Bradycardias

Question 1

Causes

Answer 1

o Physiologic: sinus bradycardia in response to ↑ p∑ tone
 Can be response to pathologic condition that ↑ p∑ tone →
* CNS, GI, genitourinary, respiratory, ocular
* Hypothermia
* Hyperkalemia
o Pathologic: neoplastic infiltration/inflammatory dz
o Pharmacologic

Question 2

Mechanism

Answer 2

o ↓ impulse initiation
 Physiologic sinus bradycardia →↑ p∑ tone activat IkAch → hyperpolarization
* ↓ slope of phase 4
o Slowed intranodal conduction
 Disruption of inter connection → sinoatrial block
o Exit block
 Distance btw P waves is a multiple of basic sinus rate
 Dx difficult because of underlying sinus arrhythmia
 Block can be Mobitz I or II → if Wenckebach = progressive P-P until dropped P

Question 3

Overdrive suppression

Answer 3

driving PM => faster vs intrinsic/spontaneous rate
o ↑ activation of Na+/K+ channel → hyperpol → suppresses spontaneous impulse in subsidiary PM