To the Editor:
First-line treatment options for hypertension are wide-ranging and include thiazide diuretics, angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), and calcium channel blockers (CCBs).1,2 Expert recommendations have until now focused on comparative analyses of cardiovascular outcomes, efficacy in reducing blood pressure (BP), adverse effects, and cost. Essential hypertension can be classified into distinct subtypes depending on the primary hemodynamic derangement, which can either be increased cardiac output (CO), as is more commonly seen in the younger age group with sympathetic nervous system overactivity; or elevated systemic vascular resistance (SVR), as is seen in older patients.3 BP may be lowered more effectively if therapy is targeted at the primary pathophysiologic derangement. Accordingly, ACE inhibitors, ARBs, and CCBs would be the drugs of choice for patients with elevated SVR, while thiazide diuretics and β-blockers would be the drugs of choice for patients with increased CO. Nevertheless, in practice, an antihypertensive drug is usually initiated without prior knowledge of the underlying hemodynamic derangement of the patient.
We are conducting a study of adult emergency department patients with systolic BP ≥160 or diastolic BP ≥100 mm Hg recorded in ≥2 measurements on 2 separate occasions, in which we measure their CO and estimate SVR using a noninvasive, transcutaneous Doppler ultrasound device to assess blood flow across the aortic or pulmonary valve (Ultrasonic Cardiac Output Monitor or USCOM, USCOM Limited, Sydney, Australia). USCOM is a portable, simple-to-use, and reliable device that may be operated by physicians or nurses.4 Among 39 patients aged 55 years or older whom we have recruited to date, 30 (76.9%) have markedly increased SVR with normal or low CO, while 4 (10.3%) have markedly increased CO with normal SVR. We hypothesize that an antihypertensive strategy that identifies the primary underlying hemodynamic derangement, and treats accordingly, will control BP more effectively. Using a diuretic as first-line treatment for this older age group, as one of the drug classes currently recommended by the National Heart, Lung, and Blood Institute and the UK’s National Institute for Health and Clinical Excellence guidelines, would not address the primary pathophysiologic abnormality in as many as 76% of cases. This may explain why a recent meta-analysis has concluded that, based on BP-lowering efficacy, thiazide diuretics are inappropriate as first-line therapy.5 Updated hypertension guidelines from the United States and the United Kingdom are eagerly awaited.6 Finally, using a device such as USCOM to tailor specific antihypertensive therapy for individual patients is a concept worthy of further investigation.