ described for anterior MI). In all 3 leads the T waves, which are normally discordant to the QRS, have become concordant.

The ECG in this case had 0 points.

Validations of Sgarbossa’s criteria have had variable results [3-13]. A meta-analysis of these studies (abstract and poster, but unpublished), found that 2 points or more is 42% sensitive and 87% specific for AMI [14]. These studies have generated considerable debate [1,15]. The American College of Cardiology and American Heart Association guideline for the treatment of AMI has previously recommended reperfu- sion therapy for patients with chest pain and new, or presumably new, LBBB [16]. However, the updated version gives no specific recommendation; rather, it suggests using the Sgarbossa criteria.

A basic flaw in Sgarbossa’s study and in all the succeeding attempts to validate it is that they do not address

the critically time-dependent question of coronary occlu- sion: does the patient need to get immediate reperfusion therapy? All these studies were based on a reference standard of CK (+-MB), not on angiographic occlusion. Thus, in these studies, concordance was less than 50% sensitive for the combined end point equivalent to the combination of STEMI and non-STEMI (absence of complete persistent coronary occlusion, not needing emer- gent reperfusion, but may have positive CK-MB). In normal conduction, ST elevation is not more than 45% sensitive for AMI by CK-MB [17-20]; but it is very sensitive (85%-96%) for complete persistent left anterior descending occlusion [21]. Thus, it may be expected that concordant, or excessively discordant, ST elevation may be significantly

Fig. 6 Normal discordance in LBBB. Notice that the ST segment and T waves are in the same direction as the QRS.

Fig. 7 A shows concordant ST elevation (ST elevation in the same direction as the QRS). B shows concordant ST depression, which is present in leads V₁ through V₃ in posterior MI. C shows excessively discordant ST elevation; the ST segment is discordant to the QRS as it should be, but it exceeds 25% of the depth of the S wave, strongly suggesting STEMI.

more sensitive for complete persistent coronary occlusion than it is for any elevation of CK-MB level.

In the emergency situation, the critical diagnosis is whether there is acute persistent coronary occlusion that requires urgent reperfusion therapy. The biomarker diagnosis of MI (non-STEMI) is of secondary importance. Sgarbossa’s data did not address this distinction. Furthermore, the Sgarbossa rule does not address the principle of proportion- ality that repolarization is proportional to depolarization and that the size of the preceding QRS determines the size of the ST-T complex. Specifically, the depth, or negative amplitude, of the preceding S wave in V₁ through V₃ determines the height of the following and normally positive (discordant) ST segment.

More recently, it has been reported in an abstract of a derivational study that in the presence of discordance in the precordial leads, an ST/S ratio of at least 0.25 (where the ST segment is measured at the J point and both are measured relative to the PR segment) is more accurate than an STE of at least 5 mm in diagnosing anterior AMI due to left anterior descending (LAD) coronary occlusion, with 92% sensitivity and 97% specificity [1,22]. This latter rule adds specificity that is necessary because LBBB with a very large S-wave amplitude in V₁ through V₃ may result in an excessive secondary (discordant) ST elevation of at least 5 mm (Fig. 8) [23]. It adds to sensitivity for those instances in which the S wave and QRS amplitude are small and, in the absence of coronary occlusion, would manifest low-amplitude discor- dant ST elevation. This rule was not tested for occlusion of other coronary arteries or in other leads, but it demonstrated the possibility of a rule regarding ST/S proportion in LBBB.

In addition, changes from previous ECGs (increase in STE) can establish the diagnosis of Acute coronary occlusion [6,24].

Right ventricular AMI is most commonly due to disruption of flow in the RV marginal branch(es) off of the right coronary artery . ST elevation in the right-sided leads, especially V₄R, is the best ECG evidence of RV AMI [25-28]. Although “anterior” AMI usually refers to the LV anterior wall, the medial RV free wall is also anterior and, in the presence of normal conduction, may also have anterior ST elevation [25]. This usually occurs in V₁ but may occur across the anterior precordial leads and results in “pseu- doanteroseptal” AMI [29-31]. When such STE across the precordium is coincident with inferior STE in leads II, III, and aVF, then one must entertain the differential diagnosis of occlusion of a very large LAD or RCA that supplies both the inferior and anterior LV walls. One must also consider proximal RCA occlusion resulting in inferior AMI with large RV involvement, as in the case presented.

To our knowledge, there is no report of ST segment findings in RV infarction in the presence of LBBB or whether RV infarction may alter the 12-lead ECG in the presence of LBBB.

Lastly, terminal T-wave inversion is one cardinal sign of reperfusion in STEMI. However, this has never been

Fig. 8 Leads V₁ through V₃ from a patient’s baseline ECG, with no MI or ischemia. It meets the Sgarbossa criteria by having more than 5 mm of STE (7 mm), but it is not out of proportion, as the preceding S wave is 63 mm, for a ratio of 11%.

described for LBBB. Fig. 5 demonstrates the presence of these “reperfusion T waves” [32,33].

A case of chest pain with LBBB and discordant ST elevation in leads II, III, and aVF, as well as V₁ through V₄ is

presented. The discordance was out of proportion to the preceding S wave, with an ST/S ratio of at least 0.25. In leads V₁ through V₄, this disproportional ST elevation is generally indicative of LAD occlusion, but in this case it was indicative of anterior RV MI due to occlusion of the RCA proximal to the RV marginal branch. This was verified by immediate angiography and was opened with angioplasty and stenting.

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