Circadian variation of ischemic threshold in syndrome X

Microvascular angina: assessment of coronary blood flow, flow reserve, and metabolism

Microvascular angina (MVA) is an often overlooked cause of significant chest pain. Decreased myocardial perfusion secondary to dysregulated blood flow in the microvasculature can occur in the presence or absence of obstructive epicardial coronary artery disease. The corresponding myocardial ischemia and angina is now a well-established diagnosis, made by detection of decreased coronary flow reserve (CFR). Although low CFR and MVA are associated with poor prognosis, there is initial evidence for reversibility of this abnormal vascular regulation with aggressive medical therapy and control of associated risk factors. Current assessment of MVA is carried out predominantly during cardiac catheterization; however, noninvasive techniques to assess CFR are being developed, including PET, MRI, and CT modalities. Quantitative tracer techniques or imaging of metabolic disturbances reflecting ischemia will likely enhance diagnostic approaches for such patients as well as allow more frequent monitoring of response to therapy.

Circadian rhythm in the cardiovascular system: chronocardiology

BACKGROUND

We reviewed recent progress in the study of the chronobiological aspects of the cardiovascular system.

METHODS

Medline was used as the main search tool, and the full texts of selected papers were obtained.

RESULTS

More than 300 references were found, and 52 of them, representing the major findings in this field, were included in the reference list. Results of these studies confirm that most cardiovascular physiological parameters (such as heart rate, blood pressure, electrocardiogram indices) and pathophysiological events (myocardial ischemia/infarction, sudden cardiac death) show circadian rhythms. Results also suggest that consideration of these rhythms is important for the diagnosis and treatment of cardiovascular disorders and that restoration of normal circadian rhythms may be associated with clinical improvement.

CONCLUSION

The study of circadian rhythms in the cardiovascular system is emerging as an important area of investigation because of its potential implications for patient management.

Parasympathetic withdrawal antedates dynamic myocardial ischemia in patients with syndrome X

This study was to evaluate the dynamic changes in cardiac autonomic control preceding electrocardiographic (ECG) myocardial ischemia in patients with syndrome X. Twenty-four-hour ambulatory ECG was obtained in 34 consecutive patients in a drug-free state. Fourteen (41%) of them, aged 58.8+/-13.5 years, presented a total of 19 ischemic episodes, mean duration 12.4+/-19.8 min (ranged 1 to 90 min). Heart rate variability was measured for 24 h; for 3 min and 30 min before, and during the 15 min (in five 3-min intervals) immediately antedating ST segment depression; and for another 3 min after ST segment back to normal. There were significant progressive shortenings in sinus cycle lengths over the 30 min preceding myocardial ischemia (-30 vs -3 minute, 822+/-32 ms vs 637+/-23 ins, P<0.05; a decrement of 22.5%). The sinus cycle lengths lengthened after ischemia ceased. High frequency activity, pNNSO and rMSS.D. were significantly reduced from the -30 min baseline to a nidus in the last 3 min before ischemia (P<0.05), whereas low frequency band and low/high frequency ratio did not present significant change. These findings strongly argue that cardiac autonomic control, especially vagal withdrawal, is involved in the pathogenesis of dynamic myocardial ischemia in syndrome X.

The "warm-up" phenomenon occurs in patients with chronic stable angina but not in patients with syndrome X

Most patients with chronic stable angina show an improvement in ischemic threshold when a second exercise test is performed a few minutes after a first positive test. In this study we evaluated whether this "warm-up" phenomenon also occurs in patients with syndrome X. We performed 2 consecutive exercise tests in 14 patients with chronic stable angina and 11 patients with syndrome X. The second exercise test was performed after 10 minutes from the end of the first one, always after complete recovery to baseline of ST segment. In patients with stable angina, heart rate (108+/-18 vs 99+/-16 beats/min, p = 0.005), rate-pressure product (17,020+/-4,541 vs 15,215+/-3,734 beats/min x mm Hg, p = 0.028), and exercise time (587+/-297 vs 444+/-244 seconds, p = 0.002) at 1-mm ST depression were higher in the second test than in the first one and a significant improvement in these parameters during the second test was also observed at peak exercise. Conversely, in patients with syndrome X, there were no significant differences between the 2 tests in heart rate (128+/-18 vs 131+/-23 beats/min), rate-pressure product (19,922+/-5,153 vs 19,390+/-5,654 beats/min x mm Hg), and exercise time (592+/-243 vs 566+/-228 seconds) at 1-mm ST-segment depression. Similarly, in this group of patients, no significant differences in exercise variables between the 2 tests were observed at peak exercise. Thus, unlike patients with chronic stable angina, patients with syndrome X have no evidence of warm-up in response to repeated exercise testing.

Cardiac autonomic function and sensitivity to pain in postmenopausal women with angina and normal coronary arteries

An increased sensitivity to painful stimuli and an abnormal cardiac autonomic function have previously been reported in patients with angina and angiographically normal coronary arteries, a syndrome that mainly affects postmenopausal women. In this study we compared both general sensitivity to pain, by evaluating time to forearm ischemic pain (FIP) provoked by sphygmomanometer cuff inflation, and cardiac autonomic function, by measuring heart rate variability (HRV), and QT and QT(c) intervals on 24-hour Holter recordings, in 25 postmenopausal women with angina and normal coronary arteries and in 22 healthy postmenopausal women. Compared with controls, patients had a reproducible strikingly lower time to FIP (149 +/- 121 vs 295 +/- 158 seconds, p <0.001), whereas there were no differences between the 2 groups in HRV variables and mean 24-hour QT and QT(c) intervals. HRV indexes, and QT and QT(c) intervals also showed similar circadian patterns. Thus, our data show that postmenopausal women with angina and normal coronary arteries have an enhanced sensitivity to systemic painful stimuli, but no detectable impairment in cardiac autonomic function compared with a well-matched control group of postmenopausal healthy women.

Ischemic-like ST-segment changes during Holter monitoring in patients with angina pectoris and normal coronary arteries but negative exercise testing

To evaluate whether Holter electrocardiographic monitoring may improve the detection of ST-segment depression in patients with anginal chest pain and normal coronary arteries, we performed symptom-limited exercise testing and 24-hour Holter monitoring in a group of 38 such patients (27 women, age 54 +/- 8 years). Patients were divided into 2 groups:group X1 included 28 patients with and group X2 10 patients without significant ST-segment depression during exercise testing. There were no significant differences between the 2 groups in age, gender, characteristics of chest pain, exercise duration, heart rate (HR), and blood pressure at peak exercise, but anginal pain during exercise testing was reported by 10 patients of group X1 (36%) and 9 of group X2 (90%) (p <0.01). Episodes of ST-segment depression on Holter monitoring were found in 17 patients of group X1 (61%) and in 5 patients of group X2 (50%) (p = NS). There were no differences between the 2 groups in daily number of ST episodes (3.6 +/- 4 vs 2.8 +/- 5 episodes per patient), symptomatic episodes (8% vs 18%), and duration of the episodes. On average, HR increased significantly, in a similar way, from 15 minutes before ST-segment depression to 1-mm ST in both groups, and its value at the onset of ischemia was similar in the 2 groups (102 +/- 22 vs 109 +/- 18 beats/min, p = NS). Finally, HR at 1-mm ST during Holter monitoring was significantly lower than that observed at 1-mm ST during exercise testing (127 +/- 16 beats/min, p < or = 0.01) in group X1, and it was also lower than that observed at peak exercise (136 +/- 22 beats/min, p < or = 0.01) in group X2. In conclusion, Holter monitoring can significantly increase the detection of ST-segment depression in patients with anginal pain and normal coronary arteries, indicating a cardiac, although not necessarily ischemic, origin of the pain. Indeed, 50% of our patients with negative symptom-limited exercise testing showed spontaneous ST changes, compatible with transient myocardial ischemia, during daily activities. Differences in the response of coronary microvascular tone to exercise testing and to stimuli operating during daily life are likely to play a significant role in determining these findings.