Bradycardia

Question 1

Describe bradycardia.

Answer 1

• Bradycardia is a condition wherein an individual has a very slow heart rate, typically defined as a resting heart rate of under 60 beats per minute (BPM) in adults.
• Bradycardia typically does not cause symptoms until the rate drops below 50 BPM.
• Sinus bradycardia is not usually less than 40bpm, any slower and you should consider an alternative cause such as heart block

Question 2

What are the symptoms of bradycardia?

Answer 2

• Asymptomatic
• Fatigue
• Nausea
• Dizziness
• Concerning symptoms include:
  
  • Syncope
  • Chest pain
  • Breathlessness

Question 3

What are the main causes of bradycardia?

Answer 3

• Physiological
  
  • athletes have low heart rates (40bpm at rest and 30bpm while sleeping)
• Cardiac
  
  • degnerative changes causing fibrosis of conductng pathways
  • post MI
  • sick sinus syndrome
  • Iatrogenic
    
    • Ablation or surgery
  • Aortic valve disease
    
    • Infective endocarditis
  • Myocarditis
  • Cardiomyopathy
  • Amyloid
  • Sarcoid
  • SLE
• Non-cardiac
  
  • Vasovagal
  • ENdocrine - hypothyroidism
  • Metabolic - Hyperkalaemia, hypoxia
  • Other
    
    • Cushings triad - hypertension, bradycardia and irregular breathing
• Drug- induced
  
  • Beta blockers
  • Digoxin
  • Amiodarone
  • Verapimil
  • Diltiazem

Question 4

Which drugs can cause bradycardia?

Answer 4

• Beta blockers
• Digoxin

Question 5

What are pacemaker cells?

Answer 5

• The cells that create these rhythmic impulses, setting the pace for blood pumping
• They directly control the heart rate
• Pacemaker cells are found at various sites throughout the conducting system, with each site capable of independently sustaining the heart rhythm.

Question 6

The rate of spontaneous depolarisation of pacemaker cells decreases down the system. What are the rates?

Answer 6

• The rate of spontaneous depolarisation of pacemaker cells decreases down the system:

1. SA node (60-100 bpm)
2. Atria (< 60 bpm)
3. AV node (40-60 bpm)
4. Ventricles (20-40 bpm)

• Under normal conditions, subsidiary pacemakers are suppressed by the more rapid impulses from above (i.e. sinus rhythm).

Question 7

When do junctional and ventricular escape rhythms arise?

Answer 7

• Junctional and ventricular escape rhythms arise when the rate of supraventricular impulses arriving at the AV node or ventricle is less than the intrinsic rate of the ectopic pacemaker.

Question 8

What are the main classifications of bradycardia?

Answer 8

Classification

1. Atrial
2. Atrialventricular nodal
3. Ventricular

Question 9

What are the subcategories for each of the main classifications of bradycardia?

Answer 9

1. Atrial
   
   1. Resiratory sinus arrythmia
   2. Sinus Bradycardia
   3. Sick sinus bradycardia
2. AV nodal
   
   1. Heart blocks
3. Ventricular

Question 10

What are respiratory sinus arrythmias? What is the pathophysiology of them?

Answer 10

• Respiratory sinus arrhythmia (RSA) is typically a benign, naturally occurring variation in heart rate that occurs during each breathing cycle.
• Specifically, heart rate increases during inspiration and decreases during expiration period.
• This is because during inspiration, intra-thoracic pressure decreases and so does atrial pressure so that blood can flow into the heart.
• This increase in blood flow triggers baroreceptors in the heart which reduces the vagal tone of the heart and increases the heart rate
• The opposite thing happens during expiration:
• Intrathoracic pressure increases and so the does atrial pressure so that blood can leave the heart.
• This reduction in volume triggers the baroreceptors to stimulate vagal activity and the heart rate drops.

Question 11

What is sinus bradycardia?

Answer 11

• This is found in healthy people and very fit athletes.
• The heart muscle of athletes has become conditioned to have a higher stroke volume, so requires fewer contractions to circulate the same volume of blood.
• It can also be normally during sleep

Question 12

What are some abnormal causes of sinus bradycardia?

Answer 12

• Drugs
• IHD
• MI
• Hypothyroidism
• Hypothermia
• Obstructive jaundice
• Uraemia
• Raised intracranial pressure
• Sick sinus syndrome

Question 13

What is sick sinus syndrome?

Answer 13

• The sinus node is not functioning properly, often due to age, so heart alternates between bradycardia and tachycardia, but P waves always followed by same narrow QRS so AVN is intact
• It can result in many complications such as bradycardia, sinus arrest, sinus bradycardia and tachycardias such as AF and atrial tachycardia, atrial flutter

Question 14

What are the complications of sick sinus syndrome?

Answer 14

• Bradycardia
• Sinus arrest
• Sinus bradycardia
• Tachycardias
  
  • Such as AF
  • Atrial tachycardia
  • Atrial flutter

Question 15

What is sinus arrest?

Answer 15

• When the SAN does not discharge an electrical signal on time and so there is a large gap in the ECG, of variable length, until the SAN fires and a p wave and subsequent QRS complex appears
• This can be an atrial escape beat and the next p wave does not appear where it is expected to

Question 16

What is sinoatrial block? And how can it lead to tachyarrythmias?

Answer 16

• Sinus node depolarises as normal but the impulse fails to reach the atria and a P wave fails to appear. However, the next P wave appears where expected
• If any of these are severe, then escape rhythms and beats may occur
• This can lead to paroxysmal tachycardias such as AF, Atrial flutter and atrial tachycardia
  
  • Paroxysmal means that the episode of arrhythmia begins and ends abruptly.
• The association of sick sinus rhythm and paroxysmal tachycardia is called tachycardia-bradycardia

Question 17

What are tachycardia-bradycardia ? What causes it?

Answer 17

• The association of sick sinus rhythm and paroxysmal tachycardia is called tachycardia-bradycardia
• Tachycardia-bradycardia occurs when the bradycardia causes an escape rhythm in response to the lack of stimulation

Question 18

What are the symptoms of sick sinus syndrome?

Answer 18

• Dizziness or light-headedness
• Syncope
• Palpitations
• Stokes-Adams attacks – fainting due to asystole or ventricular fibrillation
• Chest pain or angina
• Shortness of breath
• Fatigue
• Headache
• Nausea

Question 19

What are the causes of sick sinus syndrome?

Answer 19

• The main cause is sinus fibrosis in the elderly
• IHD
• Drugs – digoxin, quinidine, beta blockers
• Cardiomyopathy
• Amyloidosis
• Myocarditis

Question 20

How is sick sinus syndrome diagnosed?

Answer 20

Diagnosis – 24 hour ambulatory ECG recording

Question 21

How is sick sinus syndrome treated?

Answer 21

• Thromboembolism prophylaxis if episodes of AF are detected
  
  • Medical treatment for the tachycardia may exacerbate the bradycardia
• Pacemaker
  
  • Likewise, the pacemaker may exacerbate the tachycardia
• Combination of both may be required for tachycardia-bradycardia cases

Question 22

What is the cause of heart block? And what are the three types of heart block?

Answer 22

• Delayed atrioventricular conduction
• First degree
• Second degree
  
  • Mobitz type 1
  • Mobitz type 2
• Third degree

Question 23

Differentiate between the different types of heart block

Answer 23

• 1^st degree – prolongation of PR
  
  • This is caused by a delayed atrioventricular conduction
• 2^nd degree Mobitz I (Wenckebach) – progressive PR interval prolongation then QRS gets dropped and then it resets
  
  • This is caused by a disease of the AVN which causes PR interval to get progressively longer because some atrial impulses fail to reach the ventricles so then QRS gets dropped and resets
• 2^nd degree Mobitz II – wide QRS that randomly drops, no PR prolongation
  
  • This is caused by a disease of His-Purkinje system which causes P waves to be sometimes followed by QRS complexes
  • It can be intermittent or persistent, described as ratio in relation to number of P waves:QRS complexes (eg 2:1)
• 3^rd degree (complete heart block)
  
  • This is a complete disease of the AVN which does not allow excitation to propagate from the atria to the ventricles therefore there is no association between P waves and QRS complexes

Question 24

How are bradycardias treated?

Answer 24

• If assymptomatic and heart rate >40bpm, no treatment is required
• Look for a reversible cause (drugs - beta blockers, sick sinus syndrome, hypothyroidism)
• If rate is <40bpm or patient is symptomatic:
  
  1. 12 lead ECG, check electrolytes
  2. Connect patient to cardiac monitor
  3. Address the possible cause that may be irreversible
  4. ATROPINE (not for those with transplanted heart though)
  5. If atropine does not work, insert a temporary pacing wire
  6. Start isoprenaline infusion
  7. Or use external cardiac pacing
• Make sure the clinical state is assessed more than the numbers

Question 25

What is atropine? How does it work?

Answer 25

• It is an antimuscarinic (a type of anticholinergic) that works by inhibiting the parasympathetic nervous system and thus increases heart rate

Question 26

What are some side effects of atropine?

Answer 26

• abdominal distension
• anhidrosis
• anxiety
• decreased bronchial secretion
• dysphagia
• hallucination
• hyperthermia
• movement disorders
• mydriasis
• speech disorder
• taste loss
• thirst

Question 27

What are some common side effects of all anti-muscarinics?

Answer 27

• Constipation
• dizziness
• drowsiness
• dry mouth
• dyspepsia
• flushing
• headache
• nausea
• palpitations
• skin reactions
• tachycardia
• urinary disorders
• vision disorders
• vomiting