Dysrhythmias

Question 1

What is the definition of a dysrhythmia? What history and clinical signs are usually associated?

Answer 1

An abnormal heart rhythm caused by a disturbance in the heart’s electrical conduction system

History:
* Syncope
* Lethargy/weakness
* Exercise Intolerance
* ‘Funny turns’
* Known cardiac disease

Physical Examination:
* Abnormal heart rate
* Audible irregular rhythm
* Pulse deficits
* Evidence of underlying cardiac disease (e.g. murmur)

Question 2

What are the possible causes of dysrhythmias?

Answer 2

• Structural cardiac disease
• Drugs (chemotherapeutic agents)
• Toxins
• Metabolic diseases/electrolyte imbalance
• Systemic disease – sepsis, neoplasia
• Primary issue with the heart’s inherent conduction system

Question 3

When should you treat dysrhythmias? How can you treat them?

Answer 3

• When to treat – medication indicated if will improve patient survival or the patient is showing clinical signs related to the occurrence of a dysrhythmia

Treatment options
* Anti-dysrhythmic drugs
* Pacemaker
* Ablation with catheters
* Implantable cardiovertors

Question 4

What are the types of dysrhythmias?

Answer 4

• Bradyarrhythmia
  
  • Leads to a reduction in heart rate
• Tachyarrhythmia
  
  • Leads to an elevation in heart rate when present
    
    • Supraventricular - Originating from above the ventricles (AV node or SA node)
    • Ventricular - Originates from the ventricles

Question 5

What can cause a bradyarrhythmia?

Answer 5

• Markedly increased vagal tone – sinus bradycardia; consider giving atropine (parasympatholytic) and check for resolution
• Abnormal generation of an impulse at the Sino-atrial node
• Abnormal conduction of the impulse at the AV node
• ALSO consider underlying primary causes: electrolyte imbalances (esp hyperkalaemia), primary cardiomyopathy/valvular disease, drug toxicity/effect

Question 6

What are both these rhythms?

Answer 6

Sinus arrest with a ventricular escape complex
* Upside down P wave
* big gap - when SA node is temporarily not working
* Ventricular cells take over - abnormal looking QRS complex

Persistent atrial standstill
* no P waves - SA node is not working
* AV node takes over - slower rate but nice and regular
* If rate stays slow - start to see clinical signs

Question 7

What are the 3 types of atrioventricular blocks?

Answer 7

• Type 1: delay in the transmission of the impulse; prolonged P-R interval; p-waves always eventually conducted
• Type 2: occasional block; p-wave not conducted
  
  • Mobitz type I: conduction through the AVN progressively slower and then leads to a blocked beat – progressively longer P-R intervals until non-conducted P-wave
  • Mobitz type II: occasional blocked beats but P-R interval constant
• Type 3: complete block – p-waves and QRS complexes not related to each other

Question 8

What is used to treat bradyarrthmias?

Answer 8

• Underlying cause should be treated – eg correction of hyperkalaemia
• If no or limited clinical signs treatment likely not required
  
  • Sinus node dysfunction may not have associated clinical signs and sudden death is very rare.
  • Type 1 and most type 2 AV blocks often a response to increased vagal tone – often noted under GA
• In cases of sick sinus syndrome, advanced type 2 AV block and type 3 AV block an artificial pacemaker is often the only effective treatment
• Parasympatholytic or sympathomimetic drugs such as atropine or terbutaline may be attempted but are largely ineffective

Question 9

What are the different types of supraventricular tachyarrthymias? How can they be treated?

Answer 9

• Atrial tachycardia – occurs when there is an ectopic pacemaker in atria that is able to fire at a high rate;
• Accessory pathway (AP) mediated tachycardia – rare, very high heart rates; gap in insulation between atria and ventricles:
  
  • Impulse can bypass the AVN
  • Or ventricular impulse can retro-conduct back into atrium
• Atrial flutter - rare
• Atrial Fibrillation - common especially in conditions that cause significant left atrial enlargement
• Treatment: try and stop ectopic focus from firing (eg Sotalol) or slow conduction through AVN node (eg Diltiazem) with anti-arrhythmic drugs; some cases with an accessory pathway can be treated with radio-catheter ablation

Question 10

What can you see on an ECG showing atrial fibrillation? How can you treat it?

Answer 10

ECG characteristics:
- HR: normal (lone AF) to tachycardia
- Rhythm: irregular
- f-waves: P waves not seen instead fluctuations of baseline
- QRS: normal as ventricular activation via normal pathways (can have concurrent ventricular issues in some cases)

Treatment: if high rate then slow conduction through AVN; combination treatment with Diltiazem and Digoxin often effective

Question 11

What are the different types of ventricular tachyarrhythmias? How can they be treated?

Answer 11

• Ventricular Premature Beat: same causes as in premature beat slide; wide and bizarre QRS; can occur in couplets and triplets
• Ventricular Tachycardia (VTAC) – sequence of or >4 ventricular beats with a rate > 160bpm – often a fast and unstable rhythm
• Ventricular Flutter – a very rapid VTAC in which T waves and QRS are no longer distinguishable; DANGER – often precedes death
• Treatment: Is anti-arrhythmia treatment required? – Base decision on clinical signs and nature of ECG findings (rate, changing appearance to QRS complex, indistinguishable T-waves), consider Holter monitor, look for underlying cause;
• VTAC: acute setting consider lidocaine IV (constant rate infusion); oral long-term meds: mexiletine, sotalol (my 1st choice), amiodarone