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Cardiorespiratory > Lecture 19: ECG interpretation > Flashcards

Lecture 19: ECG interpretation Flashcards

1
Q

describe the points of chest leads V1-V6

A
  • -V1 — 4th intercostal space (ICS), just right of the sternum
  • -V2 — 4th ICS, just left of the sternum
  • -V3 — midway between V2 and V4
  • -V4 — 5th ICS on the mid-clavicular line
  • -V5 — anterior axillary line, same level as V4
  • -V6 — mid-axillary line, same level as V4 and V5
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2
Q

what are the extremity leads?

A

–I from the right to the left arm
–II from the right arm to the left leg
–III from the left arm to the left leg
An easy rule to remember: lead I + lead III = lead II

Other extremity leads are:

  • -AVL points to the left arm
  • -AVR points to the right arm
  • -AVF points to the feet
  • -The capital A stands for “augmented” and V for “voltage”.
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3
Q

The x-axis represents voltage. T/F

A

F

X-axis represents time

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4
Q

large vs small box on X-axis?

A
  • -Large box = 0.2 sec

- -Small box = 0.04 sec

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5
Q

Y-axis represents…

A
  • -Y-axis represents voltage:
  • -Large box = 0.5 mV
  • -Small box = 0.1 mV
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6
Q

what are the leads?

A

Electrical activity going through the heart can be measured by external (skin)electrodes. The electrocardiogram (ECG) registers these activities from electrodes which have been attached onto different places on the body. In total, twelve leads are calculated using ten electrodes.

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7
Q

what lead records?

A

A lead records a positive deflection if a wave depolarisation is towards its positive terminal.

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8
Q

what is the depolarization?

A
  • -Conversion of the impulse to a transmittable electrochemical potential
  • -The steeply rising portion of the potential energy curve (upstroke) from the threshold (approx. -70 to -50 mV) to the peak (approx. +30 mV)
  • -Primarily driven by sodium cations (Na+)
  • -Massive influx of Na+ ions through voltage-dependent Na+ channels
  • -Membrane grows closer to the equilibrium potential for Na+(+60 mV)
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9
Q

what does represent P wave?

A

Atrial contraction

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10
Q

what is the normal morphology of P wave?

A
  • -The maximal height of the P wave is 2.5 mm in leads II and / or III
  • -The p wave is positive in II and AVF, and biphasic in V1
  • -The p wave duration is shorter than 0.12 seconds
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11
Q

the abnormal P wave suggests…

A
  • -Elevation or depression of the PTa segment (the part between the p wave and the beginning of the QRS complex) can result from atrial infarction or pericarditis.
  • -If the p-wave is enlarged, the atria are enlarged.
  • -If the P wave is inverted, it is most likely an ectopic atrial rhythm not originating from the sinus node.
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12
Q

what does Q wave represent?

A

Depolarisation of septum

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13
Q

what is the interpretation of the Q wave?

A

An ECG finding that represents the beginning of ventricular depolarization. Normal Q waves are narrow (≤ 40 ms). Pathologic Q waves are abnormally wide (≥ 40 ms) and/or abnormally deep (≥ 2 mV or > 25% of the R wave amplitude) and can develop due to myocardial injury.

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14
Q

A new pathological Q wave represents myocardial infarction until proven otherwise. T/F

A

True

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15
Q

which lead is used for the best evaluation of the P wave?

A

II

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16
Q

what does R wave represent?

A

Ventricular depolarisation

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17
Q

what does the QRS complex represent?

A

The QRS complex represents depolarization of the ventricles and corresponds approximately to ventricular systole.

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18
Q

what is the normal duration of QRS?

A

≤ 100 ms = normal

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19
Q

what does prolonged QRS suggest?

A
  • -100–110 ms = incomplete bundle branch block (BBB)

- -≥ 120 ms = complete bundle branch block (BBB)

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20
Q

the increased amplitude of QRS suggests…

A
  • -Amplitude of the QRS complex in the precordial leads is used to assess for ventricular hypertrophy
  • -Hypertrophy leads to increased muscular mass of the ventricle, which generates larger spikes in the R wave in the corresponding precordial leads (left ventricular hypertrophy: V5 or V6 and right ventricular hypertrophy: V1 or V2).
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21
Q

T wave represents…

A
  • -The T wave represents the repolarization of the ventricles
  • -The T wave is physiologically concordant to the QRS complex: positive if the QRS complex is positive or negative if the QRS complex is negative
  • -Different orientations (e.g., negative T wave after positive QRS complex) are called discordance and indicate a potential pathological event. In clinical practice, the discordant T wave is simply called T-wave inversion.
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22
Q

what is the U wave?

A
  • -Repolarisation of Purkinje fibers
  • -A small, often absent, electrocardiogram waveform that is more pronounced in the context of hypokalemia or bradycardia. This occurs after the completion of the T wave.
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23
Q

how heart rate is determined on ECG?

A
  • -If the QRS rhythm is regular then the heart rate can be estimated by dividing 300 by the number of large (5 mm) squares between successive QRS complexes, or by counting the number of QRS complexes in 6 seconds and multiplying by 10.
    • if you count 5 large squares from one QRS complex to the next, then the heart rate is approximately 300 ÷ 5 = 60/min.
  • -Careful! This method is only a rough estimate.
  • -Only applies if paper speed is 25 mm/s
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24
Q

what is the interpretation of HR?

A
  • -Normal heart rate: 60–100/min
  • -Tachycardia: > 100/min (see also tachycardic arrhythmias)
  • -Bradycardia: < 50-60/min (see also bradycardic arrhythmias)
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25
Q

Alternatively, the heart rate may be estimated by multiplying the number of QRS complexes on the rhythm strip of a standard ECG by 5. True/False

A

True
E.g., if you count 12 QRS complexes, the heart rate is approx. 60/min. With a paper speed of 25 mm/s it takes about 12 s for the length of an 8.5” x 11” size page (30 cm). If 12 s is multiplied by 5, this is the approximate number of QRS complexes in 60 s = QRS complexes/min)

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26
Q

Is there a P-wave before every QRS?

A
  • -Normal ECG: Always a p wave before a QRS complex
  • -No P-waves – atrial fibrillation (atrial depolarisation not conducted to ventricle)
  • -Sawtooth pattern of p-waves – atrial flutter
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27
Q

what is the RR interval?

A

The interval of time between two successive R waves on an ECG. A sinus rhythm has a constant or regular RR interval, which is typically 0.6–1 second. Arrhythmias have variable RR intervals, which can be regularly irregular (i.e., the RR variation follows a regular pattern, as in second-degree heart block) or irregularly irregular (i.e., variable RR interval with no pattern, as in atrial fibrillation).

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28
Q

what is the PR interval?

A
  • -The time between the beginning of the P wave and the beginning of the Q wave
  • -The PR interval represents atrioventricular transmission.
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29
Q

normal PR is >0.2. T/F

A

False

PR interval ≤ 0.2 s

30
Q

what is the interpretation of a prolonged PR interval?

A

1) PR interval > 0.2 s–First-degree atrioventricular block
2) PR intervals become progressively longer (but PP intervals remain constant) until a dropped QRS complex occurs after a regular atrial depolarization–Second-degree AV block, Mobitz type I (Wenckebach)
3) Constant PR intervals (which are usually normal but may be prolonged) followed by one or more non-conducted P waves–Second-degree AV block, Mobitz type II
4) P waves and QRS complexes occur independently of each other, but in regular intervals → complete dissociation of P waves and QRS complexes–Third-degree AV block

31
Q

Mobitz type 1 vs 2?

A
    • Mobitz type 1 (Wenkebach) – progressively prolonged PR interval until a dropped QRS
    • Mobitz type 2 – prolonged PR interval with periodically dropped QRS. What is the ratio of P to QRS? 3:1 Mobitz type 2 vs 4:1 Mobitz type 2
32
Q

Absent p-waves, irregular RR interval suggests?

A

Afib

33
Q

Reverse tick shape of the ST segment suggests?

A

digoxin toxicity

34
Q

The sawtooth pattern on ECG is suggestive of…

A

A high-frequency wave with a regular morphology that represents atrial activity on ECG of patients with atrial flutter. Gives the baseline of the ECG a characteristic sawtooth appearance.

35
Q

what is the cardiac axis?

A

1) The axis represents the spread of intraventricular electrical activity projected along the frontal plane (determined from limb leads I, II, III, aVR, aVL, aVF).
2) The key here is to evaluate the QRS complex, and specifically whether it is positive or negative.
- -Positive: if the area above the isoelectric line (i.e., the amplitude) is larger than the area beneath (if the R wave is taller than the Q and S waves)
- -Negative: if the area below the isoelectric line is larger than the area above

36
Q

what is the normal cardiac axis?

A

The normal axis of the heart is between -30° and +90°.

37
Q

what is the left-axis deviation?

A
  • -(-30°)–(-90°)

- -Normal variant (especially with age), LVH, LBBB, LAFB, inferior MI

38
Q

what is the right-axis deviation?

A
  • -(+90°)–(+180°)
  • -Normal variant, RVH, LPFB, lateral MI, RV strain (e.g., PE), chronic lung disease (e.g., COPD)
  • -Extreme right-axis deviation-(-90°)–(-180°) seen in severe RVH, lateral MI
39
Q

R wave in different axis…

A

Axis Lead
I aVF
1)Left-axis deviation + -
2)Normal + +

3)Right-axis deviation - +

40
Q

most iso-electric lead on your ECG- this is the line which has

A

the smallest deflections (positive and negative)

41
Q

how leads correspond to the axis?

A
  • -I (0 degrees)
  • -II (+ 60 degrees)
  • -III (+120 degrees)
  • -aVL (- 30 degrees)
  • -aVR (- 150 degrees)
  • -aVF (+ 90 degrees)
42
Q

how to determine the cardiac axis?

A
  • -Find the most iso-electric lead on your ECG- this is the line which has the smallest deflections (positive and negative)
  • -Find the lead at right angles to this lead
  • -is that lead mainly positive or negative?
  • -so where on the axis graph is that lead positive or negative??
  • -eg Lead II is positive at 60 degrees and negative at -120 degrees
  • -So the axis of this ECG is + 60 degrees
  • -Axis is between – 30 and + 90
43
Q

what is the other method of axis determination?

A
  • -A lead is positive if its most prominent deflection is above the baseline
  • -A lead is negative if its most prominent dflection is below the baseline
  • -If leads I and II are positive, the axis is normal.
  • -If I is + and II is -, the axis is leftward.
  • -If II is + and I is -, the axis is rightward.

–This does not calculate the axis, it just determines if it is normal, left deviated or right deviated

44
Q

what is the normal duration of the PR interval?

A

Normally 120mS to 200mS

45
Q

A Q wave being present is only normal in what leads?

A

III, aVR, V1 and V6

46
Q

QRS >120mS suggests…

A

bundle branch block

47
Q

what are the ECG findings of the right BBB?

A
  • -The QRS complex must be broad (> 120mS)
  • -terminal R wave in V1 (This might be R, rR’, rsR’, rSR or qR)
  • -slurred S wave in leads I and V6
48
Q

what are the ECG findings of left BBB?

A

QRS must be broad (>120mS)
No secondary R wave in lead v1
RsR waveform should be present inLead I.
RsR waveform is also seen in V6.

49
Q

in what leads are primarily seen RBBB and LBBB?

A
  • -Signs of right bundle branch block (RBBB) are primarily seen in leads V1,2
  • -signs of left bundle branch block (LBBB) are primarily seen in leads I, V5,6
50
Q

WiLLiaM MaRRoW?

A

The name William Morrow can help you identify LBBB and RBBB by looking at the QRS morphology in V1 and V6. In LBBB the QRS looks like a W in V1 and an M in V6 (WiLLiaM), in RBBB the QRS looks like an M in V1 and a W in V6 (MoRRoW).

51
Q

what are the causes of LBBB?

A

ACS (STEMI)
Aortic stenosis
Cardiomyopathy

52
Q

what are the causes of RBBB?

A
  • -Right ventricular strain due to
    1) Chronic lung disease
    2) Pulmonary embolism
    3) ASD
53
Q

what is the left anterior hemiblock?

A

only part of the bundle branch is abnormal. If it is the anterior fascicle which is blocked, this will only manifest as left axis deviation. If the posterior fascicle is blocked, theis will show right axis deviation on the ECG

54
Q

STEMI vs NSTEMI on ECG?

A

1) STEMI
- -New ST elevation at the J point in 2 contiguous leads with the cut-points: >0.1 mV in all leads other than leads V2-V3. For leads V2-V3, the following cut points apply: ≥0.2 mV in men ≥40 years, ≥0.25 mV in men <40 years, or ≥0.15 mV in women
- -New LBBB
- -Posterior MI
2) NSTEMI
- -Horizontal or down-sloping ST depression ≥0.05 mV in two contiguous leads and/or T inversion ≥0.1 mV in two contiguous leads with prominent R wave or R/S ratio >1

55
Q

what is the ST segment?

A
  • -The ST segment represents the interval between ventricular depolarization and repolarization (The ST segment represents the period in which the ventricular myocardium maintains contracted in order to eject blood.)
  • -It is physiologically horizontal on the isoelectric line (There is neither depolarization nor repolarization during this segment.)
56
Q

what is the interpretation of ST-segment elevation on different leads?

A
  • -Lateral MI (left circumflex artery occlusion): I, aVL, V5-6
  • -Anterior MI (left anterior descending (LAD) artery occlusion): V1-4
  • -Inferior MI (terminal branches of right or left coronary artery occlusion): II, III, aVF
57
Q

Widespread ST elevations suggest…

A

pericarditis

58
Q

does ST-elevation always indicate MI?

A

No

  • -LBBB may cause ST elevations due to repolarization abnormalities, therefore ST elevation cannot be used to diagnose MI in the presence of a LBBB.
  • -Small, concave ST elevations may be a normal finding in young, healthy adults due to early repolarization.
59
Q

what are the causes of ST-depression?

A

1)subendocardial myocardial ischemia (MI) (i.e., NSTEMI)
2)Stress-induced MI (sign of coronary artery disease)
3)Reciprocal change from MI
4)Ventricular hypertrophy
–Left ventricular hypertrophy: ST depression with pre-terminal T-wave inversion in V4-6
–Right ventricular hypertrophy: ST depression with pre-terminal T-wave inversion in V1-3(4)
5)Digoxin effect
6)Hypokalemia(Hypo K+, Ca++, Mg++
0
7)LBBB

60
Q

what is the reciprocal ST-depression?

A

If a patient has STEMI in one area of the heart, the opposite side of the heart may show ST depressions on ECG. For example, if a patient has an anterior STEMI, the posterior and inferior leads may show ST depression. The mechanism of this effect is incompletely understood.

61
Q

what are the causes of ST-elevation?

A
  • -Acute transmural infarction
  • -Pericarditis
  • -Aneurysm
  • -Brugada Syndrome
62
Q

Peaked T waves are seen in…

A
  • -‘Hyperacute’ Infarction

- -Hyper K+, Ca++, Mg++

63
Q

inverted T waves are seen in

A
  • -Infarction
  • -Ischaemia
  • -Hypo K+, Ca++, Mg++
64
Q

what are the causes of LVH?

A
  • -HTN
  • -IHD
  • -Cardiomyopathy
  • -Aortic stenosis
65
Q

Sokolow-Lyon criterion vs Cornell-criterion

A

1) To diagnose left ventricular hypertrophy on the ECG one of the following criteria should be met: The Sokolow-Lyon criterion), this is most often used:
- -R in V5 or V6 + S in V1 >35 mm.
2) The Cornell-criterion has different values in men and women:
- -R in aVL and S in V3 >28 mm in men
- -R in aVL and S in V3 >20 mm in women
- -This is a better predicting criterion than the Sokolow-Lyon criterion, but less easy to remember, and therefore less often used.

66
Q

If QRS is a normal duration, then the rhythm is supraventricular or ventricular?

A

supraventricular

67
Q

arrhythmia with wide QRS means…

A

If the QRS is wide (>120mS), then the rhythm is either supraventricular with aberrant conduction, pre-excitation, ventricular pacing or of ventricular origin.

68
Q

supraventricular vs ventricular arrhythmias?

A

1) arrhythmias that originate in the sinoatrial node, atrial myocardium, or atrioventricular node (regular QRS complex)
2) arrhythmias that originate below the atrioventricular node (wide QRS complex)

69
Q

Wide QRS complex tachycardia is presumed ventricular tachycardia until proven otherwise. T/F

A

True

70
Q

example of irregularly irregular narrow supraventricular tachycardia?

A

Afib

71
Q

what is the ventricular fibrillation?

A

A life-threatening cardiac arrhythmia characterized by disorganized, high-frequency (usually > 300 bpm) ventricular contractions that result in diminished cardiac output and hemodynamic collapse. Characterized by a very irregular rhythm with indiscernible P waves or QRS complexes on ECG.

Cardiorespiratory (24 decks)

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