Effects of titrated beta blockade (metoprolol) on silent myocardial ischemia in ambulatory patients with coronary artery disease

The cardioprotective effect of different doses of vasopressin (AVP) against ischemia-reperfusion injuries in the anesthetized rat heart

The aim of the present study was to investigate the protective effect of various doses of exogenous vasopressin (AVP) against ischemia-reperfusion injury in anesthetized rat heart. Anesthetized rats were randomly divided into seven groups (n=4-13) and all of them subjected to prolonged 30 min regional ischemia and 120 min reperfusion. Group I served as saline control with ischemia, in treatment groups II, III, IV and V, respectively different doses of AVP (0.015, 0.03, 0.06 and 1.2 μg/rat) were infused within 10 min prior to ischemia, in group VI, an AVP-selective V1 receptor antagonist (SR49059, 1mg/kg, i.v.) was administrated prior to effective dose of AVP injection and in group VII, SR49059 (1 mg/kg, i.v.) was only administrated prior to ischemia. Various doses of AVP significantly prevented the decrease in heart rate (HR) at the end of reperfusion compared to their baseline and decreased infarct size, biochemical parameters [LDH (lactate dehydrogenase), CK-MB (creatine kinase-MB) and MDA (malondialdehyde) plasma levels], severity and incidence of ventricular arrhythmia, episodes and duration of ventricular tachycardia (VT) as compared to control group. Blockade of V1 receptors by SR49059 attenuated the cardioprotective effect of AVP on ventricular arrhythmias and biochemical parameters, but partially returned infarct size to control. AVP 0.03 μg/rat was known as effective dose. Our results showed that AVP owns a cardioprotective effect probably via V1 receptors on cardiac myocyte against ischemia/reperfusion injury in rat heart in vivo.

Chronobiology and chronotherapy of ischemic heart disease

The occurrence of the clinical manifestations of ischemic heart disease (IHD)--myocardial ischemia and angina pectoris, acute myocardial infarction, and sudden cardiac death--is unevenly distributed during the 24 h with greater than expected events during the initial hours of the daily activity span and in the late afternoon or early evening. Such temporal patterns result from circadian rhythms in pathophysiological mechanisms plus cyclic environmental stressors that trigger ischemic events. Both the pharmacokinetics (PK) and pharmacodynamics (PD) of many, though not all, anti-ischemic oral nitrate, calcium channel blocker, and beta-adrenoceptor antagonist medications have been shown to be influenced by the circadian time of their administration. The requirement for preventive and therapeutic interventions varies predictably during the 24 h, and thus therapeutic strategies should also be tailored accordingly to optimize outcomes. During the past decade, two first generation calcium channel blocker chronotherapies have been developed, trialed, and marketed in North America for the improved treatment of IHD. Nonetheless, there has been relatively little investigation of the administration-time (circadian rhythm) dependencies of the PK and PD of conventional anti-ischemic medications, and there has been little progress in the development of new generation IHD chronotherapies. Available epidemiologic, pharmacologic, and clinico-therapeutic evidence demonstrates how the chronobiologic approach to IHD can contribute new insight and opportunities to improve drug design and drug delivery to enhance therapeutic outcomes.

Silent myocardial ischaemia: clinical relevance and treatment

Transient myocardial ischaemia in the absence of chest pain ('silent ischaemia') commonly occurs in patients with coronary artery disease (CAD) and has important prognostic implications. However, doubts exist as to whether and how silent ischaemia should be managed. In the present article we review current knowledge regarding silent ischaemia and the role of recently developed drugs that may be effective to control its occurrence. Since the description in the 1770s of the syndrome of 'angina pectoris' by William Heberden, the importance of chest pain for the diagnosis of CAD has remained un-abated. However, several decades ago it became apparent that both myocardial infarctions and transient episodes of myocardial ischaemia could occur in the absence of chest pain. Indeed, a large proportion of patients with CAD have both silent and painful myocardial ischaemia as a manifestation of CAD. Whether the presence of asymptomatic ischaemic electrocardiographic changes in patients with CAD has prognostic importance and whether it needs medical or surgical treatment has been a matter of speculation for several decades.

Contemporary management of silent ischemia: the role of ambulatory monitoring

Silent ischemia is highly prevalent among patients with ischemic heart disease and is associated with a poor prognosis in moderate/high risk outpatients who either exhibit exercise- or pharmacological-induced myocardial ischemia, or in those patients who demonstrate silent ischemia following an acute coronary syndrome. Pharmacotherapy, including beta-blockers, angiotensin-converting enzyme inhibitors, statins, calcium channel antagonists and antiplatelet agents, have all demonstrated a reduction in silent ischemia and an improvement in cardiac prognosis. The management of patients with ischemic heart disease is currently based on patients' report of anginal symptoms: documentation of silent ischemia, usually using ambulatory electrocardiography, is not incorporated into the routine management of coronary artery disease. Yet studies comparing ambulatory electrocardiography with exercise testing have shown these tests to be complementary. We review the evidence concerning the prognostic value of ambulatory electrocardiography for monitoring silent ischemia and the prognostic value of attenuating silent ischemia. Mitigation of silent ischemia improves cardiac prognosis and ambulatory electrocardiographic monitoring before and after treatment of silent ischemia can play a valuable role in the management of coronary artery disease.

Chronobiology of rupture and dissection of aortic aneurysms

A growing body of evidence suggests that the occurrence of cardiovascular events is not evenly distributed over time, but shows peculiar temporal patterns that vary with time of day, day of the week, and month (season) of the year. These patterns coincide with the temporal variation in the pathophysiologic mechanisms that trigger cardiovascular events and the physiologic changes in body rhythms. These two factors in combination contribute to the periodicity in susceptibility to acute cardiovascular events. The classic assumption of epidemiologic studies that there is a constancy in risk for disease during the various time domains has now been challenged by the emerging new concept of chronorisk. In the last two decades temporal patterns (circadian, weekly, seasonal) have been identified for several acute cardiovascular diseases, such as acute myocardial infarction, sudden death, pulmonary embolism, and stroke, with peak incidence for most in the morning and during winter. One of the most life-threatening cardiovascular emergencies, aortic aneurysm rupture or dissection, also demonstrates periodicity, characterized by a similar temporal distribution, which suggests a common pathophysiologic mechanism or triggers similar to other cardiovascular acute emergencies. We review the data on chronobiology of acute aortic rupture or dissection, and discuss various pathophysiologic mechanisms that account for this variability. It is likely that identification of consistent recurring patterns in the underlying risk mechanisms could provide potential new insights for more precise diagnosis and efficacious therapeutic intervention.

Cardiovascular risk and therapeutic intervention for the early morning surge in blood pressure and heart rate

The incidence of most adverse cardiovascular events appears to follow a circadian pattern, reaching a peak in the morning shortly after wakening and arising. The activities of many physiologic parameters, including hemodynamic, hematologic and humoral factors, also fluctuate in a cyclical manner over the 24h. It has been suggested that, during the post-awakening hours, the phases of these cycles synchronize to create an environment that predisposes to atherosclerotic plaque rupture and thrombosis in susceptible individuals, thereby accounting for the heightened cardiovascular risk at this time of day. Blood pressure and heart rate are part of this physiologic process, following a clear circadian rhythm characterized by a fall during sleep and a sharp rise upon awakening. This so-called 'morning surge' in blood pressure may act as a trigger for cardiovascular events, including myocardial infarction and stroke. The clinical implication of these observations is that antihypertensive therapy should provide blood pressure control over the entire interval between doses. For agents taken once daily in the morning, the time of trough plasma drug level (and lowest pharmacodynamic effect) will often coincide with the early morning surge in blood pressure and heart rate. For these reasons, chronotherapeutic formulations of drugs and intrinsically long-acting antihypertensive agents provide the most logical approach to the treatment of hypertensive patients since they provide 24 h blood pressure control from a single daily dose as well as attenuating the early morning rise in blood pressure (and in some instances heart rate).

Sustained reduction of exercise perfusion defect extent and severity with isosorbide mononitrate (Imdur) as demonstrated by means of technetium 99m sestamibi

BACKGROUND

The impact of long-acting nitrates on the extent and severity of stress-induced myocardial ischemia is not well described, especially after long-term treatment.

METHODS

Forty patients with chronic stable angina and reversible ischemia on an exercise stress myocardial perfusion single photon emission computed tomography (ex-SPECT) were prospectively studied in a 6-week period. At baseline, rest thallium-201/exercise stress technetium 99m sestamibi SPECT was performed, followed by treatment with extended-release isosorbide 5-mononitrate (5-ISMN, Imdur). Follow-up ex-SPECT was performed 5 days and 6 weeks after the initiation of therapy with extended-release 5-ISMN. The exercise treadmill testing (ETT) protocol and exercise duration of the follow-up studies were the same as that of the baseline ETT. Defect extent and severity were analyzed both by means of an automated quantitative method, with CEqual software, and visually, with a 20-segment scoring system (which was also used to derive a summed stress score [SSS]).

RESULTS

In the 6-week study period, significant reductions occurred in both the extent and the severity of exercise-induced ischemia by means of quantitative SPECT (13.8% [P<.0003] and 12.7% [P<.0003], respectively). There was no significant change in these variables between stages 2 (day 5) and 3 (6 weeks), indicating no development of tolerance to the nitrate effect. Similar reductions were noted by means of the visual analysis (SSS reduction of 13.0% [P<.002]) in the entire study period.

CONCLUSIONS

Patients with chronic-stable-angina treated with a long-acting nitrate demonstrate improvement in myocardial perfusion defect extent and severity in an extended period by means of both visual and quantitative analysis of sequential exercise testing to the same rate-pressure product end point.

The effect of heart rate control on myocardial ischemia among high-risk patients after vascular surgery

Patients undergoing vascular surgery have a high risk of suffering major postoperative cardiac events. Preoperative myocardial ischemia as detected by Holter monitoring identifies a high-risk subgroup whose postoperative ischemia, similarly detected, seems to herald major cardiac events. In this study, we determined whether systematic, patient-specific postoperative heart rate control with beta-adrenergic blocker therapy decreases the incidence of postoperative ischemia among high-risk vascular surgery patients. A total of 26 of 150 patients who underwent elective vascular surgery and were monitored preoperatively by 24-h Holter were found to have significant myocardial ischemia as defined by ST-segment depression. The minimal heart rate at which this ST-segment depression occurred was identified (ischemic threshold), and these 26 patients were then randomized to receive continuous i.v. beta-blockade with esmolol or placebo plus usual medical therapy, aiming to reduce the postoperative heart rate to 20% below the ischemic threshold. All patients were monitored by Holter for 48 h postoperatively. Postoperative Holter readings were analyzed for the incidence of ischemia and for the number of hours during which heart rate was controlled below the ischemia threshold. Patients had a median of two episodes of preoperative ischemia lasting a median of 30 min (range 1-155 min). A total of 15 patients were randomized to receive esmolol, and 11 were randomized to receive placebo. The two groups were comparable with respect to clinical characteristics and incidence and duration of preoperative ischemia. Ischemia persisted in the postoperative period in 8 of 11 placebo patients (73%), but only 5 of 15 esmolol patients (33%) (P < 0.05). Of the 15 esmolol patients, 9 had mean heart rates below the ischemic threshold, and all 9 had no postoperative ischemia. A total of 4 of 11 placebo patients had mean heart rates below the ischemic threshold, and 3 of the 4 had no postoperative ischemia. There were two postoperative cardiac events among patients who had postoperative ischemia (one placebo, one esmolol) and whose mean heart rates exceeded the ischemic threshold. Our data suggest that patient-specific, strict heart rate control aiming for a predefined target based on individual preoperative ischemic threshold was associated with a significant reduction and frequent elimination of postoperative myocardial ischemia among high-risk patients and provide a rationale for a larger trial to examine this strategy's effect on cardiac risk.

IMPLICATIONS

Patients who undergo peripheral vascular surgery often experience transient cardiac complications and/or permanent heart damage just after surgery because of inadequate myocardial blood flow. In this study, we identified patients at high risk of cardiac complications after vascular surgery and showed that if their heart rate was carefully controlled for 48 h after surgery, myocardial ischemia, a common marker of heart injury, was markedly reduced.

Rationale for the use of calcium antagonists in the treatment of silent myocardial ischemia

Silent myocardial ischemia, whether it occurs at rest or during exercise, is associated with an unfavorable prognosis and may lead to sudden cardiac death. Agents used to treat silent myocardial ischemia have included nitrates, beta-blockers, and calcium antagonists (CAs). Despite treatment with traditional anti-ischemic agents, studies have shown that up to 40% of patients who receive what is considered to be clinically optimal antianginal therapy continue to have daily episodes of silent myocardial ischemia. The use of nitrates and beta-blockers is sometimes confounded by issues of tolerance and tolerability. Although the CAs have been found to be effective in decreasing the duration and frequency of episodes of silent ischemia, in general beta-blockers produce a greater reduction in these variables. Thus a need for effective and tolerable anti-ischemic agents persists. A new class of CAs, the tetralol derivatives, may show promise in this regard. The first of this new class, mibefradil, is characterized by selective blockade of T-type calcium-ion channels and has been shown in a few studies to reduce the frequency and duration of asymptomatic ischemic episodes in patients with stable exertional angina pectoris. Large-scale clinical trials are necessary before the efficacy and tolerability of this new CA can be compared fully with those of the beta-blockers and currently available CAs.

Postinfarction use of beta-blockers in elderly patients

beta-Adrenoceptor antagonists (beta-blockers) reduce mortality and recurrent myocardial infarction (MI) in older patients after both Q-wave MI and non-Q-wave MI. The effects of beta-blockers are to: (i) reduce complex ventricular arrhythmias, including ventricular tachycardia; (ii) increase the ventricular fibrillation threshold; (iii) reduce myocardial ischaemia; (iv) decrease sympathetic tone; (v) markedly attenuate the circadian variation of complex ventricular arrhythmias: (vi) abolish the circadian variation of myocardial ischaemia; and (vii) abolish the circadian variation of sudden cardiac death or MI. beta-Blockers reduce mortality in patients with MI and complex ventricular arrhythmias. In addition, they are excellent antianginal agents. Older persons with hypertension who have had an MI should be treated initially with a beta-blocker. beta-Blockers reduce mortality in patients with: (i) diabetes mellitus who have had an MI; (ii) MI and congestive heart failure with an abnormal or normal left ventricular ejection fraction; and (iii) MI and an asymptomatic abnormal left ventricular ejection fraction. Severe congestive heart failure, severe peripheral arterial disease with threatening gangrene, greater than first degree atrioventricular block, hypotension, bradycardia, lung disease with bronchospasm, and bronchial asthma are contraindications to treatment with beta-blockers.

Relation between ambulatory electrocardiographic monitoring and myocardial perfusion imaging to detect coronary artery disease and myocardial ischemia: an ACIP ancillary study. The Asymptomatic Cardiac Ischemia Pilot (ACIP) Investigators

OBJECTIVES

This study sought to explore the relation between markers of ischemia detected by ambulatory electrocardiographic (AECG) monitoring and stress myocardial perfusion single-photon emission computed tomography (SPECT).

BACKGROUND

Stress myocardial SPECT and AECG monitoring are both utilized in evaluating patients with coronary artery disease. However, information is limited regarding the relation between the presence and extent of ischemia as detected by these two modalities.

METHODS

This was an ancillary study of the Asymptomatic Cardiac Ischemia Pilot (ACIP) trial. One hundred six patients with previous coronary angiography underwent AECG monitoring and stress SPECT within a close temporal time period. The frequency and duration of ischemia as assessed by AECG monitoring and the total and ischemic stress-induced myocardial perfusion defect sizes as assessed by SPECT were quantified in separate core laboratories. Multivariate logistic regression and linear regression analysis were used to determine associations between AECG and SPECT abnormalities with regard to angiographic, demographic and treadmill exercise variables.

RESULTS

Seventy-four percent of patients with significant (> or = 50%) coronary artery stenosis had SPECT abnormalities, whereas 61% had ischemia by AECG monitoring. The most important predictors of SPECT abnormalities were severity (p < 0.001) of coronary artery stenosis, followed by total exercise duration (p = 0.016) and patient age (p = 0.04). The only predictor of AECG abnormalities was the presence of ST segment depression on the initial exercise treadmill test (p = 0.021). Only a 50% concordance for normalcy or abnormalcy was observed between the SPECT and AECG results, and no relation was observed between the frequency or duration of AECG ischemia and the quantified total or ischemic myocardial perfusion defect size as assessed by SPECT.

CONCLUSIONS

Ischemia as detected by AECG monitoring does not correlate with the presence and extent of ischemia as quantified by stress SPECT. Because these techniques appear to detect different pathophysiologic manifestations of ischemia, they may be complementary in more fully defining the functional significance of coronary artery disease and, in particular, which patients are at highest risk for adverse cardiac events.

Comparison between metoprolol orally osmotic once daily and metoprolol two or three times daily in suppressing exercise-induced and daily myocardial ischemia

Metoprolol is a widely used anti-ischemic drug with a relatively short half-life. To improve patient' compliance and to provide 24-hour coverage, its once daily ORally OSmotic (OROS) formulation was developed. In this multicenter double-blind study, the anti-ischemic effects of metoprolol OROS given once daily at doses of 190 and 285 mg were compared to the regular metoprolol formulation of 100 mg 2 or 3 times daily. Sixty-five patients with stable coronary artery disease, positive exercise tests, and ischemic episodes during daily activity as recorded by ambulatory electrocardiographic monitoring (AEM) were included. In the OROS group, 23 patients completed all 3 treatment periods. In these patients, the number of myocardial ischemic episodes decreased from 239 on placebo to 128 during the 190 mg/day dose (p < 0.0001) and to 86 during the 285 mg/day treatment period (p < 0.0001). In the metoprolol group, there were 204 episodes at baseline and 142 and 140 during the 100 mg 2 or 3 times daily treatment periods (p < 0.0001 for both). During exercise testing, time to 1-mm ST depression increased significantly in the OROS group from 6.3 minutes at baseline to 7.1 and 9.6 minutes during 190- and 285-mg treatment periods. In the metoprolol group, it increased from 5.8 to 7.2 and 8.2 minutes, respectively. Both formulations of metoprolol were well tolerated. The OROS formulation was highly effective in suppressing daily and exercise-induced ischemia and exerted its effect throughout the 24-hour period.

Spontaneous changes of heart rate, blood pressure, and ischemia-type ST-segment depressions in patients with hypertension without significant coronary artery disease: beneficial effects of beta-blockade

In hypertensives, a reduced coronary flow reserve is observed and may contribute to angina pectoris and silent (painless) myocardial ischemia, which frequently occur in these patients even in the absence of coronary artery disease (CAD). To assess the frequency of ischemia-type ST-segment depressions in these patients and the influence of heart rate (HR) and blood pressure (BP) as major determinants of myocardial oxygen demand and to test the effects of beta-blocker therapy (10-20 mg betaxolol/day for 4 weeks) on these variables, simultaneous 24-h Holter and 24-h ambulatory BP monitoring was performed in 19 patients with hypertension (age, 43-71 years; nine women, 10 men) without CAD (stenosis < 50% in angiography). Before treatment, 25 periods of significant ST-segment depressions with a total duration of 470 min were observed in nine patients. ST-segment depressions were significantly correlated with preceding increases in HR and the rate-pressure product. The majority (79%) of episodes with ST-segment depression were clinically painless. In this open study, beta-blockade significantly decreased the number of episodes with ST-segment depressions to six in four of 15 patients and the total duration to 38 min (p < 0.05). The data demonstrate that HR seems to be associated with the development of ischemic ST-segment deviations in patients with hypertension without CAD. Antihypertensive therapy in these patients should target not only sufficient BP control, but also reduction of ischemic events.

Hemodynamic changes as triggers of cardiovascular events

Although a large number of clinical studies during the past decade have documented that myocardial ischemia, acute myocardial infarction, and sudden cardiac death have definite circadian patterns, recently published work suggests that it is not necessarily a specific time of the day but the sleep/wake cycle and postural changes as well as the balance between triggers and protective factors that determine the onset of cardiovascular events. A clear understanding of the pathophysiologic processes responsible for ischemic events and the specific roles played by various triggers would be helpful in better defining the therapeutic strategies designed for the prevention and treatment of acute cardiac events. Because changes in hemodynamic parameters are of paramount importance in initiating an ischemic event, it is critical to review their role and relationship in the pathogenesis of acute coronary events.

Comparison of perioperative myocardial protection with nifedipine versus nifedipine and metoprolol in patients undergoing elective coronary artery bypass grafting

A randomized study was performed on 70 patients undergoing elective coronary bypass grafting to examine whether the combined infusion of the calcium channel blocker nifedipine (10 micrograms/kg per hour) and the beta 1-blocker metopropol (12 micrograms/kg per hour, n = 34) reduces the prevalence of perioperative myocardial ischemia and arrhythmias. The control group received nifedipine alone (n = 36). In both groups the infusion was started from the onset of extracorporal circulation and maintained over a period of 24 hours. Repeated 12-lead electrocardiographic and 3-channel Holter monitor recordings for 48 hours were used to define perioperative myocardial ischemia (transient ischemic event, myocardial infarction) and arrhythmias (sinus tachycardia, supraventricular tachycardia, atrial flutter/fibrillation, ventricular tachycardia). Hemodynamic parameters were repeatedly assessed for 24 hours and serum enzyme levels (creatine kinase, MB isoenzyme of creatine kinase) for up to 36 hours after the operation. The two groups did not differ significantly with respect to preoperative anamnestic and surgical data. No signs of perioperative myocardial infarction were detected in either group. However, a significantly lower incidence of transient ischemic episodes was observed in the nifedipine-metoprolol group than in the nifedipine group (3% vs 11%; p < 0.05). In addition, there was a tendency toward lower creatine kinase MB levels and peak values of creatine kinase and creatine kinase MB in the nifedipine-metoprolol group. With regard to perioperative arrhythmias, there was a significantly lower incidence of sinus tachycardia and atrial flutter/fibrillation in the nifedipine-metoprolol group (9% and 6%) than in the nifedipine group (33% and 27%, p < 0.05). In addition, postoperative heart rate was lower in the nifedipine-metoprolol group starting from the sixth hour after release of the aortic crossclamp (p < 0.05 and p < 0.01, respectively). No other hemodynamic parameters showed significant differences between the two groups and all returned to preoperative levels within 24 hours. In conclusion, perioperative application of nifedipine and metoprolol in patients undergoing elective coronary bypass grafting reduces the prevalence of perioperative myocardial ischemia and arrhythmias without significant negative inotropic effects. The combined infusion of the two drugs appears superior to nifedipine alone in preventing perioperative myocardial ischemia and reducing reperfusion-induced arrhythmias.

Contemporary approaches in medical management of patients with stable coronary artery disease

CAD continues to be the principal cause of mortality in the United States, and the largest group of patients with CAD are those with stable angina. Among this group of patients, the most common manifestation of CAD is presence of transient episodes of myocardial ischemia. The presence of transient ischemia and not the severity of angina has been found to be associated with poor clinical outcome in patients with stable CAD. As part of a global treatment strategy for patients with stable CAD, changes in lifestyle and modification of coronary risk factors should be emphasized as an integral part of treatment. Conventional antianginal therapy is quite effective in controlling anginal attacks. Currently, several drugs and therapeutic strategies are available for the treatment of patients with angina (see Table 5). Nitrates are highly effective antianginal drugs with complex beneficial actions in patients with CAD, but their usefulness is limited by development of tolerance during long-term use. When clinically indicated, the use of nitrates should be supplemented with another longer-acting antianginal drug, such as a beta-blocker or a calcium channel blocker. Based on the available data, beta-blockers, when tolerated, seem to be the most effective antianginal drugs for most patients with stable CAD. Beta-blockers are also the most effective anti-ischemic drugs that reduce the magnitude of myocardial ischemia detected during routine daily activities. Calcium channel blockers are also effective vasodilators and good antianginal drugs. The clinician should become familiar with the different actions that this heterogeneous group of drugs has on the heart and vessels. This knowledge allows the clinician to choose the appropriate combination of different antianginal drugs for patients on an individualized basis. It is also critical to develop the treatment strategy by carefully taking into account other associated medical conditions that are frequently encountered in patients with CAD.

Chronobiology and chronotherapy in medicine

There is a fascinating and exceedingly important area of medicine that most of us have not been exposed to at any level of our medical training. This relatively new area is termed chronobiology; that is, how time-related events shape our daily biologic responses and apply to any aspect of medicine with regard to altering pathophysiology and treatment response. For example, normally occurring circadian (daily cycles, approximately 24 hours) events, such as nadirs in epinephrine and cortisol levels that occur in the body around 10 PM to 4 AM and elevated histamine and other mediator levels that occur between midnight and 4 AM, play a major role in the worsening of asthma during the night. In fact, this nocturnal exacerbation occurs in the majority of asthmatic patients. Because all biologic functions, including those of cells, organs, and the entire body, have circadian, ultradian (less than 22 hours), or infradian (greater than 26 hours) rhythms, understanding the pathophysiology and treatment of disease needs to be viewed with these changes in mind. Biologic rhythms are ingrained, and although they can be changed over time by changing the wake-sleep cycle, these alterations occur over days. However, sleep itself can adversely affect the pathophysiology of disease. The non-light/dark influence of biologic rhythms was first described in 1729 by the French astronomer Jean-Jacques de Mairan. Previously, it was presumed that the small red flowers of the plant Kalanchoe bloss feldiuna opened in the day because of the sunlight and closed at night because of the darkness. When de Mairan placed the plant in total darkness, the opening and closing of the flowers still occurred on its intrinsic circadian basis. It is intriguing to think about how the time of day governs the pathophysiology of disease. On awakening in the morning, heart rate and blood pressure briskly increase, as do platelet aggregability and other clotting factors. This can be linked to the acrophase (peak event) of heart attacks. During the afternoon we hit our best mental and physical performance, which explains why most of us state that "I am not a morning person." Even the tolerance for alcohol varies over the 24-hour cycle, with best tolerance around 5 pm (i.e. "Doctor, I only have a couple of highballs before dinner"). Thus, all biologic functions, from those of the cell, the tissue, the organs, and the entire body, run on a cycle of altering activity and function.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Effect of amlodipine, atenolol and their combination on myocardial ischemia during treadmill exercise and ambulatory monitoring. Canadian Amlodipine/Atenolol in Silent Ischemia Study (CASIS) Investigators

OBJECTIVES

This study compared the effects of amlodipine, atenolol and their combination on ischemia during treadmill testing and 48-h ambulatory monitoring.

BACKGROUND

It is not known whether anti-ischemic drugs exert similar effects on ischemia during ambulatory monitoring and exercise treadmill testing.

METHODS

Patients with stable coronary artery disease and ischemia during treadmill testing and ambulatory monitoring were randomized to receive amlodipine (n = 51) or atenolol (n = 49). Each group underwent a counterbalanced, crossover evaluation of single drug and placebo, followed by evaluation of the combination.

RESULTS

Amlodipine and the combination prolonged exercise time to 0.1-mV ST segment depression by 29% and 34%, respectively (p < 0.001) versus 3% for atenolol (p = NS). During ambulatory monitoring, the frequency of ischemic episodes decreased by 28% with amlodipine (p = 0.083 [NS]), by 57% with atenolol (p < 0.001) and by 72% with the combination (p < 0.05 vs. both single drugs; p < 0.001 vs. placebo). Suppression of ischemia during exercise testing and ambulatory monitoring was similar in patients with and without exercise-induced angina. Exercise time to angina improved by 29% with amlodipine (p < 0.01), by 16% with atenolol (p < 0.05) and by 39% with the combination (p < 0.005 vs. placebo, atenolol and amlodipine). In patients with angina, total exercise time improved by 16% with amlodipine (p < 0.001), by 4% with atenolol (p = NS) and by 19% with the combination (p < 0.05 vs. placebo and either single drug). In those patients without angina, no therapy significantly improved total exercise time.

CONCLUSIONS

Ischemia during treadmill testing was more effectively suppressed by amlodipine, whereas ischemia during ambulatory monitoring was more effectively suppressed by atenolol. The combination was more effective than either single drug in both settings.

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.

Intermittent transdermal nitrates do not improve ischemia in patients taking beta-blockers or calcium antagonists: potential role of rebound ischemia during the nitrate-free period

OBJECTIVES

This study was conducted to determine whether rebound ischemia occurs during nitrate-free periods with intermittent cutaneous nitroglycerin therapy in patients with angina pectoris who are receiving background antianginal therapy.

BACKGROUND

Rebound angina has been suggested to be a complication of the nitrate-free period with long-term cutaneous nitroglycerin therapy given intermittently to prevent tolerance.

METHODS

Fifty-two patients with stable effort angina taking either a beta-adrenergic blocking agent (n = 25) or diltiazem (n = 22) or their combination (n = 5) completed a randomized, double-blind, placebo-controlled crossover study of cutaneous nitroglycerin patches (50 mg). Active or placebo patches were worn for 1 week, applied at 8 AM and removed at 10 PM to provide a 10-h daily nitrate-free (or placebo-free) period. During the last 48 h of each study phase, a Holter monitor was used to detect ischemia.

RESULTS

Only 31 patients experienced ischemia during either phase of the study (23 during the patch-off period). A total of 463 ischemic episodes were recorded: 246 during placebo and 217 during nitroglycerin (p = 0.8, for per patient comparison). The majority (88%) of ischemic episodes were silent. Mean (+/- SEM) duration of ischemia during the total 48-h period was similar during active and placebo phases (35.5 +/- 15.0 min/24 h for active therapy vs. 29.7 +/- 9.8 for placebo, p = 0.8). This was due to an increase in duration of ischemia with active therapy during the patch-off period (46.9 +/- 17.9 min/24 h for active therapy vs. 22.5 +/- 9.2 for placebo, p = 0.07) and a decrease during the patch-on period (27.5 +/- 14.0 min/24 h for active therapy vs. 34.5 +/- 11.0 min/24 h for placebo, p = 0.16). The pattern of diurnal distribution of ischemic episodes differed between active and placebo phases. During placebo there was a nadir in the incidence of ischemia in the overnight patch-off period, with a significantly lower incidence between midnight and 6 AM (25 episodes) compared with the mean number of episodes during the three other 6-h periods (73 episodes, p < 0.001). During the nitroglycerin patch-off period, there was a loss of this overnight nadir, with the same incidence of ischemia between midnight and 6 AM (53 episodes) as the mean number of episodes for the three other 6-h periods (54 episodes).

CONCLUSIONS

The majority of patients taking background antianginal therapy experienced no ischemia during the patch-off period. In the 44% of patients with ischemia during this period, there was a nonsignificant increase in the duration of ischemia with active therapy. Although this result was statistically inconclusive, the change in the distribution of diurnal ischemia offers suggestive evidence that rebound ischemia may be a problem with regard to intermittent cutaneous nitroglycerin.

Amlodipine reduces transient myocardial ischemia in patients with coronary artery disease: double-blind Circadian Anti-Ischemia Program in Europe (CAPE Trial)

OBJECTIVES

This study was carried out to determine the effect of the once-daily calcium channel blocking agent amlodipine (half-life 35 to 50 h) on the circadian pattern of myocardial ischemia in patients with chronic stable angina.

BACKGROUND

Myocardial ischemia during normal daily life, both symptomatic and asymptomatic, has been associated with increased risk of cardiovascular morbidity and mortality, and the circadian pattern parallels that for myocardial infarction and sudden death.

METHODS

The Circadian Anti-Ischemia Program in Europe (CAPE) was a large, 10-week international (63 sites), double-blind, parallel study. After a 2-week, single-blind placebo phase, during which stable doses of antianginal treatment were maintained (beta-adrenergic blocking agents in 65% of patients), patients with chronic stable angina with at least three attacks of angina per week, with at least four ischemic episodes or > or = 20 min of ST segment depression in 48 h of Holter monitoring, were randomized to receive treatment with either 5 mg/day of amlodipine or placebo (2:1 randomization). The dose was increased to 10 mg/day after 4 weeks. During week 7 of treatment, 48-h ambulatory ECG monitoring was repeated.

RESULTS

Three hundred fifteen of 1,160 patients screened were eligible, and 250 had complete evaluable data. Compared with placebo, amlodipine significantly reduced both the frequency of ST segment depression episodes (60% for amlodipine vs. 44% for placebo, p = 0.025) and total integrated ST ischemic area (62% mm-min vs. 50% mm-min, p = 0.042). Amlodipine reduced ischemia over the 24 h with the intrinsic circadian pattern maintained. In addition, diary data showed a significant reduction in angina (70% for amlodipine vs. 44% for placebo, p = 0.0001) and in nitroglycerin consumption (67% vs. 22%, respectively, p = 0.0006). Amlodipine and placebo demonstrated similar safety profiles (adverse events 17.3% for amlodipine and 13.3% for placebo; discontinuation rates due to adverse events were 2% vs. 4.4%, respectively).

CONCLUSIONS

Once-daily amlodipine, when added to background treatment, significantly reduced both symptomatic and asymptomatic ischemic events over 24 h in patients with chronic stable angina.

Effect of autonomic nervous system dysfunction on the circadian pattern of myocardial ischemia in diabetes mellitus

OBJECTIVES

The aim of this study was to determine the prevalence and characteristics of ambulatory myocardial ischemia in patients with diabetes mellitus and to delineate the relation between the presence and severity of autonomic nervous system dysfunction and the incidence and time of onset of myocardial ischemia.

BACKGROUND

Conflicting data exist with regard to the circadian pattern of myocardial infarction and other cardiovascular events, such as ambulatory ischemia, in diabetes.

METHODS

We performed ambulatory electrocardiographic monitoring in 60 patients with diabetes and coronary artery disease. Autonomic nervous system testing was performed in a subgroup of 25 patients with myocardial ischemia after discontinuation of all antianginal medications.

RESULTS

Thirty-eight of 60 patients had evidence of ambulatory ischemia; 91% of all ischemic episodes were asymptomatic. The 25 patients with ambulatory ischemia who underwent autonomic nervous system testing had a peak incidence of ischemia between 6 AM and noon (46 of 133 ischemic episodes, p < 0.007), compared with the other three 6-h periods. Fifteen of the 25 patients had no or mild autonomic nervous system dysfunction and demonstrated a similar peak incidence of ischemia between 6 AM and noon (p = 0.0009). However, the 10 patients with moderate to severe autonomic nervous system dysfunction did not experience a morning peak of ischemia, and the number of ischemic episodes was distributed evenly throughout the day (p = 0.4).

CONCLUSIONS

Silent ischemia is highly prevalent among patients with diabetes and coronary artery disease. Time of onset of ischemia in diabetic patients follows a circadian distribution, with a peak incidence in the morning hours. However, patients with significant autonomic nervous system dysfunction did not demonstrate such a peak, suggesting that alterations in sympathovagal balance may have an effect on the circadian pattern of cardiovascular events.

Prognostic significance of silent ischemia

This study examined the prognostic predictors in 521 patients with angiographic evidence of coronary artery disease (CAD). All patients underwent exercise single-photon emission computed tomographic thallium imaging. The patients were divided into those with symptomatic ischemia defined as reversible thallium defects, S-T segment depression (or both) and angina during exercise (n = 210, group 1), and silent ischemia defined as thallium defects or ST segment depression (or both) but no angina during exercise (n = 311, group 2). During a mean follow-up of 24 +/- 21 months, there were 30 cardiac events (death or nonfatal myocardial infarction). The extent of CAD (2.0 +/- 0.8 diseased vessels in group 1 and 2.1 +/- 0.8 diseased vessels in group 2), the left ventricular ejection fraction, the extent of perfusion abnormality (21% +/- 11% in group 1 and 24% +/- 12% in group 2), and the peak heart rate and double product were similar in the two groups. Survival analysis showed no significant difference in the event-free survival in patients with symptomatic or silent ischemia. The 2-year event-free survival rate was 95% in group 1 and 94% in group 2 (difference not significant). The extent of perfusion abnormality and history of diabetes mellitus were the most important predictors of events. Thus the prognosis of medically treated patients with CAD is comparable in those patients with silent or symptomatic ischemia and is dependent on the extent of myocardium at risk rather than presence or absence of angina pectoris during exercise.

Transdermal nitroglycerin patch therapy reduces the extent of exercise-induced myocardial ischemia: results of a double-blind, placebo-controlled trial using quantitative thallium-201 tomography

OBJECTIVES

This study prospectively evaluated whether transdermal nitroglycerin patches could limit the extent of exercise-induced left ventricular ischemia as assessed by quantitative thallium-201 tomography.

BACKGROUND

Although antianginal medications are effective at reducing chest pain symptoms in patients with coronary artery disease, there is limited evidence that these agents can also reduce myocardial ischemia.

METHODS

This was a randomized, double-blind, parallel, placebo-controlled trial evaluating nitroglycerin patch therapy in patients in stable condition with angiographic coronary artery disease and no previous myocardial infarction. All patients were weaned from antianginal agents and had a baseline symptom-limited treadmill test followed by thallium-201 tomography. Forty patients with perfusion defects involving > or = 5% of the left ventricle were randomized to receive either intermittent (12 h on/off) active nitroglycerin patch therapy (0.4 mg/h) or placebo. Exercise tomography was repeated a mean (+/- SD) of 6.1 +/- 1.8 days after randomization.

RESULTS

Patients randomized to receive active patch therapy had a significant reduction in their total perfusion defect size (-8.9 +/- 11.1%) compared with placebo-treated patients (-1.8 +/- 6.1%, p = 0.04), which was most apparent in those with the largest (> or = 20%) baseline perfusion defects (-11.4 +/- 13.4% vs. 1.0 +/- 3.6%, respectively, p < 0.02). Furthermore, 7 (33%) of 21 patients receiving active therapy had a > or = 10% decrease in their perfusion defects compared with only 1 (5%) of 19 patients randomized to receive placebo (p = 0.002). Nitrate therapy did not significantly reduce heart rate, blood pressure or double product, indicating benefit through enhancement of coronary blood flow.

CONCLUSIONS

Short-term, intermittent nitroglycerin patch therapy significantly reduces myocardial ischemia, particularly in patients with large ischemic perfusion defects. Thallium-201 tomography can be used to assess sequential changes in the extent of exercise-induced left ventricular ischemia.

Cardiac prognosis of patients with carotid stenosis and no history of coronary artery disease. Veterans Affairs Cooperative Study Group 167

BACKGROUND AND PURPOSE

Patients with carotid stenosis have a high frequency of asymptomatic coronary artery disease (CAD). The purpose of this study of patients with asymptomatic carotid stenosis was to test the hypothesis that patients without a history of CAD have the same cardiac prognosis as patients with a history of CAD.

METHODS

Men enrolled in the Department of Veterans Affairs study on the efficacy of carotid endarterectomy for asymptomatic carotid stenosis underwent a baseline cardiac evaluation (history, physical examination, and electrocardiogram) to document previous angina or myocardial infarction. Patients were randomized to medical therapy alone or medical therapy and carotid endarterectomy. Medical therapy consisted of aspirin 650 mg twice daily and treatment of risk factors. All episodes of angina, myocardial infarction, or sudden death during follow-up (average of 47.9 months) were recorded.

RESULTS

Of 444 men enrolled in the study, 200 (45%) had a history of CAD. During the study 86 (43%) of 200 patients with CAD and 81 (33%) of 244 patients without a history of CAD had cardiac ischemic events (P = .03). In patients without a history of CAD, the first cardiac event was myocardial infarction or sudden death in 45 patients (56%). Factors that were independently associated with cardiac events in patients without a history of CAD were diabetes (odds ratio [OR], 2.14; 95% confidence interval [CI], 1.15 to 3.97), intracranial occlusive disease (OR, 2.13; 95% CI, 1.13 to 4.02), and peripheral vascular disease (OR, 2.04; 95% CI, 1.14 to 3.66). Forty-two percent of patients with two of these factors and 69% of patients with all three factors had cardiac events.

CONCLUSIONS

Men with carotid stenosis and no history of CAD have a lower rate of cardiac events than men with carotid stenosis who have a history of CAD. However, a subgroup of patients with carotid stenosis and no history of CAD who have coexistent intracranial occlusive disease, diabetes, or peripheral vascular disease have a risk of cardiac events similar to that of patients with a history of CAD.

Silent myocardial ischemia: pathophysiology and perioperative management

Silent ischemia has been called the silent killer. Pain does not kill patients with coronary heart disease--ischemia does, whether it happens to be painful or silent. An increased awareness of this still puzzling phenomenon may be of great importance in the pre- and perioperative management of patients with coronary heart disease, and improved detection and management of silent ischemia are likely to reduce the risk of perioperative cardiac events.

Variability of episodic ST segment depression in chronic stable angina: implications for individual and group trials of therapeutic efficacy

OBJECTIVES

This study was conducted to quantify the variability of episodic ST segment depression in chronic stable angina and enable assessment of the impact of interventions in individual patients and clinical trials.

BACKGROUND

Episodic myocardial ischemia can be detected by ST segment depression on ambulatory electrocardiographic (ECG) monitoring and may be important for the assessment of outcome. Variability of the number and duration of episodes has important implications for monitoring and therapeutic strategies.

METHODS

We studied 36 patients, aged 37 to 77 years (median 60), with stable angina and coronary artery disease by serial ambulatory ECG monitoring for a total of 415 days. A nested analysis of variance was carried out to assess the sources of spontaneous variation, and power function analyses were performed.

RESULTS

During 415 days of monitoring, 1,882 episodes of ST segment depression were detected (mean frequency +/- SD, 4.5 +/- 4.1/day, duration 67 +/- 87 min/day, 25% in association with pain). Considerable variability was found within and between patients for both the number and the duration of ischemic episodes. For a patient monitored for 24 h before and after treatment, an 81% reduction in the number of episodes would be required to show a significant benefit; if monitoring were performed for 4 days four times before and after therapy, a 46% decrease would be significant. In clinical trials, a true reduction of > or = 15% in ischemic episodes is required to have sufficient power to obtain statistical significance.

CONCLUSIONS

The natural variability of transient myocardial ischemia in patients with chronic stable angina can be quantified and this information used to study the effectiveness of interventions in both individual patients and clinical trials.

Usefulness of simultaneous ambulatory electrocardiographic and blood pressure monitoring in detecting myocardial ischemia in patients > 70 years of age with systemic hypertension

Ischemic-type ST-segment depression is frequently observed in younger hypertensive patients. To assess the frequency of ST-segment depression in elderly hypertensive patients and to determine the influence of heart rate (HR) and blood pressure (BP) on the episodes of transient myocardial ischemia, ambulatory electrocardiographic and BP monitoring was simultaneously performed in 41 untreated hypertensive patients > 70 years of age (mean age 79 +/- 6 years; office BP > or = 160/95 mm Hg). A total of 66 episodes of significant ST-segment depression (> or = 0.1 mV, duration > or = 1 minute, interval > or = 1 minute) could be demonstrated in 15 patients (37%); 26 patients (63%) had no ST-segment changes. The 2 groups did not differ in age, gender, office or ambulatory BP, diurnal BP profile, concomitant diseases, ventricular arrhythmias, or in left ventricular (LV) mass or function. In 11 patients with ST-segment depression (73%), an increase in HR of > 15% preceded the episodes of ST-segment depression; 2 of these patients (13%) had an additional increase in BP of > 20/10 mm Hg. The extent of ST-segment depression was correlated significantly to BP, HR and HR x systolic BP product during the ischemic events, to office BP, and to LV mass. In conclusion, transient myocardial ischemia is a frequent phenomenon in elderly hypertensive patients with and without LV hypertrophy. Whereas most episodes of ischemia are preceded by an increase in HR, the extent of ST-segment depression is dependent on HR, BP and LV mass.

Effect of metoprolol and diltiazem on the total ischaemic burden in patients with chronic stable angina: a randomized controlled trial

We conducted a randomised controlled trial to study the effects of metoprolol and diltiazem on the total ischaemic burden--sum of symptomatic and silent myocardial ischaemia, in 146 patients with stable angina pectoris. One-hundred thirty-four completed the study protocol. Sixty-eight patients received metoprolol (100 mg twice daily, n = 52, 50 mg twice daily, n = 16) while 66 received diltiazem (90 mg three times daily, n = 50, 60 mg three times daily, n = 16). The drugs were given for 4 weeks. The primary outcome variables were frequency and duration of total ischaemic burden, silent and symptomatic myocardial ischaemia. These were measured on 48 h of Holter monitoring. The reductions in duration and frequency of total ischaemic burden by metoprolol, 76% and 40%, respectively, were significantly higher than by diltiazem, 43% and 24%, respectively (P < 0.01 and P < 0.02). The frequency and duration of silent myocardial ischaemia, which constituted more than 80% of the total ischaemic burden in the two groups showed similar results. However, the reduction in frequency of symptomatic myocardial ischaemia only was significantly greater by metoprolol (63% than diltiazem (24%) as the difference in reduction of duration of symptomatic ischaemia was insignificant (85% vs. 75%; P > 0.05). Whether a greater reduction of total ischaemic burden by metoprolol as compared to diltiazem has any implications for prognosis in patients with chronic stable angina remains to be established.

Subsets of ambulatory myocardial ischemia based on heart rate activity. Circadian distribution and response to anti-ischemic medication. The Angina and Silent Ischemia Study Group (ASIS)

BACKGROUND

Identification of whether episodes of ambulatory ischemia are caused by increases in myocardial oxygen demand or to episodic coronary vasoconstriction in patients with stable coronary disease may be important to guide selection of optimal anti-ischemic therapy and to gain insight into mechanisms responsible for adverse cardiac events.

METHODS AND RESULTS

Mean minute heart rate activity during ambulatory ECG (AECG) monitoring was determined for 50 patients treated with propranolol, diltiazem, nifedipine, or placebo in a randomized, double-blind, crossover trial. Periods of heart rate increases of various magnitudes and durations and starting at various baseline heart rates on each therapy were identified throughout each 48-hour AECG recording, and the proportion of these periods associated with an ischemic episode was determined. The circadian variation of ischemic episodes categorized by the presence or absence of an increase in heart rate was analyzed. Eighty-one percent of ischemic episodes were preceded by an increase in heart rate > or = 5 beats per minute. The likelihood of developing ischemia associated with a heart rate increase was proportional to the magnitude and duration of the heart rate increase and the baseline heart rate before the increases in heart rate: likelihood ranged from 4% when the heart rate increased 5-9 beats per minute and lasted < 10 minutes to 60% when the heart rate increased > or = 20 beats per minute and lasted > or = 40 minutes. The likelihoods of developing ischemia based on changes in the heart rate variables were similar for each of the therapies. Propranolol therapy significantly reduced the magnitude and duration of heart rate increase and the baseline heart rate compared with therapy with placebo, diltiazem, or nifedipine (P < .001). Ischemic episodes associated with a heart rate increase displayed a daytime peak, whereas ischemia occurring without a heart rate increase occurred evenly throughout the day. Propranolol reduced the proportion of heart rate-related ischemic episodes and increased the proportion of non-heart rate-related episodes compared with placebo (P < .02), and nifedipine exerted the opposite effect (P = .005). Multivariate analysis indicated that the probability of developing ischemia was strongly associated with heart rate variables and was unaffected by time of day.

CONCLUSIONS

Most episodes of ambulatory ischemia are associated with a preceding period of increased heart rate. The likelihood of developing ischemia is predicted by heart rate variables and unaffected by time of day. Anti-ischemic efficacy is generally a result of the medication's efficacy in reducing heart rate variables. A minority of ischemic episodes are not associated with preceding periods of increased heart rate, may be caused by episodic coronary vasoconstriction, and are more effectively reduced by nifedipine than propranolol.

Silent myocardial ischemia

The documentation of abnormalities related to myocardial ischemia, whether symptomatic or silent, is of central importance. Whenever this information is available, it should be used in the overall assessment of the patient at risk for adverse outcome. The level of concern for treatment of CAD should be based on the risk implications associated with the ischemia-related abnormalities detected during objective testing rather than on the presence or absence of pain. The exercise stress test is still the single most useful test to begin the evaluation of a patient with an analyzable ST segment. In persons suspected of having CAD, the detection of ischemic-type ST-segment depression, at a low workload (e.g., < 120 beats/min or < 6.5 METS) of > 2 mm magnitude or persisting for more than 6 min implies high risk for adverse outcome. Asymptomatic ischemia during everyday activities, detected by Holter monitoring, in the high-risk patient, most probably adds additional risk beyond the risk of an abnormal stress test alone. Left ventricular imaging by two-dimensional echocardiography, RNA, angiogram, vest, etc, showing an ejection fraction > or = 40%, reversible wall motion abnormalities in multiple regions and redistribution defects or a failure to increase ejection fraction during exercise even if the patient remains asymptomatic, also imply high risk. The presence of any of these abnormal findings, regardless of symptoms, should therefore prompt as high a degree of concern as with ischemia-related signals associated with pain. Thus any therapy chosen should be directed toward elimination of transient ischemia, not just relief of symptoms that may or may not be ischemia related. If this course is chosen, the efficacy of the therapeutic regimen and possible progression of CAD should be assessed with follow-up testing for ischemia. We believe that risk factor modification and aspirin should be considered for most, if not all, patients in whom ischemia, silent or symptomatic, is suspected or detected. If symptoms or ischemia suggesting low risk is present, anti-ischemic medical therapy may be considered, but follow-up is advised. If a high-risk ischemic signal, even without symptoms, is detected, medical therapy should be used to attempt to modify the signal. If the ischemic signal suggesting high risk persists despite medical therapy, revascularization should be considered. Until additional data from large clinical trials are available, this approach appears to have the greatest likelihood of modifying the adverse outcome of CAD.

Role of increases in heart rate in determining the occurrence and frequency of myocardial ischemia during daily life in patients with stable coronary artery disease

OBJECTIVES

The goal of this study was to investigate the role of increases in heart rate in the development of ischemic episodes recorded during ambulatory electrocardiographic (ECG) monitoring in patients with stable coronary artery disease and to establish the importance of such increases in determining the frequency of ambulatory myocardial ischemia.

BACKGROUND

The factors that determine the occurrence and frequency of episodes of myocardial ischemia that patients with stable coronary artery disease experience during daily life have not been clearly defined. In particular, the role of increases in heart rate in the development of myocardial ischemia is controversial.

METHODS

To address these issues, 54 patients (42 men and 12 women, mean age 60.5 +/- 8 years) with proved coronary artery disease who had > or = 1 mm ST segment depression during exercise testing underwent an exercise treadmill test with use of the National Institutes of Health combined protocol and a 48-h period of ambulatory ECG monitoring. The exercise ischemic threshold was determined as the heart rate at the onset of ST segment depression during exercise testing.

RESULTS

During monitoring, 48 (89%) of the 54 patients had at least one episode of ST segment depression (mean +/- SD 6.6 +/- 5 episodes, range 0 to 22). The majority (320 of 359 or 89%) of ischemic episodes were preceded by an increase in heart rate > or = 10 beats/min; the most significant increase (22.3 +/- 10 beats/min) occurred during the 5-min period before the onset of the episode. An ischemic episode occurred 80% of the times the heart rate reached the exercise ischemic threshold. A strong correlation was observed between the number of times the exercise ischemic threshold was reached during monitoring and both the number and the duration of ischemic episodes (r = 0.90 and 0.71, respectively, p < 0.0001).

CONCLUSIONS

Increases in heart rate that exceed the exercise ischemic threshold are commonly observed before the onset of episodes of ambulatory myocardial ischemia in patients with stable coronary artery disease. Moreover, such increases constitute an important determinant of the frequency of myocardial ischemia during daily life. These findings may explain the variability observed in the number of ischemic episodes and may have important implications for the mechanisms that contribute to myocardial ischemia in daily life and for the clinical evaluation of patients with coronary artery disease.

Treatment strategies for daily life silent myocardial ischemia: A correlation with potential pathogenic mechanisms

Recent investigations of SMI occurring during daily life have advanced our understanding of the pathophysiology of myocardial ischemia. These contributions have directed our attention away from "chest pain" alone and physical exertion as the central provoking factor toward transient myocardial ischemia and its broader triggers and consequences. Transient myocardial ischemic episodes, the majority of which are silent, are found in a subset of patients with any clinical manifestations of CAD (eg, stable angina, unstable angina, myocardial infarction, and sudden death), as well as in those patients with CAD who are and have been totally asymptomatic. These episodes are an independent predictor of increased risk for future cardiac events. Most medical therapy and revascularization therapies have the potential to prevent or relieve these silent episodes; however, we do not yet know which method is superior in reducing SMI episodes or preventing future cardiac events. Furthermore, the benefit of reducing SMI versus the cost and potential morbidity of these chosen therapies is not known. At least three trials are now underway to examine some of these concerns (Table 2). Focus on pain relief alone does not appear to be an adequate approach to alter outcome in patients with CAD and may prove insufficient to control SMI. Until these issues are resolved, we believe a conservative approach to the management of patients with CAD is warranted. Documentation of ischemia (painful or painless) is essential. Three general principles should be kept in mind. First, the presence of detectable ischemia is of central importance. This information should be used in the overall risk assessment of the patient. Second, the level of concern or aggressiveness of treatment should be based on the risk associated with the ischemic abnormalities documented (Table 3). The exercise stress test is the most useful to begin this process. The detection of ischemic-type ST-segment depression, either silent or painful, at a low workload (eg, less than or equal to 120 beats per minute or less than or equal to 6.5 metabolic equivalents [METS]) implies high risk for adverse outcome. Likewise, these ST-segment changes occurring in leads that reflect multiple coronary artery distribution, of greater than 2 mm in magnitude and persisting for greater than 6 minutes, are all markers for high risk. Thallium redistribution defects occurring at low work loads, in multiple areas, associated with increased lung uptake and enlargement of the cardiac pool all imply high risk.(ABSTRACT TRUNCATED AT 400 WORDS)

The total ischemic burden European trial (TIBET): design, methodology, and management. The TIBET Study Group

TIBET is a European multicenter, double-blind parallel group trial with the main objective of investigating whether total ischemic burden has important prognostic implications in patients with stable angina on treatment. A secondary objective is to compare the antianginal and antiischemic effects of atenolol (50 mg bid), nifedipine (20-40 mg bid), and their combination using standardized exercise testing and Holter monitoring techniques. The main primary end points are cardiovascular morbidity and mortality. The secondary end points are time to onset of significant ischemia, angina on exercise stress testing, exercise capacity at onset of angina, 1-mm ST-segment depression and termination of exercise, total duration and number of significant ischemic episodes during 48 hours of Holter monitoring, and their circadian distribution. The target population, the assessments, and the management of the trial are described in detail.