Ecg Diseases

Question 1

Hypokalemia

Answer 1

Flat T wave (may be inverted)
Prominent U wave
Depressed S-T segment

Question 2

hyperkalemia

Answer 2

Tall, peaked, narrow-based T wave (due to rapid repolarization)
P wave diminishes in size with prolonged P-R interval
(due to slow conduction)
Shortened Q-T interval (due to shortened APD)
In severe hyperkalemia, duration of QRS is prolonged (due to
slow conduction)

Question 3

Myocardial ischemia

Answer 3

cause “injury current” → flows from ischemic depolarized region to the
surrounding normal regions
Injury current is shown in the ECG as “elevation” or “depression” of the ST segment depending on
whether the ischemia is sub-endocardial or transmura

Question 4

Transmural ischemia causes ST segment
elevation

Answer 4

Ventricle is at rest and normally repolarized,
injury current will flow from depolarized
ischemic region to surrounding normal region.
Direction is away from overlying recording
electrode →recorded as a negative
potential→ baseline voltage prior to QRS will
be depressed (below zero).
When the ventricle becomes depolarized, all
muscle is depolarized so that zero voltage is
recorded by the electrode. This is the ST
segment.
The net effect: ST segment appears to be
elevated relative to depressed baseline

Question 5

Sub-endocardial ischemia causes ST
segment depression

Answer 5

ventricle is at rest and normally repolarized,
injury current flow from depolarized ischemic
region to the surrounding normal region.
Direction is towards the overlying recording
electrode →recorded as a positive potential
→ baseline voltage prior to QRS will be
elevated (above zero).
When the ventricle becomes depolarized, all
muscle is depolarized so that zero voltage is
recorded by the electrode. This is the ST
segment

the net effect: ST segment appears to be
depressed relative to the elevated baseline

Question 6

Myocardial infarction

Answer 6

The necrotic infarction area is electrically silent, = acts as an “electric hole” through
which the overlying electrode can see the electrical activity of the opposite side of the
heart → that is moving away from this electrode producing an initial negative Q wave

Question 7

Myocardial infarction

Answer 7

Pathological Q larger & longer duration than
the normal q wave (produced by septal depolarization)
Q wave is considered abnormal if its
height > 25% of the R wave of the same QRS complex,
and/or has duration greater than 0.04 sec (one small square) and amplitude more than 2 mm

Question 8

Heart rate

Answer 8

𝟏𝟓𝟎𝟎/𝐍𝐨.𝐨𝐟 𝐬𝐦𝐚𝐥𝐥 𝐬𝐪𝐮𝐚𝐫𝐞𝐬 𝐛𝐞𝐭𝐰𝐞𝐞𝐧 𝐭𝐰𝐨 𝐬𝐮𝐜𝐜𝐞𝐬𝐬𝐢𝐯𝐞 𝐑

Question 9

Sinus tachycardia & Sinus bradycardia

Answer 9

↑ SAN discharge →↑HR >100
Causes Stress, exercise, hyperthyroidism

↓SAN discharge→↓HR <60
Causes Sleep, hypothyroidism

Question 10

Atrial fibrillation & Atrial flutter

Answer 10

Rapid, Irregular pulse with absent P-wave (no atrial contraction), flutter wave (saw tooth pattern of atrial activation) , absent sinus P wave