Academic Day Seminar – Feb 10

✔ ECGs!

This was a very fun and interesting session, and I really enjoyed working through the ECGs using the systematic approach that Dr. Loewen taught us. I still find it challenging to read ECGs, especially ones that are not very clean or straightforward, but will aim to avoid reading the interpretations on the top of the ECG and developing this skill in future rotations!

Some key points from this session:

  • Before reading an ECG: check the date, time and patient
    • Correlate why the ECG was done, and root it to their story (e.g. symptoms, PMH)
  • Orientation to a 12 lead ECG:
    • X-axis: small box → 0.04 secs; large box (x5 small) → 0.20 secs
      • 4 sections of 2.5 seconds
      • Picture of the atria and ventricles simultaneously!
    • Y-axis: voltage/electrical activity
    • Leads: not electrodes; each electrode picks up a signal from the heart and leads are specific combinations of those signals
      = record tracing of electrical activity between two electrodes
    • Precordial (chest) leads: V1-V6; Limb leads: I-III, aVL, aVF, aVR
    • Anterior leads: V1 – V4
      • V1: closest to the RIGHT atrium
      • These make sense as “anterior” leads → think of location of the leads (see pic below)!
      • V2-V4: closest to the LEFT ventricle
        Anterior MI: Fatal kind of MI since affecting L ventricle
    • Lateral leads: I, aVL, V5-V6
    • Inferior leads: II, III, aVF
      • Looking from bottom to top → RIGHT ventricle (but not completely)
      • If signs of ischemia in these leads → add 3 leads to posterior to check for a posterior MI
    • aVR → doesn’t tell you anything (wa wa wa)
    • Rhythm strip: usually either lead II or V1 → 10 seconds long
    • Contiguous: if they are assigned to the same anatomic group (e.g. STEMI in 2 inferior leads, 2 anterior leads, etc.) or for a STEMI, contiguous is also referring to 2 numerically contiguous leads (V1-V6)
What each Lead “sees”
Leads Heart Surface Viewed
II, III, aVF Inferior
V1, V2 Septal
V3, V4 Anterior
I, V5, V6, aVL Lateral

Reference: 12 lead ECG pocket reference 

  • 6 step approach for ECG interpretation for Pharmacists: RATE, RHYTHM, CONDUCTION, AXIS, HYPERTROPHY, INJURY/ISCHEMIA/INFARCTION

1. Rate

  • Tricks to calculating the rate without reading the computer’s calculation:
    (1) Use the rhythm strip + multiply the # of QRS complexes seen by 6 (=60 secs)
    (2) 300/150/100/75/60/50 rule for each large box

2. Rhythm

  • Identify if Normal Sinus Rhythm (NSR) or Sinus Rhythm (SR)
    • SR: every P is followed by a QRS, and every QRS is preceded by a P
    • NSR: SR + bpm: 60-100
      • Tachycardia =/= NSR
      • Bradycardia =/= NSR
      • SR + PVCs =/= NSR
  • If not in sinus rhythm, identify arrhythmia
    • Atrial Fibrillation: no visible P waves (II + V1)  + R-R instability
      • R-R instability may be difficult to see if HR is elevated…may have to slow patient’s HR to definitively conclude AFib
    • Atrial Flutter: saw-toothed Ps, fixed A-V conduction ratio
    • Heart blocks (AV node is blocked):
  • 1st degree heart block → often the GoT for AV nodal blocking tx
    • PR > 200msec (more than 1 large box) + no skipped beats
    • Would not be able to see 1st degree heart block in Afib
  • 2nd degree heart block
    • Mobitz I “Wenckebach”: PR interval gets progressively longer until atrial impulse is not conducted and QRS drops
    • Mobitz II: PR interval is constant (not necessarily >200msec) and atrial impulse is not conducted and QRS drops
  • 3rd degree heart block: COMPLETE heart block → dissociation between atria and ventricles
  • PVCs:
    • Broad QRS complex > 120 msec
    • Premature
    • Discordant ST segment and T wave changes (e.g. directed opposite to main vector of QRS complex)
    • Usually followed by a full compensatory pause
    • Retrograde capture of the atria may or may not occur (e.g. inverted P wave)
  • VT: Rate >120 + >2 wide QRS complexes in a row
    • can progress to Vfib
  • VFib:
    • Chaotic irregular deflections of varying amplitude
    • No identificable P waves, QRS complexes or T waves
    • Rate 150-500 bpm
    • Amplitude decreases with duration (coarse VF → fine VF)

3. Conduction

  • PR: conduction from atria to ventricle
  • QRS: width is attainable in every lead even if it may look different
    • Helps identify wide complex arrhythmias (e.g. Vtach)
  • QTc:
    • What you see on the ECG for QT is often higher than corrected QTc (which is corrected by the R-R interval)
    • Risk of torsades increases significantly after 500msec
      → risk of non-perfusing arrhythmia
  • If give anti-arrhythmics, there is also a risk of arrhythmic death

4. Axis: mean vector of depolarization for ventricles

  • Normal “R” axis : -30 to + 110
  • L axis deviation (less than -30): sign of LVH and/or R ventricular ischemia
  • R axis deviation (more than 110): sign of RVH and/or L ventricular ischemia
    • Causes of RVH: cor pulmonale → pulmonary HTN (primary + secondary), congenital heart defects, pulmonary fibrosis (incl. caused by COPD)
  • If normal axis, doesn’t necessarily mean that have no LVH/RVH or ischemia but may be a result of a “mixed” picture

5. Hypertrophy

  • ECG = not diagnostic of hypertrophy → ECHO = diagnostics
  • Atrial  Hypertrophy (Look at V1): Bi-phasic P waves
    • E.g. clinical significance: atrial hypertrophy = risk factor for unsuccessful cardioversion
  • LVH: S wave in V1 + R wave in V5 > 35 mm (low sensitivity, high specificity)
  • RVH: Poor R wave progression (decrease in size) from II → III → aVF
  • Injury/Ischemia/Infarction: can be acute or permanent findings
    • Inferior → Anterior → Lateral → Posterior (if huge R wave in V1 would do posterior leads V5R, V6r, etc.)
    • Ischemia:
      Usually see 1st flipped Ts → ST depression → ST elevation (any point during this, you can see pathological Q waves)
    • Look for 5 things:
      1. T wave inversion = FLIPPED Ts
      2. ST depression > 1mm
      3. ST elevation > 1mm
      → remember that you have electrodes all over the body, and some are going to see the STEMI from the opposite perspective = reciprocal changes
      → E.g. a + electrode sees the STEMI head on and may produce ST elevation…but a different lead saw the STEMI from the opposite perspective, then it might demonstrate an opposite set of changes or ST depression
      4. Q waves:
      – negative deflections preceding a R wave (without a + deflection = R wave before it)
      → pathological and non-pathological Q waves
      → pathological Q waves: WIDE (>1 box in width) and/or DEEP/BIG (larger than 1/4 of the R wave or 1/3 of entire QRS complex)
      → if width is 0.04 s or more, suspect the Q wave to be pathological and possibly ECG evidence of dead myocardial tissue
      → Q waves: If see Q waves with no acute s/s of infarction → “Old inferior MI/infarct” → “age undetermined”
      → BUT..seeing pathologic Q waves does NOT mean that the STEMI is over and has run its course
      5. BBB: always have QRS widening since the R or S waves are splitting
      → look for splitting of R or S waves
      – makes it difficult to interpret and find the above 4 things
      e.g. – if have BBB and ST elevation, can’t call it a ST elevation since the BBB is affecting the ST segment → cannot diagnose ACS in BBB patients = need to rely on other diagnostics (e.g. trop, clinical presentation)
    • More profound MI: ST elevation + Q waves
      Less profound MI: ST depression + T wave inversion

Useful Diagrams:


Screenshot 2017-02-11 12.32.46.png

Screenshot 2017-02-11 19.52.33.png

Location of a Myocardial Infarction (Ref: Pocket Guide):

Location of MI Indicative Changes (leads facing affected area) Reciprocal Changes (leads opposite affected area) Affected (Culprit) Coronary Artery
Anterior V3, V4 V7, V8, V9 Left coronary artery

·         LAD – diagonal branch

Anteroseptal V1, V2, V3, V4 V7, V8, V9 Left coronary artery

·         LAD – diagonal branch

·         LAD – septal branch

Anterolateral I, aVL, V3, V4, V5, V6 II, III, aVG, V7, V8, V9 Left coronary artery

·         LAD – diagonal branch and/or

·         Circumflex branch

Inferior II, III, aVF I, aVL Right coronary artery (most common) – posterior descending branch or
Left coronary artery – circumflex branch
Lateral I, aVL, V5, V6 II, III, aVF Left coronary artery

·         LAD – diagonal branch and/or

·         Circumflex branch

Right coronary artery

Septum V1, V2 V7, V8, V9 Left coronary artery

·         LAD – septal branch

Posterior V7, V8, V9 V1, V2, V3 Right coronary or circumflex artery
Right ventricle V1R-V6R I, aVL Right coronary artery

·         Proximal branches

Other interesting/useful resources: