Prognostic value of left atrial size in hypertensive African Americans undergoing stress echocardiography

BACKGROUND

Left atrial (LA) enlargement is a marker of increased risk in the general population undergoing stress echocardiography. African American (AA) patients with hypertension are known to have less atrial remodeling than whites with hypertension. The prognostic impact of LA enlargement in AA with hypertension undergoing stress echocardiography is uncertain.

AIM

To investigate the prognostic value of LA size in hypertensive AA patients undergoing stress echocardiography.

METHODS

This retrospective outcomes study enrolled 583 consecutive hypertensive AA patients who underwent stress echocardiography over a 2.5-year period. Clinical characteristics including cardiovascular risk factors, stress and echocardiographic data were collected from the electronic health record of a large community hospital. Treadmill exercise and Dobutamine protocols were conducted based on standard practices. Patients were followed for all-cause mortality. The optimal cutoff value of antero-posterior LA diameter for mortality was assessed by receiver operating characteristic analysis. Cox regression was used to determine variables associated with outcome.

RESULTS

The mean age was 57 ± 12 years. LA dilatation was present in 9% (54) of patients (LA anteroposterior ≥ 2.4 cm/m²). There were 85 deaths (15%) during 4.5 ± 1.7 years of follow-up. LA diameter indexed for body surface area had an area under the curve of 0.72 ± 0.03 (optimal cut-point of 2.05 cm/m²). Variables independently associated with mortality included age [P = 0.004, hazard ratio (HR) 1.34 (1.10-1.64)], tobacco use [P = 0.001, HR 2.59 (1.51-4.44)], left ventricular hypertrophy [P = 0.001 , HR 2.14 (1.35-3.39)], Dobutamine stress [P = 0.003, HR 2.12 (1.29-3.47)], heart failure history [P = 0.031, HR 1.76 (1.05-2.94)], LA diameter ≥ 2.05 cm/m² [P = 0.027, HR 1.73 (1.06-2.82)], and an abnormal stress echocardiogram [P = 0.033, HR 1.67 (1.04-2.68)]. LA diameter as a continuous variable was also independently associated with mortality but LA size ≥ 2.40 cm/m² was not.

CONCLUSION

LA enlargement is infrequent in hypertensive AA patients when traditional reference values are used. LA enlargement is independently associated with mortality when a lower than “normal” threshold (≥ 2.05 cm/m²) is used.

Hyperpolarization of hepatocytes by 2,5-AM: implications for hepatic control of food intake

Because 2,5-anhydro-D-mannitol (2,5-AM) seems to stimulate feeding by acting on the liver and because the hepatic membrane potential has been suggested to play an important role in control of feeding ("potentiostatic" hypothesis), we investigated the effect of 2,5-AM on the membrane potential of liver cells with microelectrodes using a superfused liver slice technique. 2,5-AM (2.5 mM), which reduces intracellular ATP in rat liver, hyperpolarized the liver cell membrane in mouse and rat liver slices by 4-7 mV. This hyperpolarization was reversed by quinine (1 mM), an unspecific blocker of Ca2+-dependent K+ channels, and abolished by apamin (20 nM), a blocker of Ca2+-activated K+ channels with low conductance. Amiloride at 10(-3) M, but not at 10(-6) M, or a low-Na medium (26 mM) also eliminated the hyperpolarization. The K+ channel blockers cetiedil (50 microM), glibenclamide (30 microM), and Ba2+ (5 mM); flufenamic acid (100 microM), a blocker of nonselective cation channels; and ouabain (1 mM), an inhibitor of the Na+-K+-adenosinetriphosphatase, did not significantly influence the 2,5-AM-induced hyperpolarization. It is concluded that 2,5-AM hyperpolarizes the liver cell membrane by activating Ca2+-dependent K+ channels. This activation seems to be impaired when the Na+/H+ exchanger is inhibited by amiloride or a low-Na+ medium. The findings also imply that the hyperphagic effect of 2,5-AM observed in rats is not associated with a decrease in the hepatic membrane potential, as postulated by the potentiostatic hypothesis.