Adult SVT

Question 1

Signs and symptoms of unstable and rapidly deteriorating pt in SVT may include

Answer 1

Inadequate perfusion / shock (e.g. hypotension, pallor and diaphoresis)
Acutely altered conscious state or loss of consciousness
Ischaemic chest pain
APO

Usually associated with significant tachycardia (≥150bpm) unless there is impaired cardiac function

Question 2

Modified Valsalva

Answer 2

1. Position laying semi-recumbent (45° angle).
2. Forced expiration into 10mL syringe for 15 seconds.
3. Immediately lay the patient flat and raise their legs to a 45° angle for 15 seconds.
4. Return the patient to the semi-recumbent position.

Question 3

Standard Valsalva

Answer 3

1. Position patient supine.
2. Forced expiration.
   - Evidence suggests the modified Valsalva achieves superior reversion rates in comparison to other
   techniques. However, the environment, patient size and available resources may influence the choice of manoeuvre.
   - Paramedics should perform a standard Valsalva where they believe the modified Valsalva presents a
   manual handling risk or is not possible due to environmental concerns.
   - Forced expiration at the target pressure of approximately 40 mmHg can be achieved by blowing for
   15 seconds into a 10 mL syringe hard enough to move the plunger.
   - The Valsalva manoeuvre is reserved exclusively for patients with a SBP of ≥ 90 mmHg.
   - A 12 lead ECG should be recorded prior to Mx unless the patient requires immediate treatment.

Question 4

When can Valsalva (modified or standard) be preformed?

Answer 4

On stable SVT (AVNRT or AVRT) with SBP ≥90mmHg

Question 5

How many times can Valsalva be performed

Answer 5

Max 3 attempts
repeat at 2 min intervals

Question 6

SVT definition

Answer 6

Any tachycardia originating above the ventricles (AV Node) w/ HR > 100BPM. There are six types of SVT including, AVRT, AVNRT, Sinus Tachycardia, Atrial Fibrillation, Atrial Flutter and Atrial Tachycardia

Question 7

AVRT (Atrioventricular Re-entry Tachycardia)

Answer 7

Occurs when electrical signals travel from perjinke fibres via an accessory pathway
↓
Depolarise the AV node prior to SA node activation

Question 8

AVNRT (AV Nodal Re-entry Tachycardia)

Answer 8

Occurs when perfectly timed PVC hits prior to the beta (fast) pathway being in its refractory period
↓
Impulse travels down the alpha (slow) pathway and when it reaches the ‘junction’ (where impulse usually cancels out) the beta pathway is now no longer in its refractory and the cycle continues to re-enter

Question 9

S+S

Answer 9

• Palpitations
• SOB
• Dizziness
• Chest Pain
• Syncope
• Hypotension and APO – Rare but can occur in elderly

Question 10

How does forced expiration cause reversal of SVT

Answer 10

o Press snapshot on monitor (gives 12 sec record)
o Forced expiration at 40mmHg by blowing into 10mL syringe for 15 sec
o This causes ↑intrathoracic pressure and ↓venous return
o Sudden release of pressure equals sudden ↑ in venous return therefore ↑spike BP
o This causes baroreceptors in aortic arch to trigger the PSNS and ↑vagal tone (which ↑the refractory period of AV node)

Question 11

Differentials for SVT

Answer 11

• Sinus Tachycardia
• Atrial Flutter/Tachycardia
• Ischemic Chest Pain
• Psychostimulant OD?

Question 12

Risks for deterioration

Answer 12

• Inadequate Perfusion
• Altered Conscious State
• Cardiac Arrest
• Arrhythmias (VT)

Question 13

SD4 Mgx

Answer 13

1. R+R
2. Pos - semirecumbent/supine
3. MICA C1
4. IV Access - 18G R)CF
5. Snap Shot of 12lead ECG
6. Valsava Manoeuvre
7. Analgesia if required
8. MICA up/downgrade/sitrep
9. Extrication
10. Reassess 5/60
11. Load sig 1 with notification

Question 14

Valsalva Manoeuvre Indication

Answer 14

AVRT
AVNRT

Question 15

Valsalva Manoeuvre Contras

Answer 15

SBP < 90mmHg
Unstable of rapidly deteriorating pt
AF/Flutter

Question 16

Valsalva Manoeuvre Precautions

Answer 16

Nil

Question 17

What is the pathophysiology behind the Valsalva manoeuvre?

Answer 17

□ Phase 1
□ Initial increase in ITP causes a brief increase in cardiac output, baroreceptors detect change and may cause vagal response. In rare circumstances this may lead to early termination of SVT.
□ Phase 2
□ As ITP is maintained venous return is decreased leading to decreased CO. This change is sensed at carotid baroreceptors leading to increased HR, contractility and vasoconstriction
□ Sympathetic response
□ Phase 3
□ On cessation of Valsalva ITP returns to normal with sudden increase in venous return. The increased venous return, contractility and HR leads to a marked increase in BP.
□ Baroreceptors respond to increased BP by increasing vagal tone to interrupt the reentry circuit at AV node.
□ This stimulation causes an increase in the refractory period at the AV node

Question 18

Why would GTN be contraindicated in a patient presenting with a HR>150 and SVT?

Answer 18

GTN administration reduces preload and afterload

The overall decrease in blood pressure causes compensatory increase in heart rate via cardio acceleratory centre resulting in sinus tachycardia

Question 19

Explain how the Valsalva manoeuvre works to reverse SVT?

Answer 19

• Blowing on the syringe increases intrathoracic pressure
   This increase in intrathoracic pressure causes a reduction in venous return by the
  occlusion of the inferior vena cava
   This decrease in venous return is detected by the carotid sinus and aortic arch as a
  reduction in pressure. Initially there may be an increase in HR
   When the patient releases from the syringe there is a sudden rush of blood through
  these receptors
   The carotid sinus and aortic arch detect an increase in pressure and subsequently
  trigger the vagal nerve to decrease HR
   This hopefully terminates the SVT