Effects of A1 adenosine receptor agonism using N6-cyclohexyl-2'-O-methyladenosine in patients with left ventricular dysfunction

BACKGROUND

The role of adenosine as a neuromodulator in heart failure was studied with the use of a selective adenosine A1 receptor agonist, N6-cyclohexyl-2'-O-methyladenosine (SDZ-WAG 994).

METHODS AND RESULTS

Fifty patients with heart failure symptoms and moderate left ventricular systolic dysfunction had a balloon flotation catheter inserted. Patients received placebo or a single oral dose of either 1, 2, or 5 mg SDZ-WAG 994. After baseline measurements were obtained, hemodynamic and electrophysiological recordings were repeated at 30-minute intervals for the next 4 hours, then every 6 hours for the next 24 hours. Blood samples for norepinephrine, epinephrine, aldosterone, atrial natriuretic peptide, and plasma renin activity were drawn at baseline and 2 hours after drug administration. A adenosine receptor agonism produced no important effects on systemic, right atrial, pulmonary artery, or pulmonary capillary wedge pressures; cardiac index; respiratory rate; or heart rate. The PR interval (a reflection of A1 receptor-mediated activity) increased significantly in a stepwise fashion. At the 5-mg dose of SDZ-WAG 994, significant increases in atrial natriuretic peptide (216 +/- 137 to 407 +/- 146 pg/mL) and norepinephrine (477 +/- 243 to 618 +/- 237 pg/mL) levels were noted.

CONCLUSIONS

A1 adenosine receptor agonism with SDZ-WAG 994 resulted in no significant hemodynamic changes at rest in this subset of patients with left ventricular dysfunction. An increase in the PR interval and atrial natriuretic peptide level, consistent with adenosine A1 receptor-mediated activity, was observed. In addition, an increase in the norepinephrine level was observed, suggesting a role for adenosine as a peripheral nervous system neuromodulator.

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.

What does it mean to improve prognosis of patients with coronary artery disease?

When improvement in prognosis of patients with coronary artery disease is the goal, the physician must be knowledgeable about the patient-related factors and the fact that therapies influence prognosis in such patients. Further, the clinician must be very specific in choice of therapeutic agents directed toward improvement of prognosis, and this process must include prescriptions of appropriate formulation and dosage.

Relation of patient characteristics to cardiac ischemia during daily life activity (an Asymptomatic Cardiac Ischemia Pilot Data Bank Study)

Cardiac ischemia during daily life activities, detected by ambulatory electrocardiographic (AECG) monitoring has been associated with increased risk for adverse outcomes. Because daily life ischemia is usually asymptomatic, prevalence and descriptive data of patients with asymptomatic cardiac ischemia (ACI) are not well defined. Accordingly, patients screened for the Asymptomatic Cardiac Ischemia Pilot (ACIP) trial by 48-hour AECG monitoring were investigated to identify factors associated with ACI. A total of 1,820 patients with ischemia on a screening stress test and/or known or suspected coronary artery disease underwent AECG monitoring. Their mean age was 61 years, range 33 to 89; 83% were men and 81% were white. On AECG monitoring, ACI occurred in 897 patients (49%). There was a modest trend (p = 0.04) between increasing age and ACI prevalence. Increased risk for ACI was observed in patients reporting angina 6 weeks before screening (odds ratio 1.38, 99% confidence interval 1.08 to 1.77, p = 0.0008). There was a positive association between increases in heart rate during daily life and ACI prevalence (p < 0.0001). No daily, monthly, or seasonal variation in ACI prevalence was found, although ACI was more prevalent in northern than southern sites. In this group of clinically stable patients, selected on the basis of high risk for coronary artery disease, the prevalence of ACI was higher than expected from previous reports. Several readily available clinical characteristics (i.e., advanced age, recent angina, increased heart rate change with daily activity) were associated with significantly increased probability of ACI.

Comparison of subgroups assigned to medical regimens used to suppress cardiac ischemia (the Asymptomatic Cardiac Ischemia Pilot [ACIP] Study)

This report focuses on the subset of 235 patients from the Asymptomatic Cardiac Ischemia Pilot (ACIP) study receiving randomly assigned medical therapy to treat angina and suppress ischemia detected on ambulatory electrocardiography: 121 patients received the sequence of atenolol and nifedipine, and 114 diltiazem and isosorbide dinitrate. After 12 weeks of therapy, the primary end point (absence of ambulatory electrocardiographic (ECG) ischemia and no clinical events) was reached in 47% of atenolol/nifedipine- versus 31% of diltiazem/isosorbide dinitrate-treated patients (adjusted p = 0.03). A trend to increased exercise time to ST depression was seen in the atenolol and nifedipine versus diltiazem and isosorbide dinitrate regimens (median treadmill duration 5.8 vs 4.8 minutes; p = 0.04). However, when adjusted for baseline imbalances in ambulatory ECG ischemia, the 2 medical combinations were similar in suppression of ambulatory ECG ischemia. In both medication regimens, an association between mean heart rate and ischemia on ambulatory electrocardiography after 12 weeks of treatment was observed so that patients on either regimen with a mean heart rate > 80 beats/min had ischemia detectable almost twice as often as those with a mean heart rate < 70 beats/min (p < 0.001).

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.

Circadian variation in coronary tone in patients with stable angina. Protective role of the endothelium

BACKGROUND

Coronary endothelium plays a key role in the regulation of coronary tone, platelet adhesion, and aggregation, which are important factors in triggering acute cardiovascular events. However, its role in modulating the effects of circadian variations on coronary tone is not known.

METHODS AND RESULTS

Responses of 72 nonstenotic coronary segments to acetylcholine and nitroglycerin were measured in 12 patients with chronic stable angina at 6 AM and 1 PM. After baseline angiography, three infusions of acetylcholine (10(-6), 10(-5), and 10(-4) mol/L) were administered selectively into the left coronary artery, followed by nitroglycerin. Diameters (in millimeters) of proximal, middle, and distal segments were measured by quantitative techniques. Forty-seven segments showed a constrictor response to acetylcholine (group 1, dysfunctional endothelium), and 25 other segments showed a dilator response (group 2, normally functioning endothelium). In group 1, the constrictor response to acetylcholine was significantly greater in the morning than in the afternoon (23 +/- 3% and 10 +/- 1%, mean +/- SEM, respectively; P < .001), and the dilator response to nitroglycerin was also significantly greater in the morning than in the afternoon (19 +/- 2% and 11 +/- 2%; P < .01). In group 2, the dilator response to acetylcholine did not differ significantly between the morning and afternoon (22 +/- 3% and 17 +/- 2%, respectively; P = NS), and the dilator response to nitroglycerin was also similar at both times of the day (30 +/- 3% and 28 +/- 4%, respectively; P = NS).

CONCLUSIONS

Coronary segments with dysfunctional endothelium exhibit an early morning exaggeration in vasomotor activity, whereas segments with normally functioning endothelium do not show circadian variations. This suggests a potential protective role for the endothelium in modulating variations in coronary tone that may contribute to increased incidence of cardiovascular events in the early morning hours.

Effect of calcium antagonists in variant or Prinzmetal angina

Variant angina, first described by Prinzmetal in 1959, is a syndrome of recurrent ischemic-type chest pain that occurs at rest and is associated with ST segment elevation. The syndrome has been convincingly demonstrated to be caused by temporary occlusion at a site of local spasm. The objectives of this article are to review treatment of the patient with variant angina and to address the important role of calcium antagonists.

Asymptomatic Cardiac Ischemia Pilot (ACIP) Study. Improvement of cardiac ischemia at 1 year after PTCA and CABG

BACKGROUND

Cardiac ischemia on the ambulatory ECG (AECG) and/or on the exercise treadmill test (ETT) is associated with an increased risk of adverse outcome. Myocardial revascularization more often suppresses cardiac ischemia than does medical management alone. However, few studies have compared the effects of percutaneous transluminal coronary angioplasty (PTCA) with those of coronary artery bypass grafting (CABG) on cardiac ischemia and clinical outcome.

METHODS AND RESULTS

A total of 558 patients were randomly assigned to one of three treatment strategies in the Asymptomatic Cardiac Ischemia Pilot (ACIP) study: angina-guided medical strategy (n = 184), ischemia-guided medical strategy (n = 182), or revascularization (n = 192). In patients assigned to revascularization, the choice of the procedure, PTCA or CABG, was made by the clinical unit staff and patient based on a coronary angiogram usually performed within 2 months of enrollment. CABG was selected in 78 patients and PTCA in 92 patients. At 12 weeks, ischemia on the AECG was suppressed in 70% of CABG patients versus 46% of PTCA patients (P = .002). Ischemia on the ETT was no longer present in 46% versus 23% of the patients, respectively (P = .005). Angina, within 4 weeks of the follow-up visit, was absent in 90% versus 68%, respectively (P = .001). These clinical variables remained improved in both groups at 1 year. Clinical events (myocardial infarction or repeat revascularization) occurred in 1 CABG patient versus 7 PTCA patients at 12 weeks, and in 1 versus 16 patients, respectively, at 12 months (P < .001).

CONCLUSIONS

Ischemia on the AECG and ETT and angina were relieved in many patients after both procedures; however, CABG was superior to PTCA, and it was associated with a lower incidence of clinical events at 1 year. These results suggest that more complete revascularization relates to better clinical outcome. However, a large trial is needed to confirm these results.

Asymptomatic Cardiac Ischemia Pilot (ACIP) study: impact of anti-ischemia therapy on 12-week rest electrocardiogram and exercise test outcomes. The ACIP Investigators

OBJECTIVES

This report from the Asymptomatic Cardiac Ischemia Pilot (ACIP) study examines differences in the magnitude of reduction of myocardial ischemia as determined by exercise treadmill testing in patients randomized to three different treatment strategies: angina-guided medical therapy, ischemia-guided medical therapy and coronary revascularization.

BACKGROUND

No prospective randomized clinical trials in patients with exercise electrocardiographic (ECG) abnormalities and asymptomatic cardiac ischemia on ambulatory ECG monitoring have compared the impact of different treatment strategies, including coronary revascularization, in terms of reducing myocardial ischemia.

METHODS

The ACIP exercise protocol was used. Exercise variables measured included final exercise stage; presence of exercise-induced angina or ischemia; time to angina; time to 1-mm ST segment depression; number of exercise ECG leads with abnormalities; maximal depth of ST segment depression in any lead; sum of ST segment depression; ST/HR index; and rate-pressure product at time to angina, at time to 1-mm ST segment depression and at peak exertion.

RESULTS

Peak exercise time was increased by 0.5, 0.7 and 1.6 min in patients assigned to the angina-guided, ischemia-guided and coronary revascularization strategies, respectively, from the qualifying visit to the 12-week visit (p < 0.001). At the qualifying visit, the sum of exercise-induced ST segment depression was 9.4 +/- 5.0 (mean +/- SD), 9.6 +/- 4.7 and 9.9 +/- 5.5 mm (p = NS) in the three treatment strategies, respectively. At the 12-week visit, the sum of exercise-induced ST segment depression was 7.4 +/- 5.7, 6.8 +/- 5.3 and 5.6 +/- 5.6 mm (p = 0.02) in the three treatment strategies, respectively. Each treatment strategy resulted in a significant reduction in all exercise-induced variables of myocardial ischemia measured at 12 weeks.

CONCLUSIONS

Coronary revascularization significantly reduced the extent and frequency of exercise-induced myocardial ischemia compared with either medical strategy. The prognostic impact of these observations should be evaluated in a large-scale multicenter clinical trial.

Asymptomatic Cardiac Ischemia Pilot (ACIP) study: effects of coronary angioplasty and coronary artery bypass graft surgery on recurrent angina and ischemia. The ACIP investigators

OBJECTIVES

The Asymptomatic Cardiac Ischemia Pilot (ACIP) study showed that revascularization is more effective than medical therapy in suppressing cardiac ischemia at 12 weeks. This report compares the relative efficacy of coronary angioplasty or coronary artery bypass graft surgery in suppressing ambulatory electrocardiographic (ECG) and treadmill exercise cardiac ischemia between 2 and 3 months after revascularization in the ACIP study.

BACKGROUND

Previous studies have shown that coronary angioplasty and bypass surgery relieve angina early after the procedure in a high proportion of selected patients. However, alleviation of ischemia on the ambulatory ECG and treadmill exercise test have not been adequately studied prospectively after revascularization.

METHODS

In patients randomly assigned to revascularization in the ACIP study, the choice of coronary angioplasty or bypass surgery was made by the clinical unit staff and the patient.

RESULTS

Patients assigned to bypass surgery (n = 78) had more severe coronary disease (p = 0.001) and more ischemic episodes (p = 0.01) at baseline than those assigned to angioplasty (n = 92). Ambulatory ECG ischemia was no longer present 8 weeks after revascularization (12 weeks after enrollment) in 70% of the bypass surgery group versus 46% of the angioplasty group (p = 0.002). ST segment depression on the exercise ECG was no longer present in 46% of the bypass surgery group versus 23% of the angioplasty group (p = 0.005). Total exercise time in minutes on the treadmill exercise test increased by 2.4 min after bypass surgery and by 1.4 min after angioplasty (p = 0.02). Only 10% of the bypass surgery group versus 32% of the angioplasty group still reported angina in the 4 weeks before the 12-week visit (p = 0.001).

CONCLUSIONS

Angina and ambulatory ECG ischemia are relieved in a high proportion of patients early after revascularization. However, ischemia can still be induced on the treadmill exercise test, albeit at higher levels of exercise, in many patients. Bypass surgery was superior to coronary angioplasty in suppressing cardiac ischemia despite the finding that patients who underwent bypass surgery had more severe coronary artery disease.

Addition of zatebradine, a direct sinus node inhibitor, provides no greater exercise tolerance benefit in patients with angina taking extended-release nifedipine: results of a multicenter, randomized, double-blind, placebo-controlled, parallel-group study. The Zatebradine Study Group

OBJECTIVES

We examined the antianginal and anti-ischemic effects of oral zatebradine, a direct sinus node inhibitor that has no blood pressure-lowering or negative inotropic effects in patients with chronic stable angina pectoris taking extended-release nifedipine.

BACKGROUND

Heart rate reduction is considered an important pharmacologic mechanism for providing anginal pain relief and anti-ischemic action in patients with chronic stable angina, suggesting a benefit for sinus node-inhibiting drugs.

METHODS

In a single-blind placebo run-in, randomized double-blind, placebo-controlled, multicenter study, patients already receiving extended-release nifedipine (30 to 90 mg once a day) were randomized to receive zatebradine (5 mg twice a day [n = 64]) or placebo (n = 60). All subjects had reproducible treadmill exercise-induced angina at baseline, and after randomization they performed a serial exercise test 3 h after each dose for 4 weeks.

RESULTS

Zatebradine reduced rest heart rate both at 4 weeks ([mean +/- SEM] 12.9 +/- 1.23 vs. 2.3 +/- 1.6 [placebo] beats/min, p < 0.0001) and at the end of comparable stages of Bruce exercise (16.7 +/- 1.2 vs. 3.4 +/- 1.2 [placebo] beats/min, p < 0.0001). Despite the significant effects on heart rate at rest and exercise, there were no additional benefits of zatebradine from placebo baseline in measurements of total exercise duration, time to 1-mm ST segment depression or time to onset of angina. Subjects taking zatebradine also had more visual disturbances as adverse reactions.

CONCLUSIONS

Zatebradine seems to provide no additional antianginal benefit to patients already receiving nifedipine, and it raises questions regarding the benefit of heart rate reduction alone as an antianginal approach to patients with chronic stable angina.

The role of calcium antagonists in ischaemic heart disease

Calcium antagonists are well accepted in the prevention of ischaemia in patients with chronic stable angina, unstable angina, variant angina, and silent ischaemia, and in the treatment of hypertension. Although all of these compounds increase myocardial oxygen supply by reducing coronary tone and decrease myocardial oxygen demand by reducing systolic pressure and myocardial contractility, the magnitude of these effects may differ from one agent to another. Some calcium antagonists, such as verapamil and diltiazem, reduce heart rate and attenuate heart rate increases in response to stress, while in contrast, dihydropyridine calcium antagonists such as nifedipine may cause reflex increases in heart rate. These differences may be of importance in light of epidemiologic evidence that lower heart rates are associated with a reduced long-term risk of cardiovascular mortality, and experimental data showing that a lower heart rate may protect against the development of atherosclerosis. Calcium antagonists also inhibit platelet aggregation and thrombus formation which may contribute to their anti-ischaemic effects. Clinical trial data suggest that calcium antagonists may stay the progression of atherosclerosis. Mechanisms underlying an anti-atherosclerotic effect may include attenuation of endothelial dysfunction, prevention of LDL, peroxidation, stimulation of LDL receptor activity, inhibition of superoxide radical generation, and inhibition of vascular smooth muscle cell growth. Heart-rate-controlling calcium antagonists, such as verapamil and diltiazem, may reduce reinfarction rates following acute myocardial infarction and thus may have a role in post-infarction patients who do not show evidence of heart failure. Their use in heart failure patients receiving an angiotension-converting enzyme inhibitor (ACE-I) is under investigation in several large trials. Because calcium antagonists have a mechanism of action different from ACE-I, the pairing of a heart-rate-controlling calcium antagonist with an ACE-I might be expected to offer additive cardioprotective and vascular protective effects.

Time-series analysis of long-term ambulatory myocardial ischemia: effects of beta-adrenergic and calcium channel blockade

We have previously demonstrated the utility of time-series analysis applied to 72-hour ambulatory electrocardiographic data in patients with coronary artery disease. The present investigation applied time-series analysis to long-term (120-hour) ambulatory electrocardiographic data to determine the minimal period of monitoring needed (1) to detect periodicity of ischemia-related variables in ambulatory patients, (2) to describe auto-correlation and cross-correlation functions for heart rate and ischemia, and (3) to describe the effects of beta-adrenergic and calcium channel blockade on circadian characteristics and coupling of heart rate and ischemia. A double-blind crossover design was used to obtain 120-hour recordings during placebo, atenolol (200 mg/day), and diltiazem (360 mg/day) administration. During all three treatment periods, distinct circadian variation of heart rate was documented by autocorrelation and Fourier analysis. Ischemia did not exhibit clear periodicity as indexed by autocorrelation in any period; however, it was coupled to heart rate in all treatment periods as reflected in cross-correlation analysis. Although diltiazem did not quantitatively alter the circadian characteristics of heart rate or ischemia, atenolol produced a shift in the coupling between remaining ischemia and heart rate in time. Significant autocorrelation was detected for all treatment periods after 72 hours of monitoring, suggesting that 72 hours is the minimum amount of time needed for analysis of ambulatory electrocardiographic data in patients with coronary artery disease.

Daily life cardiac ischaemia. Should it be treated?

Daily life cardiac ischaemia is defined as reversible myocardial cellular hypoxia that occurs during activities of daily living, without artificial provocation. Most of these daily life ischaemic episodes are not associated with symptoms. However, it is not practical to distinguish silent versus symptomatic daily life ischaemia as both are associated with haemodynamic abnormalities and future adverse outcomes. Daily life cardiac ischaemia is best detected using ambulatory electrocardiogram (ECG) monitoring; however, there are other diagnostic tools (e.g. exercise treadmill) that can be used. Once detected, the optimal therapy for daily life myocardial ischaemia has yet to be identified. However, it does appear that usual antianginal medications including nitrates, beta-blockers, calcium antagonists and antiplatelet drugs are effective in reducing the incidence and severity of daily life myocardial ischaemia. Medical therapy and revascularisation should be utilised to obliterate all episodes of daily life cardiac ischaemia to prevent future cardiac events. Moreover, the efficacy of the chosen therapeutic regimen for each patient should be documented with follow-up objective testing. The diagnosis and management of daily life myocardial ischaemia is continually evolving. Future research as well as economic considerations will shape future management strategies.

Asymptomatic cardiac ischemia pilot (ACIP)

This pilot study demonstrated that (1) patients with CAD and asymptomatic cardiac ischemia can be randomized to medical or revascularization strategies using a complex and demanding protocol, (2) asymptomatic cardiac ischemia can be suppressed in 40-50% of patients with clinically advanced coronary disease with relatively low to moderate doses of medication titrated over a period of 12 weeks (3). Revascularization was the most effective of the treatment strategies studied in reducing ischemia. Any type of therapy, whether it be drugs or revascularization requiring repetitive monitoring with ambulatory ECG or other methods to detect ischemia over a long period of time, will escalate the cost of quality medical care for our patients. Thus, the health care costs implications and treatment of asymptomatic ischemia are enormous. But the apparent cost advantage of treating only symptoms, that is ignoring all ischemia, could disappear if treatment of ischemia reduces the risk of adverse events. The clinical question to be addressed in the future is what is necessary to reduce the cardiac-event rates of death and myocardial infarction in this group of patients? Will more aggressive drug therapy eliminate more ischemia and will therapy directed at the elimination of all detectable ischemia improved clinical outcome better than therapy directed to control angina only? These questions can only be answered by a large clinical trial. The results of such a trial will provide the basis and rationale for safe and effective therapy for patients with coronary disease and evidence of cardiac ischemia. Whatever the answer to this important medical and scientific question is, it will have tremendous economic implications.(ABSTRACT TRUNCATED AT 250 WORDS)