Ischemia

Introduction

• Based on coronary perfusion, the heart is divided into two zones:
  • Anteroseptal zone (perfused by LAD)
  • Inferolateral zone (perfused by RCA and Cx)
• There are areas of shared perfusion (depends on which vessel is more dominant)
  • I.e. Apex is perfused by the LAD if it is long, otherwise it's the RCA or sometimes Cx.
• Wall nomenclature:
  • American Imaging Society defined the following nomenclature to represent walls.
  • In the long axis:
    • Basal
    • Medial
    • Apical
    • Apex
  • In the short axis:
    • Septal
    • Anterior
    • Inferior
    • Lateral (and combinations of these)

• Below is the general perfusion map (expected blood supply to each wall. 

ST Elevation MI

• Definition of STEMI European Society of Cardiology/ACCF/AHA/World Heart Federation Task Force for the Universal Definition of Myocardial Infarction   1.  New ST elevation at the J point in ≥ 2 contiguous leads      - >0.1 mV (≥ 1mm)  in all ALL leads (Except V2-V3)          V2 and V3 Exception:  ≥0.2 mV (≥ 2mm) in men ≥ 0.15mV in women           (≥0.25 mV in men <40 years, or ≥0.15 mV in women)       2.  New or presumed new LBBB - Can be considered a STEMI equivalent   NOTE: - Displacement measured at the junction of the end of the QRS complex (the “J point,")   - In some cases, such as exercise testing, can be measured 40 and up to 80 ms after the J point. - ST segment can be described as elevated, depressed, upsloping, horizontal, or downsloping.

ST Depression

• Definition of ST Depression AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram Part IV   ≥1 mV or more at the J-point    NOTE:  - Displacement measured at the junction of the end of the QRS complex (the “J point,")   - In some cases, such as exercise testing, can be measured 40 and up to 80 ms after the J point.  - ST segment can be described as elevated, depressed, upsloping, horizontal, or downsloping.

Poor R-Wave Progression

• Poor R-wave progression can occur when the initial anterior electrical forces are reduced in amplitude or are directed posteriorly. 
• Suggests the possibility of a prior anterior MI.
• The R wave height normally becomes progressively taller from leads V1 through V6. Between leads V3 to V4, there is a transition to an R wave that has a greater amplitude than the S wave (R/S >1).
• When the R wave height does not become progressively taller from leads V1 to V3 or V4, or even remains at low amplitude across the entire precordium, slow or poor R wave progression (PRWP) is present
• Multiple definitions have been proposed, this is an example of one:

• Definition of Poor R-Wave Progression (Zema and Klingfield 1982) Zema & Klingfield (1982) ECG Poor R-wave Progression, Arch Intern Med; 142:1145-1148   1.  R-Wave Magnitude ≤ 3mm in V3 2.  R in V2 ≤ R in V3 (R-wave increasing in size as it should)   Reversed R-Wave Progression 1.  R-wave magnitude decreases between any leads V1 --> V4 (i.e. R-wave in V4 < R-wave in V3) OR 2.  R-wave in V4 ≤ 3mm   (Low Voltage or QS in V2 are excluded)

• Other possibilities to explain Poor R-wave Progression:
  • Acute MI
  • LBBB
  • LVH or RVH
  • Normal Patients (rare)
  • Others: (WPW, Dextrocardia, Lead misplacement (esp in obese), congenital heart disease)
• NOTE: Research studies show only a very weak correlation between anterior MI or anterior ischemia and PRWP.  In fact the correlation was so weak that it could be explained by chance alone.  Hence, it is no longer recommended to be used as criteria for previous MI.  See Gami et al, 2004, American Heart Journal.

Localizing Ischemic Territory

• L-Main Occlusion or Multivessel Disease

  • Vessel	Pattern
    L-main or Multivessel Disease	ST depression > 0.1 mV (1 mm) in 8 or more body surface leads (sometimes ≥7) AND ST elevation in aVR and/or V1 but is otherwise unremarkable

• Left Anterior Descending

  • Vessel	Pattern	Description
    Proximal to S1 (1st Septal Perforator)	Includes ST elevation in V1 (can include new RBBB)
    Proximal to D1 (1st Diagonal Artery)	ST Depression in inferior leads (II, III, aVF)	Anterior ST elevation forces cause ST depression in inferior leads
    Distal to D1	ST Elevation in inferior leads (II, III, aVF)	ST elevation forces are more towards apex leading to ST elevation in inferior leads

• 

• Right Coronary Artery
  • ST elevation in II, III, and aVF - occlusion is RC if a depression in ST segment is seen in Lead I
  • ST elevation in Lead I usually represents Cx ischemia

Early Repolarization

• Sometimes hard to distinguish from STEMI

• Early Repolarization Definition as per Patton et al 2016 (Circulation):   ANY of following ST Elevation without chest pain Terminal QRS slurring Terminal QRS notching

Q-Waves

• Pathologic Q-waves Definition:  Q-wave ≥30ms and > 0.1 mV deep or QS  (in LAT or INF leads - I, II, aVL, aVF, or V4-V6)      Must be in contiguous lead grouping (I, aVL,V6; V4–V6; II, III, and aVF)   POSTERIOR CLAUSE  2. R-wave ≥ 0.04 s in V1–V2 and R/S ≥ 1 with a concordant positive T-wave in the absence of a conduction defect   V2/V3 CLAUSE 3. Any Q-wave in leads V2-V3 ≥ 20ms or QS complex in V2-V3   Reference: Joint ESC/ACCF/AHA/WHF "Universal Definition of Myocardial Infarction" (2007)

• NOTE: Minor Q-waves 20-30ms that are ≥0.1 mV deep are suggestive of prior infarction if accompanied by inverted T-waves in the same lead group.

   

• NOTE: QS Complex in V1 can be normal

• Lead III: Q-wave <0.03 s and <1/4 of the R-wave amplitude in lead III is normal if the frontal QRS axis is between 30 and 0°.

  • The Q-wave may also be normal in aVL if the frontal QRS axis is between 60 and 90°.

• Septal Q-waves are small non-pathological Q-waves <0.03 s and <1/4 of the R-wave amplitude in leads I, aVL, aVF, and V4-V6.

• Reference: Joint ESC/ACCF/AHA/WHF "Universal Definition of Myocardial Infarction" (2007)

Wellens Pattern

• Profoundly negative or biphasic symmetric T-waves
• Associated with critical proximal LAD artery stenosis. 
• Criteria:

  • Criteria for Wellen's Pattern Symmetric and deeply inverted T-waves in leads V2 and V3 (Occasionally in V1, V4, V5, V6) OR   Biphasic T-wave in leads V2 and V3 PLUS   Isoelectric or minimally elevated (<1mm) ST segment No precordial Q-waves Pattern present in pain-free state Normal or slightly elevated cardiac serum markers

• Examples: Wellen's Pattern examples:
  • The more common pattern of (A-C) deeply inverted T wave
  • (D-F) less common biphasic T wave.
  • (B-F) ST-segment elevation is present (very minor)

  • 

• More Examples (A and B are Wellen's Patterns), whereas C and D are not!

  • Note the deep T-wave inversions in Wellen's

    • 

• Reference:

  • Zwaan and Wellens (1982) "Characteristic Electrocardiographic Pattern indicating critical stenosis high in the left anterior descending coronary artery in patients admitted because of impending myocardial infarction" Am. Heart J. 103(4)

  • Rhinehardt et al (2002) "Electrocardiographic Manifestations of Wellens’ Syndrome" Am. J. of Emergency Medicine, 20(7)