Benefit versus risk of calcium antagonists in hypertensive patients with concomitant risk factors

BLOOD PRESSURE REDUCTION AND CARDIOVASCULAR MORBIDITY AND MORTALITY: Several hypertension trials have shown that antihypertensive treatment can reduce the cardiovascular morbidity and mortality accompanying this condition. They have also shown, however, that the reduction does not entirely normalize the risk of hypertensive patients. STRATEGIES TO IMPROVE THE BENEFIT OF ANTIHYPERTENSIVE TREATMENT: Although some of the risk of the hypertensive patient may prove to be irreversible, pathophysiological and clinical evidence obtained in recent years suggests that some modifications to antihypertensive treatment strategies might increase the benefit. For example, greater use of drugs such as calcium antagonists and angiotensin converting enzyme (ACE) inhibitors as first-line agents might bring greater benefits, because some properties of these drugs which are additive to their blood pressure lowering effects, such as regression of cardiovascular structural changes, nephroprotection and delay of atherogenesis, may provide a degree of protection against target-organ damage. ONGOING CLINICAL TRIALS AND THE INTERNATIONAL NIFEDIPINE (GITS) GASTROINTESTINAL SYSTEM STUDY OF INTERVENTION AS A GOAL IN HYPERTENSIVE TREATMENT (INSIGHT): Several ongoing clinical trials are aimed at comparing the effects of calcium antagonists and ACE inhibitors versus beta-blockers and diuretics on cardiovascular morbidity and mortality. INSIGHT is particularly interesting because the effects of nifedipine GITS and a combined thiazide and potassium-sparing diuretic on cardiovascular morbidity and fatal events are being compared in patients with hypertension plus one or more additional risk factors, such as hypercholesterolemia, smoking, diabetes, left ventricular hypertrophy, etc. INSIGHT is therefore the first trial to address, in a prospective fashion, the prognostic influence of antihypertensive treatment in hypertensives with concomitant risk factors.

Considerations on current and future trials in hypertension

Conclusive evidence from large-scale epidemiological studies has shown that hypertension is a major risk factor for cardiovascular disease. Large-scale intervention trials have indicated that, by reducing elevated blood pressure values with antihypertensive treatment, the risk can be decreased. Despite the large body of evidence on the protective effects of the blood pressure reduction, several questions concerning the benefit of antihypertensive treatment remain unanswered. This paper briefly reviews the information provided by clinical trials on antihypertensive treatment. It also critically examines the questions that have remained partially or totally unanswered and the trials that are currently addressing them. Focus is directed on the Insight Study which addresses the benefit of antihypertensive treatment in hypertensive subjects with additional cardiovascular risk factors.

Ambulatory blood pressure monitoring

PREDICTIVE VALUE OF 24-H AMBULATORY BLOOD PRESSURE MONITORING: Average 24-h blood pressure values are more closely related to the target-organ damage of hypertension than are clinic blood pressure readings. Preliminary evidence from longitudinal studies suggests that ambulatory blood pressure is also superior to isolated clinic readings in the prognostic evaluation of hypertensive patients. This is supported by the demonstration that in hypertensive patients with left ventricular hypertrophy, regression of cardiac hypertrophy following treatment was better predicted by the drug-induced reduction in 24-h average blood pressure than clinic blood pressure.

BLOOD PRESSURE VARIABILITY

Also, 24-h blood pressure variability seems to be involved in the genesis of hypertension target-organ damage, while the clinical value of specific components of the 24-h blood pressure profile, such the nocturnal blood pressure fall, is still a matter of debate. Similar caution is needed in approaching the clinical significance of white coat hypertension, the definition of which is still affected by important methodological problems.

INSIGHT: international nifedipine GITS study intervention as a goal in hypertension treatment

The objective of the study is to compare fatal and nonfatal cardiovascular endpoints in hypertensive patients randomised to the calcium-channel blocker, nifedipine GITS or a thiazide diuretic, co-amilozide. A total of 6592 patients from nine countries (UK, France, Israel, Spain, Italy, The Netherlands, Sweden, Denmark and Norway) will be recruited, aged 55-80 and with a blood pressure (BP) > or = 150/95 or > or = 160 mm Hg (systolic). All patients will have at least one other major cardiovascular risk factor. Patients will be minimised by country and risk factors and randomised to double-blind treatment with either nifedipine GITS or diuretic. After a single dose titration, additional treatment will be atenolol or enalapril (where beta-blockade is contra-indicated). After achieving a target BP of 140/90 mm Hg patients will be followed for a total of 3 years. Primary endpoints are myocardial infarction, stroke, subarachnoid haemorrhage, heart failure and sudden cardiac death. The study has a power of 80% at 5% significance to detect a difference between 8% event rate over 3 years in diuretic-treated patients and 6% in those receiving nifedipine.

Neural cardiovascular regulation and 24-hour blood pressure and heart rate variability

The availability of ambulatory intraarterial blood pressure monitoring techniques offers a deeper insight into the features of blood pressure variability over 24 hours and allows better understanding of the mechanisms responsible for the continuous and marked blood pressure changes that occur throughout the day and at night. Among these mechanisms, central and reflex neural influences play a major role. This has led to the development of techniques for the assessment of 24-hour "spontaneous" baroreflex sensitivity through combined computer analysis of blood pressure and heart rate variations in the time or frequency domain. The recent introduction of continuous noninvasive ambulatory blood pressure monitors offers the unique possibility of obtaining dynamic information on neural cardiovascular control in clinical conditions in which the assessment of autonomic cardiovascular regulation may have diagnostic and prognostic implications.

Impaired radial artery compliance in normotensive subjects with familial hypercholesterolemia

Hypercholesterolemia impairs arteriolar dilatation, but whether the vascular abnormalities accompanying this condition include large artery function is unknown. We addressed this issue in 13 normotensive subjects with familial hypercholesterolemia (serum cholesterol 401.6 +/- 16.9 mg/dl, mean +/- S.E., FHC) and no evidence of atherosclerotic lesions, in whom radial artery (RA) diameter and blood pressure (BP) were measured beat to beat by an echotracking and a Finapres device, respectively. RA compliance (RAC) was derived from the diameter/BP relationship and expressed over the systo-diastolic BP range, both at baseline and after a 12-min brachial artery occlusion. RAC was expressed also as the area under the RAC/BP curve divided for pulse BP. Measurements included maximal forearm blood flow (plethysmography) and minimal forearm vascular resistance (FVR) which were obtained from the values following the 12-min brachial arterial occlusion. Data were collected before and after 6- and 24-month lipid lowering treatment (simvastatin 40 mg/day). Ten age-matched normotensive normocholesterolemic healthy subjects (N) served as controls. Compared to N, baseline RAC was strikingly reduced in FHC (-53.5%, P < 0.01). After ischemia RAC increased significantly and markedly in N (+38.7, P < 0.01), while only a modest and non-significant increase was observed in FHC. Minimal FVR was markedly higher in FHC than in N (3.5 +/- 0.9 vs 1.6 +/- 0.1 units, P < 0.01). In FHC (7 subjects) RAC remained unchanged after 6 months of lipid lowering treatment, but increased markedly (+55.2%, p < 0.05) when treatment was prolonged to 24 months. Lipid lowering treatment also reduced minimal FVR, the effect being significant both after 6 and after 24 months. No changes in RAC and minimal FVR were seen after 6 months in controls. Thus, in subjects with a marked increase in serum cholesterol due to FHC, not only arteriolar dilatation, but also RAC and distensibility are markedly impaired. This impairment can be favourably affected by an effective lipid lowering treatment of long duration.

Job strain and ambulatory blood pressure levels in a population-based employed sample of men from northern Italy

OBJECTIVES

The purpose of this cross-sectional study was to examine the associations between categories of perceived job strain and blood pressure, measured by clinical and ambulatory devices on a population-based sample of employed men in northern Italy.

METHODS

The study included 527 employed normotensive or mild hypertensive nonmedicated men enrolled in an age-gender stratified random sample of 821 25- to 64-year-old residents of the city of Monza (in the vicinity of Milan). The job-strain categories were classified according to the traditional quadrant-term approach and also a new approach based on the comparison of extreme tertile categories in order to enhance contrasts. Clinical blood pressure was measured according to the standardized MONICA procedure; 24-h, work, leisure, and nighttime blood pressure values were obtained with an ambulatory device. Disparities, calculated as differences between clinical and ambulatory measurements, were also analyzed.

RESULTS

Among normotensive working men the highest mean for systolic blood pressure was found in the high-strain group, and progressively lower values were found in the passive, active and low-strain categories. These patterns were observed for both the clinical and ambulatory measurements. Among the mild hypertensive subjects, lower mean values for ambulatory systolic and diastolic blood pressure were found in the passive and high job-strain categories when the tertile term approach was adopted. The passive group also showed the highest mean difference between the clinical and ambulatory measurements; this finding indicates that they may be more susceptible to alarm reactions.

CONCLUSIONS

The results indicate that job strain affects blood pressure in population-based samples and the effect is consistent across sociocultural contexts.

Heart rate-dependence of arterial distensibility in vivo

OBJECTIVES

Viscous and inertial components contribute to arterial distensibility and compliance in vitro. The purpose of our study was to determine whether this phenomenon is of relevance in vivo, namely, whether arterial compliance is altered by an increase in heart rate.

DESIGN

Arterial diameter was assessed by an echo-Doppler device in a common carotid and femoral artery, namely, in a large elastic and a muscle artery. The studies were performed in 12-week-old pentobarbitone-anaesthetized Wistar-Kyoto rats subjected to atrial pacing via a transjugular unipolar catheter at five different randomly sequenced rates (280, 310, 340, 370 and 400 beats/min). After each stage, spontaneous sinus rhythm was allowed to return. Blood pressure was measured via a catheter inserted into the carotid or femoral artery contralateral to the vessels in which the diameter was measured. Arterial compliance and distensibility values were derived according to the Langewouters formula.

RESULTS

A progressive increase in heart rate caused by pacing was accompanied by progressive and marked reductions in carotid artery compliance and distensibility. When quantified by the area under the distensibility-pressure or compliance-pressure curve the reduction was in the range 15-43%. Although a tendency to a similar phenomenon was observed in the femoral artery, in the latter vessel the reduction in distensibility and compliance was less marked and statistically insignificant.

CONCLUSIONS

In the anaesthetized rat acute increases in heart rate are accompanied by reductions in arterial compliance and distensibility. The effect is greater in elastic than in muscle arteries.

Difference between office and ambulatory blood pressure and response to antihypertensive treatment

OBJECTIVE

To investigate whether a clinic-ambulatory blood pressure difference persists with time under active drug treatment or placebo and to determine whether and how it interferes with the evaluation of the efficacy of antihypertensive treatment.

DESIGN AND METHODS

In 382 mild or moderate essential hypertensive patients (mean age +/- SD 51.5 +/- 9.2 years) clinic and ambulatory (SpaceLabs 90207 device) blood pressures were measured twice, under baseline conditions and after 4-8 weeks of antihypertensive treatment by calcium antagonists or angiotensin converting enzyme inhibitors (n = 266) or of placebo administration (n = 116). In each patient the difference between clinic and daytime average blood pressure was taken as a surrogate measure of the magnitude of the 'white-coat effect', separately for systolic and diastolic blood pressures. The changes in this difference induced by treatment and by placebo and the relationship between the blood pressure changes induced by drug treatment and by placebo and the magnitude of the difference before and during treatment or placebo, respectively, were computed.

RESULTS

Before drug treatment, the difference was 16.6 +/- 13.6 and 10.1 +/- 7.9 mmHg for systolic and diastolic blood pressures, respectively. During treatment the corresponding values were 11.9 +/- 14.2 and 6.8 +/- 9.2 mmHg; both of the reductions were statistically significant. Both for systolic and for diastolic blood pressure, the reduction in clinic blood pressure caused by treatment was directly related to the clinic-ambulatory difference before treatment, but inversely related to the magnitude of that difference persisting during treatment. The clinic-ambulatory blood pressure difference observed before placebo was attenuated during placebo, the magnitude of the attenuation being similar to that found under drug treatment. No significant difference between clinic and daytime average heart rate was ever observed before and during active treatment or placebo.

CONCLUSIONS

A considerable clinic-ambulatory blood pressure difference persists during several weeks of antihypertensive treatment, but its magnitude is significantly attenuated. This leads to an overestimation of the effectiveness of antihypertensive treatment when this is assessed by clinic blood pressure measurements only. This overestimation is greater in subjects with an initially greater difference because in these subjects the subsequent attenuation is greater. Because similar phenomena are observed with placebo, the attenuation in the difference during drug treatment is likely to reflect merely habituation to clinic blood pressure measurements with time.

Blood pressure and heart rate variability in autonomic disorders: a critical review

Spectral analysis (SA) of blood pressure (BP) and heart rate (HR) fluctuations has been proposed as a unique approach to obtain a deeper insight into cardiovascular regulatory mechanisms in health and disease. A number of studies performed over the last 15 years have shown that autonomic influences are involved in the modulation of fast BP and HR fluctuations (with a period <1 min), particularly at frequencies between 0.2 and 0.4 Hz [high frequency (HF) region or respiratory frequency] and around 0.1 Hz [mid frequency (MF) region]. In patients with secondary or primary autonomic dysfunction, SA of BP and HR signals recorded at rest or during orthostatic challenge in a laboratory environment have shown the occurrence of a reduction in the power of MF and/or HF, BP and HR components. Such a reduction is associated or may even precede the clinical manifestation of autonomic neuropathy. However, the above results collected in standardized laboratory conditions cannot reflect the features of neural cardiovascular control during daily life in ambulant individuals with autonomic failure. To investigate this issue, SA techniques have been applied to 24 h beat-to-beat intra-arterial and non-invasive finger BP recordings obtained in elderly subjects and in pure autonomic failure patients, respectively. In these conditions, HR powers displayed a reduction over a wide range of frequencies (from 0.5 to below 0.01 Hz). Conversely, BP powers underwent a complex rearrangement characterized by a reduction in the power around 0.1 Hz and by an increase in the powers at the respiratory frequency and at frequencies below 0.01 Hz. Dynamic quantification of the sensitivity of the baroreceptor-heart rate reflex by combined analysis of systolic BP and pulse interval (i.e. the interval between consecutive systolic peaks) powers around 0.1 Hz (alpha technique) has shown that in elderly subjects, and even more so in pure autonomic failure patients, baroreflex sensitivity is markedly reduced over the 24 h, and is no longer characterized by its physiological day-night modulation. In conclusion, although in some instances SA of cardiovascular signals may fail to fully reflect the features of autonomic cardiovascular control, the evidence discussed clearly demonstrates that this approach represents a promising tool for a dynamic assessment of the early impairment of neural circulatory control in autonomic failure. This is particularly the case when these analyses are performed on 24 h continuous BP and HR recordings in ambulant subjects.

Lessons to be learned from 24-hour ambulatory blood pressure monitoring

A number of cross sectional studies have shown that both the 24-hour average blood pressure value and the degree of 24-hour blood pressure variability bear a significant relation with the end organ damage of hypertension. Although longitudinal evidence of the clinical relevance of 24-hour ambulatory blood pressure monitoring data are scanty, the results of a recent prospective study have clearly shown the superiority of average 24 hour, daytime and nighttime blood pressure values over clinical readings in predicting the regression of left ventricular hypertrophy in treated hypertensive patients. Ambulatory blood pressure monitoring may also be useful in the evaluation of antihypertensive treatment, although the problem of whether ambulatory blood pressure is "normalized" by treatment remains still to be properly addressed. Moreover, currently employed discontinuous ambulatory blood pressure monitoring devices cannot adequately clarify the ability of antihypertensive drugs to buffer blood pressure variability. This interesting issue needs to be assessed in a more analytical fashion by means of recently developed beat-to-beat non-invasive ambulatory blood pressure recorders coupled with wide-band spectral analysis techniques.

Baroreflex modulation of the cardiovascular system: new insights from the joint analysis of blood pressure and heart rate signals

This paper focuses on a number of methods for the analysis of the relationship between the arterial baroreflex and different components of blood pressure and heart rate variability. Broad-band spectral analysis techniques have allowed us to obtain experimental evidence that the arterial baroreflex exerts its influence not only on fast but also on slow components of blood pressure and heart rate, i.e., on components with periods longer than 60 sec. Focusing on faster changes in blood pressure and heart rate, both time domain and frequency domain techniques have been developed to track the sensitivity of baroreflex heart rate modulation over time, either in laboratory or in daily life conditions. These approaches have considerably broadened our understanding of the role of baroreflex modulation of the heart and peripheral circulation in a number of pathological and physiological conditions.

Ambulatory blood pressure, blood pressure variability and antihypertensive treatment

Ambulatory blood pressure monitoring is frequently employed in the clinical practice to improve the diagnosis of hypertension and the appropriateness of the decision regarding initiation of antihypertensive treatment. It is also frequently employed to check the efficacy of this treatment in conditions resembling daily life. This paper will describe the effect of a number of antihypertensive drugs on ambulatory blood pressure, based on data collected by our group in the past 10 years. It will then discuss the advantages of ambulatory blood pressure in studies of efficacy of antihypertensive drugs and the importance of this approach for definition of the trough-to-peak ratio of the antihypertensive effect. Some technical and clinical problems inherent to the ambulatory blood pressure monitoring approach will also be discussed.

Evaluation of arterial compliance in humans

Compliance is a measure of the elastic properties of arterial vessels and is a function of blood pressure. In recent years new techniques have been developed which allow to measure arterial compliance non invasively and continuously over the range of existing blood pressure values. It has been thus possible to investigate the alterations of arterial compliance in a variety of diseases and to address the physiological factors involved in arterial compliance modulation. This article will focus on the new data available on these issues.

Effects of sino-aortic denervation on spectral characteristics of blood pressure and pulse interval variability: a wide-band approach

Sino-aortic denervation (SAD) is employed in cats to evaluate the baroreflex influence on blood pressure (BP) and pulse interval (PI) spectral components from 0.00008 to 0.9 Hz as assessed by FFT wide-band spectra and their 1/f modelling; and the linear coupling between BP and PI and between systolic and diastolic BP as assessed by coherence analysis. Specific procedures have been developed to obtain an effective smoothing of spectra and coherence functions. SAD induced an increase in BP powers from 0.03 to 0.0006 Hz and a power reduction of most of the remaining BP components; a reduction of PI powers at all frequencies; marked deviations of BP spectra from the 1/f trend; a reduction of the coherence between BP and PI from 0.12 to 0.5 Hz and a coherence enhancement at lower frequencies. These findings indicate that the arterial baroreflex modulates both fast and slow spectral components of BP and PI; homogeneously enhances PI fluctuations at all frequencies; produces differentiated effects on BP fluctuations along the frequency axis; and at low frequencies exerts the buffering action on BP through strategies which reduce the BP-PI linear link.

Benefit and costs of anti-hypertensive treatment

Hypertension is common throughout the world and represents the single greatest risk factor for increasing cardiovascular mortality, cardiovascular morbidity and overall mortality. Diseases associated with hypertension are not only, in general, of a chronic disabling nature, but, in most instances, require frequent hospitalization, with expensive drug treatment and management. Stroke, coronary heart disease, congestive heart failure and chronic renal insufficiency represent the most commonly encountered corollaries of inadequately treated hypertension. Anti-hypertensive treatment is accompanied by a reduction of hypertension-related cardiovascular risk and a clearcut benefit in terms of reduced incidence of major cardiovascular complications of hypertension and overall mortality. This benefit has frequently been underestimated in many clinical trials. Attempts to improve the cost-benefit ratio have included the use of treatment strategies based upon 24-h control of blood pressure, since it has been demonstrated that hypertension-related end-organ damage correlates more closely with 24-h average blood pressure and with 24-h blood pressure variability than with blood pressure measured in the clinic. It is hoped that new anti-hypertensive agents, which smoothly reduce 24-h blood pressure profile, will further reduce the incidence of hypertension-related end-organ damage.