The patient in this clinical vignette is experiencing hypertensive crisis as defined by a systolic blood pressure > 180 mmHg and/or diastolic blood pressure > 120 mmHg. Given the clinical history and exam, the patient's presentation is of concern for pheochromocytoma leading to high catecholamine levels. Giving a beta-blocker such as metoprolol can cause unopposed alpha-adrenergic receptor stimulation leading to peripheral vasoconstriction, precipitating a hypertensive crisis.
The patient has the classic triad of pheochromocytoma including hypertension, headache, and diaphoresis (sweating). Other symptoms include palpitations, anxiety, tremor, and dyspnea. The paroxysmal nature of her symptoms over the span of weeks without any other past medical history also supports a diagnosis of pheochromocytoma. Differential diagnosis can include acute coronary syndrome, panic disorder, migraines, or medications causing increased levels of catecholamines (TCA, decongestants, amphetamines, etc.). The mechanism of hypertension is complex, but is primarily affected by the alpha- and beta-adrenergic receptor stimulation caused by increased levels of catecholamines. In any patient with a suspicion of pheochromocytoma, alpha-adrenergic blockade must be achieved before beta-adrenergic blockade can be initiated. The stimulated alpha-adrenergic receptor causes vasoconstriction, but is opposed by the vasodilatory action of the stimulated beta-adrenergic receptors. However, with the beta-adrenergic receptors blocked (such as by the beta-selective antagonist metoprolol), the unopposed alpha-adrenergic receptor stimulation will cause peripheral vasoconstriction and, therefore, hypertensive crisis. Phenoxybenzamine is an irreversible non-specific alpha-adrenergic blocker used for blood pressure and arrhythmia control and should be initiated before beta-adrenergic blockade.
Answer 1: Although beta-adrenergic blockade typically leads to decreased cardiac output and, therefore, decreased blood pressure, in this patient the hypertension is primarily due to increased peripheral vascular resistance. Beta-adrenergic blockade inhibits the vasodilatory actions of the beta-adrenergic receptors, and permits unopposed alpha-adrenergic vasoconstriction.
Answer 2: Although alpha-adrenergic receptor blockade would inhibit vasoconstriction by alpha-1 and alpha-2 receptors decreasing blood pressure, metoprolol has no effect on alpha-adrenergic receptors.
Answer 3: Alpha-adrenergic receptor blockade would inhibit vasoconstriction, leading to hypotension, not hypertension. Moreover, metoprolol is a beta-blocker without alpha-adrenergic action.
Answer 5: Metoprolol has no effect on alpha-adrenergic receptors. Moreover, with combined alpha- and beta-adrenergic receptor blockade, the blood pressure should decrease.
In any patient with a suspicion for pheochromocytoma, alpha-adrenergic blockade must be achieved before beta-adrenergic blockade can be initiated to avoid precipitating a hypertensive crisis. Phenoxybenzamine is the preferred method of achieving alpha-adrenergic blockade before initiation of beta-blockers. Definitive treatment is with surgical excision of the pheochromocytoma.