SASKIA D HANDARI

Patophysiology of Supra Ventricular Tachycardia

The Role of Vagal Maneuver

Supra Ventricular Tachycardia

Definition :SVT is a broad term for a number of

tachyarrhythmias that originate above the ventricular electrical conduction system (purkinje fibers).

Classic Paroxysmal SVT has a narrow QRS complex & has a very regular rhythm. Inverted P waves are sometimes seen after the QRS complex. These are called retrograde p waves

The heart fills during diastole, and diastole is normally 2/3 the cardiac cycle. A rapid heart rate will significantly reduce the time which the ventricles have to fill. The reduced filling time results in a smaller amount of blood ejected from the heart during systole. The end result is a drop in cardiac output & hypotension.

With the drop in cardiac output, a patient may experience the following symptoms. These symptoms occur more frequently with a heart rate >150 beats per minute:

Shortness of air (S) Palpitation feeling in chest (S) Ongoing chest pain (U) Dizziness (S) Rapid breathing (S) Loss of consciousness (U) Numbness of body parts (S)

AV Nodal Reentrant Tachycardia Circuit

F = fast AV nodal pathway

S = slow AV nodal pathway (His

Bundle)

During sinus rhythm, impulses conduct preferentiallyvia the fast pathway

Initiation of AV Nodal Reentrant Tachycardia

PAC = premature atrial complex (beat)

PAC

PAC

Sustainment of AV Nodal Reentrant Tachycardia

Rate 150-250beats per min

P waves generatedretrogradely(AV node atria) andfall within orat tail of QRS

P P P P

Sustained AV Nodal Reentrant Tachycardia

Note fixed, short RP interval mimicking r’ deflection of QRS

V1

Orthodromic AV Reentrant Tachycardia

AP

Anterogadeconduction via normal pathway

Retrograde conductionvia accessorypathway (AP)

Initiation of Orthodromic AV ReentrantTachycardia

AVN

Ventricles

Atria

AP

PAC = premature atrial complex (beat)

PAC

Sustainment of Orthodromic AV Reciprocating Tachycardia

Atria

AP

AVN

VentriclesRetrograde P’s fall in the ST segmentwith fixed, short RP

Rate 150-250beats per min

Intermittent Accessory Pathway Conduction

NormalConduction

V Preex V Preex

Note “all-or-none” nature of AP conduction

Orthodromic AV Reentrant Tachycardia

NSR with V Preex

SVT:V Preex gone

Note retrograde P wavesin the ST segment

• RP intervals can be variable • RP often > PR• (Example slower than more common rate of 150-250 beats per min)

Atrial Tachycardia

V1

Differs fromAV nodal or AV reentrantSVT

Vagal ManeuversThe autonomic nervous system is composed of the sympathetic and parasympathetic divisions. This system innervates and regulates visceral functions including parenchymal cells and vascular smooth muscle cells.

In the thorax and abdomen, the vagus nerve dominates the parasympathetic nervous system.

Various physical maneuvers can elicit autonomic responses. Many of these maneuvers can be performed at the bedside or in an office setting with minimal risk.

These maneuvers can be both diagnostic (eg, in confirming carotid sinus hypersensitivity) and therapeutic (eg, terminating paroxysmal supraventricular tachycardia).

In the heart, parasympathetic (vagal) stimulation causes local release of acetylcholine, with the following effects:

●In the sinus node, there is slowing of the rate of impulse formation

●In the atrioventricular (AV) node, conduction velocity slows and the refractory period lengthens

●In atrial tissue, there is no change in conduction velocity, while the refractory period shortens

●The electrophysiologic properties of the His-Purkinje system do not change significantly.

A wide variety of physical maneuvers can have intended or unintended influence on vagal tone. These include:

●Carotid sinus massage●Valsalva maneuver●Water immersion (diving reflex)●Eyeball pressure (oculocardiac reflex)●Breath-holding●Rectal examination●Coughing●Deep respirations●Gagging●Swallowing●Intracardiac catheter placement●Nasogastric tube placement●Squatting●Trendelenburg position

Carotid Sinus Massage

Stimulation of carotid sinus triggers baroreceptorreflex and increased vagaltone, affectingSA and AV nodes

Termination of SVT by Vagotonic Maneuver (Carotid Sinus Massage)

Contraindications  

Carotid sinus massage should be avoided if there is a risk of stroke due to carotid artery disease.

The American Heart Association/American College of Cardiology (AHA/ACC) statement on syncope notes that CSM should not be performed in patients with recent transient ischemic attack or stroke, or ipsilateral significant carotid artery stenosis or carotid artery bruit.

The European Society of Cardiology (ESC) syncope guidelines recommend avoiding CSM in patients with history of transient ischemic attacks or stroke within the past three months, except if carotid Doppler studies exclude significant stenosis

Valsava Maneuver

Forceful expiration against a closed mouth and nose.

The patient is placed in a supine position and instructed to exhale forcefully against a closed glottis after a normal inspiratory effort (ie, at tidal volume).

Signs of adequacy include neck vein distension, increased tone in the abdominal wall muscles, and a flushed face.

The patient should maintain the strain for 10 seconds and then release it and resume normal breathing.

Diving reflex :

The diving reflex was first described in chickens and ducks, and has also been observed as an oxygen-conserving maneuver in diving mammals. In humans, the diving reflex has been studied as a tool to assess the autonomic nervous system

In one approach, the patient is seated in front of a basin of water with continuous electrocardiographic monitoring.

The patient should be able to lean forward comfortably to submerge his or her face. The water should be at a temperature of 10 to 20ºC and deep enough to allow complete facial immersion without the bowl touching the patient's neck

Oculocardiac reflex:

The oculocardiac reflex involves a decrease in heart rate and/or blood pressure in response to eyeball pressure. The reflex is thought to originate from the ophthalmic portion of the trigeminal nerve. Afferent stimuli move through the reticular formation and nuclei of the vagus nerve output and proceed via an efferent link through the vagus nerve to cardiovascular structures.

This oculocardiac reflex is most often recognized in the context of ophthalmic surgery. Pressure or traction on the orbital contents, globe, or extra-ocular muscles can produce unwanted and sometimes dangerous consequences, including lethal arrhythmias

CHOICE OF MANEUVER It is difficult to identify which maneuver is the most useful given that certain vagal maneuvers may be more appropriate for particular situations (eg, CSM for the diagnosis of carotid sinus hypersensitivity) and most of the published experience is with CSM.

However, there is a suggestion that the Valsalva maneuver may be the most effective in the termination of SVT.

COMPLICATIONS

Cardiac complications:

 In appropriately selected patients, vagal maneuvers are generally safe. However. interventions that alter cardiac conduction properties can result in adverse events, including the following:●Sinus pauses●AV block●Less commonly, tachyarrhythmias

In rare cases, prolonged pauses, severe bradycardia, or malignant arrhythmias can have severe consequences.

Diving Reflex Vagal Maneuver - seen on _ER_ Season 4.mp4

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