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1. Pacemakers and AMI
   • Paced rhythms cause ST-segment & T wave changes that can make identification of acute MI difficult
   • As in in LBBB, paced rhythms are expected to have ST segment & T wave changes that are discordant to the direction of the QRS complex. This is normal & referred to as the “Rule of Appropriate Discordance”
   • ST–segment deviations that are concordant(in same direction) to the QRS complex or excessively discordant are abnormal​
   • Sgarbossa Criteria
     • Sgarbossa criteria can be used to help diagnose AMI in setting of paced rhythms
     • The criteria are reviewed below:

1. Concordant STE ≥ 1mm (in any lead)
2. Concordant STD ≥ 1mm in V1, V2, or V3
3. Discordant STE ≥ 5mm (most specific)

Take-home Points:

Sgarbossa criteria appear to predict acute MI in patients with pacemakers. The criteria have low sensitivity but are very specific. Criteria C (excessively discordant ST-segment elevation) seem to be most specific in patients with pacemakers.

Reference

1. Sgarbossa EB. Recent advances in the electrocardiographic diagnosis of myocardial infarction: left bundle branch block and pacing.Pacing Clin Electrophysiol. 1996;19(9):1370–1379. PMID: 8880802
2. Sgarbossa EB, Pinski SL, Gates KB, et al. Early electrocardiographic diagnosis of acute myocardial infarction in the presence of ventricular paced rhythm. GUSTO-I investigators. Am J Cardiol. 1996;77(5):423–424. PMID: 8602576
3. Maloy KR, Bhat R, Davis J, et al. Sgarbossa Criteria are Highly Specific for Acute Myocardial Infarction with Pacemakers.West J Emerg Med. 2010;11(4):354–357. PMID: 21079708

2. de Winter T-waves

• 1-3 mm ST-depression at the J-point in the mid precordial leads, leading into tall symmetric T-waves
  
  • High risk of acute anterior MI
  • Suggestive of an acute proximal LAD occlusion (contrast to sub-acute occlusion of Wellens syndrome), or less commonly a 1^st diagonal or left circumflex occlusion
  • Although no ST-elevation, may be an unstable lesion for which urgent cath should be “strongly considered”
  • Get serial ECG’s while the patient is having pain, may progress to STEMI
  • Have high concern for potential decompensation and treat aggressively

References:

1. de Winter RJ, Verouden NJ, Wellens HJ, et al. A new ECG sign of proximal LAD occlusion. N Engl J Med. 2008 Nov 6;359(19):2071-3. PMID:18987380
2. Verouden NJ, Koch KT, Peters RJ, et al. Persistent precordial “hyperacute” T-waves signify proximal left anterior descending artery occlusion. 2009;95(20):1701–6. PMID: 19620137
3. Rokos IC, French WJ, Mattu A, et al. Appropriate cardiac cath lab activation: optimizing electrocardiogram interpretation and clinical decision-making for acute ST-elevation myocardial infarction. Am Heart J. 2010 Dec;160(6):995-1003. PMID:21146650
4. Stankovic I, Ilic I, Panic M, et al. The absence of the ST-segment elevation in acute coronary artery thrombosis: what does not fit, the patient or the explanation? J Electrocardiol. 2011; 44(1):7–10. PMID: 20591442
5. Birnbaum I, Birnbaum Y. High-risk ECG patterns in ACS—need for guideline revision. J Electrocardiol. 2013;46(6):535–9. PMID: 23863685
6. Goebel M, Bledsoe J, Orford JL, et al. A new ST-segment elevation myocardial infarction equivalent pattern? Prominent T wave and J-point depression in the precordial leads associated with ST-segment elevation in lead aVr. Am J Emerg Med. 2014;32(3):287.e5–8. PMID: 24176590

3. ST-segment elevation in aVR with ST-segment depression in multiple other leads

• Reflects global subendocardial ischemia of the left ventricle, often associated with proximal lesions or multi-vessel disease
• STE in aVR (> 1-1.5 mm) Differential
  • LMCA stenosis
  • Proximal LAD
  • Triple vessel disease
  • Any cause of severe generalized global ischemia
    • Severe anemia (e.g. GI Bleeding)
    • Type A dissection
    • Massive PE, etc.

Take-home points:

• Must be used in the correct patient with signs and symptoms of ACS! These patients typically have active anginal symptoms and look sick
• Watch out for normal variants such as LBBB, severe LVH, or SVT
• Literature is increasingly supportive of incorporating this into cath lab activation criteria

Reference:

1. Williamson K, Mattu A, Plautz CU, et al. Electrocardiographic applications of lead aVR. Am J Emerg Med. 2006 Nov;24(7):864-74. PMID: 17098112
2. Nikus KC, Eskola MJ. Electrocardiogram patterns in acute left main coronary artery occlusion. J Electrocardiology. 2008 Nov-Dec;41(6):626-9. PMID: 18790498
3. Wagner GS, Macfarlane P, Wellens H, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: Part VI: acute ischemia/infarction: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. J Am Coll Cardiol. 2009 Mar 17;53(11):1007. PMID: 19281933
4. Rokos IC, French WJ, Mattu A, et al. Appropriate cardiac cath lab activation: optimizing the electrocardiogram interpretation and clinical decision making for acute ST-elevation myocardial infarction. Am Heart J. 2010 Dec; 160(6):995-1003. PMID:21146650
5. Nikus K, Pahlm O, Wagner G, et al. Electrocardiographic classification of acute coronary syndromes: a review by a committee of the International Society for Holter and Non-Invasive Electrocardiology. 2010 Mar-Apr;43(2):93, 97-98. PMID: 19913800
6. Kosuge M, Ebina T, Hibi K, et al. An early and simple predictor of severe left main and/or three-vessel disease in patients with non-ST-segment elevation acute coronary syndrome. Am J Cardiol. 2011 Feb 15;107(4):495-500. PMID: 21184992
7. Taglieri, N., Marzocchi, A., Saia, F., et al. Short- and Long-Term Prognostic Significance of ST-Segment Elevation in Lead aVR in Patients With Non–ST-Segment Elevation Acute Coronary Syndrome. Am J Cardiol. 2011; 108(1), 21–28. PMID: 21529728
8. Kosuge M, Uchida K, Imoto K, et al. An early and simple predictor of severe left main and/or three-vessel disease in patients with non-ST-segment elevation acute coronary syndrome. J Am Coll Cardiol. 2015 Jun 16;65(23):2570-1. PMID: 26065996

Final Class IIB Take-home points

1. Use Sgarbossa criteria to diagnose acute MI in patients with pacemakers
2. Beware de Winter T-waves
3. In the right patient, beware STE in lead aVR!

Share the literature and be an advocate for your patients!

1. Criteria in LBBB
   • New LBBB is out!
     • A new or presumed new LBBB used to be a STEMI equivalent. In the past few years, increasing literature has suggested that a new LBBB does NOT predict a high likelihood of AMI/acute thrombosis.
     • The most recent STEMI Guidelines state that new or presumed new LBBB is no longer an indication for emergent CLA/lytics!Reference:O’Gara PT, Kushner FG, Ascheim DD, et al. 2013 ACCF/AHA Guideline for the Management of ST-Elevation Myocardial Infarction. JAC 2013;61(4):e78–e140. PMID: 23256914.

• Left Bundle Branch Block Basics
  • LBBB’s cause ST-segment & T wave changes that can make the identification of acute MI difficult
  • Patients with LBBB are expected to have ST segment & T wave changes that are discordant to the direction of the QRS complex. This is normal & referred to as the “Rule of Appropriate Discordance”
  • ST-segment deviations that are concordant(in same direction) to the QRS complex are abnormal​
  • Suspected ACS and new or old LBBB with hemodynamic/electrical instability or acute heart failure should go to the cath lab emergentlyReferenceNeeland IJ, Kontos MC, de Lemos JA. Evolving considerations in the management of patients with left bundle branch block and suspected myocardial infarction. J Am Coll Cardiol 2012;60(2):96–105. PMID: 22766335.

• Sgarbossa Criteria
  • Sgarbossa criteria can be used to help diagnose AMI in setting of LBBB
  • Meeting the criteria in a single lead can be specific for AMI
  • The criteria are reviewed below

Concordant STE ≥ 1mm (in any lead) = Most specific for MI

Concordant STD ≥ 1mm in V1, V2, or V3 = Specific for MI

Discordant STE ≥ 5mm = Less specific for MI

• A revised Sgarbossa C rule has been proposed (not yet validated) to increase the diagnostic utility of the rule for STEMI. This revised rule replaces the absolute criterion (discordant STE ≥5 mm) with a proportional criterion (ST-segment to S-wave ratio ≤-0.25). This is consistent with the electrophysiological principle that repolarization voltages should be proportional to depolarization voltages.
  •  
    References:
  • Smith SW, Dodd KW, Henry TD, et al. Diagnosis of ST-Elevation Myocardial Infarction in the Presence of Left Bundle Branch Block With the ST-Elevation to S-Wave Ratio in a Modified Sgarbossa Rule. Ann Emerg Med. 2012;60(6):766–776. PMID: 22939607.
  • Cai Q, Mehta N, Sgarbossa EB, et al. The left bundle-branch block puzzle in the 2013 ST-elevation myocardial infarction guideline: From falsely declaring emergency to denying reperfusion in a high-risk population. Are the Sgarbossa Criteria ready for prime time? American Heart Journal. 2013;166(3):409–413. PMID: 24016487.
  • Kontos MC, Aziz HA, Chau VQ, et al. Outcomes in patients with chronicity of left bundle-branch block with possible acute myocardial infarction. American Heart Journal 2011;161(4):698–704. PMID: 21473968.
  • Jain S, Ting HT, Bell M, et al. Utility of left bundle branch block as a diagnostic criterion for acute myocardial infarction. Am J Cardiol 2011;107(8):1111–6. PMID: 21296327.
  • Chang AM, Shofer FS, Tabas JA, et al. Lack of association between left bundle-branch block and acute myocardial infarction in symptomatic ED patients. Am J Emerg Med 2009;27(8):916–21. PMID: 19857407.

1. Classic STEMI – Use the J-point to determine the magnitude of ST-segment elevation relative to the isoelectric TP segment.
   • J-point elevation in 2 contiguous leads > 1 mm is required in all leads (except V₂/V₃) 
   • Leads V₂ and V₃ limits are age and sex dependent
     1. In males < 40 years old, J-point elevation of as much as 2.5 mm in V₂ and V₃ can be a normal finding, but decreases with age
        • Cutoff = ≥ 2.5 mm in V₂ and V₃ in men < 40 years
     2. In males ≥ 40 years old, J-point elevation as much as 2 mm in V₂ and V₃ can be a normal finding
        • Cutoff = ≥ 2 mm in V₂ and V₃ in men ≥ 40 years
     3. J-point elevation in women is less than in men, elevation as much as 1.5 mm in V₂ and V₃ can be a normal finding.
     4. Cutoff = ≥ 1.5 mm in V₂ and V₃ in women
        
        Pearl: Lesser degrees of ST displacement DO NOT exclude ischemia or evolving MI. A single ECG may miss dynamic changes, so do serial ECGs when in doubt!Reference:Thygesen K, Alpert JS, Jaffe AS, et al. Third Universal Definition of Myocardial Infarction. J Am Coll Cardiol 2012;60(16):1581–98. PMID: 22958960
2. Posterior STEMI (“inferolateral”) – the most common type of missed STEMI!
   • 4-10% of STEMI’s are isolated Posterior MI’s
   • Often misdiagnosed as just ischemia or NSTEMI
   • Only 30% are revascularized within 90 mins
   • Usually associated with inferior or lateral MI due to RCA or circumflex occlusion
   • Pearl: Even 0.5 mm of STE on posterior lead ECGs is diagnosticDifferential for ST-depression in anteroseptal leads
   • Posterior STEMI
     • Mirror image of septal STEMI in leads V₁-V₃
     • Large R waves (instead of Q waves)
     • ST-depression (instead of STE)
     • Upright T waves in V₁-V₃ (instead of inversions)
   • Anteroseptal ischemia
   •  Miscellaneous
     1. RBBB
     2. Hypokalemia, etc
        
        References:Waldo SW, Brenner DA, Li S, et al. Reperfusion times and in-hospital outcomes among patients with an isolated posterior myocardial infarction: insights from the National Cardiovascular Data Registry (NCDR). American Heart Journal 2014;167(3):350–4. PMID: 24576519Ayer A, Terkelsen CJ. Difficult ECGs in STEMI: lessons learned from serial sampling of pre- and in-hospital ECGs. Journal of Electrocardiology 2014;47(4):448–58. PMID: 24792903.Wei EY, Hira RS, Huang HD, et al. Pitfalls in diagnosing ST elevation among patients with acute myocardial infarction. Journal of Electrocardiology 2013;46(6):653–9. PMID: 23890685.Waldo SW, Armstrong EJ, Kulkarni A, et al. Clinical characteristics and reperfusion times among patients with an isolated posterior myocardial infarction. J Invasive Cardiol 2013;25(8):371-5. PMID: 23913600.

3. Post-arrest STEMI/NSTEMI
   • STEMI patients post-arrest should go to the cath lab (Class IB in national guidelines)
   • STEMI patients post-arrest who remain comatose should go to the cath lab unless they have multiple unfavorable resuscitation features (Rab T, et al.)
   • NSTE-ACS patients post-arrest who remain comatose should be assessed for unfavorable resuscitation features. Immediate consultation with cardiology and intensive care is recommended (Rab T, et al.)References:O’Gara PT, Kushner FG, Ascheim DD, et al. 2013 ACCF/AHA Guideline for the Management of ST-Elevation Myocardial Infarction. JAC 2013;61(4):e78–e140. PMID: 23256914.Rab T, Kern KB, Tamis-Holland JE, et al. Cardiac Arrest: A Treatment Algorithm for Emergent Invasive Cardiac Procedures in the Resuscitated Comatose Patient. J Am Coll Cardiol 2015;66(1):62–73. PMID: 26139060.

4.  Non-STE ACS (Class IA in national guidelines)

• Urgent/immediate invasive strategy (within 2 hours) is indicated for NSTE-ACS patients that develop hemodynamic or electrical instability (VT or VF arrest)
• Urgent/immediate invasive strategy (within 2 hours) is indicated for NSTE-ACS patients that have intractable ischemia
• Urgent/immediate invasive strategy (within 2 hours) is indicated for NSTE-ACS patients that develop acute decompensating heart failureReference:Amsterdam EA, Wenger NK, Brindis RG, et al. 2014 AHA/ACC Guideline for the Management of Patients with Non-ST-Elevation Acute Coronary Syndromes: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol 2014;64(24):e139–228. PMID: 25260718.