Cardiac arrhythmias

Question 1

Conduct pathways of the heart - Sinus rhythm (normal)

Answer 1

• SAN —> action potential —> muscle cells of atria —> depolarisation of the AVN –> slow –> IV Septum –> Bundle of His –> R and L bundle brunches –> Free walls of both ventricles –> Purkinje cells –> Ventricular myocardial cells
• SAN found at junction between SVC and RA.
• Action potential travels through gap junctions to get to the muscle cells.
• The AVN is found in the lower interatrial septum.
  The slow spread of action potential between AVN and ventricles is to allow for the complete contraction of the aorta before ventricles are excited.

Question 2

Supraventricular Tachycardia pathophys:

Answer 2

• MOST COMMON childhood arrhythmia
• AKA re-entrant tachycardia - circuit of conduction set up with premature activation of the atrium via the accessory pathway
• Electrical impulse is able to flow from AVN to atria then back to SAN via accessory pathway, leading to pre-excitation of the ventricles (wide QRS complex + delta wave on ECG)

Question 3

Clinical presentation of SVT?

Answer 3

1) Rapid heart rate 250-300bpm
2) Pulmonary oedema
3) Poor cardiac output
4) HF symptoms - ankle/sacral oedema, ascites

Question 4

Diagnosis of SVT?

Answer 4

1) ECG - Narrow complex tachycardia of 250-300bpm
- if heart failure is severe then ECG may show signs of myocardial ischaemia - T-wave inversion
- Short PR interval
- Wolf-Parkinson-White syndrome - Short PR interval and delta waves

Question 5

Treatment of SVT?

Answer 5

• Restore sinus rhythm:
  1) Tissue acidosis corrected and positive pressure ventilation if required.
  2) Vagal stimulating manoeuvres: cold ice pack to face or carotid sinus massage
  3) Atrioventricular blocker: IV adenosine (terminates tachycardia by breaking the re-entry circuit set up between AVN and accessory pathway)
  4) If adenosine fails - start electrical cardioversion with a synchronised DC shock

Question 6

Congenital Complete Heart Block aetiology/pathophys:

Answer 6

1) Usually related to the presence of anti-Ro and anti-La antibodies in maternal serum
2) These mothers will have manifest/latent connective tissue disorders
3) Antibodies prevent normal development of the electrical conduction system in the developing heart - resulting in atrophy and fibrosis of the AVN.

Question 7

Presentation of congenital complete heart block?

Answer 7

1) Death in utero/heart failure in neonatal period
2) MOST asymptomatic for many years
3) FEW become symptomatic with syncope/presyncope

Question 8

Treatment of congenital complete heart block?

Answer 8

1) Insertion of endocardial pacemaker

Question 9

Long QT syndrome pathophys and RF?

Answer 9

• Describes an ECG where ventricular depolarisation - QT interval is greatly prolonged
• Autosomal dominant inheritance
• RF: Erythromycin therapy, electrolyte disorders, head injury
• One of a group of channelopathies caused by specific gene mutations
• Abnormalities of sodium, potassium, or calcium channels leads to gain or loss of function

Question 10

Clinical presentation of long QT syndrome?

Answer 10

1) Sudden loss of consciousness during exercise, stress or emotion - (usually in late childhood)
2) If unrecognised, sudden death from ventricular tachycardia may occur.

Question 11

Ddx of Long QT syndrome?

Answer 11

Often mistaken as epilepsy

Question 12

Diagnosis of long QT syndrome?

Answer 12

1) FH of sudden unexplained death
2) History of syncope on exertion should be assessed
3) ECG - Long QT interval

Question 13

Treatment of long QT syndrome?

Answer 13

1) Beta-blockers (propranolol) to help control irregular heartbeats by slowing heart rate.
2) In high risk patients - a pacemaker or implantable cardioverter defibrillators (ICD) is required