Even Pre-Hypertension Can Lead to Enlarged Heart

NEW YORK, Jan. 8 -- Pre-hypertension appears to increase the risk of developing an enlarged heart among teens and young adults, according to a study of American Indians.

Left-ventricular hypertrophy was three times more common among participants with hypertension and two times more common among those with pre-hypertension compared with normotensive individuals, said Richard B. Devereux, M.D., of the New York Presbyterian Hospital, and colleagues, in a study published online today in the journal Circulation.

"Our results show that even small elevations in blood pressure, as seen with pre-hypertension," they wrote, "can have detrimental effects on hemodynamics and cardiovascular structure and function in an adolescent and young adult American Indian population, with many of the same risk factors plaguing the United States and industrialized countries around the world."

Previous studies have associated hypertension with changes in heart structure, but none has examined in a large, population-based cohort the effect of the relatively new pre-hypertension category established by the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure (JNC-7).

To fill this gap, the researchers analyzed cardiovascular findings from 1,940 participants from 13 American Indian communities in the Strong Heart Study. A majority of participants were women (57.5%) and the mean age was 26.8 (range 14 to 39).

The researchers found that 15% of the participants had hypertension (systolic pressure ?140 mm Hg, diastolic pressure ?90 mm Hg, or use of blood pressure medications) and 35% met criteria for pre-hypertension (systolic pressure 120 to 139 mmHg or diastolic pressure 80 to 89 mm Hg without antihypertensive treatment).

After adjustment for covariates, hypertensive and pre hypertensive participants were more likely than normotensive participants to have an enlarged heart by several measures. For the respective groups, the findings were (all P<0.001):

• Higher left-ventricular wall thickness (0.83 and 0.78 versus 0.72 cm).
• Greater left ventricular mass (182 and 161 versus 137 g).
• Larger relative wall thickness (0.30 and 0.29 versus 0.28 cm).
• More prevalent left-ventricular hypertrophy (19.9% and 11.4% versus 6.5%).

Other findings indicated increased arterial stiffness. For hypertension and pre-hypertension versus normal blood pressure, they were:

• Higher mean pulse pressure, or stroke volume index (1.24 and 1.15 versus 1.02 mm Hg/mLm²),
• Greater systolic hypertension (134.9 and 123.2 versus 108.0 mm Hg), and
• Higher total peripheral resistance index (3,027 and 2,805 versus 2,566 dynescms ^-5).

Adjusting for age, hypertensive and pre-hypertensive groups both had cardiac structural features associated with increased cardiovascular risk compared with normotensive participants. The researchers reported (respectively, all P<0.001 versus normotensive):

• Increased interventricular septal thickness (0.91 and 0.86 versus 0.79 cm).
• Increased posterior wall thickness (0.83 and 0.78 versus 0.72 cm).
• Higher relative wall thicknesses (0.30 and 0.29 versus 0.28 cm).
• Higher left ventricular mass (181.9 and 161.1 versus 136.5 g).
• Higher left-ventricular mass per body surface area (82.9 and 77.7 versus 71.9 g/m²).
• Greater left ventricular mass by height (41.4 and 38.4 versus 34.7 g/m^2.7).

Concentric left-ventricular hypertrophy was rare in the study (0% among hypertensive, 0.3% among pre-hypertensive, and 0.4% among normotensive participants), which "may reflect their generally mild hypertension."

There was a high prevalence of eccentric left ventricular hypertrophy (19.9%, 11.1%, and 6.1%, respectively), which "may be related to the high prevalence of obesity in our population, with a larger volume of circulating plasma," they wrote.

While previous studies found that lower stress-corrected midwall shortening predicted a higher rate of cardiovascular events, the study did not show differences in these measures. For hypertensive and pre-hypertensive versus normotensive participants, the findings were:

• No differences in stress-corrected midwall shortening (112% and 112% versus 1139%, P=NS for all comparisons).
• No significant differences in circumferential end-systolic stress/end-systolic volume index (1.04 and 1.05 versus 1.12x10 kdynescm^-2m^-2, P=NS for all comparisons).

"The lack of difference in these contractility indexes between young normotensive and hypertensive [Strong Heart Study] participants indicates that myocardial function has not yet been compromised despite left ventricular geometric abnormalities at this early and relatively mild stage of hypertension," the authors wrote.

The researchers said future studies are needed to determine whether the left-ventricular structure abnormalities found in the study will be related to subsequent cardiovascular events.

"Although our data suggest parallels between cardiovascular effects of pre-hypertension in adolescents and young adults and the well-known detrimental effects of hypertension," they wrote, "further data from longitudinal observational and therapeutic studies are needed before we can draw conclusions about the clinical implications of pre-hypertension."

Overall, Dr. Devereux and colleagues concluded that pre-hypertension does represent an intermediate point between hypertension and normal blood pressure for the structural and hemodynamic measures considered in the study, as expected.

Although the study looked at a sample population of American Indians with higher rates of overweight and diabetes than the general U.S. population, the researchers said the findings are likely generalizable and relevant to young adults in developed countries who are overweight or have diabetes.

The study was funded in part by the National Institutes of Health. The authors reported no financial disclosures.