Electrocardiography (Wed 18th and Tues 24th) Flashcards

1
Q

Electrocardiogram

A

Recording of the electrical activity of the heart made by placing electrodes on the surface of the skin. Only detects changes in electrical activity

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2
Q

P Wave represents?

A

Atrial depolarisation/ contraction. Is the smallest peak.

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3
Q

QRS Complex represents?

A

Ventricular depolarisation/ contraction. Tallest.
Q: the tiny deflection below isoelectric point at start
R: big peak above isoelectric point
S: last deflection below isoelectric point.

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4
Q

T wave represents?

A

Ventricular repolarisation (The repolarization phase usually returns the membrane potential back to the resting membrane potential, resets for another contraction). In between the two.

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5
Q

Why is atrial re-polarisation not picked up?

A

Happens during ventricular depolarisation/ QRS

complex.

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6
Q

P-R/Q interval?

A

Should not be longer than 0.2 seconds clinically. The PR-interval is from the start of the P-wave to the start of the Q wave. It represents the time taken for electrical activity to move between the atria and ventricles.

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7
Q

Arrhythmia

A

Abnormal or irregular heart rhythms

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8
Q

Third degree block- a problem with impulse propogation

A

Impulse not passed to ventricles. So ventricles contract at their own slow rate. No QRS complex in ECG. Implant pacemaker

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9
Q

Problems with impulse initiation

A
  1. Atrial Fibrillation: Usually due to abnormal group of cells. Laser remove these cells.
  2. Ventricular Fibrillation: Squiggly line. All cells randomly fire, so heart stops being an effective pump. Try defibrillation and shock to depolarise all heart cells, and hopefully SAN take over.
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10
Q

S-T segment?

A

The ST-segment starts at the end of the S-wave and finishes at the start of the T-wave.

The ST segment is an isoelectric line that represents the time between depolarization and repolarization (repolarization refers to the change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential has changed the membrane potential to a positive value. The repolarization phase usually returns the membrane potential back to the resting membrane potential, resets for another contraction) of the ventricles (i.e. contraction).

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11
Q

Calculating HR from ECG

A

Heart rate can be calculated using the following method (if regular):
◦Count the number of large squares present within one R-R interval (qRs- qRs)
◦Divide 300 by this number to calculate the heart rate

If irregular count no. R-R peaks in 6 seconds and times by 10

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12
Q

Conditions that can be identified from ECG?

A

1) In First Degree Heart Block, the impulse conducting from atria to ventricles through the atrioventricular node is delayed and travels slower than normal. This results in a prolonged P-R wave (greater than 0.2 seconds)
2) If p wave is short, this means the impulse is getting from the SAN to the AVN faster somehow. Simply, the P-wave is originating from somewhere closer to the AV node so the conduction takes less time (the SA node is not in a fixed place and some people’s atria are smaller than others!)
◦The atrial impulse is getting to the ventricle by a faster shortcut instead of conducting slowly across the atrial wall.

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