Cardio. SVT. Chap 47 Flashcards

1
Q

Define SVT:

two types:

A

rapid cardiac rhythms originate in the atria or AV junction (above the bundle of His) or (2) involve the atria or AV junction as a critical component of a tachyarrhythmia circuit

atrial tachyarrhythmias or
AV node–dependent tachyarrhythmias

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2
Q

Tx why?

name:

A

abnormal rhythms result from structural heart disease & can cause of structural heart disease

tachycardia-induced cardiomyopathy

any young to middle-aged dog presenting with a clinical picture of DCM should have tachycardiomyopathy on ddx

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3
Q

C/S

A

poor CO
pulsing of the ears or bobbing of the head with HR
may be dx initially w. primary GI

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4
Q

Dx:
first ddx SVT vs VT:
suggested criteria:

A

SVTs w BBB that develops during SVT or antegrade conduction of a tachycardia over an accessory pathway
(rarely conduct antegrade that fast) is difficult to ddx:
1. p-wave SVT
2. fusion beat VT
3. vagal SVT
4. lidocaine trial VT

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5
Q

ddx SVT is atrial or AV node–dependent:

A

SVT is irregularly irregular = a-fib

ddx of regular SVTs involves several steps:

  • initiation and termination of the SVT are important -
  • if an SVT continues despite AV block, it is atrial in origin
  • if VPC terminates the SVT, likely AV node–dependent
  • if vagal maneuver term. SVT, likely AV node–dependent
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6
Q

Most common mechanisms of SVT:

A
  1. A-fib
  2. intraatrial reentrant tachycardia
  3. orthodromic AV reciprocating
    (a macroreentrant circuit in which an impulse is carried
    from the atria to the AV node–His-Purkinje system to the ventricles to a retrograde-conducting accessory pathway to the atria)
  4. automatic atrial tachycardia
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7
Q

Treatment:
ID underlying cause if there is one:
Dual treatments:

A
  1. Acid-base, electrolyte, ischemia/anemia, hypoxemia

dual therapy:
one drug to slow AV nodal conduction
second drug to inhibit the atrial automatic focus or interrupt conduction

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8
Q

Tx:
Vagal:

A

may terminate the SVT if it is AV node dependent most effective vagal maneuver is carotid sinus massage
-sustained, gentle compression is applied for 5 to 10s carotid sinus, caudal to the dorsal aspect of the larynx

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9
Q

Tx pharm 4:

A

diltiazem, esmolol, adenosine, procainamide
direct current cardioversion and overdrive pacing
pre-cordial thump

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10
Q

Tx first line:

A

Diltiazem 0.125mg/kg
normal dogs demonstrated the superior efficacy of intravenous diltiazem in slowing AV nodal conduction while maintaining a favorable hemodynamic profile

Esmolol was a significantly less effective negative dromotrope and caused a severe drop in LV contractility

Adenosine, even at dosages of 2 mg/kg, was
ineffective in slowing canine AV nodal conduction

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11
Q

MoA B1 stimulation:

>HR because of stimulation of which channels:

A

Gs coupling of β1 receptors with adenyl cyclase
- > cyclic AMP production
= increased HR to stimulation
1. funny current (If)
2. L-type calcium current
3. enhanced myocardial contractility through L-type calcium current influx stimulating increased sarcoplasmic reticular calcium release
3. improved myocardial relaxation through phosphorylation of phospholamban
4. enhanced automaticity of subsidiary pacemakers

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12
Q

procainamide MoA:

A

sodium and potassium channel blocker
decreases abnormal automaticity
slows conduction
prolongs the effective refractory in atrial (and ventricular), accessory pathway, and retrograde fast AV nodal tissue.

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13
Q

DC - direct current cardioversion

failure to terminate

A

overdrive pacing can be performed without general anesthesia if the patient is depressed or moribund

jugular furrow can be locally anesthetized with lidocaine, a catheter introducer placed in the external jugular vein, and a multipolar catheter guided fluoroscopically

failure to terminate or rapid resumption of the tachyarrhythmia can indicate either an SVT caused by an automatic mechanism or successful termination but then rapid reinitiation

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14
Q

Long term tx:
Atrial tachyarrh. vs.
AV:

A

Atrial tachyarrhythmias typically are managed by dual antiarrhythmic therapy, one drug to slow AV nodal conduction and a second to terminate the atrial tachyarrhythmia itself

occasionally will respond to single- agent therapy aimed at slowing AV nodal conduction. In reality, however, these tachyarrhythmias most often require combination therapy as well.

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15
Q

Long term drugs:

A

Diltiezam or atenolol
Catheter abalation = only way to “cure” but first must map

radiofrequency energy is delivered to the tip electrode, causing thermal dessication of a small volume of tissue to permanently interrupt the tachycardia circuit.

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