Heart Block

Question 1

Definition?

Answer 1

AV heart block is defined as impaired conduction from the atria to the ventricles. There are 3 degrees, the first is PR interval> 0.2 s, the second I is Progressive prolongation of the PR interval with eventual loss of AV conduction for 1 beat. The second II is Occasional loss of AV conduction for 1 beat, but no prolongation of PR intervals. The third is complete in which there is no co-ordination between atrial and ventricular contraction.

Question 2

RF?

Answer 2

• Age
• Higher vagal tone-younger, athletic pts
• CAD
• Acute coronary syndrome
• AVN-blocking agents-BB, CCBs, AAs
• CHF
• HT
• Cardiomyopathy
• Surgery
• Electrolyte disturbances
Myotonic dystrophy, Erb dystrophy

Question 3

ddx?

Answer 3

• Junctional rhythm-retrograde P waves inverted in inferior leads
• AF or multifocal atrial tachycardia-distinct P waves and grouped patterns of RR intervals
• Sinus rhythm-if junctional escape rate is the same as the sinus rate
• Tachy-brady syndrome-irregular and short RR intervals but SAN slow to take over so ventricular rate slows down.
SVT-p waves inverted in inferior leads

Question 4

Epidemiology?

Answer 4

Age: elderly
Sex: male
Ethnicity:
Prevalence:

Question 5

Aetiology

Answer 5

IHD, fibrosis, aortic valve calcification, surgery, digoxin toxicity and infiltration

Question 6

CP?

Answer 6

• RF
• Age more than 50
• Syncope-Stokes-Adams attacks
• Bradycardia
• Male
• Fatigue
• Cardinal CVS signs of hypoperfusion
• High BP
• Cannon A waves-JVP-contraction against closed tricuspid valve

Question 7

Pathophysiology?

Answer 7

• Lev’s disease-part of ageing but can also be congenital
• Fibrosis develops in the bundle of His, preventing from an impulse being conducted to the ventricles
• IHD-necroed heart tissue cannot conduct impulses at the same frequency-irritation and abnormal firing
Slow escape beats

Question 8

Investigations-first line?

Answer 8

12-lead ECG-no consistent PR relationship
Serum troponin-elevated
Potassium-low/high
Calcium-low/high
pH-low or high
Digitalis-normal/high if taken or toxicity shows

Question 9

Management-first line?

Answer 9

• Condition specific management and discontinuation of AVN-blocking drugs
  
  • Digoxin immune Fab for digitalis toxicity
  • Glucagon fro beta-blocker toxicity
  • Calcium chloride for CCB toxicity
• PPM or cardiac resynch therapy and ICD placement
  
  • For AV block, usually a dual-chamber (1 right atrial and 1 right ventricular lead) pacemaker is placed.
  • The procedure includes a 2-inch incision at the non-dominant shoulder, placement of the leads through the subclavian vein, and placement of the pulse generator in a small subcutaneous pocket. The entire procedure usually takes a few hours and requires an overnight hospital stay.
  • Biventricular pacemaker (placement of a third wire, in a branch of the coronary sinus, to enable left ventricular pacing), with or without an implantable cardioverter-defibrillator (ICD) placement, may be considered when the left ventricular ejection fraction is <35%
  • Atropine in severe bradycardia

Question 10

Management severe?

Answer 10

• Condition specific management and discontinuation of AVN-blocking drugs and temporary pacing
  
  • When the ventricular rate is significantly low (<40 to 45 bpm) or the blood pressure is low (mean arterial pressure <65 mmHg), temporary (transcutaneous or transvenous) pacing should be considered. Transvenous pacing is much more reliable than transcutaneous pacing and should be performed by a cardiologist when the heart block leads to haemodynamic instability.

PPM or cardiac resynch and ICD placement

Question 11

Prognosis?

Answer 11

• Third degree irreversible block has a high risk of progression to ventricular asystole so must be implanted with a permanent pacemaker, which has a low rate of complications

Question 12

Complications?

Answer 12

Pacemaker implantation-bleeding, trauma, pneumothorax, cardiac tamponade, pocket haematoma development, infection of lead, lead malfunction