Arrhythmias - AV Node (Heart) Blocks

Question 1

What is 1st Degree Heart Block?

Answer 1

Delayed conduction through the AV node.

Question 2

ECG Representation of 1st Degree Heart Block (2).

Answer 2

1. PR Interval is greater than 0.2 seconds.
2. Each P Wave is still followed by a QRS complex.

Question 3

Causes of 1st Degree or Mobitz Type I Heart Block (4).

Answer 3

1. High Vagal Tone e.g. Athletes.
2. Acute Inferior MI.
3. Electrolyte Abnormalities e.g. Hyperkalaemia.
4. Drugs e.g. DHP CCBs, B-Blockers, Digoxin, Cholinesterase Inhibitors.

Question 4

What is Second Degree Heart Block?

Answer 4

Some of the atrial impulses do not make it through the AV node to the ventricles.

Question 5

What are the 2 main types of Second Degree Heart Block?

Answer 5

1. Mobitz Type I (Wenckebach’s Phenomenon).
2. Mobitz Type II.

Question 6

What is Mobitz Type I Heart Block?

Answer 6

The atrial impulses become gradually weaker until it does not pass through the AV node; after failing, the atrial impulse returns to being strong.

Question 7

ECG Representation of Mobitz Type I Heart Block (2).

Answer 7

1. Increasingly larger PR interval until P wave no longer is followed by a QRS complex.
2. Cyclical.

Question 8

What is Mobitz Type II Heart Block?

Answer 8

Intermittent failure or interruption of AV conduction.

Question 9

ECG Representation of Mobitz Type II Heart Block.

Answer 9

1. Set Ratio of P Waves to QRS Complexes.
2. PR Interval is normal.

Question 10

What is the main risk associated with Mobitz Type II?

Answer 10

ASYSTOLE.

Question 11

What is Third Degree Heart Block?

Answer 11

Complete Heart Block.

Question 12

ECG Representation of Third Degree Heart Block.

Answer 12

No observable relationship between P waves and QRS complexes.

Question 13

What is the main risk associated with Third Degree Heart Block?

Answer 13

ASYSTOLE.

Question 14

Clinical Presentation of Third Degree Heart Block (6).

Answer 14

1. Syncope.
2. Heart Failure.
3. Regular Bradycardia.
4. Wide Pulse Pressure.
5. JVP Cannon Waves in Neck.
6. Variable Intensity of S1.

Question 15

Management of Stable Heart Block.

Answer 15

Conservative.

Question 16

Management of Unstable/Asystole Risk Heart Block (4).

Answer 16

1. 1st Line - Atropine (Anti-Muscarinic) 500mcg IV.
2. Repeat up to a total of 6 doses (3mg).
3. Other Inotropes e.g. Noradrenaline.
4. Transcutaneous Cardiac Pacing using a Defibrillator.

Question 17

Management of High-Risk Asystole Patients (2).

Answer 17

1. Temporary Transvenous Cardiac Pacing.
2. Permanent Implantable Pacemaker.

Question 18

What is Temporary Transvenous Cardiac Pacing?

Answer 18

An electrode on the end of a wire is inserted into a vein and fed through the venous system to directly stimulate the right atrium or ventricle.

Question 19

How does Atropine work?

Answer 19

It is an anti-muscarinic that blocks vagus nerve activity on the heart, which increases the firing rate of the SA node.