Effect of enalapril on myocardial infarction and unstable angina in patients with low ejection fractions

Significance of angiotensin I-converting enzyme and angiotensin II type 1 receptor gene polymorphisms as risk factors for coronary heart disease

The D allele of an insertion/deletion (I/D) polymorphism in the angiotensin I-converting enzyme (ACE) gene is associated with a risk of myocardial infarction, and the relative risk associated with the ACE D allele is increased by the C allele of an angiotensin II type 1 receptor (AT1R) gene polymorphism (an A-->C transversion at nucleotide position 1166) [28]. The relation of the ACE and AT1R gene polymorphisms to coronary heart disease and the severity of coronary artery stenosis has now been investigated in 133 patients with myocardial infarction (MI) or angina pectoris who underwent coronary angiography and in 258 control subjects. The frequency of the ACE DD genotype as compared with non-DD was significantly higher in the patients who experienced an MI and in the low-risk patients than that in the controls (P < 0.05). The DD genotype showed a significantly increased risk of MI (odds ratio 1.85). The frequency of the AT1R A/C genotypes did not differ between the patients and the controls. The severity of coronary stenosis in the patients was estimated by the number of affected vessels (> 75% stenosis) and the coronary score of Gensini. Neither the number of affected vessels nor the coronary score differed among the ACE I/D genotypes. However, the number of affected vessels was significantly greater in patients with the AT1R AC genotype than in those with the 4A genotype (1.93 +/- 0.27 vs. 1.27 +/- 0.99; P < 0.05) (CC genotype was not found in the patients). After excluding patients with diabetes mellitus, the coronary score of those with the AC genotype was also significantly higher than in those with the AA genotype (51.7 +/- 34.4 vs. 18.2 +/- 23.3; P < 0.01). These results suggest that the ACE D allele is associated with the occurrence of myocardial infarction, while the AT1R C allele is involved in the development of the coronary artery stenosis.

Calcium channel antagonists in the modern era of coronary thrombolysis: benefit or detriment?

Calcium channel antagonists are among the world's most widely prescribed class of drugs and are used most often in patients with hypertension and coronary artery disease. However, in the recent past serious questions have been raised concerning their potentially detrimental effects. One area of considerable clinical importance that deserves close inspection is the role of calcium channel antagonists following coronary reperfusion. Specifically, is there benefit or detriment?

Angiotensin-converting enzyme inhibition after acute myocardial infarction with special reference to the Fourth International Study of Infarct Survival (ISIS-4)

Role of ACE inhibitors in the management of asymptomatic or symptomatic left ventricular (LV) dysfunction after acute myocardial infarction (AMI) is well established. More recently, large clinical trials have evaluated the use of angiotensin-converting enzyme (ACE) inhibitors early after AMI, ie, within 24 hours of symptom onset. This concept has emerged with the understanding of pathophysiological changes occurring after AMI. Neurohormonal activation and ventricular remodelling after AMI form the basis of these changes, whereas the extent of LV dysfunction remains strongly predictive of poor outcome. The large clinical trials with mortality end point have shown modest benefit with early use of ACE inhibitors in an unselected population. However, the generalized use of ACE inhibitors remains controversial because of an overall small benefit. We review the pathophysiological changes occurring after AMI, the rationale for early use of ACE inhibitors, and the data available from the large clinical trials. We recommend consideration of early ACE inhibitor in all but the lowest risk patients. Clinical features of such a low-risk population would include small and nonanterior infarctions in patients less than 65 years of age and with LV ejection fractions greater than 50%. Objective assessment of LV function is warranted during hospitalization for AMI to appropriately select patients for ACE inhibitor therapy. Dosing should be started carefully to avoid hypotension and should be titrated to the goal of doses used in the large trials. Duration of therapy in patients at high risk for death or ventricular enlargement should be indefinite. Further large-scale secondary prevention trials with long-term treatment are underway to assess the effect of ACE inhibition on coronary disease progression and reinfarction.

Purification and assay methods for angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE; EN 3.4.15.1) is a peptidyl dipeptide hydrolase that removes the carboxyl terminal His-Leu from angiotensin I to produce the octapeptide angiotensin II. In addition, ACE inactivates bradykinin, a vasodilator peptide/mediator of inflammation, as well as substance P, enkephalins and endorphins. Because of the importance of ACE and its active site-directed inhibitors in the pathogenesis and treatment of cardiovascular disorders such as hypertension and heart failure, ACE purification and assay are of clinical and commercial, as well as scientific interest. This review summarizes the historical development of ACE purification and assay methods and presents some innovative high-performance liquid chromatography-based techniques developed in our own laboratory for high yield and efficient purification and sensitive and specific assay of ACE.

Angiotensin-converting enzyme inhibition with quinapril improves endothelial vasomotor dysfunction in patients with coronary artery disease. The TREND (Trial on Reversing ENdothelial Dysfunction) Study

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors may exert some of their benefits in the therapy of hypertension, congestive heart failure, and acute myocardial infarction by their improvement of endothelial dysfunction. TREND (Trial on Reversing ENdothelial Dysfunction) investigated whether quinapril might improve endothelial dysfunction in normotensive patients with coronary artery disease and no heart failure, cardiomyopathy, or major lipid abnormalities so that confounding variables that affect endothelial dysfunction could be minimized.

METHODS AND RESULTS

Using a double-blind, randomized, placebo-controlled design, we measured the effects of quinapril (40 mg daily) on coronary artery diameter responses to acetylcholine using quantitative coronary angiography. The primary response variable was the net change in the acetylcholine-provoked constriction of target segments between the baseline (prerandomization) and 6-month follow-up angiograms. The constrictive responses to acetylcholine were comparable in the placebo (n = 54) and quinapril (n = 51) groups at baseline. After 6 months, only the quinapril group showed significant net improvement in response to incremental concentrations of acetylcholine (4.5 +/- 3.0% [mean +/- SEM] versus -0.1 +/- 2.8% at 10(-6) mol/L and 12.1 +/- 3.0% versus -0.8 +/- 2.9% at 10(-4) mol/L, quinapril versus placebo, respectively; overall P = .002).

CONCLUSIONS

TREND shows that ACE inhibition with quinapril improved endothelial dysfunction in patients who were normotensive and who did not have severe hyperlipidemia or evidence of heart failure. These benefits of ACE inhibition are likely due to attenuation of the contractile effects and superoxide-generating effects of angiotensin II and to enhancement of endothelial cell release of nitric oxide secondary to diminished breakdown of bradykinin.

Inhibitor of angiotensin-converting enzyme modifies myointimal origin in an arterial autograft model

Pharmacologic modulation by an inhibitor of angiotensin-converting enzyme (IACE: cilazapril) of vascular proliferative response to a full-thickness arterial injury (autograft) was studied in rats. An arterial autograft 5 mm long was made in the right common iliac artery of 50 female Sprague-Dawley rats (weight 250-300 g) by microsurgical techniques. The animals were divided into two study groups: group I (controls), 20 animals that underwent arterial autograft but received no other treatment; and group II (cilazapril-treated), 20 rats that underwent arterial autograft and received cilazapril (Roche), 10 mg/day orally (p.o.) in an excipient of 2% arabic gum, for 4 days before operation. Animals were killed on postoperative days 7, 14, 21, 30, and 50, and grafts were studied by light microscopy, scanning and transmission electron microscopy, and morphometry. In the control group, the hyperplasic response had begun by postoperative day 14 and was established by postoperative day 50. In the medial layer, the muscle cells changed in phenotype from contractile to secretory cells. The adventitia had a highly proliferative appearance. In the cilazapril-treated group, fibrin deposits and platelets formed a layer on the internal elastic lamina. This layer appeared to evolve toward an intimal hyperplasia that became quantifiable by postoperative day 21. The medial layer was clearly thinned and showed intense accumulation of lipid microvacuoles, elastic degeneration, and vacuolized cells. Our results suggest that the use of an inhibitor of ACE modified the origin of the intimal hyperplasia in the arterial autograft model. Enhancement of the thrombogenicity of the luminal surface favors myointimal development by thrombus reorganization.

Benefit of converting enzyme inhibition on left ventricular volumes and ejection fraction in patients receiving beta-blockade after myocardial infarction. CONSENSUS II multiecho study group

Beta-blockers reduce infarct size and improve survival after acute myocardial infarction (MI). Post-MI angiotensin-converting enzyme inhibition also improves survival and may attenuate left ventricular (LV) dilatation. We evaluated the effect of early enalapril treatment on LV volumes and ejection fraction (EF) in patients on concomitant beta-blockade after MI. Intravenous enalaprilat or placebo was administered <24 hours after MI and was continued orally for 6 months. LV volumes were assessed by echocardiography 3 +/- 2 days, 1 and 6 months after MI. Change in LV diastolic volume during the first month was attenuated with enalapril (2.7 vs placebo 6.5 ml/m2 change; p < 0.05), and significantly lower LV diastolic and systolic volumes were observed with enalapril treatment compared with placebo at 1 month (enalapril 47.21 23.9 vs placebo 53.1/29.2 ml/m2; p < 0.05) and at 6 months (enalapril 47.9/24.8 vs placebo 53.8/29.6 ml/m2; p < 0.05). EF was also significantly higher 1 month after MI in these patients (enalapril 50.4% vs placebo 46.4%; p < 0.05). Our date demonstrate that early enalapril treatment attenuates LV volume expansion and maintains lower LV volumes and higher EF in patients receiving concurrent beta-blockade after MI. A possible additive effect of combined therapy should be evaluated prospectively.

Effect of enalapril initiated early after acute myocardial infarction on heart failure parameters, with reference to clinical class and echocardiographic determinants. CONSENSUS II Multi-Echo Study Group

BACKGROUND AND HYPOTHESIS

Although the angiotensin-converting enzyme inhibitor enalapril has recently been shown to reduce mortality and the need for hospitalization in patients with left ventricular dysfunction and congestive heart failure, this drug was found to have no significant impact on short-term mortality after acute myocardial infarction (AMI) in the CONSENSUS II trial. The effect of enalapril initiated early after AMI on clinical and echocardiographic determinants of left ventricular (LV) function was studied in a subset of patients from CONSENSUS II.

METHODS

Symptoms and signs of heart failure were classified as NYHA and dyspnea classes. Echocardiography included LV end-systolic volumes (ESV) and end-diastolic volumes (EDV), as well as ejection fraction (EF), wall motion index (WMI), and mitral flow indices. In all, 428 patients were included and followed for an average of 5.1 months by serial examinations, starting 2-5 days after myocardial infarction (MI) and repeated after 1 month and at the completion of the study.

RESULTS

There was no beneficial effect of enalapril on clinically determined function. Changes (i.e., changes in NYHA class) in the functional status remained correlated with changes in echocardiographic determinants throughout the study in patients belonging to the placebo group: EDV index (r = 0.36, p = 0.002, ESV index (r = 0.49, p < 0.001), EF (r = -0.41, p < 0.001), and WMI (r = 0.29, p = 0.008). In a stepwise logistic regression model, the best baseline parameters to predict NYHA class at final visit in all patients were age (p = 0.014) and ESV index (p = 0.001).

CONCLUSION

Enalapril treatment for an average period of 5.1 months following MI resulted in no clinically significant beneficial effects on NYHA and dyspnea class. Changes in clinical function class were correlated with changes in echocardiographic determinants in placebo-treated patients, but not in patients given enalapril.

Verapamil and angiotensin-converting enzyme inhibitors in patients with coronary artery disease and reduced left ventricular ejection fraction

Verapamil is effective as antianginal medication but contraindicated in patients with congestive heart failure. Angiotensin-converting enzyme (ACE) inhibitors improve survival in patients with congestive heart failure but have limited effect on patients with angina pectoris. No studies have been published on the combined treatment with verapamil and ACE inhibitors in patients with stable angina pectoris and left ventricular dysfunction. We performed an open study in 14 patients with angina pectoris and ejection fraction < 40%. The patients received verapamil 180 mg and trandolapril 2 mg twice daily for 3 months. We found a significant increase in ejection fraction from 28 +/- 6 to 35 +/- 11 (p < 0.03), wall motion index from 1.0 +/- 0.3 to 1.2 +/- 0.3 (p < 0.03), exercise duration from 6.9 +/- 2.5 to 7.7 +/- 2.9 minutes (p < 0.01), and ratio of exercise to rest rate-pressure product from 2.2 +/- 0.4 to 2.5 +/- 0.6 (p < 0.02). Use of nitroglycerin and number of angina pectoris attacks were both significantly reduced after 3 months of treatment. These findings support the hypothesis that the combination of verapamil and trandolapril is useful in patients with attenuated left ventricular function and angina pectoris.

Primary and secondary prevention of myocardial infarction

The prevention of coronary artery disease (CHD) and particularly of myocardial infarction (MI) is based on some well designed strategies aimed at treating both asymptomatic high-risk patients (primary prevention) and patients with established CHD (secondary prevention). A positive impact from primary prevention can be basically achieved trough a reduction in high blood pressure and by correcting dyslipidemia. The benefit can be substantially increased by smoking cessation, increasing physical exercise, reduction of body weight, use of post-menopausal oestrogen, moderate alcohol consumption and use of high doses of vitamin E in those patients who are compliant with the specific strategies. Secondary prevention of MI can be again obtained by controlling blood pressure and reducing serum cholesterol in patients surviving acute MI who can also benefit from the administration of beta-blockers, aspirin and probably ace-inhibitors particularly in presence of left ventricular dysfunction. We suggest that in both arms of prevention, significant results can be achieved mainly by a multifactorial approach capable of correcting all the modifiable risk factors that contribute to the rather complex pathogenesis of CHD.

Ongoing clinical trials of angiotensin-converting enzyme inhibitors for treatment of coronary artery disease in patients with preserved left ventricular function

At present there is considerable activity in the area of prevention of atherosclerosis-related events using angiotensin-converting enzyme inhibitors. Large trials have demonstrated significant reduction in cardiovascular morbidity and mortality with long-term use of angiotensin-converting enzyme inhibitors in patients with left ventricular dysfunction, heart failure or acute myocardial infarction. Reductions in acute ischemic events (e.g., myocardial infarction, unstable angina and need for early revascularization) were independent of ejection fraction and were greater than would be expected from the small reduction in blood pressure that occurred, suggesting that other patients with coronary artery disease may benefit from angiotensin-converting enzyme inhibitor therapy. This hypothesis is being tested in multiple double-blind, randomized, controlled clinical trials with durations of follow-up of 3 to 5 years that will involve approximately 30,000 patients. The trials vary with respect to patient population (e.g., normotensive vs. hypertensive, normolipidemic vs. hyperlipidemic, with vs. without diabetes mellitus), angiotensin-converting enzyme inhibitor used and outcome measures. When available, the results of these clinical trials could have very important implications for the role of long-term angiotensin-converting enzyme inhibitor therapy for preventing or delaying the development of atherosclerosis-related ischemic events.

Lack of ventricular remodeling in non-Q-wave myocardial infarction

We prospectively examined 45 patients with serial echocardiography to measure left ventricular end-diastolic volume index within 1 week and at 6 weeks after infarction. Left ventricular volume increased in patients with Q-wave infarction but not in those with non-Q or in control patients without recent infarction. Peak creatine phosphokinase levels were greater in Q-wave infarction compared with those in non-Q-wave infarction. There was a strong correlation between the change in the left ventricular end-diastolic index and the peak creatine phosphokinase level. After correcting for infarct size, there was still a difference between the two groups. Our data indicate that ventricular remodeling does not occur in non-Q-wave as opposed to Q-wave infarcts, and this may be related both to the limited amount of myocardial necrosis and to the nontransmural extent of the necrosis.

Mild systolic dysfunction in heart failure (left ventricular ejection fraction >35%): baseline characteristics, prognosis and response to therapy in the Vasodilator in Heart Failure Trials (V-HeFT)

OBJECTIVES

This analysis sought to evaluate the clinical characteristics and outcome in heart failure with mild systolic dysfunction.

BACKGROUND

Although heart failure with mild systolic dysfunction occurs commonly, this is an understudied area because clinical trials have usually excluded patients with ejection fraction >35%.

METHODS

The 422 patients with left ventricular ejection fraction </=35% were compared with 172 with a left ventricular ejection fraction >35% in the Vasodilator in Heart Failure Trial (V-HeFT I), whereas in V-HeFT-II 554 patients with a left ventricular ejection fraction </=35% were compared with 218 patients with a left ventricular ejection fraction >35% for mortality and clinical care. For a left ventricular ejection fraction >35%, treatment with hydralazine/isosorbide dinitrate was compared with prazosin and placebo therapy in V-HeFT I, and hydralazine/isosorbide dinitrate was compared with enalapril in V-HeFT II for mortality, clinical course and change in physiologic variables: ejection fraction, plasma norepinephrine levels, ventricular tachycardia and echocardiographic variables.

RESULTS

In both studies, patients with a left ventricular ejection fraction >35% differed principally in hypertensive history, higher functional capacity and radiographic and echocardiographic cardiac dimension from patients with a left ventricular ejection fraction </=35%, and plasma norepinephrine levels differed in V-HeFT II (p < 0.01). Patients with a left ventricular ejection fraction >35% had a lower cumulative mortality than those with a left ventricular ejection fraction </=35% (p < 0.0001) and less frequent hospital admissions for heart failure (p < 0.014, V-HeFT I; p < 0.005, V-HeFT II). Although cumulative mortality and morbidity did not differ between treatment groups in V-HeFT I, enalapril decreased overall mortality versus hydralazine/isosorbide dinitrate (p < 0.035) in V-HeFT II. For physiologic variables in V-HeFT II, enalapril decreased ventricular tachycardia at follow-up (p < 0.05).

CONCLUSIONS

In V-HeFT, heart failure with mild systolic dysfunction was associated with different characteristics and a more favorable prognosis than heart failure with more severe systolic dysfunction. Enalapril decreased overall mortality and sudden death compared with hydralazine/isosorbide dinitrate. Prospective trials are needed to address therapy for heart failure with mild systolic dysfunction.

Adverse effects of enalapril in the Studies of Left Ventricular Dysfunction (SOLVD). SOLVD Investigators

In the Studies of Left Ventricular Dysfunction (LVD), enalapril or placebo was administered in a double-blind fashion to 6797 participants with ejection fraction < or = 0.35. During 40 months' average follow-up, 28.1% of participants randomized to enalapril reported side effects compared with 16.0% in the placebo group (p < 0.0001). Enalapril use was associated with a higher rate of symptoms related to hypotension (14.8% vs 7.1%, p < 0.0001), azotemia (3.8% vs 1.6%, p < 0.0001), cough (5.0% vs 2.0%, p < 0.0001), fatigue (5.8% vs 3.5%, p < 0.0001), hyperkalemia (1.2% vs 0.4%, p = 0.0002), and angioedema (0.4% vs 0.1%, p < 0.05). Side effects resulted in discontinuation of blinded therapy in 15.2% of the enalapril group compared with 8.6% in the placebo group (p < 0.0001). Thus enalapril is well tolerated by patients with LVD; however, hypotension, azotemia, cough, fatigue, and other side effects result in discontinuation of therapy in a significant minority of patients.

Angiotensin II-modified LDL is taken up by macrophages via the scavenger receptor, leading to cellular cholesterol accumulation

The incidence of myocardial infarction is significantly higher in hypertensive patients with increased plasma concentration of angiotensin (Ang) II. Ang II was shown to bind to LDL in vitro, and in the present study we showed its binding to LDL in vivo. Ang II (10(-7) mol/L) was incubated with LDL for 3 hours at 37 degrees C, followed by reseparation of the modified lipoprotein (Ang II-LDL) and its incubation with J-774 A.1 macrophages. Binding of Ang II to LDL significantly increased the lipoprotein protein degradation (by 25%) and its cell association (by 75%) compared with nontreated LDL. Unlike Ang II-LDL, both Ang I-LDL and Ang III-LDL were taken up by macrophages similar to native LDL. The lipid composition and size of Ang II-LDL were similar to those of native LDL, and it was not aggregated. Ang II-LDL was not oxidized, as the contents of malondialdehyde and peroxides were not different from those found in native LDL. On heparin-Sepharose column chromatography, Ang II-LDL was eluted in the void volume, like acetylated LDL (Ac-LDL) and unlike native LDL, which binds to heparin. The cellular degradation of Ang II-125I-labeled LDL by J-774 A.1 macrophages of Ang II-125I-labeled LDL by J-774 A.1 macrophages was studied in the presence of a 50-fold excess of nonlabeled native LDL, Ang II-LDL, Ac-LDL, or oxidized LDL (Ox-LDL). Whereas native LDL had no effect on the degradation of Ang II-125I-LDL by the macrophages, Ac-LDL, Ox-LDL, and Ang II-LDL reduced the cellular uptake of the lipoprotein by 77%, 82%, and 87%, respectively. Similarly, fucoidin but not free Ang II reduced macrophage degradation of the labeled Ang II-LDL. We conclude that Ang II can modify LDL to a form that is not oxidized or aggregated but is still taken up at an enhanced rate by macrophages via the scavenger receptor.

Clinical benefit of angiotensin-converting enzyme inhibitors in chronic heart failure

The ideal therapy for patients with chronic heart failure should reduce symptoms related to pulmonary congestion or low perfusion, prevent the progression of left ventricular dysfunction and, ultimately, should reduce mortality. Extensive studies in humans have investigated the effects of angiotensin-converting enzyme (ACE) inhibitors on these goals of therapy. As an example, the ACE inhibitor cilazapril significantly improved exercise tolerance, as borne out by a meta-analysis of six placebo-controlled, randomized 3-month trials. Comparison of the effects of cilazapril and captopril vs. placebo in one of the trials documented similar improvement in exercise tolerance (14 vs. 17%). Results from other randomized comparative trials suggest that the improvement in symptoms represents a class effect of ACE inhibitors. A beneficial effect of ACE inhibition on the progression of left ventricular dysfunction has also been demonstrated in the SOLVD trial, and a reduction of mortality has been amply documented in several mortality trials (CONSENSUS I, SOLVD, V-HeFT-II, SAVE, AIRE, SMILE) in patients with or without preceding myocardial infarction. Reports that ACE inhibitors also reduce the incidence of reinfarction after myocardial infarction have not been confirmed in all studies but raise the interesting concept that ACE inhibition may interact, in a beneficial but thus far not well-understood way, with key processes in the development of atherosclerosis, thereby preventing plaque rupture, thrombus formation, and myocardial infarction. Taken together, a large database convincingly demonstrates that ACE inhibitors are effective not only in improving symptoms but also in the prevention of progression of left ventricular dysfunction, in the reduction of mortality, and possibly in stabilizing the atherosclerotic disease process.

Quality of life with ACE inhibitors in chronic heart failure

The randomized trials assessing the effect of angiotensin-converting enzyme (ACE) inhibitors in chronic heart failure (CHF) are reviewed. The Minnesota Living with Heart Failure Questionnaire has demonstrated the benefits of enalapril in some but not all circumstances and the Yale Dyspnea-Fatigue Index improves with lisinopril. A recent trial of both cilazapril and captopril vs. placebo employed the Sickness Impact Profile and supports the concept that ACE inhibitors have a small (and in this trial nonsignificant) beneficial effect on mobility. Other vasodilators and inotropes may also have small benefits on quality of life, such that comparisons of an ACE inhibitor with vasodilators, as was done in the V-HeFT II trial, fail to reveal any different effects on quality of life.

Diabetic vascular injury and ACE. Potential for pharmacological prevention of complications of later life

Experimental studies have indicated that angiotensin converting enzyme (ACE) inhibitors have multiple actions on the kidney and blood vessels which include both haemodynamic and antitrophic effects. Inhibition of angiotensin II and potentiation of bradykinin have both been postulated to be major mechanisms in mediating the effects of ACE inhibitors. Clinical studies have indicated that these agents postpone end-stage renal failure in macroproteinuric patients with insulin-dependent diabetes mellitus (IDDM). Indeed, these drugs are useful in both hypertensive and normotensive diabetic patients with macroproteinuria. In IDDM patients with microalbuminuria, ACE inhibitors have been shown to decrease albuminuria and to retard the development of overt renal disease. The role of these agents in patients with non-insulin-dependent diabetes mellitus (NIDDM) and early or overt renal disease remains to be clearly delineated. However, preliminary studies suggest a similar beneficial renoprotective effect of ACE inhibitors in NIDDM. It should be appreciated that the presence of micro- or macroproteinuria in NIDDM is a predictor of cardiovascular rather than renal morbidity and mortality. The possibility of cardiovascular protection, in addition to renal protection, being conferred by these drugs needs to be considered in both IDDM and NIDDM, although this issue has not been evaluated in detail.

Sympathetic tone assessed by washout of iodine 125-labeled metaiodobenzylguanidine from the murine left ventricle--influence of immobilization stress and inhibition of the renin-angiotensin system

BACKGROUND

Because it is not metabolized as is norepinephrine (NE), most of the metaiodobenzylguanidine (MIBG) taken up by the heart is considered to be lost subsequently by release concomitant with sympathetic stimulation. Therefore we examined whether the washout of MIBG is influenced by sympathetic tone, which we modulated by using immobilization stress or activation of the renin-angiotensin system (RAS).

METHODS AND RESULTS

In 175 male ddY mice, left ventricular radioactivity was counted 30 minutes or 4 hours after injection of 74 kBq (2 microCi) of iodine 125- or iodine 131-labeled MIBG (125I- or 131I-MIBG). The washout rates of MIBG were determined under immobilization stress or under sodium loading or restriction in combination with losartan (10 mg/kg) or cilazapril (1 mg/kg) pretreatment. Immobilization enhanced the washout of 125I-MIBG (80.9% vs 57.9% in the control animals); this was determined to be related to washout from the neuronal compartment, because the nonneuronal component assessed through desipramine pretreatment was not affected. Pretreatment with losartan or cilazapril decreased the facilitation of 125I-MIBG washout in sodium-restricted mice (40.9% and 33.7%, respectively, vs 43.5% in the control animals), but not in sodium-loaded mice.

CONCLUSIONS

Measurement of MIBG washout may be feasible for determining the changes in sympathetic tone caused by immobilization stress or activation of the RAS.

Genetic linkage of the ACE gene to plasma angiotensin-converting enzyme activity but not to blood pressure. A quantitative trait locus confers identical complex phenotypes in human and rat hypertension

BACKGROUND

An allelic variant of the ACE gene has been found to be linked to plasma angiotensin-converting enzyme (ACE) activity in humans and has been implicated in the etiology of some common cardiovascular disorders. Previously, we have shown significant genetic linkage of blood pressure to a region on rat chromosome 10 that contains ACE in an experimental F2-intercross between the stroke-prone spontaneously hypertensive rat (SHRSPHD) and the normotensive Wistar-Kyoto (WKYHD-0) reference strain. Subsequent investigations revealed marked differences in plasma ACE activity among the SHRSPHD and WKYHD-0 strains. Nonetheless, the physiological relevance of these findings remained obscure. We therefore investigated the genetic determination of plasma ACE activity and its relation to blood pressure and dietary NaCl exposure in a model of experimental genetic hypertension, the SHRSPHD.

METHODS AND RESULTS

We conducted a further crossbreeding experiment between SHRSPHD and a congenic reference strain, WKYHD-1, that carries a 6-centimorgan (cM) long, SHRSP-homologous segment introgressed in chromosome 10, 26 cM remote from ACE. This allowed us to contrast effects on blood pressure and ACE activity conferred by the ACE locus with other more remote loci within the congenic chromosomal region. Genetic analysis in this F2 (WKYHD-1 x SHRSPHD) cross revealed that plasma ACE activity was determined almost entirely by genetic effects of the ACE gene locus (lod score = 43). However, neither plasma ACE nor the ACE locus showed any cosegregation with blood pressure before or after dietary NaCl exposure.

CONCLUSIONS

These results demonstrate that a molecular variant of the ACE gene determines plasma ACE activity but exhibits no direct effect on blood pressure. Moreover, the findings also exclude the possibility that plasma ACE is secondarily affected by blood pressure or excess dietary NaCl exposure. Our results reconcile the previous discrepancy between findings in human and experimental hypertension.

Angiotensin induction of PAI-1 expression in endothelial cells is mediated by the hexapeptide angiotensin IV

Recent studies from this laboratory have demonstrated that angiotensin II (Ang II) stimulates the expression of plasminogen activator inhibitor 1 (PAI-1) in cultured endothelial cells. This response does not appear to be mediated via an interaction with either the AT1 or the AT2 receptor subtype. Since a novel angiotensin receptor has been identified in a variety of tissues that specifically binds the hexapeptide Ang IV (Ang II, [3-8]), we therefore examined the effects of Ang IV on the expression of PAI-1 mRNA in bovine aortic endothelial cells. Ang IV stimulated dose- and time-dependent increases in the expression of PAI-1 mRNA. The effect of Ang IV (10 nM) was not inhibited by Dup 753 (1.0 microM), a highly specific antagonist of the AT1 receptor, or by PD123177 (1.0 microM), a highly specific antagonist of the AT2 receptor. In contrast, the AT4 receptor antagonist, WSU1291 (1.0 microM), effectively prevented PAI-1 expression. Although larger forms of angiotensin (i.e., Ang I, Ang II, and Ang III) are capable of inducing PAI-1 expression, this property is lost in the presence of converting enzyme or aminopeptidase inhibitors. These results indicate that the hexapeptide Ang IV is the form of angiotensin that stimulates endothelial expression of PAI-1. This effect appears to be mediated via the stimulation of an endothelial receptor that is specific for Ang IV.

Sensitive method for quantitation of angiotensin-converting enzyme (ACE) activity in tissue

A novel sensitive and specific method for the measurement of tissue angiotensin-converting enzyme (ACE) activity utilizing HPLC is described. ACE activity was determined in detergent-extracted canine hearts utilizing the synthetic ACE-specific substrate hippuryl histidyl leucine (HHL), both in the presence and the absence of the site-specific inhibitor captopril. Tissue ACE activity was quantitated from the moles of hippuric acid (HA) formed, in time-fixed assays, utilizing HPLC separation of HA from HHL and UV-spectrophotometry for quantitation of HA as in the standard Cushman and Cheung assay (Cushman DW and Cheung HS, Biochem Pharmacol 20: 1637-1648, 1971). Separation of HA from HHL was performed by reverse phase HPLC on a phenyl silica gel column with an eluent consisting of 20% acetonitrile in 0.1 M aqueous ammonium phosphate buffer, pH 6.8. After the standard liquid/liquid extraction procedure with ethyl acetate, HPLC analysis revealed the presence of unreacted substrate, HHL, in amounts comparable to the product of interest, HA, in the final assay; moreover, the amount of HA formed did not fall completely to zero in the presence of captopril. Regional studies of canine cardiac ACE activity utilizing the HPLC-based assay and the standard assay method showed a significantly higher ACE activity in the right ventricle compared with the left ventricle (2.37 +/- 0.7 vs 1.24 +/- 0.18 mU/g, P < 0.05 [N = 6], respectively) in the HPLC-based assay, but no difference in right and left ventricular ACE activities by the standard assay (0.25 +/- 0.08 vs 0.31 +/- 0.09 mU/g [N = 6], respectively). Kinetic studies utilizing the HPLC-based assay coupled with the use of captopril showed Km (1.34 +/- 0.08 mM) and Vmax (36.8 +/- 11.5 x 10(-10) M/min) values in agreement with those in the literature. Our results demonstrate that the application of HPLC to the standard Cushman and Cheung assay improves the sensitivity and specificity of the standard assay and enables the use of much smaller amounts (approximately 4 vs approximately 400 mg for the Cushman and Cheung assay) of tissue for ACE activity assay.

Molecular genetics: cardiac disease and risk-related genes

Molecular genetics is playing an increasing role in the diagnosis, treatment, and prevention of cardiac disease. Moreover, most of the genes that may cause cardiac disease or predispose an individual to cardiac disease are anticipated to be identified within the next 10 years. Several genes with risk for heart disease have been identified, such as the ACE genotype DD. Replacement gene therapy as well as use of promoter-specific drugs to act on genetic regulatory elements will encompass the future treatment of cardiovascular disease. This article provides a summary of the potential roles of genetic screening for cardiac risk factors and genetic interventions in cardiovascular disease.

Digoxin and mortality in survivors of acute myocardial infarction: observations in patients at low and intermediate risk. The SPRINT Study Group. Secondary Prevention Reinfarction Israeli Nifedipine Trial

Controversy surrounds the safety of digoxin use in patients recovering from acute myocardial infarction. Previous observations yielded contradictory conclusions. To determine whether digoxin therapy is associated with increased mortality in patients recovering from acute myocardial infarction, we analyzed data from 1731 survivors of acute myocardial infarction enrolled in the Secondary Prevention Reinfarction Israeli Nifedipine Trial (SPRINT), from which patients with severe heart failure were excluded. At the time of hospital discharge, 175 patients (10%) were taking digoxin. Mortality over 1 year after infarction was significantly higher in patients treated with digoxin than in patients who were not receiving digoxin [27 of 175 (15%) vs. 60 of 1556 (4%); p < 0.0001]. Digoxin administration was associated with increased mortality in several subsets of patients. Since patients treated with digoxin had baseline characteristics predictive of mortality more frequently than their counterparts, we adjusted for these differences. Multivariate analysis performed by the Cox proportional hazards model identified treatment with digoxin as an independent determinant associated with increased death during the first year after myocardial infarction [relative risk (RR) 2.8; 90% confidence interval (CI) 1.8-4.2]. Subgroup multivariate analysis indicated digoxin as an independent predictor of first year death in 464 patients who developed heart failure during their hospital stay (RR 2.3; 90% CI 1.3-4.0), as well as among 1267 patients who did not (RR 3.4; 90% CI 1.7-6.9). The present study suggests a significant excess mortality associated with digoxin therapy after myocardial infarction. The increased mortality risk may be related to unidentified variables associated with the severity of disease in patients treated with digoxin. However, our findings raise concern that the administration of digoxin may contribute to increased mortality in survivors of acute myocardial infarction.

Long-term prognostic significance of M mode echocardiography in young men after myocardial infarction

OBJECTIVE

To evaluate the power of measurements of left ventricular size and function for predicting long term (82 month) mortality by performing echocardiography in 97 men who had survived an acute myocardial infarction.

SETTING

University hospital specialising in cardiology.

PARTICIPANTS

97 consecutive male patients who had survived a myocardial infarction.

MAIN OUTCOME MEASURES

The additive prognostic value of functional measurements to that provided by primary risk factors (smoking habits and lipoprotein levels), radiological heart size, exercise capacity, and number of major coronary arteries with haemodynamically significant stenoses was evaluated. An echo index was calculated from three echocardiographic variables (yielding one score point each if: left ventricular diameter at the end of diastole (LVDD) > or = 5.7 cm, left ventricular fractional shortening < or = 24%, and E point-separation (EPSS) > or = 10 mm).

MAIN OUTCOME

17 cardiac deaths occurred during follow up.

RESULTS

Univariate analysis showed that treatment with loop diuretics for heart failure (P < 0.01), LVDD (P < 0.01), left ventricular diameter at the end of systole (LVDS) (P < 0.001), left atrial diameter (P < 0.001), fractional shortening (P < 0.05), and echo index (P < 0.001) were all associated with cardiac death. Angiographically determined regional wall motion disturbances (P < 0.005) and angiographic ejection fraction (P < 0.001) were also associated with cardiac death, as was the number of major coronary arteries with significant stenosis (P < 0.05). When all significant echocardiographic variables from univariate analysis were entered into Cox proportional hazards survival analysis, LVDS and left atrial diameter contributed independently to the prediction of cardiac death. If angiographic data were also entered into the model, the echo index made an independent contribution to the prediction of cardiac death.

CONCLUSIONS

Among young male patients with a previous myocardial infarction, a simple M mode echocardiographic examination can identify high and low risk patients and improve the prediction of cardiac death made from clinical information, exercise test, chest x ray and angiographically determined ejection fraction.

New concepts regarding events that lead to myocardial infarction

In addition to new knowledge concerning the mechanisms whereby conventional risk factors act, other risk factors have been newly described, such as dietary antioxidants, lack of exercise, insulin resistance, excess iron stores, increased plasma angiotensin-converting enzyme, and left ventricular hypertrophy. An intact endothelium protects both by the formation of nitric oxide, which is a vasodilator and also an inhibitor of platelet aggregation and neutrophil adhesion, and by manufacturing tissue plasminogen activator. The acute thrombotic event occurs with a diurnal variation but may be precipitated by acute exertion, especially in untrained individuals, and reflects a balance between vasoconstrictory and vasodilatory stimuli from the vascular endothelium, as well as procoagulant versus anticoagulant effects of complex balancing systems. Increased risk of sudden cardiac death in the morning is thought to be a reflection of transient risk factors, such as a blood pressure increase, heart rate increase, and changes in coagulation factors, as well as changes in platelet aggregation. There is an apparent paradox between the acute effect of exercise in promoting sudden cardiac death and the chronic effect of exercise training in decreasing the risk of myocardial infarction. The explanation may be that chronic exercise training has an inhibitory effect on adrenergic discharge.

ACE inhibitors and calcium antagonists in the treatment of congestive heart failure

The increased mortality after myocardial infarction is related to the risk of reinfarction, sudden death, and the development and progression of heart failure; in congestive heart failure it is due to the progression of heart failure and sudden death. ACE inhibitors have been proven to prevent cardiovascular events, especially the progression of heart failure, in postinfarct patients with reduced ejection fraction and heart failure in the SAVE and AIRE trials. In patients with congestive heart failure, ACE inhibitor treatment has prevented cardiovascular death and reduced morbidity due to progressive heart failure in the SOLVD trials. In post-myocardial infarction patients, the calcium antagonist nifedipine did not affect mortality or morbidity; diltiazem improved prognosis in patients without congestive heart failure and in patients with non-Q-wave infarction; and verapamil improved prognosis by prevention of reinfarction and sudden death. Combination treatment with both verapamil, which has pronounced antiischemic properties and prevents sudden death and reinfarction, and an ACE inhibitor, which prevents the progression of heart failure, is a possibility for future cardiovascular therapy that should be evaluated.

Failure of protective effect of captopril and enalapril on exercise and dipyridamole-induced myocardial ischemia

Fifteen patients with angiographic evidence of significant coronary artery disease, exertional myocardial ischemia, and positive dipyridamole echocardiographic test results at basal conditions and after 7 days of placebo treatment were prospectively studied to see whether captopril (containing sulfhydryl) and enalapril (nonsulfhydryl) modify myocardial ischemia induced by exercise testing and the effects of dipyridamole echocardiographic testing on regional myocardial contractility. Patients were randomized to captopril (150 mg/day in 3 separate doses) or enalapril (20 mg/day) for 1 week. At the end of this period each patient crossed over to the alternate regimen after a washout period of 7 days. Exercise stress testing and dipyridamole echocardiographic testing were repeated at the end of each treatment period. Neither captopril nor enalapril had a significantly greater anti-ischemic effect than placebo in any patient. Exercise duration, time to onset of ST-segment depression, maximal workload, degree of ST-segment depression, and rate-pressure product were not affected by either drug. Neither captopril nor enalapril improved dipyridamole-induced mechanical dysfunction or ST-segment depression.

Contemporary management of acute myocardial infarction

Acute myocardial infarction, the leading cause of death in western society, has been the focus of more randomized clinical trial effort over the past decade than any other area of medicine. As a result of this worldwide effort, involving hundreds of thousands of patients with myocardial infarction, data have accumulated showing substantially lower mortality of acute myocardial infarction with simple interventions such as i.v. thrombolytic therapy, aspirin, beta-blockers, and angiotensin-converting enzyme inhibitors. Emergency coronary angioplasty appears to be a suitable alternative to i.v. thrombolytic therapy in skilled centers. Several previously recommended therapies (routine i.v. lidocaine, calcium channel blockers, magnesium, nitrates) have not been proved to be life-saving. Whether routine coronary arteriography should be employed after myocardial infarction remains controversial, but it is generally accepted that patients with evidence of residual ischemia after infarction, either spontaneous or provoked by stress testing, should undergo prophylactic coronary revascularization.

Clinical trials: specific problems associated with the use of a placebo-control group

In order to test hypotheses prospectively with hard data and against placebo, the scientific method of clinical trials has been developed. The present paper focuses on specific problems associated with the use of a placebo control group. (a) The placebo highlights the ethical dilemma that a controlled clinical trial can place us in. (b) Also, in a trial an atmosphere is created of enhanced risks of placebo effects. (c) "Significantly different from placebo" does not necessarily mean clinically relevant. (d) A biased placebo period due to carry-over effect is a common problem of controlled trials with a cross-over or self-controlled design. (e) Likewise an asymmetric placebo group is also a common problem in parallel-group designs. (f) The response to a placebo is generally small in comparison with the response to active treatment and is therefore sometimes more susceptible to bias. It is emphasized that routinely accounting for such problems may further improve the powerful method of controlled clinical trials.

Insertion/deletion polymorphism in the angiotensin-I-converting enzyme gene is associated with coronary heart disease in IDDM patients with diabetic nephropathy

Insulin-dependent diabetic (IDDM) patients with diabetic nephropathy have a highly increased morbidity and mortality from coronary heart disease. An insertion (I) /deletion (D) polymorphism in the angiotensin-I-converting enzyme (ACE) gene has been shown to be associated with coronary heart disease. Therefore, we have investigated the role of this ACE/ID polymorphism in 198 IDDM patients with diabetic nephropathy and 190 normoalbuminuric IDDM patients. The prevalence of myocardial infarction and other coronary heart disease was significantly elevated in patients with nephropathy, 19% (38/198) vs 8% (15/190), p < 0.001. In the nephropathic group 12 of 63 (19%), 23 of 95 (24%), and 3 of 40 (7.5%) patients with the DD, ID and II genotypes, respectively had a history of coronary heart disease, II vs DD and ID, p < 0.05 when compared to nephropathic patients without coronary heart disease. Multiple logistic regression analysis of the risk factors associated with coronary heart disease in univariate analysis revealed that the II genotype acts as an independent protective factor against coronary heart disease, odds ratio II/DD + ID 0.27 (95% confidence interval 0.07-0.97, p < 0.05). There was no difference in genotype or allele frequency (D/I) between patients with and without nephropathy, 0.56/0.44 in both groups, but plasma ACE concentration was elevated in patients with nephropathy 609 (151-1504) ng/ml as compared to patients with normoalbuminuria, 428 (55-1630) ng/ml, p < 0.001. We suggest that ACE/ID polymorphism may influence the frequency of life-threatening cardiac complications in IDDM patients suffering from diabetic nephropathy, a condition characterized by increased plasma ACE concentration.

Association of angiotensinogen gene T235 variant with increased risk of coronary heart disease

Several genes, including some encoding components of the renin angiotensin system, are associated with the risk of cardiovascular diseases. There have been reports linking a homozygous deletion allele of the angiotensin converting enzyme (ACE) gene (DD) with an increased risk of myocardial infarction, and some variants of the angiotensinogen gene with an increased risk of hypertension. In a case-control study of a caucasian population from New Zealand, we examined the associations with coronary heart disease (CHD) of ACE DD and of a mis-sense mutation with methionine to threonine aminoacid substitution at codon 235 in the angiotensinogen gene (T235). We studied 422 patients (mean age 62 years, 81% male) with documented CHD (50% with myocardial infarction) and 406 controls without known CHD (frequency-matched to cases by age and sex). Risk factors for CHD were assessed by standard questionnaire, physical examination, and blood tests. Genomic DNA from leucocytes was analysed for various ACE and angiotensinogen alleles. Angiotensinogen T235 homozygotes were at significantly increased risk of CHD generally (odds ratio 1.7, 2 p = 0.008) and of myocardial infarction specifically (1.8, 2 p = 0.009). Adjustment for several risk factors increased the estimate of CHD risk associated with this allele to 2.6 (2 p < 0.001) and the estimate for myocardial infarction risk to 3.4 (2 p < 0.001). By contrast, there was no evidence of a significant increase in the risk of CHD or myocardial infarction among individuals with ACE DD. We conclude that the T235 polymorphism of the angiotensinogen gene is an independent risk factor, which carries an approximately two-fold increased risk of CHD. In this study, however, ACE DD was not associated with any detectable increase in CHD risk.

Identifying the patient with heart failure

Heart failure is becoming an increasing concern to healthcare worldwide, and of particular concern in the Western world where the age of the population continues to rise. Furthermore, it has now become clear that, if heart failure is identified and treated in the earliest stages of ventricular dysfunction, the possibility of recovery from or substantial delay in progression to complete heart failure is extremely good and will give the patient a considerably improved quality of life. Certain signs and symptoms found on routine examination, coupled with knowledge of patient history, can indicate early heart failure. Patients will normally present to their family practitioner, who is likely to have long term, firsthand knowledge of the patient's medical and family history. Consequently, the general practitioner has a key role in identifying individuals with early heart failure. It is essential that the general practitioner is aware of the signs and symptoms of early heart failure, can interpret them correctly and knows what follow-up tests are necessary to confirm the diagnosis. Guidelines are presented here to assist the general practitioner in this task.

Angiotensin-converting enzyme inhibitors and calcium antagonists after acute myocardial infarction

This article examines trials of the use of two types of drugs in the treatment of myocardial infarction: angiotensin-converting enzyme (ACE) inhibitors and calcium antagonists. ACE inhibitors are an established treatment for hypertension and heart failure and have been shown to reduce mortality from heart failure and after myocardial infarction. Six large studies have been carried out. In 1 in which an ACE inhibitor was given 3-16 days after infarction in patients with an ejection fraction < 40%, mortality was reduced by 17%. In a second study of patients who had evidence of heart failure and were followed up for 15 months, treatment with ACE inhibitors was given 3-10 days after myocardial infarction and mortality was reduced by 27%. Two other studies of 11,000 and 50,000 unselected patients with myocardial infarction showed only marginal clinical benefit. Calcium antagonists were introduced to treat hypertension and angina pectoris. In trials with patients with heart failure, the results have not been encouraging, and in some patients these agents seem to be harmful. Recently, long-acting calcium antagonists have become available, and these may avoid the deleterious effects of short-acting drugs. Since calcium antagonists act on smooth muscle, they may increase myocardial blood flow to improve function after "stunning" or "hibernation." This idea was investigated with a long-acting dihydroyridine calcium, antagonist in a randomized double-blind, placebo-controlled study (Doppler Flow, Echocardiography, and Functional Improvement Assessment of Nisoldipine Therapy-I--DEFIANT I), and a further study is being carried out. At present the widespread use of calcium antagonists after infarction is not recommended.

Angiotensin-converting enzyme gene polymorphism is associated with myocardial infarction but not with development of coronary stenosis

BACKGROUND

Although both genetic and nongenetic factors contribute to the pathogenesis of coronary artery disease, the identification of specific genetic lesions has lagged behind the identification of critical environmental risk factors. A reported association between myocardial infarction (MI) and the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene in European men suggests a critical role for this genomic region. However, the generality of this association remains to be determined. It also is not clear at what stage in disease progression the association with the ACE I/D polymorphism becomes important.

METHODS AND RESULTS

We evaluated the ACE I/D polymorphism in patients who had undergone coronary angiography (402 men and 295 women) and in 203 representative control subjects. After polymerase chain reaction amplification, genotypes were determined by agarose gel sizing and by hybridization with allele-specific oligonucleotides. After patients were categorized by the degree of coronary artery stenosis and the occurrence of an MI, the distribution of ACE I/D genotypes was evaluated by log linear analysis. Patients were genetically representative of the regional population, and patients with > 60% stenosis of their coronary arteries had the same distribution of ACE I/D genotypes as did patients with < 10% stenosis. However, among patients with stenosis, the occurrence of an MI was significantly associated with the D allele in all patients (odds ratio [OR], 1.59; P = .002) and in men alone (OR, 1.63; P = .006). The lack of significance in women (OR, 1.40; P = .263) is probably due to the fact that only 36 women in the present study had experienced an MI. Furthermore, the association between MI and the ACE I/D polymorphism was independent of blood pressure, smoking habits, and body mass index.

CONCLUSIONS

Segregation of the ACE I/D polymorphism is a pervasive genetic risk factor for MI in whites but has no evident effect on the events leading to stenosis of the coronary arteries. This suggests that risk of MI is influenced by two independent processes--atherogenesis that leads to coronary stenosis followed by conversion to MI. The renin-angiotensin system appears to confer significant risk of infarction by influencing the conversion to MI but has no apparent effect on the development of atherostenosis.