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Flashcards in ECG Deck (47):
1

P wave

Atrial depolarization (sum of R + L)

Smaller amplitude due to less total muscle mass

2

QRS Complex

Ventricular depolarization; occurs simultaneously as atrial repolarization, obscuring the signal

Upward deflection of R wave corresponds to phase 0 of action potential; isoelectric ST segment links QRS to T wave and corresponds to phase 2 of the action potential (long plateau)

Normal duration is 0.06-0.10s

3

T wave

Repolarization of the ventricles, corresponding to phase 3 of the action potential

T wave (hyperpolarization moving away from the lead) should deflect in the same direction as QRS (depolarization moving toward the lead)

4

QT Interval

Total duration of ventricular depolarization and repolarization

5

PR interval

Spans from the onset of the P wave to the onset of the QRS complex

Represents AV node conduction time

Normal duration is 0.12-0.20s

6

ECG paper speed

25 mm/s

7

ECG chronology - small vs. large squares

Thin lines (small squares) are spaced 0.04s apart

Thick lines (large squares) are spaced 0.2s apart

8

Unipolar leads

Measure the difference in electrical potential between one point on the body and a virtual reference point set at 0 electrical potential, located in the center of the heart

aVR, aVL, aVF
V1-V6

9

Bipolar leads

Measure the difference in electrical potential between two different points on the body

Standard Limb Leads I, II, and III

10

ST depression - Interpretation

Caused by ischemia due to sudden high oxygen demand in the presence of a fixed coronary obstruction

Resting ST segment is normal but during exercise there is a ST depression due to transient ischemia

11

T wave inversion - Interpretation

Caused by ischemia due to acute coronary artery obstruction during low oxygen demand; ischemia may be transient or result in tissue injury

Recall that normally T waves deflect in the same direction as QRS complex

12

ST elevation - Interpretation

Sign of transmural cardiac injury in an acute coronary syndrome, usually acute myocardial infarction

13

Significant Q wave - Definition & Interpretation

Defined as a Q wave that is:

1. Greater than or equal to 1/4 the amplitude of the R wave
2. Greater than or equal to one small box (0.04s) wide
3. Seen in at least 2 leads reflecting the same region of the ventricle

Absence of normal transmural vector produces a negative deflection in leads over infarcted tissue

14

Lateral Leads

I and AVL

15

Inferior Leads

II, III, and AVF

16

Right Chest Leads

V1 and V2

Monitor the RV

17

Left Chest Leads

V5 and V6

Monitor the LV

18

ECG features of transmural myocardial infarction

ST elevation with Q waves

19

ECG features of subendocardial myocardial infarction

ST depression without Q waves

20

QT Interval - Definition & Causes

Defined as a QT interval that is more than half of the RR interval

Caused by:
Hypocalcemia, hypokalemia, hypomagnesemia
Class 1A or 3 anti-arrhythmic drugs
Hypothermia
Congenital Long QT Syndrome

21

ECG features of Left Ventricular Hypertrophy

Big R waves in L-sided leads:

I, aVL, V5, V6

22

ECG features of Right Ventricular Hypertrophy

Big R waves in R-sided leads:

V1, V2

23

ECG features of Hypercalcemia

Shortened QT interval

24

ECG features of Hypocalcemia

Prolonged QT interval

25

U wave

A small, variable wave following the T wave; thought to represent repolarization of the Purkinje fibers

26

Sinus Tachycardia

Regular, fast heart rate > 100bpm with normal P and QRS features

Commonly occurs during exercise or emotional stress; increased cardiac oxygen demand may precipitate angina in patients with coronary artery disease

No treatment usually needed; may be treated with beta blockers, if severe

27

Sinus bradycardia

Regular, slow heart rate ( seen in the elderly

Treatment with atropine or cardiac pacemaker

28

1st degree AV block

Defined as a PR interval > 0.2 seconds; interpreted as delayed conduction through the AV node

Caused by drugs (B-blockers, digitalis) and conduction system disease

29

2nd degree AV block

Some P waves conduct normally to the ventricles but others do not and therefore are not followed by R waves

Rate may be too slow to support adequate CO, resulting in syncope or confusion requiring the use of a pacemaker

Caused by conduction system disease and high vagal tone

30

3rd degree AV block

P waves and QRS show regular rhythm but occur at different rates with P rate > QRS rate

Caused by AV node failure secondary to severe conduction system disease; may cause syncope or sudden death, usually requires a pacemaker

31

Atrial Flutter

P waves flutter at rate of 240-320 bpm; pulse may be regular or irregular and ventricular rates vary but are typically rapid

Some risk of embolic stroke due to clot in the left atrium; treated with Warfarin for anti-coagulation and B-blockers, Ca2+ channel blockers, or Digoxin for rate control

32

Atrial Fibrillation

Irregular ventricular rhythm without P waves

Risk of embolic stroke due to atrial thrombi, heart failure due to rapid heart rate and loss of atrial kick

Treatment: Anti-coagulation, cardioversion (electrical or medical), and rate control with drugs

33

Atrial Tachycardia

Characterized by rapid HR (>180 bpm) with narrow QRS complexes and abnormal P waves

Terminated by adenosine infusion; recurrence prevented by ablation of re-entry pathway

34

Junctional Rhythm

Regular rhythms arising from the AV node; usually characterized by a narrow QRS without P waves, which are buried within the QRS signal

When P waves are present they are usually inverted because the wave is conducted upward from the AV node rather than downward from the SA node

35

Ventricular Tachycardia

Ectopic ventricular focus conducted by slow myocardium; caused by fibrosis, infiltrate, dilation - long path allows re-entry

Characterized by repetitive wide-abnormal QRS without preceeding P wave

36

Lead I

Standard (Bipolar) Limb Lead

L. arm (+)
R. arm (-)

37

Lead II

Standard (Bipolar) Limb Lead

L. foot (+)
R. arm (-)

38

Lead III

Standard (Bipolar) Limb Lead

L. foot (+)
L. arm (-)

39

aVF

Augmented (Unipolar) Limb Lead

L. foot (+)

40

aVR

Augmented (Unipolar) Limb Lead

R. arm (+)

41

aVL

Augmented (Unipolar) Limb Lead

L. arm (+)

42

V1 & V2

Precordial Chest Leads

R. ventricle + septum

43

V3 and V4

Precordial Chest Leads

Septum

44

V5 and V6

Precordial Chest Leads

L. Ventricle

45

Evolution of ECG in transmural myocardial infarct

1. Peaked T wave ("hyperacute T wave")

2. T-wave inversion - sign of ischemia

3. ST elevation - sign of transmural, ischemic injury occurring within 1-2 hours of insult

4. Q wave + ST elevation + T inversion - typical of transmural infarcts

OR

5. ST depression with no Q wave - typical of subendocardial infarcts

46

Atrial Premature Beats

P wave occurs too early following the last T wave and looks slightly different from other P waves; QRS is normal

Mostly benign

47

Premature Ventricular Contraction (PVC)

Depolarization originates in the ventricle and contraction occurs via contractile myocytes

Characterized by wide QRS signal without P waves

Common in normal subjects; treatment usually not required