How can exercise provoke myocardial ischemia

Our objective was to determine the incidence of myocardial ischemia in cardiac rehabilitation programs according to myocardial perfusion SPECT in exercise programs based on the anaerobic threshold. Thirty-nine patients 35 men and 4 women diagnosed with coronary artery disease by coronary angiography and stress technetiumm-sestamibi gated SPECT associated with a baseline cardiopulmonary exercise test were assessed.

Ages ranged from 45 to 75 years. Mastrocolla 1 , A. Ferraz 1 , S. Buglia 1 , L. Piegas 3 and A. Carvalho 4. Correspondence and Footnotes. Key words : Exercise test; Anaerobic threshold; Myocardial ischemia; Coronary artery disease; Technetium; 99m Tc-sestamibi.

According to current guidelines, exercise intensity in cardiac rehabilitation programs should not precipitate myocardial ischemia during a training session However, it has been shown by SPECT myocardial perfusion imaging that physical exercise within the functional capacity, based on standard exercise stress testing, may cause ischemia, characterized by a reversible perfusion defect, even without angina symptoms or ST-segment depression 7.

With the current widespread use of cardiopulmonary exercise testing, exercise intensity can be defined on the basis of the anaerobic threshold At this level of physical exertion, exercise training improves the overall functional capacity of the patients and may be applied even to those with coronary artery disease and ventricular dysfunction 12 , However, it has not yet been established whether exercise intensity determined by anaerobic threshold elicits myocardial ischemia.

Myocardial perfusion studies are more effective in identifying exercise-induced ischemia than other methods used for the diagnosis and risk stratification of obstructive atherosclerotic coronary artery disease The objective of this study was to assess the incidence of myocardial ischemia in exercise prescription based on the anaerobic threshold in cardiac rehabilitation programs, using the myocardial perfusion SPECT test.

At the initial analysis, 95 patients with at least one of the following characteristics were excluded: age over 75 years, presence of atrial fibrillation, pacemaker, left bundle branch block, preexcitation syndrome, hemodynamically significant valvular heart disease, difficulty in undergoing study procedures appropriately, impossibility to participate in an exercise program after the study, and patients already attending a cardiac rehabilitation program.

The remaining 58 patients underwent history taking, clinical examination, and standard lead electrocardiography, in addition to repeat SPECT myocardial perfusion following a cardiopulmonary exercise test using a Medical Graphics CardiO 2 system USA.

This was performed without discontinuation of any medication taken regularly. An individualized ramp protocol with a cycle ergometer was used. Criteria for exercise termination were those established by the American College of Cardiology and American Heart Association guidelines A Mbq or 20 mCi amount of technetiumm-sestamibi 99m Tc-sestamibi was administered to patients weighing 85 kg or less, and an amount of 0.

The radiotracer was injected at near-maximum heart rate HR; defined as age or in the presence of impending exhaustion, exertional ST-segment depression equal to or greater than 0. After the injection, exercise was continued for 30 to 60 s, and myocardial perfusion SPECT was performed 60 min later. Rest myocardial perfusion SPECT was performed within a week of the first cardiopulmonary exercise test. Under regular medication, only 39 patients showed a persistent reversible defect on myocardial perfusion SPECT images and were eligible for the next phase of the study.

Ages ranged from 45 to 73 years mean The second cardiopulmonary exercise test was similar to the first, but was not associated with myocardial perfusion imaging, and was used to determine the anaerobic threshold using the V-slope method Training level was set at the workload and HR corresponding to the anaerobic threshold. The third cardiopulmonary exercise test was performed at the workload prescribed for tests on mechanically braked bicycles, the same as used in the cardiac rehabilitation program, during over a period of 20 min, corresponding to the continuous aerobic phase of a cardiac rehabilitation program session.

The 99m Tc-sestamibi dose was injected approximately 19 min into the test, and images were acquired 60 min later. Qualitative and semiquantitative analyses were performed. Radiotracer uptake was compared in 17 segments of the myocardium.

Myocardial perfusion images were analyzed by 3 observers blind to patients' data using a score system for each of the 17 segments based on five tomographic views: basal short-axis slice, midventricular short-axis slice, apical short-axis slice, vertical long-axis slice, and horizontal long-axis slice. For each slice, the segment with the highest uptake was graded zero. The remaining segments were graded according to the following criteria: one, mildly reduced uptake; two, moderately reduced uptake; three, severely reduced uptake, and four, absent uptake.

No difference between the summed stress score and summed rest score indicated absence of stress-induced hypoperfusion, that is to say, absence of ischemia. The Bonferroni multiple comparison test was used to detect differences between cardiopulmonary exercise tests and the scores derived from SPECT images obtained at rest, at peak stress, and during the prescribed exercise.

Summed difference score peak - rest and prescription exercise - rest were compared by the Wilcoxon test. Mean HR was compared using the paired Student t -test. ST-segment changes between rest, 99m Tc-sestamibi injection at peak stress and prescribed exercise were analyzed by the McNemar test. Age was compared by the Student t -test. The clinical and angiographic characteristics of the patients are shown in Table 1.

Coronary angiography revealed significant stenosis involving the left anterior descending artery in 27 patients, the right coronary artery in 25 patients, and the left circumflex artery in 28 patients.

The cardiopulmonary variables evaluated in all three cardiopulmonary exercise tests are shown in Table 2. Mean workload achieved was Mean HR ranged from Second cardiopulmonary exercise test for the determination of the level of exercise prescription. If you have too many cholesterol particles in your blood, cholesterol may accumulate on your artery walls. Eventually, deposits called plaques may form. The deposits may narrow — or block — your arteries. These plaques can also burst, causing a blood clot to form.

Myocardial ischemia occurs when the blood flow through one or more of your coronary arteries is decreased. The low blood flow decreases the amount of oxygen your heart muscle receives.

Myocardial ischemia can develop slowly as arteries become blocked over time. Or it can occur quickly when an artery becomes blocked suddenly. The same lifestyle habits that can help treat myocardial ischemia can also help prevent it from developing in the first place. Leading a heart-healthy lifestyle can help keep your arteries strong, elastic and smooth, and allow for maximum blood flow.

Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. The duration of the progression is dependent upon the extent of myocardial injury and remodelling. In patients with non-ST segment elevation myocardial infarction NSTEMI with complete revascularisation and without remaining ischaemia, exercise can be increased faster to previous levels.

More intense training and participation in competition should only be considered after a successful, progressive increase in the exercise load. If they are receiving dual antiplatelet therapy DAPT , because of the risk of bleeding, they should be advised to avoid contact sports. Advice on eligibility to participate in sport must be combined with recommendations to perform proper warm-up and cool-down procedures and ensure adequate hydration.

Patients should also be made aware of the need to be mindful of any symptoms occurring during resumed exercise. Continuous long-term cardiac evaluation, at least annually, is then advised. The risk factor profile should be managed pharmacologically and with lifestyle modifications.

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