Suspected myocardial infarction and left bundle branch block: electrocardiographic indicators of acute ischaemia

Diagnosis of myocardial infarction and ischemia in the setting of bundle branch block and cardiac pacing

The diagnosis of myocardial infarction (MI) in the presence of left bundle branch block (LBBB) or during ventricular pacing (VP) is challenging because of inherent changes in the sequence of ventricular depolarization and repolarization associated with both conditions. Although LBBB and right ventricular (RV) pacing may both produce abnormalities in the ECG, it is often possible to diagnose an acute MI (AMI) or an old MI based on selected morphologic changes. Primary ST-segment changes scoring 3 points or greater according to the Sgarbossa criteria are highly predictive of an AMI in patients with LBBB or RV pacing. The modified Sgarbossa criteria are useful for the diagnosis of AMI in patients with LBBB; however, these criteria have not yet been studied in the setting of RV pacing. Although changes of the QRS complex are not particularly sensitive for the diagnosis of an old MI in the setting of LBBB or RV pacing, the qR complex and Cabrera sign are highly specific for the presence of an old infarct. Diagnosing AMI in the setting of biventricular (BiV) pacing is challenging. To date there is minimal evidence suggesting that the traditional electrocardiographic criteria for diagnosis of AMI in bundle branch block may be applicable to patients with BiV pacing and positive QRS complexes on their ECG in lead V1. This report is a careful review of the electrocardiographic criteria facilitating the diagnosis of acute and remote MI in patients with LBBB and/or VP.

Left bundle branch block without concordant ST changes is rarely associated with acute coronary occlusion

BACKGROUND

The Sgarbossa score has been used to identify acute myocardial infarction on ECG in the presence of LBBB but has relied on elevated CK-MB for validation rather than angiographic evidence of vessel occlusion.

METHODS

We determined (a) the presence or absence of Sgarbossa criteria with concordant (S-con) or discordant (S-dis) ST changes, (b) the presence of acute coronary occlusion or likely recent occlusion on angiography and (c) the biochemical evidence of myocardial infarction (Troponin T >0.10 μg/L, Troponin I >1.0 μg/L) in patients field-triaged with suspected AMI and LBBB.

RESULTS

Between April 2004 and March 2009, 102 patients had field ECGs transmitted by paramedics for triage--8 with S-con, 26 with S-dis and 68 with LBBB alone. Acute coronary occlusion was present in 8/8 with S-con but none of the S-dis or LBBB alone patients, and in all 8 S-con patients reperfusion resulted in resolution of S-con changes. Likely culprit lesions with TIMI 3 flow were found in 3 S-dis patients but stenting did not result in resolution of S-dis. LBBB did not resolve in any patient. Troponin was elevated in 26 patients--11 with occlusion or likely culprit lesions, 15 with non-ischaemic causes.

CONCLUSIONS

In the absence of S-con, LBBB is not associated with acute coronary occlusion and should not be used as criteria for reperfusion therapy in myocardial infarction.

Evolving considerations in the management of patients with left bundle branch block and suspected myocardial infarction

Patients with a suspected acute coronary syndrome and left bundle branch block (LBBB) present a unique diagnostic and therapeutic challenge to the clinician. Although current guidelines recommend that patients with new or presumed new LBBB undergo early reperfusion therapy, data suggest that only a minority of patients with LBBB are ultimately diagnosed with acute myocardial infarction, regardless of LBBB chronicity, and that a significant proportion of patients will not have an occluded culprit artery at cardiac catheterization. The current treatment approach exposes a significant proportion of patients to the risks of fibrinolytic therapy without the likelihood of significant benefit and leads to increased rates of false-positive cardiac catheterization laboratory activation, unnecessary risks, and costs. Therefore, alternative strategies to those for patients with ST-segment elevation myocardial infarction are needed to guide selection of appropriate patients with a suspected acute coronary syndrome and LBBB for urgent reperfusion therapy. In this article, we describe the evolving epidemiology of LBBB in acute coronary syndromes and discuss controversies related to current clinical practice. We propose a more judicious diagnostic approach among clinically stable patients with LBBB who do not have electrocardiographic findings highly specific for ST-segment elevation myocardial infarction.

Using the 12-lead ECG to diagnose acute myocardial infarction in the presence of left bundle branch block

The 12-lead ECG is a powerful clinical tool used to risk stratify patients presenting to the emergency department with chest pain. In particular the ECG is used as the diagnostic tool to instigate reperfusion therapy in patients with acute coronary syndromes. The ECG features of acute myocardial infarction (AMI) may be masked by the presence of left bundle branch block (LBBB) and the ECG may be difficult to interpret. Invariably this results in delays to the provision of thrombolysis to these patients despite the mounting body of evidence which demonstrates that patients with AMI who present with LBBB have greater in-hospital mortality than those who do not. Difficulties in interpreting the ECG in these patients can therefore delay treatment and compromise their prognosis. The utility of the ECG for the diagnosis of AMI in the presence of LBBB has recently received renewed attention. ECG criteria have been identified which have a high association with AMI in patients with LBBB and two ECG tools have been evaluated in clinical practice which utilise these ECG criteria. The use of these simple algorithmic tools is recommended for clinical practice.

Electrocardiographic Diagnosis of Myocardial Infarction during Left Bundle Branch Block

The electrocardiographic diagnosis of myocardial infarction (MI) in the presence of left bundle branch block (LBBB) has long been considered problematic or even almost impossible. Many proposed ECG markers in the old literature have now been discarded. However, the advent of reperfusion therapy has generated greater interest in the ECG diagnosis of acute MI in LBBB where ST-segment deviation is the only useful sign. As such, the ST-segment criteria cannot be used to rule out MI, but they can help to rule it in. Criteria for old MI (based on QRS changes) have not been reevaluated for almost 20 years and continue to exhibit low sensitivity, but high specificity.

Acute coronary syndromes

Despite technologic advances in many diagnostic fields, the 12-lead ECG remains the basis for early identification and management of an acute coronary syndrome. This article reviews the use of the ECG in acute coronary syndromes.

Unraveling the spectrum of left bundle branch block in acute myocardial infarction: insights from the Assessment of the Safety and Efficacy of a New Thrombolytic (ASSENT 2 and 3) trials

BACKGROUND

Left bundle branch block (LBBB) complicates the diagnosis of acute myocardial infarction (AMI). The Sgarbossa criteria were developed from GUSTO I to surmount this diagnostic challenge but have not been prospectively validated in a large population with presumed AMI. We evaluated their utility in the diagnosis and risk stratification of AMI patients in ASSENT 2 & 3.

METHODS

Baseline electrocardiograms (ECG) of LBBB patients were scored using Sgarbossa's criteria (0-10) by 2 readers blinded to the CK/CK-MB data and clinical outcomes; 267 (1.2%) patients had LBBB on their baseline ECG.

RESULTS

Among 253 LBBB patients with available peak CK/CK-MB data, 158 (62.5%) had peak CK/CK-MB levels > 2x ULN, thereby qualifying for the diagnosis of AMI. A Sgarbossa score of 3 was shown in 48.7% of LBBB patients with elevated CK/CK-MB versus in 12.6% of those without a CK/CK-MB rise (P < .001). Patients with higher Sgarbossa scores, ie, 3, had a higher mortality compared with those with a score < 3, (23.5% vs 7.7% at 30 days P < .001; and 33.7% vs 20.2% at 1 year, P < .001, respectively).

CONCLUSIONS

Our findings validate the utility of Sgarbossa criteria for diagnosing AMI in the setting of LBBB. These criteria provide a simple and practical diagnostic approach to risk stratify this diagnostically challenging high-risk group and optimize risk-benefit of acute therapy.

ECG Patterns Confounding the ECG Diagnosis of Acute Coronary Syndrome: Left Bundle Branch Block, Right Ventricular Paced Rhythms, and Left Ventricular Hypertrophy

The ECG has limitations in the evaluation of the chest-pain patient, including the presence of confounding ECG patterns; the ECG patterns that confound the diagnosis of acute myocardial infarction(AMI) include left bundle branch block (LBBB), ventricular paced rhythms (VPR), and left ventricular hypertrophy (LVH). These patterns produce new ST-segment/T-wave abnormalities, which are the new normal findings in these patients and may lead the clinician astray in two distinct instances: (1) diagnosing ECG change related to acute coronary syndromes (ACS) when the abnormality results solely from the confounding pattern; and (2) not acknowledging the confounding nature of these ECG patterns in the evaluation of potential ACS, thereby placing excessive diagnostic confidence in the ECG. This article highlights the diagnostic dilemma encountered in these confounding ECG patterns; the discussion focuses on the expected ECG abnormalities in these patients and the findings seen in ACS.

Simplifying thrombolysis decisions in patients with left bundle branch block

OBJECTIVES

To redesign and simplify an existing decision algorithm for the management of patients who present to the emergency department with chest pain and left bundle branch block (LBBB) based on the Sgarbossa criteria. To compare its reliability with the current algorithm.

METHODS

A simplified algorithm was created and tested against the existing algorithm. Electrocardiograms (ECGs) of patients with LBBB were presented to 10 emergency department doctors with both old and new algorithms a week apart. Six ECGs displayed the relevant criteria for thrombolysis and had proven acute myocardial infarction (AMI) based on a gold standard of enzyme measurements. Subjects were asked whether or not they would thrombolyse a patient presenting with the given ECG using each of the algorithms as a guide.

RESULTS

The new algorithm has demonstrated improvements in terms of an increase in appropriate thrombolysis and a reduction in inappropriate thrombolysis. Specificity for AMI rose from 0.85 to 0.99 and sensitivity from 0.38 to 0.6. kappa score showed greater agreement with the gold standard.

CONCLUSION

Patients with AMI and LBBB have a significantly poorer outcome than those without LBBB. Despite this, thrombolysis is less likely to be given to patients with AMI and LBBB. This study demonstrates that in part this is because of cognitive difficulties using the current algorithm. The proposed proforma addresses these issues and provides a simple tool to aid appropriate treatment in this group of patients.

Body surface mapping improves early diagnosis of acute myocardial infarction in patients with chest pain and left bundle branch block

OBJECTIVE

To test prospectively depolarisation and repolarisation body surface maps (BSMs) for mirror image reversal, which is less susceptible to artefact, in patients with acute ischaemic-type chest pain, and to compare these BSM criteria with previously published 12 lead ECG criteria.

METHODS

An 80 lead portable BSM system was used to map patients presenting with acute ischaemic-type chest pain and a 12 lead ECG with left bundle branch block (LBBB). Acute myocardial infarction (AMI) was defined by serial cardiac enzymes. Each 12 lead ECG was assessed by the criteria of Sgarbossa et al and Hands et al for diagnosis of AMI. Depolarisation and repolarisation BSMs were assessed for loss of mirror image reversal of QRS with ST-T isointegral map patterns and a change in vector angle from QRS to ST-T outside 180+/-15 degrees -findings typically seen in LBBB with AMI.

RESULTS

Of 56 patients with chest pain and LBBB, 18 had enzymatically confirmed AMI. Patients with loss of BSM image reversal were significantly more likely to have AMI (odds ratio 4.9, 95% confidence interval 1.5 to 16.4, p = 0.007). Loss of BSM image reversal was significantly more sensitive (67%) for AMI than either 12 lead ECG method (17%, 33%) albeit with some loss in specificity (BSM 71%, 12 lead ECG 87%, 97%). Patients with AMI compared with those without AMI had a greater mean change in vector angle outside the normal range (180+/-15 degrees ), particularly between QRS isointegral and ST60 isopotential (the potential 60 ms after the J point at each electrode site) BSMs (19 degrees v 9 degrees, p = 0.038). Loss of image reversal and QRS-ST60 vector change outside 180+/-15 degrees had 61% sensitivity and 82% specificity for AMI (odds ratio 7.0, 95% confidence interval 2.0 to 24.4, p = 0.001).

CONCLUSIONS

BSM compared with the 12 lead ECG improved the early diagnosis of AMI in the presence of LBBB.

Prehospital thrombolysis: lessons from Sweden and their application to the United Kingdom

OBJECTIVE

To study the successful implementation of paramedic administered prehospital thrombolysis in Sweden, and to consider the implications of this for the UK.

METHODS

A series of research visits were undertaken, including visits to Uppsala Hospital and dispatch centre, ambulance stations in several counties of Sweden and Dalarna County, which has one of the longest experiences of telemedicine supported prehospital thrombolysis in Europe. Data relating to prehospital thrombolysis, stages in successful implementation, and potential barriers to change were identified.

RESULTS

Two thirds of the hospitals in Sweden now have some form of prehospital thrombolysis. A nationally agreed and standardised training programme and the fact that many ambulance paramedics are also qualified nurses has facilitated successful introduction, but Sweden's low population density is also an important factor. Data from Dalarna County indicate that the median "pain to needle" time has been reduced by 45 minutes with a concurrent reduction in complications from 50% to 25% (p=0.018). Inhospital mortality has also reduced from 12% to 6%, but with the small numbers involved this improvement does not achieve statistical significance (p=0.36).

CONCLUSION

If the outcome of acute myocardial infarction in the United Kingdom is to be improved, and National Service Framework targets met, then prehospital thrombolysis is an important development. Several technical solutions already exist, and a single bolus thrombolytic agent is now available, but the main barriers to full implementation are related to the establishment of an effective training programme and the organisational changes that will facilitate this new practice. High quality research is urgently needed to guide the implementation of prehospital thrombolysis in a clinically and cost effective way.

Value of the ECG in suspected acute myocardial infarction with left bundle branch block

Uncomplicated left bundle branch block (LBBB) is characterized by true ST-segment shifts resulting from delayed repolarization in the left ventricle with respect to the right ventricle. When acute coronary occlusions develop in the setting of previous or new LBBB, 12-lead eCG manifestations of injury may also appear. They consist of a more pronounced ST-segment elevation, of ST-segment deviations opposite to those of uncomplicated LBBB, or both. We have reported that the only 3 independent ECG signs of acute MI during LBBB among patients with chest pain or history of coronary disease are: ST elevation > or = 1 mm in leads with a positive QRS, ST-depression > or = 1 mm in V1 to V3, and ST elevation > or = 5 mm in leads with a negative QRS. In our study, the clinical prediction rule score values of these signs were 5; 3; and 2, respectively. A score > or = 3 made a diagnosis of MI with a 90% specificity and a score of 2 with > 80%, specificity. Recent validation studies have confirmed that the presence of any of these ECG signs is associated with a sensitivity of 44 to 79% and a specificity of 93 to 100%. Sensitivity increases if serial or previous ECGs are available for comparison. Interobserver agreement is very high. While current practice guidelines recommend thrombolysis for all patients with chest pain and LBBB, concern among physicians about hemorrhagic stroke prevents many of these patients from receiving timely treatment. In a population with LBBB and chest pain where our proposed ECG criteria were not ascertained, only 73% of eligible patients received thrombolysis; on the other hand, 48% of patients with no biochemical evidence of MI were thrombolyzed. For the latter group, the clinical prediction rule had a score of 0. Instead, 79% of patients with confirmed acute MI had a prediction rule score > or =2. Similar values applied to a subgroup of patients with serial ECGs. We propose that thrombolysis among patients with chest pain and LBBB be decided on the basis of a systematic ECG review to "rule patients in". This provision may result in both a significant reduction in the number of patients without infarction who receive thrombolysis and in timely treatment of those who do have MI.

Electrocardiographic diagnosis of acute myocardial infarction: Current concepts for the clinician

BACKGROUND

Over the past 2 decades, the 12-lead electrocardiogram has attained special significance for the diagnosis and triage of patients with chest pain because timely detection of myocardial injury and a rapid assessment of myocardium at risk proved pivotal to implementing effective reperfusion therapies during acute myocardial infarction. However, this wealth of information could still be underutilized by clinicians who may restrict their diagnostic quest in patients with chest pain to the more classic electrocardiographic signs.

METHODS

The medical literature on electrocardiographic manifestations of acute myocardial infarction was extensively reviewed.

RESULTS

The widespread utilization of both coronary angiography and methods to determine myocardial function and metabolism in patients with acute myocardial infarction over the last 10 years has provided the means for rigorous comparisons with electrocardiographic information. We summarize these electrocardiographic signs and patterns in terms of their relevance to the clinician to help reduce the incidence of "nondiagnostic electrocardiograms" and improve timely decision-making.

CONCLUSIONS

The electrocardiogram continues to be an invaluable tool in the initial evaluation of patients with chest pain. The plethora of data currently available on electrocardiographic changes correlating with myocardial injury allows clinicians to make faster and better decisions than ever before.

ECG criteria in diagnosis of acute myocardial infarction in the presence of left bundle branch block

BACKGROUND

The diagnosis of acute myocardial infarction in the presence of left bundle branch block is difficult. Recently a diagnostic ECG scoring system was suggested, showing good diagnostic abilities. This scoring system has never been tested in a prospective manner; we have done so and investigated if it might bear prognostic information.

METHODS

A prospective multi-centre study. Consecutive patients with left bundle branch block and suspicion of acute myocardial infarction, admitted to 14 Swedish coronary care units. Recruitment from March 1996 to December 1997. ECG registered on admission and after 12-24 h.

RESULTS

One hundred and fifty-eight patients were included, mean age 74.9 years. Seventy-six patients (48%) had an acute myocardial infarction. The proposed cut-off total score of > or = 3 of the ECG scoring system for the diagnosis of acute myocardial infarction had a sensitivity of 17.1% (95% CI 8.6-25.6%) and specificity of 94.0% (95% CI 88.9-99.1%). Clinical judgement of acute myocardial infarction resulted in a sensitivity of 15.8% (95% CI 7.6-24%) and specificity of 96.0% (CI 92.3-100%). No difference was seen in 3-month or 1-year survival between those with total ECG score > or = 3 versus total score < 3.

CONCLUSION

The diagnostic abilities of the proposed ECG criteria are low and not better than the clinical judgement. The criteria are therefore not suitable for screening patients with suspicion of acute myocardial infarction in the presence of left bundle branch block, nor do they seem to identify high risk patients.