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Post exercise vasovagal syncope: Difference between revisions
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The main point is that PEH is common after moderate-intensity dynamic exercise. In general, this is a benign process and in the majority of individuals PEH is insufficient to cause syncopal symptoms. | The main point is that PEH is common after moderate-intensity dynamic exercise. In general, this is a benign process and in the majority of individuals PEH is insufficient to cause syncopal symptoms. | ||
The magnitude of PEH can be exaggerated in the seated or standing positions (compared to supine) | The magnitude of PEH can be exaggerated in the seated or standing positions (compared to supine) <cite>Kenney</cite><cite>Bjurstedt</cite> and arterial pressure may fall to the level at which pre-syncopal signs or symptoms occur. | ||
=== Neurally mediated syncope after exercise === | === Neurally mediated syncope after exercise === | ||
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It appears that the underlying mechanism for neurally mediated syncope occurring after the termination of exercise are similar to that of PEH. The sudden removal of the muscle pump activity, decreasing cardiac preload, may be a trigger, along with a rapid return of vagal tone to the heart at the termination of exercise 1] | It appears that the underlying mechanism for neurally mediated syncope occurring after the termination of exercise are similar to that of PEH. The sudden removal of the muscle pump activity, decreasing cardiac preload, may be a trigger, along with a rapid return of vagal tone to the heart at the termination of exercise 1] | ||
Characteristically, these events occur while the individual is standing motionless during the first 5 to 10 min after exercise | Characteristically, these events occur while the individual is standing motionless during the first 5 to 10 min after exercise <cite>Bjurstedt</cite><cite>Tsutsumi</cite>. Individuals rapidly recover in the supine position. It has been estimated that the incidence rate of neurally mediated syncope after routine treadmill testing may be in the order of 0.3-3 % <cite>Holtzhausen</cite>. However, when treadmill testing is immediately followed by passive head-up tilt testing, this percentage can increase up to 50-70% <cite>Holtzhausen</cite><cite>Sakaguchi</cite>. Neurally mediated syncope after exercise is considered to be a benign occurrence <cite>Krediet</cite>. | ||
In a minute minority of cases of syncope during (exertional) exercise the vasovagal reaction is thought to be the underlying pathophysiological mechanism | In a minute minority of cases of syncope during (exertional) exercise the vasovagal reaction is thought to be the underlying pathophysiological mechanism <cite>Krediet</cite>. How the reaction in this circumstance is triggered remains to be elucidated <cite>Krediet</cite><cite>KredietCT</cite>. Nausea prior to such episode is a commonly reported symptom. The following mechanisms may be involved. | ||
#Supra-physiological stimulation of ventricular mechanoreceptors in the left ventricle, especially when cardiac filling is decreased at a high heart rate is thought to be a trigger for vasovagal reactions (i.e. the Bezold-Jarisch hypothesis). | #Supra-physiological stimulation of ventricular mechanoreceptors in the left ventricle, especially when cardiac filling is decreased at a high heart rate is thought to be a trigger for vasovagal reactions (i.e. the Bezold-Jarisch hypothesis).<cite>Hainsworth</cite> Abrahamsen and Thoren made the observation that such stimulation leads also to reflex gastric dilatation and eventual vomiting in the cat.<cite>Abrahamsson</cite> However many dispute the Bezold-Jarisch hypothesis because evidence for the existence of ventricular mechanoreceptors in man is lacking.<cite>Hainsworth</cite> The newly discovered mechano receptors in the coronaries of the dog could provide an alternative explanation for the results that once were thought to demonstrate the existence of the ventricular mechanoreceptors.<cite>Wright</cite> | ||
#Holmqvist et al showed, using pancreatic polypeptide as a measure for vagal activity in man that abdominal vagal activity increases during maximal exercise, reaching its highest values after exertion. | #Holmqvist et al showed, using pancreatic polypeptide as a measure for vagal activity in man that abdominal vagal activity increases during maximal exercise, reaching its highest values after exertion.<cite>Holmqvist</cite> They suggest that such high vagal outflow may also cause nausea. | ||
Although patients suffering from “vasovagal syncope during exercise” have been studied intensely, there are no objectified observations of such loss of consciousness during exercise. This raises the question whether this disease as a separate entity truly exists. If not, this form of syncope could actually be the same as vasovagal occurring after exercise, only differing in time between time between stopping and loss of consciousness. In cases where this comes within a certain amount of time patients will be inclined to report that the lost consciousness during exercise, where in fact it happened shortly after. The importance of detailed history taking is also in these cases beyond doubt. | Although patients suffering from “vasovagal syncope during exercise” have been studied intensely, there are no objectified observations of such loss of consciousness during exercise. This raises the question whether this disease as a separate entity truly exists. If not, this form of syncope could actually be the same as vasovagal occurring after exercise, only differing in time between time between stopping and loss of consciousness. In cases where this comes within a certain amount of time patients will be inclined to report that the lost consciousness during exercise, where in fact it happened shortly after. The importance of detailed history taking is also in these cases beyond doubt. | ||