Over the past three centuries the Valsalva manoeuvre (VM) has clearly transgressed a singular otic functionality as proposed by its namesake Antonio Maria Valsalva in the publication De Aure Humana Tractatus.1 2 The VM is used in a variety of medical conditions such as urinary incontinence, spinal pressure gradients, heart valve defects and autonomic nervous system dysfunction.1^–4 The relatively recent application of the VM to the setting of emergency medicine for the reversion of supraventricular tachycardia (SVT)—specifically atrioventricular nodal re-entrant tachycardia (AVNRT) and atrioventricular re-entrant tachycardia (AVRT)—has implications for prehospital emergency care practice. Currently, many paramedic services use the VM as a first-line management tool for haemodynamically stable SVT (AVNRT and AVRT), yet the efficacy of this practice is purely speculative in the absence of research. The objective of this study was to identify the recommended technique, its biomechanical basis, and the implications for the prehospital emergency care field employing the VM in the haemodynamically stable patient presenting with SVT.

METHODS

A comprehensive search strategy was developed to include both the peer-reviewed and non-peer-reviewed literature, and a search strategy developed by the Cochrane prehospital field (see online Appendix)5 was used to assist with the identification of prehospital literature. The databases searched included Medline (1950 to end of November 2007), EMBASE (1974 to end of November 2007) and the Cumulative Index for Nursing and Allied Health Literature (CINAHL) (1986 to end of November 2007).

In addition to a search of electronic databases, two journals that were not electronically indexed were also searched: Australasian Journal of Emergency Care (June 1997 – June 2000) and Journal of Primary Emergency Health Care (Volume 1, Issue 1, 2003 to Volume 5, Issue 3, 2007).

The databases and journals were searched using the following key terms: supraventricular tachycardia, atrio-ventricular nodal re-entry tachycardia (AVNRT), Valsalva, paramedic, ambulance.

Inclusion criteria required use of the VM to manage SVT (AVNRT or AVRT), a description of the biomechanics of the VM, comparison of the VM with other vagal techniques for the reversion of SVT, or demonstration of the efficacy of the VM in the clinical setting. Papers were excluded if the Valsalva technique was used for clinical applications other than the management of SVT.

RESULTS

A total of 447 documents were found across the range of searches. After cross-referencing to eliminate duplications and filtering results according to the mechanics, technique, comparison of efficacy or application of the VM, there remained 24 of relevance. Of these, six were clinical trials providing a variety of evidence of varying quality that demonstrated efficacy or comparison of the manoeuvre,4 6^–11 and three papers defined the pathophysiology of SVT while discussing the impact of VM on the arrhythmia.12^–14 No clinical studies were identified which examined the technique, efficacy or application of the VM in the prehospital care setting.

DISCUSSION

Biomechanics of the VM

The VM is described as an increase in intrathoracic pressure resulting in a reduction in venous return affecting the autonomic nervous system through activation of a sympathetic response via baroreceptors. This is achieved by exhaling against a closed glottis or by blowing against a pneumatic resistance for a period of time.2 4 6 7 10 15^–18 The effect of the VM involves four phases of activation:

• Phase 1: onset of strain and transient rise in mean arterial blood pressure;

• Phase 2:

  • atrial filling pressure decrease leading to mean arterial blood pressure (MABP) increase;

  • increased sympathetic activity leading to increased peripheral vascular resistance (small rise in MABP and heart rate);

• Phase 3: release of strain (and of intrathoracic pressure) leading to sudden fall in MABP;

• Phase 4: overshoot of MABP due to persistent sympathetic activity and vascular tone, resulting in reflex bradycardia and stimulation of baroreceptors.1 11

It has been shown that the greatest effect of the VM is achieved at phase 2 and phase 4, delineating the effect on specific nodal channels.4 10 11 19 20 This is important in the reversion of AVNRT and AVRT as these arrhythmias rely on an established circuit that is best interrupted by affecting the refractory nature of nodal tissue. These definitions serve to rationalise the mechanics of the VM, but leave considerable flexibility in interpretation of the nature of the technique.

Clinical studies of VM efficacy

Four of the six clinical studies compared the efficacy of the VM with other vagal manoeuvres.4 7 10 17 All four studies were randomised controlled trials with termination of the SVT as the outcome measure. Common limitations included a potential operator bias due to lack of blinding of assessed results. The results demonstrated a measure of efficacy of the VM over other vagal manoeuvres including carotid sinus massage (CSM) and facial immersion or dive reflex (measured in two out of three studies). The results are shown in table 1.

The studies in table 1 suggest benefit in the use of the VM as a primary tool for reversion of SVT in the prehospital setting due to its higher success rate. This is specifically mentioned in the paper by Taylor et al.17 Of note is the small number of participants in each study. While providing statistical validity in their own setting, they represent an opportunity to explore larger cohorts in an effort to clarify the efficacy. The prevalence of haemodynamically stable AVNRT and AVRT in the prehospital setting has not been previously published.

Defining a recommended Valsalva technique from the available literature

Defining the essential elements of the VM and its inherent characteristics in order to demonstrate the most effective means of achieving reversion is made difficult by variance in what constitutes a standardised VM technique, as shown from comparisons of efficacy against a variety of techniques across the sample.4 7 10 17 Application to the prehospital setting would necessitate selecting a technique in the absence of consistency or evidence of effect. This is obviously not a practical option and lends weight to an argument for further research specific to the needs of the field.

Variations in the technique found within available studies (where detailed) are shown in table 2.

When examining the literature it was found that the technique employed under the auspices of a VM varied across authors whose work examined the efficacy, biomechanics, utilisation and technique of producing the VM. Taylor et al make specific reference to this aspect of variation when considering the differences in their results compared with other clinical trials.17 Five other papers demonstrated variance in the VM technique.6 8 9 16 19

To identify a commonality of VM technique, two clinical studies6 11 were identified in order to best describe the effect of variance in the composite elements of the technique (pressure, duration and position). Wong and Taylor6 reported a clinical study demonstrating the biomechanics of the VM that hinted at technique as a factor in efficacy. This work specifically—supported by other authors generally—provided an evidence base for an appropriate VM technique.6 11 15 This suggested technique recognised three previously identified composites to the VM to produce an optimum baroreflex effect:

• minimum pressure of 40 mm Hg

• optimal duration of 15 s

• ideal posture: supine

These three composites combined comprise a “gold standard” VM technique.

Minimum pressure of 40 mm Hg

When considering the appropriate pressure necessary for an optimum baroreflex effect, the work of Looga11 and Dawson et al19 provide insight through an increased prevalence of intra-strain bradycardia at pressures generated above 40 mm Hg that are absent at lower pressures. The rationale for pressure and duration is obtained from the biomechanics of effect demonstrated by Wen et al.10

Optimal duration of 15 s

Duration of strain during the VM is discussed by Looga11 in relation to maximum effect and onset of side effects, and proposes that a shorter duration of strain (8–15 s) provides a more significant effect while a longer duration (20–40 s) has a more gradual response and a post-strain result of brief hyperventilation, with the potential for heart rate influence. Taylor and Wong support the use of a short duration strain in order to generate maximum VM effect without complications.6

Ideal posture: supine

Posture as a factor in achieving the optimum Valsalva effect is more readily described.6 8 Taylor and Wong6 found that the supine posture provided the best method of achieving a reflex bradycardia (and hence affecting the circuit) while averting significant changes to blood pressure, thus ensuring the avoidance of syncope during or after performance. These findings are echoed by Singer et al8 who support the reduced risk of hypotension in the supine patient, but they noted that age and gender also influence vagal tone owing to their effect on the autonomic response.

Patient compliance with instructions in the technique in order to obtain maximum effect is a variable that is difficult to measure. The instructions should demonstrate clearly what is required and each aspect of the technique should be reproducible, yet each patient will exhibit differing traits that complicate uniformity. The literature provides few insights on how this may be overcome. Patient compliance in the prehospital environment is likely to remain a variable, dependent upon the skill of the instructor and the ability of the patient to understand and reproduce what is required.

Alternative non-pharmacological vagal manoeuvres

Alternative vagal manoeuvres such as CSM or ice-to-face (dive reflex) are most commonly used in the emergency medical setting.4 7 10 16 These non-invasive techniques involve massaging of the neck to produce a vagal response through stimulation of baroreceptors within the carotid bodies, or immersing the patient’s face briefly in cold or icy water to achieve a similar increase in vagal tone. Apart from the studies that suggest poorer reversion efficacy due to a lesser vagal potency,4 7 inherent aberrant side effects occur with CSM, the most significant being asystole.4 This is a significant consequence within the prehospital environment and therefore this technique is unsuitable for prehospital practice. The use of ice or cold packs in dive reflex techniques presents a challenge to maintain them within the environment of an ambulance vehicle in a variety of weather conditions. As a result of the likely cost and logistical issues, this method is also deemed to be inappropriate for the prehospital setting.

Limitations of the review of the VM in prehospital emergency care

The ability to evaluate the efficacy of the VM was affected by the variation in VM technique used. Age was also found to have a significant effect on the effectiveness of vagal manoeuvres generally in reverting AVNRT and AVRT. This was emphasised when examining the effect of the ice-to-face technique which appears to have greater efficacy in infants, and the effect of cardiovascular disease on the effectiveness (and risk of side effects) in the elderly. In addition, there was low overall efficacy of successful reversion from AVNRT and AVRT when a variety of techniques were used. Further studies may lead to quantification of the effects of early reversion attempts on success rates, as suggested by Taylor and Wong,6 15 and the prehospital environment provides an appropriate setting for such work.

The limitations of such studies will similarly include subject age, pre-existing disease and an absence of comparative data in the initial work.

Recommendations

Justification for the use of the VM in the prehospital setting is currently defined by studies performed in the emergency medical setting as no evidence is available in the prehospital setting.4 6–11 15 These in-hospital studies suggest benefit to patients through early intervention, an inherent safety in performance of the technique over other manoeuvres such as CSM, and improved reversion rates in a number of studies.4 7 10 While the VM is currently used in the prehospital setting, in the absence of any prehospital studies it will continue to provide a first-line management tool for haemodynamically stable SVT (AVNRT and AVRT) based on the evidence generated from in-hospital studies. However, its continued use without any evidence of sound practice of technique and efficacy of reversion neither supports nor enhances the field of prehospital emergency care.

CONCLUSIONS

It is important to examine further the practice of the VM in the prehospital environment through research that evaluates current practice and leads to the development of evidence-based models of practice for the future. Studying the efficacy and technique of the VM in the prehospital setting may also provide further evidence regarding the impact of early intervention in SVT reversion and confirm its suitability for use in this setting.