Silent myocardial ischemia as a potential link between lack of premonitoring symptoms and increased risk of cardiac arrest during physical stress

Antagonism of the TRPv1 receptor partially corrects muscle metaboreflex overactivity in spontaneously hypertensive rats

The circulatory response to exercise is exaggerated in hypertension potentially increasing the risk for adverse cardiovascular events. Evidence suggests the skeletal muscle metaboreflex contributes to this abnormal circulatory response. However, as the sensitivity of this reflex has been reported to be both reduced and potentiated in hypertension, its role remains controversial. In addition, the receptor mechanisms underlying muscle metaboreflex dysfunction in this disease remain undetermined. To address these issues, metaboreflex activity was assessed during 'supra-stimulation' of the reflex via ischaemic hindlimb muscle contraction. This manoeuvre evoked significantly larger increases in mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) in spontaneously hypertensive rats (SHR) compared to normotensive Wistar-Kyoto (WKY) rats. The skeletal muscle TRPv1 receptor was evaluated as a potential mediator of this metaboreflex response as it has been shown to contribute significantly to muscle reflex activation in healthy animals. Stimulation of the TRPv1 receptor by injection of capsaicin into the arterial supply of the hindlimb evoked significantly larger elevations in MAP and RSNA in SHR compared to WKY. The pressor and sympathetic responses to ischaemic muscle contraction in WKY and SHR were attenuated by the administration of the TRPv1 receptor antagonist capsazepine with the magnitude of the capsazepine-induced reductions being greater in SHR than WKY. TRPv1 protein expression in dorsal root ganglia, but not skeletal muscle, was significantly greater in SHR than WKY. The results suggest the muscle metaboreflex is overactive in hypertension. Further, this reflex overactivity can be partially normalized by antagonizing TRPv1 receptors in skeletal muscle.

The blood pressure response of older men to maximum and sub-maximum strength testing

Strength testing is commonly used to determine the muscular strength of older individuals participating in a resistance training program. The purpose of this study was to non-invasively examine and compare the blood pressure (BP) and heart rate (HR) response of maximum and sub-maximum strength tests in older men. Twenty-four healthy men aged 70-80 yr were recruited for the study. Participants completed a 1 repetition maximum (RM) strength test and four days later a sub-maximum strength test on an incline squat. Systolic blood pressure (SBP), diastolic blood pressure (DBP) and HR were measured by plethysmography during and immediately after the strength tests. SBP, DBP and HR were (P<0.001) higher during the 1RM and sub-maximum strength tests compared to resting values. Twenty seconds post 1RM, SBP and HR were higher than resting values. Twenty seconds post sub-maximum strength testing SBP and DBP were lower (P<0.02) and HR (P<0.001) was higher than resting values. SBP, DBP and HR were higher (P<0.001) during sub-maximum strength testing compared to 1RM testing. Twenty seconds post testing, SBP and DBP were lower (P<0.001) and HR was higher (P<0.001) for the sub-maximum strength tests compared to the 1RM. The results of our study demonstrate that sub-maximum strength testing resulted in greater changes in BP and HR compared to 1RM strength testing. The lower cardiovascular stress experienced during the 1RM shows that this may be a safer method of testing compared to sub-maximum strength testing in men aged 70-80 yr.

Skeletal muscle reflex-mediated changes in sympathetic nerve activity are abnormal in spontaneously hypertensive rats

In hypertension, the blood pressure response to exercise is exaggerated. We demonstrated previously that this heightened pressor response to physical activity is mediated by an overactive skeletal muscle exercise pressor reflex (EPR), with important contributions from its metaboreflex and mechanoreflex components. However, the mechanisms driving the abnormal blood pressure response to EPR activation are largely unknown. Recent evidence in humans suggests that the muscle metaboreflex partially mediates the enhanced EPR-induced pressor response via abnormally large changes in sympathetic nerve activity (SNA). Whether the muscle mechanoreflex induces similarly exaggerated alterations in SNA in hypertension remains unknown, as does the role of the mechanoreceptors mediating muscle reflex activity. To address these issues, the EPR was selectively activated by electrically inducing hindlimb muscle contraction in decerebrate normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Stimulation of the EPR evoked significantly larger increases in mean arterial pressure (MAP) and renal SNA (RSNA) in SHR compared with WKY (ΔRSNA from baseline: 140 ± 11 vs. 48 ± 8%). The mechanoreflex was stimulated by stretching hindlimb muscle which likewise elicited significantly greater elevations in MAP and RSNA in SHR than WKY (ΔRSNA from baseline: 105 ± 11 vs. 35 ± 7%). Blockade of mechanoreceptors in muscle with gadolinium significantly attenuated the MAP and RSNA responses to contraction and stretch in SHR. These data suggest that 1) the exaggerated pressor response to activation of the EPR and muscle mechanoreflex in hypertension is mediated by abnormally large reflex-induced augmentations in SNA and 2) this accentuated sympathetic responsiveness is evoked, in part, by stimulation of muscle mechanoreceptors.

Exaggerated sympathetic and pressor responses to handgrip exercise in older hypertensive humans: role of the muscle metaboreflex

Recent animal studies have reported that exercise pressor reflex (EPR)-mediated increases in blood pressure are exaggerated in hypertensive (HTN) rodents. Whether these findings can be extended to human hypertension remains unclear. Mean arterial pressure (MAP), muscle sympathetic nerve activity (MSNA), and venous metabolites were measured in normotensive (NTN; n = 23; 60 ± 1 yr) and HTN (n = 15; 63 ± 1 yr) subjects at baseline, and during static handgrip at 30 and 40% maximal voluntary contraction (MVC) followed by a period of postexercise ischemia (PEI) to isolate the metabolic component of the EPR. Changes in MAP from baseline were augmented in HTN subjects during both 30 and 40% MVC handgrip (P < 0.05 for both), and these group differences were maintained during PEI (30% PEI trial: Δ15 ± 2 NTN vs. Δ19 ± 2 HTN mmHg; 40% PEI trial: Δ16 ± 1 NTN vs. Δ23 ± 2 HTN mmHg; P < 0.05 for both). Similarly, in HTN subjects, MSNA burst frequency was greater during 30 and 40% MVC handgrip (P < 0.05 for both), and these differences were maintained during PEI [30% PEI trial: 35 ± 2 (NTN) vs. 44 ± 2 (HTN) bursts/min; 40% PEI trial: 36 ± 2 (NTN) vs. 48 ± 2 (HTN) bursts/min; P < 0.05 for both]. No group differences in metabolites were observed. MAP and MSNA responses to a cold pressor test were not different between groups, suggesting no group differences in generalized sympathetic responsiveness. In summary, compared with NTN subjects, HTN adults exhibit exaggerated sympathetic and pressor responses to handgrip exercise that are maintained during PEI, indicating that activation of the metabolic component of the EPR is augmented in older HTN humans.

Water Exercise in Patients With and Without Cardiovascular Disease: Benefits, Rationale, Safety, and Prescriptive Guidelines

Research regarding the benefits of exercise-based cardiac rehabilitation is extensive and well documented. Water exercise, in the form of stretching, walking, jogging, aerobics, strength and balance training, and swimming, provides an attractive alternative from traditional land-based exercise for achieving improved health and fitness. Patients with orthopedic or musculoskeletal limitations, pulmonary disease, excess adiposity, and other medical conditions may significantly benefit from a water-based exercise program. Although water exercise is beneficial for varied patient populations, the safety and appropriateness of higher intensity activities such as swimming should be considered. Because coronary patients have a reduced ability to identify ischemic symptoms in water, water exercise should be prescribed with caution in high-risk patients, individuals with limited swimming skills, and those with significant left ventricular dysfunction. Furthermore, the acute physiological responses during water submersion and exercise may vary considerably from land-based activity and require attention when prescribing a water-based exercise program for patients with and without coronary artery disease.

Evidence for functional alterations in the skeletal muscle mechanoreflex and metaboreflex in hypertensive rats

Exercise in hypertensive individuals elicits exaggerated increases in mean arterial pressure (MAP) and heart rate (HR) that potentially enhance the risk for adverse cardiac events or stroke. Evidence suggests that exercise pressor reflex function (EPR; a reflex originating in skeletal muscle) is exaggerated in this disease and contributes significantly to the potentiated cardiovascular responsiveness. However, the mechanism of EPR overactivity in hypertension remains unclear. EPR function is mediated by the muscle mechanoreflex (activated by stimulation of mechanically sensitive afferent fibers) and metaboreflex (activated by stimulation of chemically sensitive afferent fibers). Therefore, we hypothesized the enhanced cardiovascular response mediated by the EPR in hypertension is due to functional alterations in the muscle mechanoreflex and metaboreflex. To test this hypothesis, mechanically and chemically sensitive afferent fibers were selectively activated in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) decerebrate rats. Activation of mechanically sensitive fibers by passively stretching hindlimb muscle induced significantly greater increases in MAP and HR in SHR than WKY over a wide range of stimulus intensities. Activation of chemically sensitive fibers by administering capsaicin (0.01-1.00 microg/100 microl) into the hindlimb arterial supply induced increases in MAP that were significantly greater in SHR compared with WKY. However, HR responses to capsaicin were not different between the two groups at any dose. This data is consistent with the concept that the abnormal EPR control of MAP described previously in hypertension is mediated by both mechanoreflex and metaboreflex overactivity. In contrast, the previously reported alterations in the EPR control of HR in hypertension may be principally due to overactivity of the mechanically sensitive component of the reflex.

Exercise and acute cardiovascular events placing the risks into perspective: a scientific statement from the American Heart Association Council on Nutrition, Physical Activity, and Metabolism and the Council on Clinical Cardiology

Habitual physical activity reduces coronary heart disease events, but vigorous activity can also acutely and transiently increase the risk of sudden cardiac death and acute myocardial infarction in susceptible persons. This scientific statement discusses the potential cardiovascular complications of exercise, their pathological substrate, and their incidence and suggests strategies to reduce these complications. Exercise-associated acute cardiac events generally occur in individuals with structural cardiac disease. Hereditary or congenital cardiovascular abnormalities are predominantly responsible for cardiac events among young individuals, whereas atherosclerotic disease is primarily responsible for these events in adults. The absolute rate of exercise-related sudden cardiac death varies with the prevalence of disease in the study population. The incidence of both acute myocardial infarction and sudden death is greatest in the habitually least physically active individuals. No strategies have been adequately studied to evaluate their ability to reduce exercise-related acute cardiovascular events. Maintaining physical fitness through regular physical activity may help to reduce events because a disproportionate number of events occur in least physically active subjects performing unaccustomed physical activity. Other strategies, such as screening patients before participation in exercise, excluding high-risk patients from certain activities, promptly evaluating possible prodromal symptoms, training fitness personnel for emergencies, and encouraging patients to avoid high-risk activities, appear prudent but have not been systematically evaluated.

Exercise and Acute Cardiovascular Events

Habitual physical activity reduces coronary heart disease events, but vigorous activity can also acutely and transiently increase the risk of sudden cardiac death and acute myocardial infarction in susceptible persons. This scientific statement discusses the potential cardiovascular complications of exercise, their pathological substrate, and their incidence and suggests strategies to reduce these complications. Exercise-associated acute cardiac events generally occur in individuals with structural cardiac disease. Hereditary or congenital cardiovascular abnormalities are predominantly responsible for cardiac events among young individuals, whereas atherosclerotic disease is primarily responsible for these events in adults. The absolute rate of exercise-related sudden cardiac death varies with the prevalence of disease in the study population. The incidence of both acute myocardial infarction and sudden death is greatest in the habitually least physically active individuals. No strategies have been adequately studied to evaluate their ability to reduce exercise-related acute cardiovascular events. Maintaining physical fitness through regular physical activity may help to reduce events because a disproportionate number of events occur in least physically active subjects performing unaccustomed physical activity. Other strategies, such as screening patients before participation in exercise, excluding high-risk patients from certain activities, promptly evaluating possible prodromal symptoms, training fitness personnel for emergencies, and encouraging patients to avoid high-risk activities, appear prudent but have not been systematically evaluated.

Exercise pressor reflex function is altered in spontaneously hypertensive rats

In hypertension, exercise elicits excessive elevations in mean arterial pressure (MAP) and heart rate (HR) increasing the risk for adverse cardiac events and stroke during physical activity. The exercise pressor reflex (a neural drive originating in skeletal muscle), central command (a neural drive originating in cortical brain centres) and the tonically active arterial baroreflex contribute importantly to cardiovascular control during exercise. Each of these inputs potentially mediates the heightened cardiovascular response to physical activity in hypertension. However, given that exercise pressor reflex overactivity is known to elicit enhanced circulatory responses to exercise in disease states closely related to hypertension (e.g. heart failure), we tested the hypothesis that the exaggerated cardiovascular response to exercise in hypertension is mediated by an overactive exercise pressor reflex. To test this hypothesis, we used a rat model of exercise recently developed in our laboratory that selectively stimulates the exercise pressor reflex independent of central command and/or the arterial baroreflex. Activation of the exercise pressor reflex during electrically induced static muscle contraction in the absence of input from central command resulted in significantly larger increases in MAP and HR in male spontaneously hypertensive rats as compared to normotensive Wistar-Kyoto rats over a wide range of exercise intensities. Similar findings were obtained in animals in which input from both central command and the arterial baroreflex were eliminated. These findings suggest that the enhanced cardiovascular response to exercise in hypertension is mediated by an overactive exercise pressor reflex. Potentially, effective treatment of exercise pressor reflex dysfunction may reduce the cardiovascular risks associated with exercise in hypertension.

Safety of Cardiac Rehabilitation in a Medically Supervised, Community-Based Program

The time to occurrence of cardiovascular complications after the beginning of an exercise rehabilitation program is variable. It is not clear whether such complications are related to the duration in the program. The aim of the present study was to assess the timing of cardiovascular events occurring during the activity and the long-term safety of a medically supervised cardiac rehabilitation program performed in the community, in a large cohort. We retrospectively evaluated 3,511 patients with a history of myocardial infarction, coronary artery bypass grafting and risk factors for coronary artery disease, participating in exercise training, for 69 months. The total number of patient-hours was 338,688 with an event rate of 1/58,902 patient-hours/year (0.02%). Non-fatal events occurred in 11 patients and fatal cardiovascular events in 2 patients; 1 was successfully resuscitated. Most of the non-fatal events (62%) occurred during the first 4 weeks from the beginning of the exercise program. One third of the patients who experienced cardiovascular events, resumed the exercise program with no further complications. Medically supervised cardiac rehabilitation program is accompanied by a very low incidence of cardiovascular events. Nevertheless, special caution should be undertaken during the first sessions of the program.

Cardiac risk of coronary patients after reintegration into occupations with heavy physical exertion

The job related reintegration of patients with coronary artery disease (CAD) is a central part of cardiac rehabilitation. However, specific occupational demands like jobs with heavy physical exertion (> 6 METs) could increase the cardiovascular risk because the relative risk for acute myocardial infarction (MI) and cardiac death is temporarily elevated after vigorous exertion ("hazard period"). Thus, in 2001 any male patient with proven CAD who performed a job with heavy exertion until the occurrence of an index event (MI/ACS, any interventional or surgical revascularization measure) received a questionnaire after an average of 20 months. Complete data were available in 108 from 119 included patients (90.8%), aged 51.8+/-7.8 years. Ejection fraction was 61.5+/-13.1% and the functional capacity at the time of hospital discharge averaged 130.1+/-31.2 W. 75% of the patients had a previous MI and 59.3% underwent bypass surgery. During follow-up the previous job with heavy exertion was performed over a cumulated time of 74 years. The aim of the study was to compare the observed and the expected incidence of MI and cardiac death with and without job performance. The expected ("basal") risk for MI and cardiac death without heavy physical exertion was determined from pooled study results and assumed to be 5.2% per year. The combined risk due to performing an occupation with strenuous exertion can be calculated from time periods with and without working hours and amounts to 11.9%. There could be expected 0.119 . 74=8.8 cardiac events related to the job. In contrast, 5 MIs (4 NSTEMI, 1 STEMI) were observed (6.8%). The relative risk for an expected event compared to the basal risk without heavy exertion was 2.3 (95% CI: 0.7-7.4). The relative risk for the observed cardiac events amounts to 1.3 (95% CI: 0.4-4.8). The lower observed risk is probably due to the high grade of physical fitness in this patient group. In spite of several limitations, our study showed no convincing evidence for increasing the cardiac risk of patients with CAD performing occupations with heavy physical exertion. Because of the importance of this prognostic finding, a representative and prospective study is strongly required.

American College of Sports Medicine position stand. Exercise and hypertension

Hypertension (HTN), one of the most common medical disorders, is associated with an increased incidence of all-cause and cardiovascular disease (CVD) mortality. Lifestyle modifications are advocated for the prevention, treatment, and control of HTN, with exercise being an integral component. Exercise programs that primarily involve endurance activities prevent the development of HTN and lower blood pressure (BP) in adults with normal BP and those with HTN. The BP lowering effects of exercise are most pronounced in people with HTN who engage in endurance exercise with BP decreasing approximately 5-7 mm HG after an isolated exercise session (acute) or following exercise training (chronic). Moreover, BP is reduced for up to 22 h after an endurance exercise bout (e.g.postexercise hypotension), with greatest decreases among those with highest baseline BP. The proposed mechanisms for the BP lowering effects of exercise include neurohumoral, vascular, and structural adaptations. Decreases in catecholamines and total peripheral resistance, improved insulin sensitivity, and alterations in vasodilators and vasoconstrictors are some of the postulated explanations for the antihypertensive effects of exercise. Emerging data suggest genetic links to the BP reductions associated with acute and chronic exercise. Nonetheless, definitive conclusions regarding the mechanisms for the BP reductions following endurance exercise cannot be made at this time. Individuals with controlled HTN and no CVD or renal complications may participated in an exercise program or competitive athletics, but should be evaluated, treated and monitored closely. Preliminary peak or symptom-limited exercise testing may be warranted, especially for men over 45 and women over 55 yr planning a vigorous exercise program (i.e. > or = 60% VO2R, oxygen uptake reserve). In the interim, while formal evaluation and management are taking place, it is reasonable for the majority of patients to begin moderate intensity exercise (40-<60% VO2R) such as walking. When pharmacological therapy is indicated in physically active people it should be, ideally: a) lower BP at rest and during exertion; b) decrease total peripheral resistance; and, c) not adversely affect exercise capacity. For these reasons, angiotensin converting enzyme (ACE) inhibitors (or angiotensin II receptor blockers in case of ACE inhibitor intolerance) and calcium channel blockers are currently the drugs of choice for recreational exercisers and athletes who have HTN. Exercise remains a cornerstone therapy for the primary prevention, treatment, and control of HTN. The optimal training frequency, intensity, time, and type (FITT) need to be better defined to optimize the BP lowering capacities of exercise, particularly in children, women, older adults, and certain ethnic groups. based upon the current evidence, the following exercise prescription is recommended for those with high BP: Frequency: on most, preferably all, days of the week. Intensity: moderate-intensity (40-<60% VO2R). Time: > or = 30 min of continuous or accumulated physical activity per day. Type: primarily endurance physical activity supplemented by resistance exercise.

Effect of Physical Training on Corrected QT Dispersion in Patients With Nonischemic Heart Failure

BACKGROUND

The effect of physical training (PT) on QTc dispersion and ventricular tachycardia (VT) remains unclear in patients with nonischemic heart failure.

METHODS AND RESULTS

Eight patients with nonischemic heart failure performed PT using a bicycle ergometer and their exercise tolerance increased (4.9+/-1.8 to 7.0+/-2.5 METs, p<0.05) and QTc dispersion decreased (71+/-22 to 48+/-24 ms, p<0.05). However, PT did not change the frequency of VT.

CONCLUSION

Physical training could improve QTc dispersion in patients with nonischemic heart failure, possibly by improving the autonomic nerve system.

Sudden cardiac death after manual or automated snow removal

To examine the proximate circumstances of sudden cardiac death (SCD) in the setting of major snowstorms, we reviewed records from the medical examiners' offices of 3 counties in the weeks before, during, and after 2 heavy snowfalls that occurred in the greater metropolitan Detroit area. Of those who experienced SCD due to atherosclerotic cardiovascular disease (n = 271), 36 (33 men, 3 women) were engaged in snow removal, representing the largest number of exertion-related deaths after heavy snowfalls reported to date.

Exercise-induced nonsustained ventricular tachycardia: a significant marker of coronary artery disease?

Diagnostic exercise stress testing is commonly performed in patients with known or suspected cardiovascular disease. The significance of an ischemic response, manifested as significant ST-segment depression, angina pectoris, transient myocardial perfusion abnormalities, or combinations thereof, is well established. However, the diagnostic implications of exercise-induced nonsustained VT are uncertain, especially as an isolated finding. The patient had threatening ventricular arrhythmias at peak exercise without an ischemic response. Subsequent cardiac catheterization revealed significant CAD requiring percutaneous coronary intervention.

How much exercise is enough for the coronary patient?

Prescribing exercise for cardiac patients is comparable in many ways to prescribing medications; that is, one recommends an optimal dosage according to individual needs and limitations. For in-patients, simple exposure to orthostatic or gravitational stress can obviate much of the deterioration in exercise tolerance that normally follows a cardiovascular event or intervention. On the other hand, the continuum of exercise therapy for outpatients may range from brisk walking to marathon running. Upper body and resistance training also have been shown to be safe and effective for clinically stable patients. Moderate intensity exercise training can produce beneficial changes in functional capacity, cardiac function, coronary risk factors, psychosocial well being, and possibly improve survival in patients with coronary artery disease. These findings may be especially relevant for the previously sedentary patient, in whom the subjective discomfort of vigorous exercise may serve as a deterrent to long-term compliance with physical training. (c) 2000 by CHF, Inc.

Exercise therapy for older persons with cardiovascular disease

Cardiac rehabilitation with exercise training after myocardial infarction in persons younger than 70 years has been found to cause a significant decrease in all-cause mortality, cardiovascular mortality, and fatal reinfarction, but no significant difference in nonfatal reinfarction. After myocardial infarction or coronary revascularization in older individuals, such programs significantly improve physical work capacity, body mass index, percent body fat, serum lipids, behavioral characteristics, and quality of life. Exercise modalities should include aerobic, resistance, and flexibility exercises. Less intense exercise of longer duration should be performed by older persons with coronary artery disease. Exercise training programs in patients with congestive heart failure produce significant improvement in peak oxygen consumption, exercise duration, and power output. The benefits of exercise training in patients with congestive heart failure may be due to an increase in cardiac output, an improvement in skeletal muscle metabolism, and an increase in peak blood flow to the exercising limb caused by a reduction in vascular resistance.

Physical activity and exercise training prescriptions for patients

The dominant outcome from exercise prescription is an increase in various markers of exercise capacity. A very large group of studies have demonstrated that the VO2max is increased in response to exercise performed according to well-accepted principles of exercise prescription. Other markers of exercise capacity, such as the VT, also improve substantially following exercise training. Finally, improvement in exercise capacity is generally related to improved quality of life, particularly in patients with exercise capacity limited by various disease processes. Beyond the specific physiologic gains from training, exercise contributes to a better overall clinical outcome. Although there are few data conclusively demonstrating that exercise independently causes favorable changes in other risk factors, it should be recognized that exercise can contribute indirectly to modulation of other risk factors. Exercise represents positive health advice. Since most of our other recommendations to patients are in the nature of negative advice (e.g., don't smoke, don't eat high-fat foods), and since people are infamous for ignoring negative advice, the value of using a positive recommendation that may indirectly lead the patient to discontinue bad behaviors can hardly be overstated.

Exercise testing in cardiac rehabilitation. Exercise prescription and beyond

The prescription of exercise, either as a part of a formal exercise training program or as a means to increase physical activity in general, has been and will remain a primary component of cardiac rehabilitation and secondary prevention programming. Wherever possible, this prescription should be based on a recent exercise test that documents the cardiac patient's functional capacity, cardiac and hemodynamic responses to exercise, and signs and symptoms associated with exertion. Clearly the prescription of exercise and suggestions for increasing levels of physical activity must be based on accepted principles of exercise physiology and expected training responses. Nonetheless, the art of exercise prescription should guarantee flexible methodologies to meet the specific needs of each individual patient. Although the patient must accept ultimate responsibility for participation, the clinician bears the burden of continually attempting to reinforce the importance of increasing caloric expenditure and motivating patients to initiate and commit to long-term participation in a safe and appropriately designed program of exercise and increasing physical activity.

Myocardial ischemia during physical exercise in patients with stable coronary artery disease: predictability and prevention

AIMS

We assessed whether exercise-induced myocardial ischemia during intensive group exercise sessions can be predicted in patients with coronary artery disease and stable angina pectoris.

METHODS AND RESULTS

Twenty-three patients underwent cardiac catheterization, 201-thallium scintigraphy, and exercise testing prior to participation in group training sessions. Heart rates and myocardial ischemia were documented by Holter monitoring. The individual training heart rate was calculated as a percentage of the maximal heart rate achieved during symptom-limited exercise testing. Myocardial ischemia occurred significantly more often during group exercise sessions (15 of 23 patients) than during treadmill testing (4 of 23 patients, P<0.001). Maximal heart rate (145+/-23 vs. 134+/-21 beats/min, P<0.004) and maximal plasma lactate concentrations (6.0+/-2.9 vs. 4.3+/-2.0 mmol/l, P<0.05) were significantly higher than during symptom-limited exercise testing. Ischemic episodes occurred significantly more often during jogging than during competitive ball games or interval training. Myocardial ischemia occurred in patients who exceeded their individual target training heart rates (43 of 44 episodes; P<0.001). Duration of ischemic episodes did not correlate with any marker obtained at the beginning of the study.

CONCLUSION

These data demonstrate that routine diagnostic procedures do not sufficiently identify patients at risk for exercise-induced myocardial ischemia. Ischemic events are only effectively prevented by choosing adequate types of exercise and, above all, by the strict adherence to individual target heart rates.

Recurrent ventricular fibrillation in a marathon runner during exercise testing

We report a case of a marathon runner who presented with chest tightness, ST-segment depression, and ventricular fibrillation following treadmill exercise testing. At cardiac catheterization, the patient was found to have an isolated lesion in the left anterior descending (LAD) artery that was hemodynamically insignificant by accepted angiographic and coronary flow reserve standards. Ventricular fibrillation was thought to be idiopathic, and an implantable cardioverter defibrillator was placed. Chest pain and ST-segment depression followed by ventricular fibrillation was reproduced during follow-up treadmill testing, prompting reconsideration of the original diagnostic hypothesis. A coronary stent was deployed in the LAD artery. The patient has been asymptomatic and arrhythmia free during follow-up treadmill testing and recreational running.

Occlusions of epicardial arteries might not directly induce symptoms in ischemic heart disease

It is accepted that primary occlusions of epicardial arteries by thromboses, stenotic coronary artery disease (CAD), and spasm directly induce symptoms in ischemic heart disease (IHD). Because of this acceptance, there has been little interest in alternate mechanisms for IHD--as the spasm of resistance vessel (S-RV) concept of IHD, which asserts that S-RV directly induces symptoms in IHD. To stimulate interest in the S-RV concept, evidence against the primacy of occlusions of epicardial arteries was presented, as well as evidence for this position to provide a balanced discussion; while the evidence was mixed, overall findings appeared to weigh significantly against the primacy of occlusions of epicardial arteries. Also, the S-RV concept was discussed; the discussion included presenting the theory's explanations for events in epicardial arteries, with the aim of demonstrating that the concept provides more consistent explanations than the standard position. It is suggested that there is sufficient information to warrant renewed consideration of the S-RV concept.

Identification of patients at risk during swimming by Holter monitoring

Cardiac arrest during swimming accounts for a considerable number of deaths during physical exercise in patients with coronary artery disease. A link between ST-segment depression and cardiac arrest has been observed in previous studies. In this study, exercise-induced myocardial ischemia was assessed in 23 patients with coronary artery disease by bipolar Holter monitoring during swimming, jogging, and treadmill testing. During treadmill testing, Holter monitoring and standard electrocardiograms were simultaneously recorded. Detection of ST-segment depression during swimming was standardized in a group of normal volunteers (n = 7). All patients with silent myocardial ischemia (n = 8) documented by thallium-201 scintigraphy had ST-segment depression during treadmill testing and swimming when recorded by Holter monitoring, whereas the standard electrocardiogram during treadmill testing was negative in 5 patients. Heart rate at 1 mm ST-segment depression was significantly lower during swimming (110 +/- 11 beats/min) than during treadmill testing (documented by standard electrocardiogram) (133 +/- 23 beats/min, p < 0.002) and jogging (125 +/- 21 beats/min, p < 0.03). However, there was no significant difference in heart rate at onset of angina pectoris in symptomatic patients, suggesting a delayed sensation of ischemic symptoms during swimming. The only clinical event in our group during 8 years of swimming occurred during this study. One patient with silent myocardial ischemia developed ST-segment depression during swimming that degenerated into ventricular fibrillation, requiring resuscitation. Therefore, Holter monitoring can be considered a valuable addition in identifying patients with silent myocardial ischemia during swimming, and thus identifying patients at risk for exertion-related life-threatening ventricular tachyarrhythmias.

Efficacy of a single dose of slow-release isosorbide dinitrate in the treatment of silent or painful myocardial ischemia in stable angina pectoris

A double-blind study was performed in 32 patients with stable angina pectoris to assess the effects of slow-release isosorbide dinitrate (ISDN) (a single dose of 120 mg/day) on the frequency and duration of painless and painful ischemic episodes, and on electrocardiographic changes and exercise tolerance. Forty-eight-hour electrocardiographic monitoring and treadmill exercise tests were performed before, and at 20 and 21 days of therapy. Holter monitoring showed a significant decrease in the frequency of painful and silent episodes (p less than 0.001), and in the duration of painful (1,623 +/- 664 seconds vs 323 +/- 161 seconds; p less than 0.001) and silent episodes (2,818 +/- 1,496 seconds vs 223 +/- 102 seconds; p less than 0.001). The magnitude of painful and silent ST-segment depression was significantly reduced (2.7 +/- 0.9 mm to 0.7 +/- 0.7 mm and 2.0 +/- 1.1 mm to 0.7 +/- 0.5 mm, respectively; p less than 0.001). Time of exercise testing to the onset of ST-segment depression (442 +/- 137 seconds vs 858 +/- 110 seconds; p less than 0.001) or anginal pain was doubled (461 +/- 128 seconds vs 830 +/- 130 seconds; p less than 0.001). The work load increased from 6 to 10 METs (p less than 0.001). ISDN in a single dose of 120 mg/day is a valuable drug for stable angina pectoris, decreasing the frequency of silent and painful ischemic episodes and the magnitude of ST-segment depressions, and increasing exercise tolerance. It particularly shortened the duration of silent episodes. For patients' compliance, a once-daily dose of ISDN could be advantageous.

Circadian variation of myocardial ischemia in patients with stable coronary artery disease

The circadian variation of myocardial ischemia detected during 24-h ambulatory electrocardiographic monitoring (AEM) was analyzed in 123 patients with stable angina pectoris, positive exercise test, and angiographically proven coronary artery disease. A total of 437 ischemic episodes (ST-segment depression greater than or equal to 1 mm and duration greater than or equal to 1 min) were observed; 333 (76%) episodes remained asymptomatic, and only 104 (24%) episodes were accompanied by anginal pain. Ischemic episodes predominantly occurred during the morning hours, between 6 a.m. and noon, and another smaller peak was observed in the afternoon, between 4 and 5 p.m.; this diurnal pattern was influenced neither by the extent of coronary artery disease nor the degree of left ventricular dysfunction. The circadian variation was restricted to the 345 (78%) ischemic episodes preceded by increases in heart rate; the 92 (22%) episodes without prior heart rate changes occurred randomly throughout the day. The morning peak in ischemic episodes was not associated with less myocardial oxygen supply; in contrast, heart rate profile showed parallel increases during the morning and afternoon hours, indicating elevated myocardial demand during these periods. Ischemia-related ventricular arrhythmias were concentrated during the morning hours, but their overall prevalence was low--28 (6%) of 437 ischemic episodes. These findings may provide further insight into the pathomechanisms of acute clinical events in patients with coronary artery disease, since the circadian variation of myocardial ischemia is very similar to that observed for the onset of myocardial infarction and sudden cardiac death.