Physiology of the Valsalva Manoeuvre

Here’s a refresher on the physiology of the Valsalva in order to maximise your chance of success.

Phase 1: (Initiation of manoeuvre): Raised intra-thoracic pressure leads to a transient increase in venous return leading to a rise in BP. Note that phase 1 does NOT start at time 0 in the figure.

Phase 2: (Straining): The sustained rise in intra-thoracic pressure leads to reduced venous return, reduced filling of the heart,  reduced cardiac output and a fall in BP. There is a compensatory increase in heart rate.

Phase 3: (Release): The sudden reduction in intra-thoracic pressure means that the venous reservoir is momentarily empty and there is a fall in BP.

Phase 4: There is rapid return of cardiac output and a corresponding rise in BP. This elicits a parasympathetically mediated reflex bradycardia. This is what hopefully terminates the SVT.

To increase the chances of a Valsalva being successful you therefore need to:

• Explain carefully to the patient that they may feel faint and experience an initial increase in heart rate. Insufficient explanation may result in high anxiety (and high sympathetic activity) which will antagonise the desired parasympathetic bradycardia
• Make sure the patient performs the manoeuvre for long enough (15-20 seconds if possible). Insufficient time spent in phases 1 and 2 may not elicit the necessary compensatory changes
• Words of encouragement are allowed
• The Valsalva manoeuvre should be augmented by putting the patient head down and raising his/her legs just prior to release of the ‘strain’ phase (by further increasing venous return) as per the REVERT study [4]. This simple modification improved the success of the valsalva manoeuvre from 17% to 43%.

Learning bite

In a patient with re-entrant SVT, a Valsalva is the vagal manoeuvre of choice.