Prevention of Cardiovascular Events in Hypertensive Patients

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Citation
European Cardiovascular Disease 2006 - Issue 1;2006:2(1):28-31
DOI
http://dx.doi.org/10.15420/ecr.2006.1.28

Hypertension is the single most important preventable cause of premature death in the Western world. The quest to find the most effective treatment both in terms of blood pressure control and prevention of events, such as heart attacks and strokes, is on-going. The issue of which antihypertensive agent to use first-line has been the subject of debate for over two decades. The lack of a coherent decision has led directly to differing recommendations for first-line hypertension treatment. For example, even within the UK, the British Hypertension Society (BHS) and the National Institute for Clinical Excellence (NICE) had, until recently, differing viewpoints. However, it seems that the recent landmark Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT) study may now offer a solution to this international dilemma. The purpose of this article is to explain the background to the ASCOT study and provide a clear summary of the results and their implications.

The development of angiotensin converting enzyme (ACE) inhibitors came from studies of the venom of the Brazilian viper Bothrops jararaca. This venom potentiated the effect of the vasodilator peptide bradykinin, strongly enhancing its hypotensive effect to cause shock in the snakeÔÇÖs prey. Further work with the venom showed that the bradykinin effect was caused by inhibition of its breakdown. It was then realised that this metabolising enzyme also catalysed the conversion of angiotensinogen to active angiotensin II; and so ACE inhibitors were born. The possibility of ACE inhibition as a target for hypertension therapy followed. The first clinical trials of the active peptide extracted from the snake venom were carried out in the UK, and subsequently the US. After successfully reducing blood pressure in 14 of the 17 patients tested, an orally active formulation of the peptide was developed that eventually became captopril, launched in the US in 1981. The success of captopril was developed by the pharmaceutical industry and there are now 11 ACE inhibitors licensed in the UK.

Subsequent trials with captopril suggested the possibility that its beneficial effects were not all restricted to an effect on blood pressure. The first studies took place with heart failure (HF) patients. The classic study, Cooperative North Scandinavian Enalapril Survival Study (CONSENSUS) examined the survival benefit of enalapril in patients with severe HF and showed dramatic benefits. In the Survival And Ventricular Enlargement (SAVE) study, patients who had survived the acute phase of myocardial infarction (MI) were given captopril or placebo. The group receiving captopril had a 25% decrease in recurrent MI and a 24% reduction in the need for revascularisation. The observations that ACE inhibitors had effects beyond blood pressure lowering led to large-scale clinical trials to further investigate these other clinical outcomes.

Ramipril and Perindopril

Following the launch of ramipril the landmark trial Acute Infarction Ramipril Efficacy (AIRE) enrolled patients who had an MI with HF three to 10 days previously. Treatment with ramipril resulted in a 27% reduction in the risk of all-cause mortality.

The Heart Outcomes Prevention Evaluation (HOPE) trial was the second key study to assess ramipril. In HOPE ramipril was given to patients older than 55 at high risk of cardiovascular disease (CVD) events (a history of CVD or diabetes plus at least one other risk factor). Ramipril proved effective in reducing the primary end-point of the combination of MI, stroke or death from CV events by 17.8%. The improvements were seen in the presence of modest blood-pressure (BP) lowering effects. The HOPE investigators concluded that ramipril offered numerous benefits to these high-risk patients, perhaps beyond the effect of a small reduction in BP. HOPE was criticised by some authors because a small ambulatory blood pressure sub-study showed substantial nocturnal BP falls. Nevertheless, the unarguable benefit of ACE inhibitors was confirmed in a population without HF.

The EUropean trial on Reduction Of cardiac events with Perindopril in stable coronary Artery disease (EUROPA) trial investigated patients at lower risk of developing CVD, regardless of their age or other risk factors. This study population was therefore more representative of the general population. EUROPA assessed the effects of perindopril, a long-acting ACE inhibitor that regulates hypertension over a 24-hour period in patients with stable coronary artery disease (CAD) but without HF.

Importantly in the EUROPA trial perindopril was given alongside the patientÔÇÖs standard treatment (aspirin, ╬▓-blockers, statins or other lipid-lowering drugs). Perindopril treatment lowered BP by an average of 5/2mmHg, and resulted in a 20% reduction in the combined risk of CV death, non-fatal MI and cardiac arrest, a 24% reduction in fatal and non-fatal MI, and a 39% reduction in HF. EUROPA investigators concluded that perindopril was of benefit to all patients regardless of their baseline BP, and with or without HF. PerindoprilÔÇÖs benefits were seen in addition to any other preventative treatments the patients may have been taking. Furthermore, perindopril was associated with significant decreases in morbidity and mortality in all patients, whether at low, medium or high risk of cardiac events.

All This from Lower Blood Pressure

ACE inhibitors were discovered and developed as agents to reduce BP, but the mechanism by which they exert their positive secondary effects on HF, recurrent MI, and stroke remains unestablished. Some researchers have suggested that these effects are nothing more than additional serendipitous consequences of the reduction in BP. However, others suspect they could be directly attributed to the ACE inhibitor itself - an important study published in September 2004 confirmed this.

The A Coronary disease Trial Investigating Outcome with Nifedipine (ACTION) study investigated the effects of long-acting nifedipine gastrointestinal therapeutic system (GITS) (Adalat® LA in the UK) in stable coronary heart disease (CHD) patients. Nifedipine has been a mainstay of treatment for angina and hypertension for many years. The criteria for inclusion and exclusion in the ACTION study were similar to those used in EUROPA. Although nifedipine successfully lowered BP by an average of 6/3mmHg, it had no effect on major cardiac events. Some secondary end-points were improved, mainly through an important reduction in the need for coronary procedures and interventions, confirming the value of nifedipine GITS for symptom control. There was also a benefit in transient ischaemic attack (TIA) prevention. The contrast in results between ACTION and EUROPA offers support to the idea that the CV benefits provided by ACE inhibitors do not arise solely from their BP lowering activity. Similar levels of BP lowering were achieved among similar patients in ACTION and EUROPA, yet perindopril reduced CV events by 21%. Furthermore, in EUROPA similar results were seen in patients with low or high BP at entry, and among those in whom BP did not fall during the study.

The Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT) has attracted much attention amongst healthcare professionals since its early cessation in December 2004. The announcement of the preliminary results in March 2005, suggesting that the treatment combination of amlodipine/perindopril offered superior benefits over the more traditional first-line treatment of atenolol/bendroflumethiazide in terms of reducing the risk of death, MI, stroke and new-onset diabetes means that many doctors have been eagerly awaiting the full results to find out exactly what the long-term implications of these results are for the future of hypertension management. The full results were presented at the European Society of Cardiology (ESC) Annual Congress in early September 2005 to great scientific acclaim.

ASCOT - How It All Began

By 1990 it was clear that lowering BP in hyper-tensive patients with the drugs available at that time, principally ╬▓-blockers and diuretics, reduced stroke risk but had much less effect on CHD events. There was a belief, although no data, that the new drugs for hypertension could be more effective than the older ones. Moreover, it was becoming apparent that combination therapy might be required.

ASCOT recruited 19,257 patients from the UK, Ireland and the Nordic countries. The study set out to test whether a newer antihypertensive combination treatment, comprising the calcium channel blocker amlodipine and the ACE inhibitor perindopril, was more effective at preventing CHD than an older combination regimen consisting of the ╬▓-blocker atenolol and the diuretic bendroflumethiazide.

Study Design

The patients recruited to ASCOT were men and women between the ages of 40 and 79 years, who were all hypertensive (an untreated systolic/diastolic BP of 160/100mmHg, or a treated systolic/diastolic BP of 140/90mmHg). As well as high BP they all had at least three other risk factors for future CV events (see Box 1).

Patients were excluded if they were contraindicated to any of the treatments used in the study, or if they had a previous MI, current angina, recent stroke or TIA, congestive HF (CHF) or uncontrolled arrythmias.

Patients received treatment towards a target BP of Ôëñ140/90mmHg (non-diabetic patients) and Ôëñ130/80mmHg (diabetic patients) following the treatment algorithm outlined in Table 1. The treatment was planned to continue for five years or until 1,150 primary events had occurred - whichever was longer. Follow-up visits took place after six weeks, three months, six months, and subsequently six-monthly.

Study End-points

The primary end-point of the study was the effect of treatment on combined risk of non-fatal MI and fatal CHD.

There were a number of critical secondary end-points for the trial, including:

  • all-cause mortality;
  • CV mortality;
  • fatal and non-fatal stroke;
  • total coronary end-points; and
  • total CV events and procedures.

 

Results and Discussion
Treatment Combinations

Most patients (77.8%) required an average of 2.2 antihypertensive agents to reach their target BP. Only 14.5% and 8.9% were taking amlodipine and atenolol monotherapy, respectively. This supports previous findings that most hypertensive patients need at least two agents to reach currently recommended targets. This insight is pertinent given the BHS and NICE guidelines. Until recently NICE has recommended initial treatment with a low-dose diuretic with the addition of a ╬▓-blocker when necessary (this would be most patients). However, they do warn against this approach in those patients at an increased risk of new-onset diabetes. The BHS bases therapy on the scientific premise of individual renin status. The BHS proposes the AB/CD system of treatment - in patients younger than 55 and non-black patients, treatment starts with an ACE inhibitor, angiotensin receptor blocker (ARB) or ╬▓-blocker, before adding a calcium channel blocker (CCB) or diuretic (avoiding ╬▓-blocker/diuretic combinations); black patients or patients older than 55 should start with a CCB or diuretic and add in an ACE inhibitor, ARB or ╬▓-blocker.

End-points

ASCOT was terminated early because of a large difference in mortality between the older drugs and the newer ones. The early cessation of the study meant that there was not enough statistical power for the planned primary end-point to quite reach statistical significance. The study was powered for 1,150 individuals to experience the primary end-point, whereas this had only occurred in 903 people at the final follow-up. Critically, there were a number of important and substantial reductions in the secondary and tertiary end-points, as outlined in Table 2. On a broader scale, the extent of the CV benefits seen across all 18 subgroups (see Figure 1) demonstrates that the reduction in CV outcomes associated with amlodipine/perindopril applies to a wide range of patients, regardless of the underlying risk factors observed in the study.

BP Difference

At baseline, over 80% of patients were on antihypertensive treatment, although BP levels were still quite high (164/95mmHg). BP fell to 136.9/78.3mmHg across both treatment groups during the course of the trial; an average reduction of 26.6/16.6mmHg. Throughout the trial, patients allocated to the amlodipine/perindopril strategy had a consistently lower BP than those allocated to the atenolol/thiazide strategy. The average difference throughout the trial was 2.7/1.9mmHg and the difference was largest (5.9/2.4mmHg) at three months.

A 2.7mmHg systolic BP difference would be expected to generate a difference of 4-8% in coronary events and 11-14% in strokes, based on the findings observed in previous randomised trials, as opposed to the 13% and 23% benefits seen in ASCOT. The effects of the newer drugs do therefore seem greater than would be expected from BP reduction alone. One possible explanation is the higher body mass index (BMI), serum triglyceride, creatinine levels and fasting blood glucose levels, and lower high-density lipoprotein (HDL)-cholesterol levels found among those allocated to the atenolol/thiazide strategy. This would tie in with previous research that has questioned the use of ╬▓-blockers in hypertensive patients compared with other antihypertensive treatments, in terms of their lack of CV benefits.

Atenolol and Hypertension

Atenolol in particular has come under scrutiny. The Losartan Intervention For Endpoint reduction in hypertension study (LIFE) study found that patients on the angiotensin receptor blocker (ARB) losartan-based regimen had significantly reduced end-points of CV death, MI and stroke compared with those being treated with atenolol. More recently, in 2004, a meta-analysis of nine studies found that when atenolol was compared with placebo it was effective at lowering BP and reduced the incidence of stroke, but offered no reduction in risk of death from heart attack or stroke. When atenolol was compared with other anti-hypertensives it offered no major differences in terms of lowering BP, and if anything was associated with a slightly greater risk of death due to CVD, strokes and heart attacks.

These studies would suggest that poor performance of atenolol in comparison with the amlodipine-perindopril combination may offer a partial explanation for the results seen in ASCOT. An alternative explanation is that amlodipine and perindopril, on top of their superior BP ability, have 'specialÔÇÖ effects that extend beyond BP lowering. This would corroborate previous research that has found cardioprotective effects, particularly for ACE inhibitors.