Is there a preferred antihypertensive therapy for isolated systolic hypertension and reduced arterial compliance?

Hypertension in an ageing population: Diagnosis, mechanisms, collateral health risks, treatments, and clinical challenges

Ageing population is considerably increasing worldwide, which is considered to reflect an improved quality of life. However, longevity in the human lifespan has increased the burden of late-life illnesses including cancer, neurodegeneration, and cardiovascular dysfunction. Of these, hypertension is the most common condition with huge health risks, with an increased prevalence among the elderly. In this review, we outline the current guidelines for defining hypertension and examine the detailed mechanisms underlying the relationship between hypertension and ageing-related outcomes, including sodium sensitivity, arterial stiffness, endothelial dysfunction, isolated systolic hypertension, white coat effect, and orthostatic hypertension. As hypertension-related collateral health risk increases among the elderly, the available management strategies are necessary to overcome the clinical treatment challenges faced among elderly population. To improve longevity and reduce adverse health effects, potential approaches producing crucial information into new era of medicine should be considered in the prevention and treatment of hypertension among elderly population. This review provides an overview of mechanisms underlying hypertension and its related collateral health risk in elderly population, along with multiple approaches and management strategies to improve the clinical challenges among elderly population.

Electrical modelling of tissue experiments confirms precise locations of resistance and compliance in systemic arterial tree-they are mutually exclusive

This study presents electrical modelling of the arterial system to understand the effect of adrenaline on the aortae and small arteries in terms of their resistance and compliance. There is no categorical documentation in the current literature on the precise locations of arterial resistance (R) and compliance (C) in vasculature. Knowledge of their exact locations in the arterial tree enables re-assessment of the differential action of vasoactive drugs on resistance versus compliance vessels once we resolve beat-to-beat changes in R and C in response to these drugs. Isolated goat aortae and small arteries were perfused with a pulsatile pump and lumen pressures were recorded before and after addition of adrenaline. Equivalent electrical models were simulated, and biological data was compared against the electrical equivalents to derive interpretations. In the aortae, systolic pressure increased, diastolic pressure decreased, pulse pressure increased (P = .018); but the mean pressure remained the same (P = .357). Whereas in small artery, vasoconstriction caused an increase in systolic, diastolic, and mean pressures (P = .028). Simulations allow us to infer that vasoconstriction in the aorta leads to a reduction in compliance, but an increase in resistance if any, is not sufficient to alter the mean aortic pressure. Whereas vasoconstriction in small arteries increases resistance, but a decrease in compliance, if any, does not affect any of the pressure parameters measured. The presented study is first of its kind to give experimental evidence that large arteries and aorta are the only compliance vessels and small arteries are the only resistance vessels.

Effectiveness of olmesartan-based treatment on home and clinic blood pressure in elderly patients with masked and white coat hypertension

Few large-scale studies have evaluated the effectiveness of angiotensin receptor blockers in patients with masked hypertension (MH) and white coat hypertension (WCH) based on age using real-world blood pressure (BP) data. We used data from the Home BP measurement with Olmesartan Naive patients to Establish Standard Target BP (HONEST) study to investigate the effectiveness of olmesartan-based treatment by patient age (<65 years of age, n=9817; 65–74 years of age, n=6792; ⩾75 years of age, n=4732), focusing on morning home BP (strongly associated with cardiovascular disease and useful for MH and WCH diagnosis). Sixteen weeks of treatment changed morning home BP (mean systolic/diastolic) by −18.1/−9.7, −15.9/−7.4 and −14.2/−6.4 mm Hg and clinic BP by −20.1/−11.3, −17.3/−8.7 and −15.4/−7.2 mm Hg, in these age groups, respectively (P<0.0001). Pulse pressure decreased (−7.8 to −8.8 mm Hg, P<0.0001). Patients aged ⩾80 years experienced similar BP and pulse pressure changes. In patients aged ⩾75 years, mean morning and clinic BP after 16 weeks was 137.5/74.8 and 129.7/70.4 mm Hg, respectively, in MH patients and 132.3/72.2 and 139.7/72.7 mm Hg, respectively, in WCH patients. Regardless of age, only elevated clinic or home BP values decreased to target ranges. The incidence of adverse effects associated with excessive BP lowering was low in all of the age groups. In conclusion, our study suggests that olmesartan-based treatment was safe and useful for managing MH, WCH and sustained hypertension in elderly patients. The lack of a placebo group was a limitation of the study.

Does long‐term losartan‐ vs atenolol‐based antihypertensive treatment influence collagen markers differently in hypertensive patients? A LIFE substudy

BACKGROUND

The aim of this study was to investigate the effects of losartan- vs atenolol-based antihypertensive treatment on circulating collagen markers beyond the initial blood pressure (BP) reduction.

METHODS

In 204 patients with hypertension and left ventricular (LV) hypertrophy we measured serum concentration of carboxy-terminal telopeptide of type I procollagen (ICTP), carboxy-terminal propeptide of type I procollagen (PICP), amino-terminal propeptide of type III procollagen (PIIINP), amino-terminal propeptide of type I procollagen (PINP) and LV mass by echocardiography at baseline and annually during 4 years of losartan- or atenolol-based antihypertensive treatment; 185 patients completed the study.

RESULTS

Beyond the first year of treatment systolic and diastolic BP, LV mass index (LVMI) as well as collagen markers did not change significantly and were equal in the two treatment groups. Changes in PICP during first year of treatment were related to subsequent changes in LV mass index after 2 and 3 years of treatment (r=0.28 and r=0.29, both p<0.05) in patients randomized to losartan, but not atenolol.

CONCLUSION

Long-term losartan- vs atenolol-based antihypertensive treatment did not influence collagen markers differently, making a BP-independent effect of losartan on collagen markers unlikely. However, initial reduction in circulating PICP may predict later regression of LV hypertrophy during losartan-based antihypertensive treatment.

Inhibition of the renin-angiotensin-aldosterone system to prevent ischemic and atherothrombotic events

Blood pressure (BP) is a continuous risk factor for ischemic and atherosclerotic events such as stroke and ischemic heart disease, and controlling BP is a well-established component of any cardiovascular or cerebrovascular risk reduction regimen. In most patients, > or =2 medications with different mechanisms of action will be necessary to reach recommended BP goals. The neuroendocrine effects of the renin-angiotensin-aldosterone-system (RAAS) have proven to be excellent therapeutic targets for BP lowering. A number of antiatherosclerotic effects have been attributed to angiotensin-converting enzyme inhibitors and angiotensin receptor blockers in addition to their antihypertensive effects. Because they have complementary actions on the RAAS, combination therapy with these agents has become the focus of recent clinical trials. This review describes the clinical data assessing the efficacy of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers individually and in combination in reducing the risk of stroke and ischemic heart disease.

The evolution of systolic blood pressure as a strong predictor of cardiovascular risk and the effectiveness of fixed-dose ARB/CCB combinations in lowering levels of this preferential target

Elevated blood pressure is an important cardiovascular risk factor. Although targets for both diastolic blood pressure (DBP) and systolic blood pressure (SBP) are defined by current guidelines, DBP has historically taken precedence in hypertension management. However, there is strong evidence that SBP is superior to DBP as a predictor of cardiovascular events. Moreover, achieving control of SBP is assuming greater importance amongst an aging population. In spite of the growing recognition of the importance of SBP in reducing cardiovascular risk and the emphasis by current guidelines on SBP control, a substantial proportion of patients still fail to achieve SBP targets, and SBP control is achieved much less frequently than DBP control. Thus, new approaches to the management of hypertension are required in order to control SBP and minimize cardiovascular risk. Fixed-dose combination (FDC) therapy is an approach that offers the advantages of multiple drug administration and a reduction in regimen complexity that favors compliance. We have reviewed the latest evidence demonstrating the efficacy in targeting SBP of the most recent FDC products; combinations of the calcium channel blocker (CCB), amlodipine, with angiotensin receptor blockers (ARBs), valsartan or olmesartan. In addition, results from studies with new classes of agent are outlined.

Pulse Pressure and Cardiovascular Events in Postmenopausal Women With Coronary Heart Disease

BACKGROUND

Pulse pressure (PP) has been shown to predict risk for cardiovascular events in men; however, this association has not been well established in women. Hormone replacement therapy may improve arterial compliance, but findings from cross-sectional and prospective studies report inconsistent results. We sought to examine the relationship between PP and risk for cardiovascular events, and to determine the effect of hormone therapy on PP in postmenopausal women with coronary heart disease (CHD).

METHODS AND RESULTS

A total of 2,763 postmenopausal women (mean age, 66 +/- 7 years [+/- SD]) with CHD in the Heart and Estrogen/Progestin Replacement Study, a randomized, placebo-controlled, secondary CHD prevention trial of estrogen plus progestin, were followed up on average for 4.1 years. BP was measured at baseline and annually. Mean baseline PP was 62 +/- 16 mm Hg. There were 361 myocardial infarctions (MIs) or CHD deaths, 265 hospitalizations for congestive heart failure (CHF), and 215 strokes or transient ischemic attacks (TIAs). Women in the highest quartile of PP at baseline had a 47% increase in risk for MI or CHD death and more than a twofold increase in risk for stroke and TIA events or hospitalization for CHF (p < 0.01 for each outcome). After adjustment for other cardiovascular risk factors and mean arterial pressure, PP remained significantly associated with incident stroke or TIA events (odds ratio, 1.25; p = 0.02) and hospitalizations for CHF (odds ratio, 1.31; p < 0.01) but not with MI or CHD death. After adjustment for diastolic BP, systolic BP was similarly associated with stroke or TIA (odds ratio, 1.30; p < 0.01) and hospitalized CHF (odds ratio, 1.30; p < 0.01) and was also weakly associated with risk for MI and CHD death (odds ratio, 1.18; p = 0.02). Mean PP was 1- to 2-mm Hg higher in women randomized to hormone replacement therapy vs those receiving placebo (p < 0.01).

CONCLUSIONS

PP had predictive value for CHF and stroke or TIA, but not MI or CHD death in this cohort of postmenopausal women with CHD. Use of hormone replacement therapy produced a small, statistically significant increase in PP. Further research is necessary to determine the clinical utility of PP as a potential therapeutic target.

Markers of collagen synthesis is related to blood pressure and vascular hypertrophy: a LIFE substudy

Cardiac fibrosis and high levels of circulating collagen markers has been associated with left ventricular (LV) hypertrophy. However, the relationship to vascular hypertrophy and blood pressure (BP) load is unclear. In 204 patients with essential hypertension and electrocardiographic LV hypertrophy, we measured sitting BP, serum collagen type I carboxy-terminal telopeptide (ICTP) reflecting degradation, procollagen type I carboxy-terminal propeptide (PICP) reflecting synthesis and LV mass by echocardiography after 2 weeks of placebo treatment and after 1 year of antihypertensive treatment with a losartan- or an atenolol-based regimen. Furthermore, we measured intima-media thickness of the common carotid arteries (IMT), minimal forearm vascular resistance (MFVR) by plethysmography and ambulatory 24-h BP in around half of the patients. At baseline, PICP/ICTP was positively related to IMT (r=0.24, P<0.05), MFVR(men) (r=0.35, P<0.01), 24-h systolic BP (r=0.24, P<0.05) and 24-h diastolic BP (r=0.22, P<0.05), but not to LV mass. After 1 year of treatment with reduction in systolic BP (175+/-15 vs 151+/-17 mmHg, P<0.001) and diastolic BP (99+/-8 vs 88+/-9 mmHg, P<0.001), ICTP was unchanged (3.7+/-1.4 vs 3.8+/-1.4 microg/l, NS) while PICP (121+/-39 vs 102+/-29 microg/l, P<0.001) decreased. The reduction in PICP/ICTP was related to the reduction in sitting diastolic BP (r=0.31, P<0.01) and regression of IMT (r=0.37, P<0.05) in patients receiving atenolol and to reduction in heart rate in patients receiving losartan (r=0.30, P<0.01). In conclusion, collagen markers reflecting net synthesis of type I collagen were positively related to vascular hypertrophy and BP load, suggesting that collagen synthesis in the vascular wall is increased in relation to high haemodynamic load in a reversible manner.

Hypertension and the elderly: more than just blood pressure control

Hypertension is a major risk factor for cardiovascular disease in both young and elderly persons; therefore, good blood pressure control is at the center of improved cardiovascular health. The recently issued seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure and the European Society of Hypertension/European Society of Cardiology 2003 guidelines for hypertension management emphasize the importance of treatment efficacy rather than age in treating elderly persons with hypertension. Most hypertension clinical trials have been carried out with younger hypertensives, but this is changing with trials such as the Systolic Hypertension in the Elderly Program, the first Swedish Trial of Old Patients With Hypertension, and the Systolic Hypertension in Europe trial. These trials have clearly demonstrated the benefits of good blood pressure control in reducing the risk of stroke in elderly persons. With many safe and effective antihypertensive drugs on the market, the question becomes how elderly persons should be treated. Elderly patients often have isolated systolic hypertension, which is related to loss of arterial elasticity or compliance with aging and is more recalcitrant to treatment than essential hypertension. In addition, with advancing age there is the likelihood that other disease states are present in addition to hypertension. The newer antihypertensive drugs that interfere with the renin angiotensin system, such as angiotensin-converting enzyme inhibitors and angiotensin-receptor blockers, have the potential of improving cardiovascular outcomes in elderly persons in addition to offering effective blood pressure reduction. Their use should be considered within a comprehensive risk assessment that includes individualized risk-benefit considerations.

Prevalence and implications of uncontrolled systolic hypertension

Risk of cardiovascular disease (CVD) increases incrementally with blood pressure, even within the high-normal range. In the general population, 27% of CVD in women and 37% in men is attributable to hypertension. A high percentage of these hypertension-related events occur in those with high-normal blood pressure and mild hypertension; about one-fourth of CVD events in elderly women and one-third in elderly men in the Framingham Study occurred in persons who had blood pressures of 140-159 mm Hg systolic and/or 90-95 mm Hg diastolic. The average systolic blood pressure (SBP) at which coronary heart disease occurs is rather modest (141 mm Hg), as is the pulse pressure (59-63 mm Hg). Of the CVD events in elderly participants in the Framingham Study, 24% in men and 36% in women occurred in persons receiving treatment for hypertension. There is a growing recognition of the importance of the systolic component of blood pressure. About 65% of hypertension in the elderly is isolated systolic hypertension (ISH), and CVD risk increases with pulse pressure. Pulse pressure is not simply a marker for stiff diseased arteries; treatment of ISH in trials promptly reduces the CVD risk, indicating that the pulse pressure generated by the stiff artery is the culprit. Analysis of data from clinical trials indicates that greater reliance should be placed on systolic pressure in evaluating the CVD potential of hypertension. Hypertension, including ISH, seldom occurs in isolation from other risk factors and overt CVD. Risk varies widely depending on the burden of accompanying risk factors. This makes global risk assessment mandatory for evaluating risk and the urgency and nature of treatment required. Evidence incriminating systolic pressure as the dominant blood pressure determinant of CVD has not been translated into clinical practice. Most of the uncontrolled hypertension observed in the Framingham Study is concentrated in those with ISH. This also extends to African-Americans, people with diabetes mellitus and the elderly. When should SBP be considered controlled? Substantial evidence supports the value of treating ISH with SBP exceeding 160 mm Hg. Trial data are not yet available to support recommendations to treat lesser elevations of ISH or pulse pressure per se, but since one-half of patients with mild ISH have two or more additional risk factors, most are candidates for treatment. In such patients, ISH should be considered controlled when their global CVD risk is reduced to below the average for their age.

Epidemiologic appraisal of hypertension as a coronary risk factor in the elderly

Five decades of epidemiologic research has established elevated blood pressure as a major contributor to atherosclerotic cardiovascular diseases in the elderly, including coronary heart disease. Clinicians formerly favored the diagnosis and treatment of hypertension in terms of the diastolic blood pressure and categorical "hypertension." Epidemiologic data now emphasize the essential role of systolic blood pressure, pulse pressure, and a graded influence of blood pressure, even within the high-normal range. The risk of coronary heart disease, the most common lethal sequela of hypertension, increases with the extent of risk factor clustering. Among hypertensive persons, about 39% of coronary events in men and 68% in women are attributable to the presence of two or more additional risk factors. When risk factor clustering is associated with glucose intolerance, obesity, and dyslipidemia, it may be attributed to insulin resistance promoted by abdominal obesity. Other hazardous influences often accompanying hypertension in the elderly are the presence of an elevated heart rate, elevated levels of fibrinogen, and left ventricular hypertrophy. Because clustering with other risk factors is characteristic of hypertension in the elderly, it is essential to screen for them and for the presence of comorbid cardiovascular diseases, target organ disease, and subclinical vascular disease likely to be present. Multivariate risk assessment profiles enable global estimation of hypertensive risk of developing coronary heart disease. Hypertensive elderly patients are more appropriately targeted for antihypertensive therapy by such risk stratification than by relying solely on the severity of the blood pressure elevation. The goal of therapy should be to improve the multivariate risk profile as well as the level of the blood pressure.

The effect of a losartan-based treatment regimen on isolated systolic hypertension

This study was conducted to compare the antihypertensive efficacy and tolerability, over 12 weeks, of a losartan-based treatment regimen and placebo in patients with isolated systolic hypertension. Three hundred eight patients > or =35 years of age with isolated systolic hypertension, defined as trough sitting blood pressure between 140 and 200 mm Hg systolic and between 70 and 89 mm Hg diastolic, were randomized to losartan 50 mg (n=157) or placebo (n=151) once daily, with titration as necessary to achieve a goal trough sitting systolic blood pressure (SBP) <140 mm Hg. At baseline, mean trough sitting SBP was 140-159 mm Hg in 20.5% of patients, 160-179 mm Hg in 62.7%, and 180-200 mm Hg in 16.9%, and was similar in the two groups (losartan, 165.3 mm Hg; placebo, 166.1 mm Hg). At 12 weeks, mean trough sitting SBP decreased significantly (p<0.001) in both the losartan-based treatment group (by 19.2 mm Hg) and in the placebo group (by 7.6 mm Hg). The reduction in sitting SBP was significantly greater for losartan than placebo (-11.6 mm Hg; 95% confidence interval, -14.8 to -8.4). In patients with isolated systolic hypertension, a once-daily losartan-based treatment regimen significantly lowered SBP. The losartan-based regimen exhibited antihypertensive efficacy that was superior to that of placebo, with a similar tolerability profile.

Isolated Systolic Hypertension in the Elderly

Isolated systolic hypertension (ISH) is the predominant form of hypertension in persons older than 50 years, who represent the majority of individuals with hypertension. Systolic blood pressure (SBP) determines Joint National Committee blood pressure stage, and therefore the need for therapy, far more often than diastolic blood pressure (DBP). SBP consistently is associated with greater risk for overall mortality, coronary heart disease, stroke, congestive heart failure, renal failure, and other end points. In addition, clinicians are far less aggressive and less successful at controlling SBP compared with DBP. Thus, SBP should be acknowledged as the major criterion that determines diagnosis, staging, and therapeutic management in older individuals. Several recent large, randomized, placebo-controlled trials of drug therapy targeting ISH in the elderly have shown dramatic reductions in cardiovascular end points and mortality. The treatment of patients with ISH must occur within the framework of the larger goals associated with treatment of hypertension generally. Lifestyle modification, including salt restriction and increasing physical activity, may contribute to improvements in arterial compliance and control of ISH in particular. In clinical trials, most antihypertensive agents decrease SBP more than DBP. However, certain drug classes, such as angiotensin-converting enzyme inhibitors and nitrates, have advantageous properties that may make them particularly useful for the treatment of ISH.

Improved arterial compliance by a novel advanced glycation end-product crosslink breaker

BACKGROUND

Arterial stiffening with increased pulse pressure is a leading risk factor for cardiovascular disease in the elderly. We tested whether ALT-711, a novel nonenzymatic breaker of advanced glycation end-product crosslinks, selectively improves arterial compliance and lowers pulse pressure in older individuals with vascular stiffening.

METHODS AND RESULTS

Nine US centers recruited and randomly assigned subjects with resting arterial pulse pressures >60 mm Hg and systolic pressures >140 mm Hg to once-daily ALT-711 (210 mg; n=62) or placebo (n=31) for 56 days. Preexisting antihypertensive treatment (90% of subjects) was continued during the study. Morning upright blood pressure, stroke volume, cardiac output, systemic vascular resistance, total arterial compliance, carotid-femoral pulse wave velocity, and drug tolerability were assessed. ALT-711 netted a greater decline in pulse pressures than placebo (-5.3 versus -0.6 mm Hg at day 56; P=0.034 for treatment effect by repeated-measures ANOVA). Systolic pressure declined in both groups, but diastolic pressure fell less with ALT-711 (P=0.056). Mean pressure declined similarly in both groups (-4 mm Hg; P<0.01 for each group, P=0.34 for treatment effect). Total arterial compliance rose 15% in ALT-711-treated subjects versus no change with placebo (P=0.015 versus ALT-711), an effect that did not depend on reduced mean pressure. Pulse wave velocity declined 8% with ALT-711 (P<0.05 at day 56, P=0.08 for treatment effect). Systemic arterial resistance, cardiac output, and heart rate did not significantly change in either group.

CONCLUSIONS

ALT-711 improves total arterial compliance in aged humans with vascular stiffening, and it may provide a novel therapeutic approach for this abnormality, which occurs with aging, diabetes, and isolated systolic hypertension.

The effect of antihypertensive drugs on vascular compliance

Measurement of vascular compliance has assumed increasing importance as a marker of early disease of the vascular wall, a predictor of future vascular disease, and a way to monitor the effects of vasoactive agents on arterial wall stiffness. Vascular compliance can be estimated by several methods: measurement of the pulse pressure, or pulse pressure-stroke volume ratio; analysis of the systolic pulse wave augmentation index and the diastolic pulse wave contour; ultrasonic echo-tracking; and MRI. Because few comparative studies have been done, the physiologic significance of the measures of compliance obtained by each method is uncertain. Antihypertensive drugs may improve vascular compliance by reducing blood pressure, relaxing vascular smooth muscle, or promoting long-term effects on vascular smooth muscle and cardiomyocyte growth and remodeling. Angiotensin converting enzyme (ACE) inhibitors have been reported to improve vascular compliance in nearly all studies, suggesting a beneficial class effect independent of blood pressure reduction. Favorable changes in the vascular wall-lumen ratio of small vessels from subcutaneous gluteal biopsy specimens after treatment with ACE inhibitors and the persistence of improved vascular compliance after withdrawal of therapy indicate that these agents may produce long-term vascular remodeling. Although few studies have been done, angiotensin II receptor antagonists improve vascular compliance, possibly by blocking angiotensin II-mediated cell proliferation and increasing apoptosis via unopposed AT1 receptor stimulation. In contrast, calcium antagonists and beta-blockers have variable effects on vascular compliance, although beta-blockers with intrinsic sympathomimetic activity improve vascular compliance. Diuretics have little effect on vascular compliance beyond their blood pressure-lowering actions, except for spironolactone, which by improving vascular compliance may have contributed to the reduction in heart failure mortality seen in the Randomized Aldactone Evaluation Study.

Predominance of isolated systolic hypertension among middle-aged and elderly US hypertensives: analysis based on National Health and Nutrition Examination Survey (NHANES) III

The purpose of the present study was to examine patterns of systolic and diastolic hypertension by age in the nationally representative National Health and Nutrition Examination Survey (NHANES) III and to determine when treatment and control efforts should be recommended. Percentage distribution of 3 blood pressure subtypes (isolated systolic hypertension, combined systolic/diastolic hypertension, and isolated diastolic hypertension) was categorized for uncontrolled hypertension (untreated and inadequately treated) in 2 age groups (ages <50 and >/=50 years). Overall, isolated systolic hypertension was the most frequent subtype of uncontrolled hypertension (65%). Most subjects with hypertension (74%) were >/=50 years of age, and of this untreated older group, nearly all (94%) were accurately staged by systolic blood pressure alone, in contrast to subjects in the untreated younger group, who were best staged by diastolic blood pressure. Furthermore, most subjects (80%) in the older untreated and the inadequately treated groups had isolated systolic hypertension and required a greater reduction in systolic blood pressure than in the younger groups (-13.3 and -16.5 mm Hg versus -6.8 and -6.1 mm Hg, respectively; P:=0.0001) to attain a systolic blood pressure treatment goal of <140 mm Hg. Contrary to previous perceptions, isolated systolic hypertension was the majority subtype of uncontrolled hypertension in subjects of ages 50 to 59 years, comprised 87% frequency for subjects in the sixth decade of life, and required greater reduction in systolic blood pressure in these subjects to reach treatment goal compared with subjects in the younger group. Better awareness of this middle-aged and older high-risk group and more aggressive antihypertensive therapy are necessary to address this treatment gap.