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Flashcards in 117 ECG 1 Deck (27)
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1
Q

Why are R and T waves usually positive?

A

The T wave is generally upright because the first cell to depolarize is usually the last to repolarize (ECG=AP 1-2). If the sequence were reversed (first to depolarize, first to repolarize), T waves would be down (inverted), as in AP 1-3.

2
Q

What do parts of ECG represent

A
  • P-wave: atrial depolarization
  • Note: sinus node cannot be recorded on the surface ECG because it is too small to generate an extracellular signal
  • QRS complex: initial activation of ventricles
  • T wave: ventricular repolarization
  • PR interval: from initiation of atrial to initiation of ventricular activation (most of the delay in the AV node)
  • QRS interval: total time of ventricular activation
  • ST segment: plateau
  • QT interval: sum total of AP duration in ventricle
3
Q

How to label QRS

A

Q wave: Always the initial deflection; always down.

R wave: Any upward deflection

S wave: Any downward deflection that is not the initial deflection

4
Q

Kirchoff’s law

A

•Kirchoff’s law: sum of all potential differences in a closed circuit=0:

LL+LA+RA=0

5
Q

Eintheoven’s triangle, positioning of ecg leads

A

So think about how the ECG waveform resulting from a propagated wave (thick arrow) that is horizontal and points to the right would look:

  • •In lead I: upright because the waveform is going towards the + end of lead I
  • •Leads II: Mainly upright, wavefront is going towards the + end of lead II
  • •Lead III: Downward: wavefront is going away from the + end of lead III
  • •aVR: negative: wavefront is going away from its + end.
  • •aVL: Positive: wavefront is going towards the + end of aVL.
  • •aVF: Isoelectric: average direction is neither up nor down because the wavefront is perpendicular to aVF.
  • •For this arrow, we would say that the AXIS is +0º
6
Q

Positioning of precordial leads

A
  • V1: 4th intercostal space, right sternal border
  • V2: 4th intercostal space, left sternal border
  • V3: midway between V2 and V4 (therefore, apply it AFTER applying V4)
  • V4: 5th intercostal space, mid-clavicular line
  • V5: horizontal with V4, anterior axillary line
  • V6: horizontal with V4, mid-axillary line
7
Q

Positioning and “equals” of 12 leads

A

•3 bipolar leads

  • I=LA-RA
  • II=LL-RA
  • III=LL-LA

•3 augmented unipolar limb leads

  • aVR=RA-(LL+LA)/2
  • aVL=LA-(LL+RA)/2
  • aVF=LL-(RA+LA)/2

•6 unipolar precordial leads, V1-V6

  • Vx= Vx-(LL+LA+RA)= Vx-0
8
Q

How does the sequence of depolarization in the ventricle explain the normal QRS waveform?

A
9
Q

ECG graph paper

A
10
Q

ECG paper lead alignments

A
11
Q

Quick easy estimate of HR based on ECG boxes

A

•Quick and easy estimate: Count big boxes between beats: Memorize: 300, 150, 100, 75, 60, 50, which=HR for 1,2,3,4 and 5 boxes between beats

12
Q

Standard ECG interval times

A
13
Q

QTc

A
14
Q

How to measure axis to the closest 90º quadrant

A
15
Q

Left axis deviation

A
16
Q

Right axis deviation

A
17
Q

Parallel leads in axis measuring

A
18
Q

Normal ECG things:

A
  • ·intervals, QRS and T wave axes and rate are normal
  • ·P waves are upright in lead II
  • ·every P wave is followed by a QRS complex.
  • ·normal sinus rhythm is present
  • ·the TP, PR, and ST segments are all on about the same level
  • ·the P, T waves, and QRS complex all point in approximately the same direction (put another way, their axes should be about the same)
  • ·from V1 to V6, there is a smooth and progressive transition from a predominantly downward to a predominantly upward QRS waveform
19
Q

Causes of ST depression/elevation

A

because current flows from healthy cells to dead cells (dead cells have lower volutages) we can see changes in usual waveform

•ST depression when the ischemia or injury is subendocardial (panel A)

•ST elevation when it is transmural (panel B)

  • ST depression (≥ 1mm) if it is subendocardial (typical in angina) and non-ST elevation MI (NSTEMI)
  • ST elevation ≥1mm (≥ 0.5mm in V2-3) if it is transmural (as in a transmural MI or ST elevation MI, STEMI). The ST segment is often (not always) convex when viewed from above.
20
Q

T wave inversion

A
21
Q

Q wave in MI

A

Criteria for an Abnormal Q-wave:

Duration: ≥0.03sec, just about 1 small box; ≥0.02sec in V2 or V3

AND

  • has an amplitude ≥ 0.1 mV (1 small box)
  • Present in at least 2 contiguous leads (i.e. 2 inferior leads, 2 anterior leads, 2 lateral leads)

Not present in all MIs:

  • For a Q wave to appear there must be a substantial area of necrosis.
  • In smaller MI’s, Q waves do not appear on the ECG.
  • The diagnosis is made from the other ECG changes (ST segment shifts, T wave inversion), the clinical situation and cardiac enzyme
  • Older terminology for non q-wave MI is non-transmural or subendocardial MI. These terms have been abandoned by many but you hear them occasionally
  • Non-Q wave MI has a better short term prognosis than Q wave MI (because it’s usually smaller) but may imply a high risk for subsequent MI
22
Q

Which ECG leads show which areas of heart best

A

Electrical activity in the anterior wall of the LV is best seen in leads V1-V4

Electrical activity in the lateral wall of the LV is best seen in leads I, aVL, V4-V6

Electrical activity in the inferior wall of the LV is best seen in leads II, III, aVF

23
Q

Markings of the age of MI

A
  • •Earliest stage: Hyperacute phase, characterized by presence of tall, peaked, hyperacute T-waves, with or without ST elevation: minutes to a few hours…and usually gone by the time the patient arrives at the emergency department
  • •Acute, ST Elevation MI (STEMI): ST segments elevated ≥ 1 small box; hyperacute T-waves resolve; q-waves may start to appear: minutes up to a few days.
  • Eventually (hours to a few days), T waves invert. ST segments may remain elevated during this time, but gradually return to baseline

Old:

  • •Eventually, ST segments return to baseline
  • –usually!!
  • •in some pts in whom an aneurysm develops, ST elevation persists indefinitely
  • •Q waves persist indefinitely in most patients
  • •T wave inversion may or may not persist
  • •The only definitive proof that an MI is old is that it was present on an old ECG!!
24
Q

Other Causes of ST Elevation

A
  • •Normal variant: “early repolarization” or “J-point elevation”
    • –Seen especially in young people
    • –ST segment is usually elevated in multiple leads (instead of in leads that localize the changes to a specific region)
    • –ST segment is usually concave (viewed from above)
  • •Ventricular aneurysm
    • –Persistent ST elevation after an MI suggests the presence of an aneurysm (an area of scar that bulges out during systole…also called a dyskinetic area)
  • •Pericarditis
    • –ST segment is usually elevated in multiple leads
    • –Associated with clinical picture of pericarditis instead of that of MI
    • –Sometimes associated with PR segment depression
    • –Sequential ECG changes differs from those of MI
25
Q

Atrial enlargement on ECG

A
26
Q

Left or right Atrial Abnormality (Enlargement): Criteria

A
27
Q

Ventricular enlargement ecg

RVH

LVH

A

RVH: Criteria:

  • V1: R wave is larger than S wave and/or
  • V6: S wave is larger than R wave
  • Limb leads: Right axis deviation (axis between 90º and 180º)
  • Usually, right atrial p-wave abnormality is present

LVH Criteria:

  • S-wave in V1 + R-wave in V5 or V6 ≥ 35 mm
  • R in I + S in III ≥ 25
  • R in aVL ≥ 12 mm
  • Know that other criteria exist (you’ll learn about them later) and that LVH is often accompanied by the strain pattern.