Hydralazine in Severe Hypertension with Bradycardia
Hydralazine is actually an excellent choice for severe hypertension in the setting of bradycardia because it causes reflex tachycardia through baroreceptor-mediated sympathetic activation, which can counteract the bradycardia while lowering blood pressure. 1, 2
Mechanism Supporting Use in Bradycardia
Hydralazine produces peripheral vasodilation through direct relaxation of vascular smooth muscle, which decreases arterial blood pressure (diastolic more than systolic) and increases heart rate, stroke volume, and cardiac output through reflex sympathetic discharge 1
In a prospective study of 21 patients with symptomatic sinus bradycardia, hydralazine increased heart rate by 20% or greater in approximately two-thirds of hypertensive patients and half of normotensive patients, with amelioration of symptoms and no important side effects 2
The reflex tachycardia that is typically considered an adverse effect of hydralazine in most hypertensive patients becomes therapeutically beneficial when bradycardia is present 1, 2
Dosing and Administration
For acute severe hypertension, administer hydralazine 10 mg via slow IV infusion initially (maximum initial dose 20 mg), repeated every 4-6 hours as needed 3, 4
Blood pressure begins to decrease within 10-30 minutes with effects lasting 2-4 hours, requiring monitoring for the full duration of action 3, 5
Wait 2-4 hours to assess full effect before giving additional doses to avoid cumulative hypotensive effects 5
Critical Safety Parameters
Hold hydralazine if diastolic blood pressure falls below 60 mmHg, particularly in patients with diabetes mellitus, those over 60 years of age, or those with coronary artery disease and heart failure with evidence of myocardial ischemia 6, 5
Monitor for symptoms of hypoperfusion including dizziness, syncope, chest pain, altered mental status, or oliguria 5
The myocardial stimulation produced by hydralazine can cause anginal attacks and ECG changes of myocardial ischemia, so use with caution in patients with suspected coronary artery disease 1
Important Caveats
While hydralazine's reflex tachycardia is beneficial for bradycardia, the unpredictable blood pressure response and prolonged duration of action (2-4 hours) make it less desirable than more titratable agents like nicardipine or labetalol for most acute hypertensive situations 3, 5, 7
In a prospective study of 94 hospitalized patients receiving 201 doses of IV hydralazine, blood pressure reduction was highly variable (24/9 ± 29/15 mmHg), with 11 patients experiencing hypotension as an adverse event 8
Hydralazine causes sodium and water retention, which may require concurrent diuretic therapy in non-acute settings 3, 1
Avoid using hydralazine as monotherapy for chronic hypertension—it must be combined with a beta-blocker and diuretic to counteract reflex tachycardia and sodium retention in non-bradycardic patients 3