S.A. Thom

Segmentation of blood vessels from red-free and fluorescein retinal images

The morphology of the retinal blood vessels can be an important indicator for diseases like diabetes, hypertension and retinopathy of prematurity (ROP). Thus, the measurement of changes in morphology of arterioles and venules can be of diagnostic value. Here we present a method to automatically segment retinal blood vessels based upon multiscale feature extraction. This method overcomes the problem of variations in contrast inherent in these images by using the first and second spatial derivatives of the intensity image that gives information about vessel topology. This approach also enables the detection of blood vessels of different widths, lengths and orientations. The local maxima over scales of the magnitude of the gradient and the maximum principal curvature of the Hessian tensor are used in a multiple pass region growing procedure. The growth progressively segments the blood vessels using feature information together with spatial information. The algorithm is tested on red-free and fluorescein retinal images, taken from two local and two public databases. Comparison with first public database yields values of 75.05% true positive rate (TPR) and 4.38% false positive rate (FPR). Second database values are of 72.46% TPR and 3.45% FPR. Our results on both public databases were comparable in performance with other authors. However, we conclude that these values are not sensitive enough so as to evaluate the performance of vessel geometry detection. Therefore we propose a new approach that uses measurements of vessel diameters and branching angles as a validation criterion to compare our segmented images with those hand segmented from public databases. Comparisons made between both hand segmented images from public databases showed a large inter-subject variability on geometric values. A last evaluation was made comparing vessel geometric values obtained from our segmented images between red-free and fluorescein paired images with the latter as the ground truth. Our results demonstrated that borders found by our method are less biased and follow more consistently the border of the vessel and therefore they yield more confident geometric values.

Left Ventricular Hypertrophy and QT Dispersion in Hypertension

The interlead variation in QT length on a standard electrocardiograph reflects regional repolarization differences in the heart. To investigate the association between this interlead variation (QT dispersion) and left ventricular hypertrophy, we subjected 100 untreated subjects to 12-lead electrocardiography and echocardiography. Additionally, 24 previously untreated subjects underwent a 6-month treatment study with ramipril and felodipine. In the cross-sectional part of the study, QT dispersion corrected for heart rate (QTc dispersion) was significantly correlated with left ventricular mass index (r = .30, P < .01), systolic pressure (r = .30, P < .01), the ratio of peak flow velocity of the early filling wave to peak flow velocity of the atrial wave (E/A ratio) (r = -.22, P = .02), isovolumic relaxation time (r = .31, P < .01), and age (r = .21, P < .04). In the treatment part of the study, lead-adjusted QTc dispersion decreased from 24 to 19 milliseconds after treatment, and after a subsequent 2 weeks of drug washout remained at 19 milliseconds (P < .01). The changes in left ventricular mass index at these stages were 144, 121, and 124 g/m2 (P < .01). Systolic pressure decreased from 175 to 144 mm Hg and increased again to 164 mm Hg after drug washout (P < .01). The E/A ratio (0.97, 1.02, and 1.02; P = 69) and isovolumic relaxation time (111, 112, and 112; P = .97) remained unchanged through the three assessment points. In conclusion, QT dispersion is increased in association with an increased left ventricular mass index in hypertensive individuals. Antihypertensive therapy with ramipril and felodipine reduced both parameters. If an increased QT dispersion is a predictor of sudden death in this group of individuals, then the importance of its reduction is evident.

Tissue Doppler E/E′ ratio is a powerful predictor of primary cardiac events in a hypertensive population: an ASCOT substudy

AIMSnPatients with controlled hypertension are at risk of future cardiac events, but predicting first events remains difficult. We hypothesized that modern echocardiographic measures of left ventricular diastolic function may be more sensitive than traditional echocardiographic methods of risk prediction and set out to test this in a cohort of patients with well-controlled hypertension.nnnMETHODS AND RESULTSnConventional and tissue Doppler echocardiography was performed on 980 participants in the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT). All subjects had hypertension, but no known cardiac disease. Cardiac events were defined as fatal and non-fatal myocardial infarction (including silent myocardial infarction), coronary revascularization procedures, new-onset angina (stable or unstable), fatal and non-fatal heart failure, and life-threatening arrhythmias. Analysis was performed by a single, blinded observer. There were 56 primary cardiac events during 4.2 +/- 0.7 years follow-up. The ratio of transmitral Doppler early filling velocity to tissue Doppler early diastolic mitral annular velocity (E/E) was the strongest predictor of first cardiac events in Cox-proportional hazards models. Following adjustment for covariates, a unit rise in the E/E ratio was associated with a 17% increment in risk of a cardiac event (HR 1.17, CI 1.05-1.29; P = 0.003).nnnCONCLUSIONnTissue Doppler E/E, a non-invasive estimate of left atrial filling pressure, independently predicts primary cardiac events in a hypertensive population and out-performed traditional echocardiographic measures in this moderately sized, well-treated hypertensive population. E/E represents a simple, effective tool for assessing cardiac risk in a hypertensive population.

RANDOMISED DOUBLE-BLIND CROSS-OVER TRIAL OF POTASSIUM ON BLOOD-PRESSURE IN NORMAL SUBJECTS

A randomised double-blind cross-over study of increased oral potassium 64 mmol a day versus placebo was conducted in 20 young healthy males on normal sodium unrestricted diet. A significantly greater proportion had lower systolic and diastolic blood-pressures on potassium than on placebo. The mean diastolic pressure was significantly lowered, by 2.4 mm Hg, during potassium supplementation. Change in diastolic pressure correlated negatively with change in 24-hour urinary potassium and positively which change in 24-hour urinary sodium/potassium ratio in individual subjects.

Regression of hypertensive left ventricular hypertrophy and left ventricular diastolic function

The effect of antihypertensive therapy on regression of left ventricular hypertrophy and left ventricular diastolic function was investigated in 25 hypertensive patients for up to 18 months after initiation of treatment. Left ventricular mass index was calculated by two-dimensional echocardiography and left ventricular diastolic function assessed by transmitral pulsed doppler ultrasound. Significant reduction in left ventricular mass index was observed after 9 months of treatment. Only 13 patients had a reduction in mass greater than the intraobserver variability of the technique. There was no change in doppler indices of left ventricular diastolic function. In 7 patients who were studied for a further 9 months after regression had occurred there was still no appreciable difference in left ventricular diastolic function. These findings indicate that there is no direct relation between left ventricular mass and abnormal left ventricular diastolic function.

Ethnic Differences in the Hypertensive Heart and 24-Hour Blood Pressure Profile

Black hypertensive persons have been observed to have a greater degree of left ventricular hypertrophy than white hypertensives. However, previous studies have matched groups for blood pressure (BP) measured in the clinic, and it has been demonstrated that black hypertensives have an attenuated nocturnal BP dip. Clinic BPs may thus underestimate mean 24-hour BP in this group. To investigate whether the differences in left ventricular hypertrophy can be accounted for by the greater mean 24-hour BP in black hypertensives, 92 previously untreated hypertensives were studied with 24-hour ambulatory BP monitoring and echocardiography. The 46 black hypertensives (24 men and 22 women) were matched with the 46 white hypertensives for age, gender, and mean 24-hour BP. Despite similar mean 24-hour BPs (blacks, 142/93 mm Hg; whites, 145/92 mm Hg; P=.53/.66), the black group had a smaller mean nocturnal dip than the white group (blacks, 8/8 mm Hg; whites, 16/13 mm Hg; P<.01). In addition, mean left ventricular mass index (LVMI) was greater (blacks, 130 g/m2; whites, 107 g/m2; P<.001). Mean 24-hour systolic BP was significantly related to LVMI in both groups (blacks, r=.45, P<.01; whites, r=.56, P<.01). However, systolic BP dip correlated inversely with LVMI only in the black group (blacks, r=-.30, P<.04; whites, r=.05, P=.76). In a multiple regression model, LVMI was independently related to both mean daytime BP and mean nocturnal BP dip in black subjects but only to mean daytime BP in white subjects. In conclusion, the increased left ventricular hypertrophy observed in black hypertensives compared with white hypertensives is not accounted for by differences in mean 24-hour BP. However, LVMI in black hypertensives appears to be more dependent on nocturnal BP than that in white hypertensives; this, coupled with the attenuated BP dip in black hypertensives, suggests that the BP profile rather than 24-hour BP may be important in determining the differences in left ventricular hypertrophy.

Ethnicity and left ventricular diastolic function in hypertension an ASCOT (Anglo-Scandinavian Cardiac Outcomes Trial) substudy.

OBJECTIVESnWe investigated whether diastolic function differs between hypertensive patients of African-Caribbean or white European origin and established whether differences could be explained by confounding variables.nnnBACKGROUNDnAfrican Caribbeans are known to have a higher prevalence of heart failure than white Europeans but it is unclear whether this is a result of known risk factors. Tissue Doppler technology now allows accurate quantification of diastolic function, which is recognized as an important factor in the development of heart failure.nnnMETHODSnParticipants from a single center participating in the ASCOT (Anglo-Scandinavian Cardiac Outcomes Trial), composed of patients with hypertension but no evidence of heart failure, were studied. Left ventricular structure and function were measured in 509 patients using conventional and tissue Doppler echocardiography. Diastolic function was assessed using the tissue Doppler early diastolic velocity E (averaged from 3 left ventricular segments) and the ratio of this and the transmitral early filling velocity E (E/E).nnnRESULTSnIn African-Caribbean patients, mean E was significantly lower (7.7 cm/s vs. 8.6 cm/s, p = 0.003) and mean E/E was significantly higher (8.85 vs. 7.93, p = 0.003). After adjustment for confounding variables-age, gender, systolic blood pressure, pulse pressure, cholesterol, smoking, ejection fraction, left ventricular mass index, and diabetes mellitus-the effect of African-Caribbean ethnicity on diastolic function remained highly significant (E: 7.52 vs. 8.51; p < 0.001; E/E: 8.89 vs. 7.93; p = 0.003; African Caribbeans vs. white Europeans for both comparisons).nnnCONCLUSIONSnDiastolic function is significantly worse in hypertensive patients of African-Caribbean origin than in white Europeans. This difference in diastolic performance is not due to known confounding variables.

Differential Effects of Antihypertensive Treatment on Left Ventricular Diastolic Function: An ASCOT (Anglo-Scandinavian Cardiac Outcomes Trial) Substudy

OBJECTIVESnWe hypothesized that an amlodipine-based regimen would have more favorable effects on left ventricular (LV) diastolic function.nnnBACKGROUNDnDifferent antihypertensive therapies may vary in their effect on LV diastolic function.nnnMETHODSnThe HACVD (Hypertension Associated Cardiovascular Disease) substudy of ASCOT (Anglo-Scandinavian Cardiac Outcomes Trial) collected detailed cardiovascular phenotypic data on a subset of 1,006 participants recruited from 2 centers (St. Marys Hospital, London, and Beaumont Hospital, Dublin). Conventional and tissue Doppler echocardiography and measurement of plasma B-type natriuretic peptide (BNP) were performed approximately 1 year after randomization to atenolol-based or amlodipine-based antihypertensive treatment to assess LV diastolic function.nnnRESULTSnOn-treatment blood pressure (BP) (mean +/- SD) was similar in both groups: atenolol-based regimen, systolic BP of 137 +/- 17 mm Hg, diastolic BP of 82 +/- 9 mm Hg; amlodipine-based regimen, systolic BP of 136 +/- 15 mm Hg, diastolic BP of 80 +/- 9 mm Hg. Ejection fraction did not differ between groups, but early diastolic mitral annular velocity (E), a measure of diastolic relaxation, was lower in patients on the atenolol-based regimen: atenolol-based regimen, 7.9 +/- 1.8; amlodipine-based regimen, 8.8 +/- 2.0. A measure of left ventricular filling pressure, E/E, and BNP were significantly higher in patients on the atenolol-based regimen. Differences in E, E/E, and BNP remained significant after adjustment for age and sex. Further adjustment for systolic BP, LV mass index, and heart rate had no impact on differences in mean E or BNP. The difference in E/E was attenuated.nnnCONCLUSIONSnPatients receiving treatment with an amlodipine-based regimen had better diastolic function than patients treated with the atenolol-based regimen. Treatment-related differences in diastolic function were independent of BP reduction and other factors that are known to affect diastolic function.

Comparison between three‐dimensional volume‐selective turbo spin‐echo imaging and two‐dimensional ultrasound for assessing carotid artery structure and function

To compare a volume‐selective three‐dimensional turbo spin echo (TSE) technique with ultrasound (US) for assessing carotid artery wall structure and function.

QT dispersion in athletic left ventricular hypertrophy.

OBJECTIVEnTo assess whether physiologic left ventricular hypertrophy as a result of physical training is associated with an increased QT length or dispersion.nnnMETHODSnThirty-three subjects were assessed. These consisted of a group of international endurance athletes (including 8 rowers, 2 cyclists, and 1 triathlete), a group of 12 professional soccer players, and a further group of 10 control subjects. Each underwent 2-dimensional echocardiography and 12-lead electrocardiographic examination.nnnRESULTSnLeft ventricular mass index was considerably greater in both the endurance athlete (163.3 +/- 14.4 g/m2; P <.01) and soccer player groups (144.2 +/- 5.5 g/m 2; P <.05) compared with the controls (109.2 +/- 6.3 g/m2). In spite of these large differences in cardiac structure there were no significant differences in QT parameters between the groups (QT dispersion 56.9 +/- 5.5, 68.5 +/- 9.5, and 67.2 +/- 12.6 ms; QTc dispersion 61.4 +/- 9.2, 69.4 +/- 13.3, and 54.2 +/- 6.5 ms; maximum QT 402 +/- 10.3, 404 +/- 9.6, and 392 +/- 14.0 ms; and maximum QTc 404 +/- 7.0, 413 +/- 9.3, and 399 +/- 9.9 ms among endurance athletes, soccer players, and controls, respectively).nnnCONCLUSIONnLeft ventricular hypertrophy occurring as a consequence of athletic training does not appear to be associated with a major increase in QT length or QT dispersion.