Bradycardias Flashcards

1
Q

normal sinus rhythm

A

60-100 bpm

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2
Q

sinus bradycardia

A

*HR < 60 bpm
*usually seen during rest or sleep (40-50 bpm)
*due to low sympathetic or high vagal tone
*common due to aging, disease, or medications
*not always pathologic

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3
Q

sinus tachycardia

A

*HR > 100 bpm
*seen with exercise, infection, blood loss
*sympathetic stimulation (ex. anxiety) or in infants
*inappropriate sinus tachycardia (IST) > 90 bpm average HR on 24h ambulatory monitoring without identified cause

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4
Q

how can bradycardia happen?

A

*problems with SA node
*problems with AV node
*age (degenerative fibrosis)
*drugs
*other systemic disorders

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5
Q

why is the sinus node the pacemaker?

A

*SA node has the fastest automaticity; SA overdrive suppresses all foci (since all foci have a slower inherent pacing rate)
*SA node inherent rate: 60-100bpm
*AV node inherent rate: 60-80 bpm
*junctional foci inherent rate: 40-60 bpm
*ventricular foci inherent rate: 20-40 bpm

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6
Q

concept of escape rhythms

A

*if there is an interruption of the normal mechanism of conduction, usually another electrically active area of the heart will take over and beat

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7
Q

mechanisms of sinus node problems

A
  1. failure of impulse formation (sinus node doesn’t fire)
  2. SA node fires but the signal is blocked from exiting the SA node/perinodal tissue (sino-atrial exit block)
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8
Q

atrio-ventricular (AV) block

A

*any scenario when a P wave (atrial depolarization) FAILS TO GENERATE A QRS COMPLEX (ventricular depolarization)
*could be due to:
1. block at level of AV node; common, sometimes physiologic and sometimes pathologic
2. block in His-Purkinje system; usually abnormal due to disease or aging

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9
Q

comparing the different types of AV block

A
  1. first-degree AV block: every P makes a QRS, but with a LONG PR INTERVAL
  2. second-degree AV block: regular P waves; some but not all P waves make QRS complexes [dropped QRS complexes] (note - there are 2 types of second-degree heart block)
  3. third-degree heart block: constant and independent atrial and ventricular rates; no P conducts to a QRS
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10
Q

first degree heart block - EKG

A

*prolonged PR interval (>200 msec or > 1 big box)
*no dropped beats

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11
Q

first degree heart block - causes

A

*increased vagal tone (sleeping)
*drugs that slow AV node conduction
*aging (degeneration/scarring of the conduction system)
*myocardial disease/ischemia

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12
Q

first degree heart block - symptoms & treatment

A

*usually asymptomatic; benign
*treatment: none required

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13
Q

second degree heart block: Mobitz type I (Wenckebach) - EKG

A

*progressive lengthening of PR interval until a beat is “dropped” (P wave not followed by a QRS)
*variable RR interval with a pattern (regularly irregular)
*typical location of the block: within the AV node

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14
Q

second degree heart block: Mobitz type I (Wenckebach) - causes

A

*increased vagal tone (sleeping)
*drugs
*acute inferior MI (usually transient)

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15
Q

second degree heart block: Mobitz type I (Wenckebach) - symptoms & treatment

A

*usually asymptomatic
*treatment: none required

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16
Q

second degree heart block: Mobitz type II - EKG

A

*dropped beats that are not preceded by a change in PR interval
*consistent PR interval, with some P waves not followed by a QRS
*typical location of block: below the AV node, in the His-Purkinje system

17
Q

second degree heart block: Mobitz type II - causes

A

*usually indicates a structural abnormality such as ischemia or fibrosis
*aging, sometimes with an acute anterior MI

18
Q

second degree heart block: Mobitz type II - risk & treatment

A

*high risk of progression to third-degree (complete) heart block
*treatment: pacemaker

19
Q

advanced (high-grade) AV block

A

*two or more consecutive non-conducted sinus P waves (2+ P waves without a following QRS)
*usually infranodal block (bundle of His)
*unless a reversible cause is found, permanent pacemaker usually required

20
Q

third degree (complete) heart block - EKG

A

*P waves and QRS complexes rhythmically dissociated
*atria and ventricles beat independently of each other
*regular interval between the P waves & regular interval between QRS complexes, but no relationship between the two
*atrial rate > ventricular rate
*no stimuli from the atria are transmitted to the ventricles

21
Q

third degree (complete) heart block - causes

A

*aging
*drugs
*MI
*cardiac surgery (aortic valve replacement)
*aortic valve infection (endocarditis)
*Lyme disease

22
Q

third degree (complete) heart block - risk & treatment

A

*serious, potentially fatal arrhythmia
*usually requires permanent pacemaker

23
Q

signs/symptoms of bradycardia

A

*often asymptomatic
*fatigue
*decreased exercise tolerance (“chronotropic incompetence”)
*heart failure
*syncope

24
Q

treatment of bradycardia

A

*pacemaker is not always the answer
*treat the underlying cause
*look for reversible factors as much as possible to avoid pacemakers