Syncope

Question 1

What is 1st degree heart block

Answer 1

PR interval >200 ms

AV conduction problem

Question 2

List some causes of 1st degree block

Answer 2

• Myocarditis
• AV nodal disease
• Acute MI
• Drugs (Ca hannel blockers)

Question 3

Name the two types of 2nd degree blocks?

Give a description of each

Answer 3

• Mobitz type 1; Wenckebach

Progressive lengthening of PR interval, until P is not conducted. Cycle starts again. AV cell dysfunction; they tend to fatigue until drop a beat

• Mobitz type 2

Intermittent non-conducted P waves. P-P interval constant. P-R interval constant when conducted.

Failure of conduction at His-Purkinjee system, below the AV node. Most likely structural.

Question 4

List 3 causes of Mobitz type 1 block

Answer 4

• Myocarditis
• Ca channel blockers
• Inferior MI

Question 5

Give 3 causes of Mobitz type 2 block

Answer 5

• Hyperkalaemia
• Digoxin
• Anterior MI, affecting septum (bundles of His)

Question 6

What is type 3 heart block?

Answer 6

Complete AV dissociation

P and QRS completely independent of eachother.

Often bradycardia.

Ventricular or junctional escape rhythms cause contraction

End point of Mobitz type 1 or 2. Either progressive fatigue of AV nodal cels after increased vagal tone following acute MI. Or sudden onset His-Purkinjee failure, secondary to anterior (septal) MI.

Question 7

Give 3 causes of type 3 heart block

Answer 7

• Inferior MI
• AV nodal blocking drugs (Ca channel blockers)
• Conducting system degeneration (Lev’s disease)

Or any of the causes of type 2 block

Question 8

What may be the cause of a RBBB?

Answer 8

Atrio-septal defect

Question 9

What may be the cause of LBBB?

Answer 9

Ischaemia, ie. stenosis

If patient has had sever chest pain and has LBBB, consider MI; might need thrombolysis.

Question 10

What are the 2 differences between the membrane potential curves of nodal cells compared to myocytes?

Answer 10

Nodal cells do not plateau

They do not depolarise via Na channels, only have voltage gated Ca channels

Nodal cells’ baseline creeps up

Resting potential is unstable. Have a high rate of decay due to efflux of K+ over time

Question 11

At what voltage are nodal potentials initiated?

What ion initiates nodal depolarisation?

Answer 11

-40, compared to -74 for myocytes

Initiated by Ca influx

Question 12

What is the duration of a normal PR interval, and what does it represent?

Answer 12

120 - 200ms

It reflects conduction through the AV node

Question 13

What are the characteristic ECG features of Wolf-Parkinson white syndrome?

Answer 13

• Short PR
• Wide QRS
• Delta waves of the QRS complex

Question 14

What are the characteristi ECG signs of a PE?

Answer 14

• Sinus tachycardia
• RBBB
• T inversion on Right leads
• Right axis deviation
• S1 Q3 T3 pattern (not sensitive nor specific but…)
  
  • Seep S wave in lead 1
  • Pathological Q wave in lead 3
  • Inverted T wave in lead 3

Question 15

What is the duration of a normal QT interval, and what does it represent?

Answer 15

• Inversely proprotional to the heart rate; decreases as the heartrate increases
• It reflects the time taken from ventricular depolarisation to repolarisation

Question 16

What is the duration of a normal QRS complex, and what does it represent?

Answer 16

70 - 100ms

It represents ventricular contraction