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Vasovagal syncope typically occurs in young patients following a trigger (prolonged standing with or without an emotional stressor) and is preceded by prodromal features (warmth, nausea, diaphoresis, sweating, and lightheadedness).


  1. Reflex syncope refers to a group of related disorders that trigger inappropriate cardiovascular reflexes producing hypotension and syncope.

    1. The predominant reflex may be bradycardia (cardioinhibitory type), vasodilatation (vasodepressor type), or both.

    2. This distinction may affect the choice of therapy, with pacemakers a potential option for patients with severe, recurrent symptomatic cardioinhibitory reflex syncope.

    3. Types of reflex syncope include vasovagal (or neurocardiogenic syncope), situational syncope, and carotid hypersensitivity.

    4. The triggers vary with the type of reflex syncope:

      1. Vasovagal syncope: upright posture with or without stress

      2. Carotid sinus hypersensitivity: Carotid pressure, see below

      3. Situational syncope: associated with defecation, micturition, or prolonged coughing

  2. The remainder of this section focuses on vasovagal syncope.

    1. Most common cause of syncope (20–33% of cases)

    2. The pathophysiology is illustrated in Figure 31-4 and includes:

      1. Prolonged standing causes venous pooling, decreasing venous return thereby decreasing left ventricular (LV) preload (which may be accentuated by dehydration).

      2. Superimposed anxiety, pain, or fear triggers a sympathetic surge, which augments ventricular contraction.

      3. Vigorous contraction coupled with decreased LV preload results in a markedly low end-systolic volume, which triggers intracardiac mechanoreceptors.

      4. The mechanoreceptors trigger the vagal reflex.

      5. The vagal reflex triggers bradycardia, vasodilatation, or both, resulting in hypotension and syncope.

Figure 31-4.

Pathophysiology of vasovagal syncope


  1. History

    1. No single finding is very sensitive for vasovagal syncope (14–60%).

      1. Triggers include prolonged standing (37%), warm environment (42%), lack of food (23%), fear (9–21%), and acute pain (14%).

      2. Prodromal symptoms include sweating (32–66%), nausea (13–60%), and warmth (6–18%).

      3. Venous pooling after exercise may also trigger vasovagal syncope. However, syncope during exercise suggests cardiac syncope.

    2. However, certain findings are fairly specific and increase the likelihood of vasovagal syncope when present.

      1. image Prolonged standing (LR+, 9.0)

      2. image Abdominal discomfort prior to syncope (LR+, 8)

      3. image Occurring during injection/cannulation (LR+, 7)

      4. Dehydration (LR+, 3.7)

      5. Nausea after syncope (LR+, 3.5)

  2. Laboratory and radiologic tests

    1. Patients with a typical history, a normal physical exam and ECG, and no red flags (syncope while supine, sitting or during exertion, associated chest pain, palpitations or dyspnea, age over 60, or prior history of heart disease or family history of sudden death [see Figure 31-2]) do not require further testing.

    2. Patients over 40, those with an atypical history (ie, without a clear precipitant) and those with heart disease or red flags require additional evaluation including an echocardiogram and potentially tilt-table testing and/or an implantable loop recorder (ILR).

    3. Tilt-table testing in vasovagal syncope

      1. The patient is initially supine for 20–45 minutes.

      2. The table is then tilted to 70 degrees and the patient kept upright for 30–40 minutes during which time the pulse and BP are continuously ...

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