Send Orders for Reprints to reprints@benthamscience.net Current Cardiology Reviews, 2021, 17, 41-49 41 REVIEW ARTICLE Conduction Disorders in the Setting of Acute STEMI Kjell Nikus1,*, Yochai Birnbaum2, Miquel Fiol-Sala3, Jani Rankinen1 and Antoni Bayés de Luna4 1 Department of Cardiology, Heart Center, Tampere University Hospital, Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland; 2The Section of Cardiology, Baylor College of Medicine and Texas Heart Insti- tute, Baylor St. Luke Medical Center, Houston, TX, USA; 3Illes Balears Health Research Institut (IdISBa), and Hospital Son Espases, Palma, Spain; 4Cardiovascular Research Foundation, Cardiovascular ICCC- Program, Research Institute Hospital de la Santa Creu i Sant Pau, IIB-Sant Pau, Barcelona, Spain Abstract: ST-elevation myocardial (STEMI) is frequently associated with conduction disorders. Regional myocardial ischemia or injury may affect the cardiac conduction system at various loca- tions, and neural reflexes or changes in the balance of the autonomous nervous system may be in- volved. Sinoatrial and atrioventricular blocks are more frequent in inferior than anterior STEMI, ARTICLE HISTORY while new left anterior fascicular block and right bundle branch block indicate proximal occlusion of the left anterior descending coronary artery. New left bundle branch block is associated with multi-vessel disease. Received: February 23, 2020 Revised: February 28, 2020 Accepted: March 12, 2020 Most conduction disorders associated with STEMI are reversible with reperfusion therapy, but they may still impair prognosis because they indicate a large area at risk, extensive myocardial infarction DOI: or severe coronary artery disease. 10.2174/1573403X16666200702121937 Acute STEMI recognition is possible in patients with a fascicular or right bundle branch block, but future studies need to define the cut-off values for ST depression in the leads V1-V3 in inferolateral MI and for ST elevation in the same leads in anterior STEMI. In the left bundle branch block, con- cordant ST elevation is a specific sign of acute coronary artery occlusion, but the ECG feature has low sensitivity. Keywords: Conduction disorder, acute coronary syndrome, acute myocardial infarction, bundle branch block, atrioventricular block, pacemaker. 1. INTRODUCTION (LCX) in about one fifth of individuals [5]. The side branch may also take off directly from the aorta. Very proximal 1.1. Bradyarrhythmias occlusion of the RCA caused by thrombus or aortic 1.1.1. Sinoatrial Block dissection may result in occlusion of the SA nodal branch, but occlusion may also result from stenting over the side Sinus bradycardia is frequent in acute inferior ST- branch ostium or from embolization. Ischemia of the cardiac elevation myocardial infarction (STEMI), especially during conduction system may be the result of these the first hours after occlusion of the coronary artery [1, 2]. pathophysiological processes. Sinus bradycardia was three times more common in inferior than in anterior acute myocardial infarction (MI) [3]. Brady- SA nodal branch occlusion may result in sinus bradycar- cardia may be caused by depressed automatism. The Bezold- dia, sinoatrial block or even asystole. Because the SA nodal Jarisch reflex includes a triad of bradycardia, hypotension branch also irrigates parts of the atrial walls, bradycardia and vasodilation, and inferior wall myocardial ischemia may may be accompanied by atrial MI. In practice, it is not possi- elicit this reflex [4]. The reflex is thought to result from the ble to distinguish between abnormalities in impulse forma- stimulus of cardiopulmonary mechanoreceptors that are as- tion, impulse conduction, or a combination, in the standard sociated with unmyelinated vagal afferent nerve fibers, clas- 12-lead ECG in patients with intermittent absence of sinus P sified as C-fibers. The sinoatrial (SA) nodal side branch (or waves. In sinus bradycardia and SA block, vagally induced artery) originates from the right coronary artery (RCA) in bradycardia will disappear with atropine while ischemic about two thirds (Fig. 1) and from the left circumflex artery bradycardia persists. Serrano et al. compared inferior STEMI patients based *Address correspondence to this author at the Department of Cardiology, on the culprit artery and the level of occlusion [2]. Sinus Heart Center, Tampere University Hospital, Ensitie 4, 33520 Tampere, bradycardia in the admission ECG was noted in 15% of the Finland; Tel: +358 50 5575 396; E-mail: kjell.nikus@sydansairaala.fi patients with RCA occlusion, but in none of the patients with 1573-403X/21 $65.00+.00 © 2021 Bentham Science Publishers 42 Current Cardiology Reviews, 2021, Vol. 17, No. 1 Nikus et al. as partial IAB. In STEMI patients (n=198) without a history of atrial arrhythmias treated successfully with primary percu- taneous coronary intervention (PCI), about half of the pa- tients had partial or advanced IAB at presentation, while six hours after PCI, the prevalence of IAB had decreased to one quarter [8]. RCA stenosis and diffuse coronary artery disease were associated with IAB at admission. Partial IAB on ad- mission and six hours post-PCI were independent predictors of atrial fibrillation at 12-month follow-up. In a registry study (n=972) of STEMI patients in sinus rhythm at hospital discharge, 21.3% had partial and 5.9% advanced IAB [9]. Patients with IAB had higher all-cause mortality than pa- tients without IAB, but the association was explained by older age and other variables, while the multivariable analy- sis did not show any independent association between IAB and prognosis. In patients (n=109) undergoing elective PCI of the RCA or LCX, atrial branch occlusion was associated with more frequent intra-atrial conduction delay, atrial tachycardia and atrial fibrillation [10]. After adjustment by a propensity score, atrial branch occlusion was an independent predictor of periprocedural infarction and atrial arrhythmias. The authors speculated that atrial ischemic episodes might be Fig. (1). Coronary angiography of the right coronary artery to illus- considered as a potential cause of atrial fibrillation in pa- trate the typical take-off of the side branch to the sinoatrial node. (A tients with coronary artery disease. higher resolution / colour version of this figure is available in the electronic copy of the article). 1.1.3. Atrioventricular Block LCX occlusion, and proximal RCA occlusion was more of- Atrioventricular (AV) block is a rather frequent finding ten associated with sinus bradycardia than mid or distal oc- in acute inferior STEMI. This is partly explained by the fact clusion. that the side branch to the AV node takes off distally from the posterolateral branch of the RCA (Fig. 2). In left- 1.1.2. Interatrial Block dominant circulation, the AV nodal branch arises from the Interatrial block (IAB) is a distinct ECG pattern caused LCX. The mechanism of AV conduction disturbance in by conduction delay between the right and left atrium, acute STEMI is different depending on the infarct location. probably resulting from local fibrosis reflected in the surface In a recent study of STEMI patients, RCA culprit predicted ECG as a biphasic morphology of the P wave in the inferior second degree Mobitz 2 or third-degree AV block (high de- leads (II, III, aVF) [6, 7]. This, together with a P-wave dura- gree AV block, HDAVB) with an odds ratio of 3.80 [11]. tion of ≥120 ms is considered as advanced IAB. P-wave du- RCA occlusion increases acetylcholine release from the ration ≥120 ms with normal P-wave morphology is defined myocardium of the inferior wall, and this contributes to the AV block. As for ischemia of the SV node, vagal overdrive Fig. (2). Coronary angiography of the right coronary artery shows the typical location of a branch to the atrioventricular node taking off from the right posterolateral (RPL) branch in the right-dominant coronary circulation. There is some atherosclerotic narrowing in the proximal part of the artery before the take-off of a large acute marginal branch and the right posterior descending branch (RPD). (A higher resolution / colour version of this figure is available in the electronic copy of the article). Conduction Disorders in the Setting of Acute STEMI Current Cardiology Reviews, 2021, Vol. 17, No. 1 43 disappears following the administration of intravenous atro- referred to previously, anterior, but not inferior location was pine, while AV block of ischemic origin persists. Ischemic associated with increased in-hospital mortality in HDAVB AV block usually presents a fast heart rate, while vagally patients after multivariate adjustment [18]. induced block does not [12]. According to Lie et al., in pa- The HORIZONS-AMI investigators also studied the in- tients with acute inferior MI and HDAVB, escape beats of cidence and prognostic implications of worsening AV block left bundle branch block (LBBB) morphology represent con- post-primary PCI [20]. They reported a 1.5% progression of ducted beats (AV junctional escape beats), while those with both second and third degree AV block after one year. Ante- right bundle branch block (RBBB) morphology most proba- rior STEMI was associated with worsened AV block, which bly represent fascicular of ventricular escape rhythm requir- was an independent predictor of all-cause death and major ing pacemaker implantation [13]. adverse cardiac events. The authors speculated that HDAVB Mobitz 1 (Wenckebach) second-degree AV block is most probably was the result of chronic damage to the AV con- frequent in inferior STEMI caused by RCA occlusion, and it duction system, related to left anterior descending (LAD) is usually transient and supra-Hisian, while Mobitz 2 -block coronary artery culprit lesions associated with extensive is usually infra-Hisian and implies a worse prognosis. In myocardial injury or infarction in these patients. infra-Hisian Mobitz 2 -block, the PQ-interval prolongation is usually mild, or the PQ interval may even be normal [12, 2. WHICH PATIENTS NEED A TEMPORARY 14]. PACEMAKER The prognostic implications of third-degree (complete) Although AV block associated with inferior STEMI is AV block depend on the STEMI location. When it occurs in usually temporary, benign and nearly always resolves with association with inferior STEMI, it usually evolves from a reperfusion therapy, temporary pacemaker therapy may be first-degree block, the QRS complex is narrow and the block necessary in case of hemodynamic compromise or bradycar- is supra-Hisian [12]. Advanced AV block presenting in an dia-related ventricular arrhythmias. According to the 2017 anteroapical infarction is usually accompanied by an infra- ESC Guidelines for the management of acute myocardial Hisian escape rhythm with a wide QRS complex, which may infarction in patients presenting with ST-segment elevation, result in hemodynamic deterioration. In this scenario, pace- temporary pacing is required in cases of sinus bradycardia maker implantation is indicated, but the outcome of the pa- with hemodynamic intolerance or HDAVB without stable tient is dependent on the extent of the infarction and the de- escape rhythm if the arrhythmia does not respond to positive gree of left ventricular dysfunction. In inferior STEMI, ad- chronotropic medication [21]. AV sequential pacing should vanced AV block is more often seen in patients with terminal be considered in patients with complete AV block, right ven- QRS distortion (Sclarovsky-Birnbaum grade III ischemia) tricular infarction, and hemodynamic compromise. Accord- than in those with grade II ischemia in the leads with ing to the 2013 ACCF/AHA STEMI guidelines, temporary ST-segment elevation [15]. pacing is indicated for symptomatic bradyarrhythmias unre- Berger et al. reported a 19% incidence of second- or sponsive to medical treatment, and application of transcuta- third-degree AV block in acute inferior MI by combining neous pacing pads for potential use is reasonable treatment results from studies published in the 1960’s - 1980’s [16]. In in HDAVB caused by inferior STEMI [22]. Prophylactic the recent HORIZONS-AMI trial, where almost all 3,115 placement of a temporary pacing system is recommended for study STEMI patients had primary PCI, HDAVB was found HDAVB in patients with anterior/lateral MI. in 1.5% of the patients [11]. Of the patients with HDAVB, 60.9% had a temporary pacemaker implanted in the cathe- 3. INTRAVENTRICULAR BLOCK terization laboratory. The incidence of HDAVB in a recent national survey from 2010 was 2.1% [17]. In a recent large 3.1. Fascicular Block STEMI registry study (n=16,536), the incidence of HDAVB The presence of a new left anterior fascicular block was 6.6% in inferior STEMI, but only 0.3% in anterior (LAFB) associated with anterior STEMI strongly supports a STEMI [18]. In a recent study of 4,799 patients with the culprit artery location in the proximal part of the LAD, be- acute coronary syndrome (ACS) (STEMI in 55.7%), 1.9% cause the left anterior fascicle receives its blood supply from presented with complete AV block [19]. the first major septal branch of the LAD [23]. The develop- HDAVB has been associated with an increased risk for ment of LAFB in the course of an inferior infarction (RCA in-hospital complications and higher mortality rates during or LCX occlusion) indicates significant concomitant stenosis follow-up; in the old study by Berger et al., the mean in- of the LAD before the first major septal branch. hospital mortality rate was 23% [16]. In the recent HORI- The appearance of the left posterior fascicular block, ZONS-AMI study, 30-day mortality in HDAVB was 8.8% which causes clear rightward deviation of the frontal plane compared with 2.3% (p=0.005) in the patients without QRS axis, is extremely rare in STEMI patients, and they are HDAVB. typically published as case reports. The left posterior fascicle In ACS patients with complete AV block in the previ- is the least vulnerable division of the intraventricular con- ously mentioned publication by Aguiar Rosa et al., 79.1% duction system. Compared with the left anterior fascicle, the had inferior STEMI compared with 21.9% in the patients left posterior fascicle is larger, has faster de- and repolariza- without complete AV block, and in-hospital mortality was tion, receives its blood supply from two coronary systems almost eightfold higher in patients with complete AV block (the LAD and the RCA), and runs through a more protected (23.1% vs. 3.5%) [19]. In the large STEMI registry study area, the left ventricular inflow tract with less mechanical 44 Current Cardiology Reviews, 2021, Vol. 17, No. 1 Nikus et al. Fig. (3). The ECG of a patient with proximal left anterior descending coronary artery occlusion: ST elevation in V1-V4, I and aVL and recip- rocal ST depression in II, III, aVF, and V5-V6. There is a right bundle branch block and left anterior fascicular block. In addition, there is grade III ischemia (J-point /R wave ratio of >0.5 in I, aVL, V2-V3). (A higher resolution / colour version of this figure is available in the electronic copy of the article). pressure impact [24]. Transient rightward shift of the frontal tively inhibiting conduction to the right bundle branch; the QRS axis in patients with acute anterior MI has been associ- His bundle is dually supplied by the AV nodal branch ated with severe two- or three-vessel disease, typically with (proximal His bundle) and the first septal branch of the LAD collateral circulation between the LAD and the RCA [25]. (distal His bundle) [14, 29]. Ischemia of the left posterior fascicle was suggested as the RBBB and LAFB were demonstrated in more than half etiologic factor. of the patients with acute total left main occlusion in a small The existence of a tetrafascicular intraventricular conduc- patient series (Fig. 4) [30]. In addition, there was typically tion system, including a left septal fascicle, remains debat- ST-segment elevation in the precordial leads from V2 to V4- able. A consensus statement ended up with some discrepan- 6 and in leads I and aVL, accompanied by ST-segment de- cies and, despite agreeing on the possible existence of an pression in the inferior leads. anatomical left septal fascicle, the electrocardiographic and A unique situation occurs when LAFB obscures RBBB, vectorcardiographic characteristics of a left septal fascicular abolishing the terminal S waves in leads I and aVL and the block (LSFB) were not universally accepted [7]. The most terminal R (R’) wave in V1 [31]. The existence of an RBBB important criteria to indicate the existence of LSFB is its is indicated by a broad QRS, wide R’ in lead aVR and a wide intermittent nature because other causes of prominent ante- S wave in leads V5 and V6. rior QRS forces, such as right ventricular hypertrophy, septal hypertrophy, lateral wall myocardial infarction, and lead RBBB does not interfere with the diagnosis of acute switch have to be considered in the ECG diagnosis. The pro- STEMI, and the ECG criteria for STEMI are the same as for posed ECG criteria for LSFB include normal or slightly in- patients with a narrow QRS. Diagnosing ST elevation in the creased (up to 110 ms) QRS duration, R-wave voltage of V1 anterior, inferior and lateral leads can easily be done in pa- ≥ 5 mm, R wave of V2 > 15 mm, and absence of a q wave in tients with RBBB. However, the diagnosis of inferolateral the left precordial leads V5, V6 and in the lead I [26]. Two STEMI equivalent in patients with RBBB and baseline ST case reports from patients with ST-elevation ACS, one with depression in V1-V3 is a challenge, and prospective studies anterior and one with inferior ST elevation, and prominent are needed to define the threshold for ST deviations in this anterior forces, indicating LSFB, were reported [27, 28]. setting. In acquired RBBB, there is typically an initial Q wave, while in pre-existing RBBB, there is rRS’ configura- 3.2. Right Bundle Branch Block tion [14] (Figs. 3 and 4). The right bundle branch receives its blood supply from RBBB was associated with increased mortality in acute an anterior septal branch of the LAD alone or jointly with MI patients in a meta-analysis, which included a consider- the AV nodal artery [29]. Therefore, a proximal LAD occlu- able proportion of acute STEMI patients [32]. A radical sion may result in a new RBBB, which is often accompanied change has recently taken place in the treatment recommen- by LAFB, because the right bundle branch and the left ante- dations for patients with new or presumably new RBBB and rior fascicle receive essentially the same blood supply (Fig. suspicion of acute MI. The Fourth Universal Definition of 3). RBBB + LAFB is a type of bifascicular block. These Myocardial Infarction (UDMI) states: “New, or presumed intraventricular blocks are mostly reversible with reperfusion new, RBBB without associated ST-segment or T wave therapy. changes is associated with thrombolysis in myocardial in- farction (TIMI) 0-2 flow in as many as 66% of patients Transient RBBB in inferior STEMI is rare, and is proba- (compared with >90% in those with ST-segment or T wave bly explained by ischemia of the proximal His bundle, selec- changes)” [33]. The 2017 ESC guidelines for STEMI also Conduction Disorders in the Setting of Acute STEMI Current Cardiology Reviews, 2021, Vol. 17, No. 1 45 Fig. (4). A patient with acute total occlusion of the left main coronary artery. The ECG shows ST elevation in V2-V6, I and aVL and recip- rocal ST depression in II, III, aVF. There is no ST elevation in leads aVR or V1, probably caused by the cancellation of electrical forces due to transmural ischemia from myocardial segments of both the left anterior descending and the left circumflex coronary artery. There is right bundle branch block associated with left anterior fascicular block and ventricular extrasystoles. (A higher resolution / colour version of this figure is available in the electronic copy of the article). specify: “Patients with myocardial infarction and RBBB Another clinical point related to RBBB is, whether a have a poor prognosis. It may be difficult to detect transmu- lower threshold for ST elevation than for narrow QRS ral ischaemia in patients with chest pain and RBBB. There- should be used in anterior STEMI because of the baseline fore, a primary percutaneous coronary intervention strategy secondary ST depression in the right precordial leads associ- (emergent coronary angiography and percutaneous coronary ated with this conduction disorder. Future studies should intervention if indicated) should be considered when persis- address this issue, and also the cut-off values for ST depres- tent ischaemic symptoms occur in the presence of RBBB” sion in the leads V1-V3 in inferolateral MI need to be estab- [21]. These recommendations are mainly based on a retro- lished. spective study by Widimsky et al. [34]. That study included 6,742 patients with AMI and showed that among the 427 3.3. Left bundle Branch Block patients with RBBB (53% with concomitant ST elevation), TIMI 0 flow in the infarct related artery was found in 51.7%, The left bundle branch is a larger and less vulnerable and primary PCI was performed in 80.1% of the patients. structure than the right bundle branch. The blood supply to TIMI flow 0 in the infarct-related artery was found in sig- the left bundle branch is clearly of dual origin as the anterior nificantly more patients with new or presumably new RBBB fascicle is supplied mainly by anterior septal branches of the (55%) than in the group with old RBBB (34.9%), old LBBB LAD and the posterior fascicle from the AV nodal artery, (28%) or new or presumably new LBBB (41.1%). It is which originates from the RCA or the LCX depending on somewhat surprising that also RBBB without ST elevation coronary artery dominance. Accordingly, severe two- or has been added as a STEMI equivalent ECG manifestation in three-vessel disease should typically be present for a new the new guidelines. The study results by Widimsky et al. LBBB to develop. apply to patients with adjudicated acute MI, not necessarily Sgarbossa et al. introduced three criteria to help in identi- to patients in the emergency care settings, and not all study fying acute MI in patients with LBBB [36]. They were: (1) patients underwent emergent angiography according to a ST-segment elevation ≥1 mm and concordant with the QRS primary PCI protocol. Significant coronary artery lesions in complex (5 points); (2) ST-segment depression ≥1 mm in patients with RBBB are not necessarily new culprit lesions. leads V1, V2 or V3 (3 points); and (3) ST-segment elevation Therefore, outcome data are needed in patients with chest ≥5 mm and discordant with the QRS complex (2 points). A pain, presumably new RBBB and no significant ST deviation total score of three or more points was considered diagnostic treated with or without primary PCI. Also the usefulness of of acute MI, whereas a score of 2 points suggests an acute primary PCI for patients presenting with RBBB and atypical MI. A meta-analysis reported the Sgarbossa criteria to be symptoms (shortness of breath, acute heart failure, etc.) specific (98%) but with low sensitivity (20%) [37]. Concor- should be prospectively tested. dant ST elevation has proved to be the single most specific A more recent article by Neumann et al. included 4,067 criterion for the diagnosis of acute MI in the presence of patients with suspected acute MI [35]. RBBB was found in LBBB, and improves the detection of this “STEMI equiva- 3.1% of the patients, and of them, only 20.8% had a final lent” [38] (Fig. 5). An adaptation of the Sgarbossa criteria, diagnosis of acute MI (six had STEMI and 17 non-ST eleva- including ST-elevation to S-wave ratio may be somewhat tion MI). Mortality for patients with RBBB at 1-year follow- complicated for use in the emergency setting [39]. Also, se- up was 10.7% compared to 3.2% in the patients without rial ECG recordings may be helpful for acute MI diagnosis broad QRS. The study data challenge the concept of RBBB in patients with acute chest pain or equivalent and LBBB as an indication for emergent coronary angiography, as the [40]. likelihood of MI was similar to that of patients without bun- In a study from the Minneapolis Heart Institute STEMI dle branch block. protocol (n=3,903), new or presumably new LBBB was pre- 46 Current Cardiology Reviews, 2021, Vol. 17, No. 1 Nikus et al. a) b) Fig. (5). The ECG of a 74-year old man recorded 2.5 h after the initiation of chest pain. The medical history contains permanent atrial fibril- lation with poorly controlled warfarin therapy, peripheral atherosclerosis, chronic obstructive pulmonary disease and frequent ventricular extrasystoles. The ECG in (a) shows LBBB with concordant ST elevation in I, and V5-V6. There is discordant ST elevation in V3-V4, but less than five mm. Coronary angiography showed single vessel disease with an occluded diagonal branch, possibly of embolic origin. (b) A previous ECG of the patient showing atrial fibrillation and LBBB (QRS 168 ms) with the “normal” secondary discordant ST/T changes asso- ciated with the conduction disorder. (A higher resolution / colour version of this figure is available in the electronic copy of the article). sent in 3.3% of the patients [41]. The LBBB patients were giography. Of these, 22% had a culprit vessel occlusion, older, more commonly women, with a lower ejection frac- while the emergent revascularization rate was 11.6%. tion, and more often presented with cardiac arrest or heart In a recent large registry study of patients with a definite failure than those without new LBBB. The patients with new diagnosis of acute MI, crude in-hospital mortality of patients LBBB had fewer culprit arteries (54.2% vs. 86.4%, with LBBB was 16.2% versus 6.5% for patients with STEMI p<0.001), but at one-year follow-up they had higher all- [43] The patients with LBBB were older, with a greater bur- cause mortality. The authors tested a hierarchical algorithm den of risk factors and comorbidity, and they were less likely based on hemodynamic instability and Sgarbossa concor- to receive medication and invasive therapy. dance criteria. The algorithm yielded high sensitivity (97%) and negative predictive value (94%) for identification of a In patients (n=8,830) with suspected acute MI, LBBB culprit lesion, while specificity was 48%. was present in 2.8%, and of these 30% had a final MI diag- nosis, with similar incidence in those with known LBBB vs. Another study from the US reported new or presumably those with presumably new LBBB [44]. ECG criteria had new LBBB in 69/802 (8.6%) patients in the hospital primary low sensitivity (1%-12%) but high specificity (95%–100%) PCI laboratory activation database [42]. Less than 30% of for acute MI. The study showed that combining ECG criteria the patients with new or presumably new LBBB had tro- with high sensitive troponin testing allows early and accurate ponin elevation, and 54% underwent emergent coronary an- diagnosis of acute MI in LBBB. Conduction Disorders in the Setting of Acute STEMI Current Cardiology Reviews, 2021, Vol. 17, No. 1 47 The fourth UDMI states: “In patients with LBBB, ST- MI = Myocardial Infarction segment elevation ≥1 mm concordant with the QRS complex PCI = Percutaneous Coronary Intervention in any lead may be an indicator of acute myocardial ische- mia” [31]. The conclusion was that since the detection of RBBB = Right Bundle Branch Block ischemia by the ECG in LBBB is difficult, decisions con- RCA = Right Coronary Artery cerning urgent reperfusion therapy should be based mainly on symptoms and hemodynamic parameters. SA = Sinoatrial According to the 2013 ACCF/AHA STEMI guidelines, STEMI = ST-elevation Myocardial Infarction   “New or presumably new LBBB has been considered a TIMI = Thrombolysis In Myocardial Infarction STEMI equivalent. Most cases of LBBB at time of presenta- tion, however, are “not known to be old” because of prior UDMI = Universal Definition of Myocardial Infarc- electrocardiogram (ECG) is not available for comparison. tion New or presumably new LBBB at presentation occurs infre- quently, may interfere with ST-elevation analysis, and CONSENT FOR PUBLICATION   should not be considered diagnostic of acute myocardial in- Not applicable.   farction (MI) in isolation” [22]. The 2017 ESC STEMI guidelines specify: “In the presence of LBBB, the ECG di- FUNDING   agnosis of acute myocardial infarction is difficult but often possible if marked ST-segment abnormalities are present. None.   Somewhat complex algorithms have been offered to assist the diagnosis, but they do not provide diagnostic certainty. CONFLICT OF INTEREST   The presence of concordant ST-segment elevation (i.e. in leads with positive QRS deflections) appears to be one of the The authors declare no conflict of interest, financial or best indicators of ongoing MI with an occluded infarct ar- otherwise.   tery. Patients with a clinical suspicion of ongoing myocardial ischaemia and LBBB should be managed in a way similar to ACKNOWLEDGEMENTS   STEMI patients, regardless of whether the LBBB is previ- Declared none.   ously known. It is important to remark that the presence of a (presumed) new LBBB does not predict an MI per se”. [20]. REFERENCES Hence, recognition of an impending acute myocardial [1] Zipes DP. The clinical significance of bradycardic rhythms in acute infarction in patients with LBBB remains a challenge. Deci- myocardial infarction. 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