Endothelial control of lower limb blood flow in chronic heart failure

BACKGROUND

Limitation of the blood supply to skeletal muscle in chronic heart failure may contribute to the symptoms of fatigue and diminished exercise capacity. The pathophysiology underlying this abnormality is not known. The purpose of this study was to assess the effect of endothelium dependent and independent vasodilator agents on blood flow in the leg of patients with heart failure.

METHODS AND RESULTS

Blood flow in the leg was measured in patients with heart failure (n = 20) and compared with that in patients with ischaemic heart disease and normal left ventricular function (n = 16) and patients with chest pain and normal coronary arteries (n = 8). External iliac artery blood flow was measured using intravascular Doppler ultrasound and quantitative angiography. Flow was recorded at rest and in response to bolus doses of the endothelium independent vasodilator, papaverine. Endothelium dependent responses were measured by infusion of acetylcholine and substance P. Mean (SEM) baseline blood flow was reduced at rest (2.9 (0.4) v 4.5 (0.3) ml/s, P < 0.001) and vascular resistance was raised (37.4 (3.6) v 27.1 (3.0) units, P < 0.05) in patients with heart failure compared with that in controls. The peak blood flow response to papaverine (8 mg), acetylcholine (10(-7)-10(-5) mol/l), and substance P (5 pmol/min) was reduced in heart failure, with greater impairment of the response to acetylcholine than substance P. There was a correlation between baseline blood flow in the heart failure group and diuretic dose (r = -0.62, P = 0.003), New York Heart Association classification (r = -0.65, P = 0.002), and left ventricular ejection fraction (r = 0.80, P = 0.0004).

CONCLUSIONS

There is reduced blood flow and raised vascular resistance at rest in the legs of patients with heart failure. The degree of impaired blood flow in the leg correlates with the severity of heart failure. There is impairment of the response to both endothelium dependent and independent vasodilators. Abnormal function of the vascular myocyte in heart failure may explain these results as would structural abnormalities of the resistance vessels.

Regional changes in angiotensin II receptor density after experimental myocardial infarction

The plasma and cardiac renin-angiotensin systems may be activated after myocardial infarction. The myocardium may therefore be exposed to increased concentrations of angiotension II, which may contribute to myocardial injury. The purpose of this study was to identify the potential sites of action of angiotensin II in the infarcted heart. Myocardial infarction was induced in rats by left coronary artery ligation, and the hearts were removed for study after 18 h, 7 days, or 8 months. The regional ventricular angiotensin II receptor density was assessed by [125I](Sar1,Ile8)angiotensin II binding and quantitative autoradiography. The [125I](Sar1,Ile8)angiotensin II binding was unchanged at 18 h, but was increased at 7 days in the infarcted region of the left ventricle (73.2 +/- 3.2 amol/mm2, mean +/- S.E.M.) compared with the non-infarcted region (1.6 +/- 0.2 amol/mm2, P < 0.0001) and with the left ventricular myocardium of sham-operated control animals (1.3 +/- 0.1 amol/mm2, P < 0.0001). The increased [125I](Sar1,Ile8)angiotensin II binding density was still present, but diminished, at 8 months after coronary ligation (49.0 +/- 5.7 amol/mm2, P < 0.0001 v control, P = 0.0058 v 7-day infarcts). The increased binding of [125I](Sar1,Ile8)angiotensin II was antagonised by losartan, an AT1 receptor antagonist, but not by an AT2 receptor antagonist. Microautoradiography of [125I](Sar1,Ile8) angiotensin II, and assessment of collagen deposition using picrosirius staining and immunostaining demonstrated that the regional increase in AT1 receptor density in the infarcted region of myocardium was associated with fibroblast infiltration and collagen deposition. The infarct scar and the cardiac fibroblasts within it express high levels of angiotension II receptors and therefore represent potential targets for the actions of angiotensin II after myocardial infarction.

Changes in coronary sinus pH during dipyridamole stress in patients with hypertrophic cardiomyopathy

OBJECTIVES

The presence of angina pectoris and myocardial scarring in patients with hypertrophic cardiomyopathy (HCM) suggests that myocardial ischemia is a factor in the pathophysiology of the disease. The clinical evaluation of ischaemia is problematic in HCM as baseline electrocardiographic abnormalities are frequent and thallium-201 perfusion abnormalities correlate poorly with anginal symptoms. Coronary sinus pH measurement using a catheter mounted pH electrode is a validated sensitive technique for the detection of myocardial ischaemia.

METHODS AND RESULTS

11 patients with HCM and chest pain (eight men; mean (SD) (range) age 36 (11) (19-53) years) and six controls (two men; mean (SD) (range) age 49 (11) (31-62) years) with atypical pain and normal coronary angiograms were studied. Eight patients with HCM had baseline ST segment depression of > or = 1 mm and four had reversible perfusion defects during stress 201TI scintigraphy. A catheter mounted hydrogen ion sensitive electrode was introduced into the coronary sinus and pH monitored continuously during dipyridamole infusion (0.56 mg/kg over four min). The maximal change in coronary sinus pH during dipyridamole stress was greater in patients with HCM than in controls (0.082 (0.083) (0 to -0.275) v 0.005 (0.006) (0 to -0.012), P = 0.02). In six patients (four men; mean (SD) (range) age 29 (9) (19-40 years) the development of chest pain was associated with a gradual decline in coronary sinus pH (mean 0.123 (0.089)), peaking at 442 (106) s. There were no relations among left ventricular dimensions, maximal wall thickness, and maximum pH change. In patients with HCM there was a correlation between maximum pH change and maximum heart rate during dipyridamole infusion (r = 0.70, P = 0.02).

CONCLUSION

This study provides further evidence that chest pain in patients with HCM is caused by myocardial ischaemia. The role of myocardial ischaemia in the pathophysiology of the disease remains to be determined but coronary sinus pH monitoring provides a method for quantifying and prospectively assessing its effects on clinical presentation and prognosis.

Tissue expression of endothelin-1 mRNA in endotoxaemia

Circulating endothelin-1 concentrations are elevated in animal models of sepsis. The major actions of endothelin-1 appear to be as a local autocrine and paracrine factor, rather than as a circulating hormone, and plasma concentrations may not reflect local tissue concentrations. We therefore measured tissue expression of mRNA encoding pre-pro-endothelin-1 by RNase protection assays, as an indicator of local production of ET-1 in an in vivo rat model of endotoxaemia. The effects of dexamethasone pre-treatment were also examined. There was a tissue-specific increase in pre-pro-endothelin-1 mRNA in endotoxaemia, apparent at 6h after endotoxin challenge in heart and lung. No significant changes in expression were seen in kidney or skeletal muscle. Dexamethasone pre-treatment significantly attenuated the rise in pre-pro-endothelin-1 mRNA in heart at 6h. Therefore, we have demonstrated tissue-specific differences in the effect of endotoxin upon pre-pro-endothelin-1 mRNA expression and in sensitivity to dexamethasone. This could account for some of the inter-tissue differences seen in local vascular response to endotoxin.

Acceleration of contraction by beta-adrenoceptor stimulation is greater in ventricular myocytes from failing than non-failing human hearts

Myocytes from failing human ventricle contract and relax more slowly than those from non-failing. This has been suggested to result from the lowering of basal cyclic AMP level in failing myocardium, and the consequent withdrawal of a tonic lusitropic effect. We present data to support this hypothesis by demonstrating that the acceleration of contraction and relaxation by beta-adrenoceptor stimulation is greater in myocytes from failing than non-failing heart. This is despite the desensitisation of the inotropic effect of isoprenaline in the same failing cells. Following beta-adrenoceptor stimulation, speeds of contraction and relaxation are normalised in myocytes from failing heart, with final values not significantly different from non-failing.

Reduced contraction and altered frequency response of isolated ventricular myocytes from patients with heart failure

BACKGROUND

Previous work has failed to demonstrate reduced maximal contraction of isolated ventricular myocytes from failing human hearts compared with nonfailing control hearts. The effect of alterations in stimulation frequency and temperature on the contraction of isolated ventricular myocytes has been investigated. Left ventricular myocytes were isolated from the hearts of patients with severe heart failure undergoing heart transplantation and compared with myocytes isolated from myocardial biopsies from patients with coronary disease but preserved left ventricular systolic function or from myocytes from rejected donor hearts.

METHODS AND RESULTS

Myocytes were exposed to either a maximally activating level of extracellular calcium at 37 degrees C or to 2 mmol/L calcium at 32 degrees C. There was no significant difference in the contraction amplitude between myocytes from failing and nonfailing hearts at 0.2 Hz. With increasing stimulation frequency, there was a reduction in contraction amplitude in cells from failing hearts relative to control hearts in both maximal calcium from 0.33 Hz (4.5% versus 6.6%) to 1.4 Hz (3.9% versus 8.8%) (ANCOVA, P < .001) and at 2 mmol/L calcium from 0.50 Hz (2.3% versus 3.5%) to 1.4 Hz (1.8% versus 3.9%) (ANCOVA, P < .001). The time to peak contraction and the times to 50% and 90% relaxation were prolonged in myocytes from failing hearts at stimulation rate of 0.2 Hz (P < .01), but only the time to 50% relaxation was prolonged at 1.0 Hz (P < .05).

CONCLUSIONS

Reduced contraction, slowed relaxation, and impaired frequency response occurring at the level of the individual ventricular myocyte can be demonstrated in human heart failure. This demonstrates that disruption of myocyte function can contribute to both the systolic and the diastolic abnormalities that occur in the failing human heart.

Left ventricular volume in thrombolysed patients with acute anterior myocardial infarction: the effect of captopril and xamoterol

We measured left ventricular volume in 70 asymptomatic patients after first Q-wave anterior myocardial infarction in order to determine whether ventricular dilatation occurs and whether there is evidence for its attenuation or prevention by treatment with captopril or xamoterol--PRevention Of VEntricular Dilatation?: the PROVED? study. 77% of patients received thrombolytic treatment. Patients were randomised a mean of 11 days after infarction to receive either captopril 25 mg three times daily, xamoterol 200 mg twice daily or matching placebo. After 6 months of treatment, 6 patients from the placebo group (n = 24), 1 from the captopril group (n = 23) and 3 from the xamoterol group (n = 23) had been withdrawn from the study because of clinical complications. Left ventricular volume was measured using magnetic resonance imaging, before randomisation and after 6 months of treatment. Changes in left ventricular end-diastolic and end-systolic volume after 6 months of treatment were defined prospectively as the primary endpoints. Mean initial end-diastolic volume index was 85 (S.D. 19) ml/m2, mean end-systolic volume index was 45 (S.D. 18) ml/m2, and mean ejection fraction was 48 (S.D. 11)% for the whole group. There was no significant change in left ventricular volume index in the placebo or either treatment group after 6 months of treatment. Only minimal left ventricular dilatation was evident at 11 days. No further increase in left ventricular volume occurred after six months and there was no additional benefit from treatment with either captopril or xamoterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell geometry and contractile abnormalities of myocytes from failing human left ventricle

OBJECTIVES

Systolic and diastolic dysfunction of the failing human heart may be due to changes in myocyte function, or to extracellular influences such as necrosis, fibrosis or repositioning of viable cells. In order to determine the contribution of cellular factors we have characterised the contraction amplitudes, and contraction and relaxation velocities of single myocytes isolated from failing human left ventricle.

METHODS

Myocytes were enzymatically isolated from the left ventricles of 42 subjects, superfused at 32 degrees C and paced at 0.2 Hz. Using a video/edge tracking system we obtained contraction amplitude and contraction and relaxation velocities as well as times to peak contraction (TTP) and to 50% and 90% relaxation (R50 and R90). Concentration-response curves to Ca2+ were constructed for each cell.

RESULTS

There was little difference in contraction amplitude at any Ca2+ concentration between cells from failing and non-failing hearts at this low frequency. At maximally activating Ca2+ concentrations (6-20 mM) there was a 30% slowing of relaxation velocity in myocytes from patients with both mild-moderate (P < 0.001) and severe (P < 0.001) congestive heart failure. Contraction and relaxation times were increased in myocytes from failing hearts [TTP: 0.46 +/- 0.02 s (n = 34 patients) vs. 0.35 +/- 0.02 s (n = 6), P < 0.01 and R50: 0.25 +/- 0.02 s (n = 34) vs. 0.16 +/- 0.02 s (n = 6), P < 0.001]. Impaired relaxation was seen with most etiologies, including ischemic and dilated cardiomyopathies and mitral valve disease. Myocytes from failing hypertrophied ventricles were more severely affected than those from failing non-hypertrophied hearts for both contraction and relaxation velocities. Cells from failing hypertrophied ventricles had a significantly larger area than from non-failing or failing non-hypertrophied ventricles, although cell length and sarcomere length were similar between groups. Larger myocytes did not show a more pronounced change in relaxation velocity than normally sized cells from the same hypertrophied ventricle.

CONCLUSIONS

Significant impairment of relaxation can be observed in ventricular myocytes from failing human heart under conditions where contraction amplitude appears normal. The defect is not confined to one etiology of disease, but is exacerbated during hypertrophy. An increase in cell size, although observed in myocytes from hypertrophied ventricle, does not itself account for changes in relaxation. Cellular changes contribute to diastolic dysfunction in the failing human heart.

Abnormalities of the myocytes in ischaemic cardiomyopathy

Acute myocardial ischemia and subsequent reperfusion result in biochemical and ionic changes in cardiac myocytes which cause contracture of the muscle and a reduced contractile force. Whether changes observed in single myocytes isolated from ischaemic ventricles are a direct consequence of the acute insult, or develop more slowly due to subsequent alterations in load and neurohumoural environment, is controversial. Myocytes from ischemic hearts have a similar contraction amplitude to those from non-failing hearts at physiological or maximally activating levels of ca2+. This could be partly due to the method of cell selection, or could represent the detection of a population of myocytes that have recovered from the original insult. However, there are significant decreases in the velocities of contraction and, particularly, relaxation in myocytes from the ischaemic heart. These resemble alterations caused by anoxia/reperfusion, but similar changes have also been observed in non-ischaemic causes of heart failure. Responses of beta-adrenoceptor stimulation are reduced in single cells from the failing heart, and a post-receptor defect has also been detected. Treatment with pertussis toxin, which reduces the activity of the inhibitory guanine-nucleotide binding protein (Gi) was able to restore beta-adrenoceptor responses to normal. The hypothesis that alterations in the beta-adrenoceptor/Gi/cAMP pathway represent the response of the myocyte to continued exposure to noradrenaline, because of the high sympathetic drive in these patients, is supported by the strong parallels observed with catecholamine-treated animals, and by the fact that non-ischemic aetiologies exhibit similar desensitization. It is concluded that the surviving myocytes in an ischaemic heart are damaged by the neurohumoral alterations that represent the body's attempt to restore cardiac output.

Insulin resistance syndrome in postmenopausal women with cardiological syndrome X

OBJECTIVE

To determine whether postmenopausal women with cardiological syndrome X (chest pain and abnormal exercise electrocardiogram despite normal coronary angiography) exhibit disturbances in the full range of proposed components of the putative "insulin resistance syndrome".

PATIENTS AND METHODS

20 postmenopausal women with syndrome X and 20 healthy controls each underwent measurement of insulin resistance (by minimal model analysis of the intravenous glucose tolerance test), lipid, lipoprotein, and apolipoprotein concentrations, a range of haemostatic variables, serum uric acid concentration, and centrality of body fat distribution (by dual energy x ray absorptiometry).

RESULTS

Women with syndrome X had higher fasting triglyceride concentrations than controls (median: 1.60 v 1.02 mmol/l, P < 0.05). Concentrations of high density lipoprotein cholesterol were lower (1.33 v 1.61 mmol/l, P < 0.05) as were those of the high density lipoprotein apolipoproteins AI and AII. Insulin and C peptide responses to the intravenous glucose tolerance test were higher (27.6 v 19.8 microU/ml/min, P < 0.01; 101 v 72 pmol/ml/min, P < 0.05, respectively), and insulin sensitivity was lower (1.89 v 3.09 min/microU/ml, P < 0.05). There were, however, no significant differences between other proposed components of the insulin resistance syndrome (blood pressure, glucose tolerance, proportion of central body fat, serum uric acid concentration, and plasminogen activator inhibitor-1 activity). Antithrombin III activity was higher in women with syndrome X (121 v 113%, P < 0.01).

CONCLUSIONS

Women with syndrome X tend to be insulin resistant and have lipid and lipoprotein abnormalities, but do not exhibit all characteristics of the insulin resistance syndrome. Such variation in correlated risk factors is consistent with underlying heterogeneity in the insulin resistance syndrome and cardiological syndrome X.

Significant differences between side-mounted and end-mounted intracoronary Doppler flow probes for the measurement of blood flow velocity

Use of the intracoronary Doppler flow probe is an established method for the assessment of coronary blood flow velocity. The aim of this study was to perform an in vitro comparison of two commonly used Doppler probes, which differ in the location of the piezoelectric crystal (end-mounted vs side-mounted). Blood flow velocity was measured over a wide range of flow rates in a flow simulator using heparinized whole blood. Measurements were made with both Doppler probes assessed in two positions (supported and unsupported) within the tubing. The results were compared with estimated true velocities. Further measurements were made with six side-mounted probes, correcting for the assumed crystal mounting angle and for the angle calculated from magnified images of the individual crystals. Mean velocities for end- and side-mounted probes correlated highly with predicted velocities (all r > or = 0.99), but the side-mounted probes significantly overestimated velocity by > 100%. Estimation of the true crystal mounting angle of the side-mounted probe revealed considerable variability (range 30-42 degrees) and was lower than the recommended angle correction factor of 60 degrees. Velocities corrected for the individual crystal mounting angles agreed more closely with predicted mean velocities. Although both probes are adequate for the assessment of relative changes in flow, the side-mounted probe considerably overestimates mean velocity, which is partly explained by the variable mounting angle of the crystal. The demonstrated limitations of the side-mounted Doppler flow probe in vitro should be considered in undertaking measurement of intracoronary blood flow velocity.

17 beta-Estradiol attenuates acetylcholine-induced coronary arterial constriction in women but not men with coronary heart disease

BACKGROUND

Women are protected from coronary artery disease until the menopause. Ovarian hormones are vasoactive substances that influence both hemodynamic parameters and atheroma formation. Intravenous ethinyl estradiol has been shown to reverse acetylcholine-induced vasoconstriction in cynomolgus monkeys and humans, and 17 beta-estradiol improves exercise-induced myocardial ischemia in female patients. We investigated the effect of the naturally occurring estrogen 17 beta-estradiol on the coronary circulation in postmenopausal women and men with coronary artery disease.

METHODS AND RESULTS

We studied nine postmenopausal women 59 +/- 3 years old, mean +/- SEM, and seven men 52 +/- 4 years old with proven coronary artery disease. They underwent measurement of coronary artery diameter and coronary blood flow after intracoronary infusion of acetylcholine 1.6 and 16 micrograms/min before and 20 minutes after intracoronary administration of 2.5 micrograms of 17 beta-estradiol into atherosclerotic, nonstenotic coronary arteries. Changes in coronary artery diameter were measured by quantitative angiography, and changes in coronary blood flow were measured with an intracoronary Doppler catheter. In female patients, acetylcholine 1.6 and 16 micrograms/min caused constriction before the administration of 17 beta-estradiol (-6 +/- 2% and -8 +/- 5%, respectively, compared with baseline). This constrictor response was converted to dilatation after intracoronary administration of 17 beta-estradiol (+8 +/- 2% and +9 +/- 3%, respectively; P < .01 before versus after estrogen). Acetylcholine 1.6 and 16 micrograms/min increased coronary blood flow before and after the infusion of 17 beta-estradiol. However, the mean acetylcholine-induced increases in coronary flow were significantly greater (P < .009) after (126 +/- 37% and 248 +/- 89%, respectively) than before (94 +/- 31% and 143 +/- 49% mL/min, respectively) the administration of 17 beta-estradiol. 17 beta-Estradiol alone had no significant effect on coronary diameter or coronary blood flow (P > .05). Isosorbide dinitrate (1 mg) caused dilatation of the coronary arteries by 11 +/- 2% (P < .005). In men, acetylcholine 1.6 and 16 micrograms/min caused constriction both before and after the administration of 17 beta-estradiol and caused similar increases in coronary blood flow both before and after the intracoronary administration of 17 beta-estradiol. Infusion of intracoronary placebo in six female control patients 55 +/- 3 years old and six male control patients 56 +/- 3 years old did not change coronary diameter responses or coronary blood flow responses to acetylcholine.

CONCLUSIONS

17 beta-Estradiol modulates acetylcholine-induced coronary artery responses of female but not male atherosclerotic coronary arteries in vivo. These human data confirm reports from studies in cynomolgus monkeys that estrogen modulates the responses of atherosclerotic coronary arteries. An enhancement of endothelium-dependent relaxation by natural estrogen (as used in most hormone replacement therapy) may be important in postmenopausal women with established coronary heart disease and may contribute to the acute effect of 17 beta-estradiol on blood flow and its long-term protective effect on the development of coronary artery disease.

Decreased contractile responses to isoproterenol in isolated cardiac myocytes from aging guinea-pigs

We have characterized the age-related changes of contractility and beta-adrenoceptor function in isolated cardiac myocytes from guinea-pigs. We used either adult animals from 2 to 14 weeks of age, where body weight increases linearly with age, or senescent ones aged between 53-65 weeks. There was some indication of a decrease in contractility in maximum Ca2+ with age, with significant differences between a young (< or = 4 weeks, weight < 400 g) and aged (> or = 8 weeks, weight > 600 g) group in contraction amplitude expressed as percentage shortening (but not when expressed as micron change in length) or contraction and relaxation velocities. This decline was continued into senescence, and ANOVA showed a significant difference between the three groups for contraction amplitude (percentage shortening, 12.2 +/- 0.9%, young, n = 31; 9.5 +/- 0.6%, n = 28 aged; 6.7 +/- 0.8%, n = 6, senescent; P = 0.005), and contraction or relaxation velocities (P < 0.001). There was a more pronounced decline in maximum response to isoproterenol with age. ANOVA for the maximum isoproterenol response for the three divisions showed significant differences for percentage shortening (11.8 +/- 0.7%, n = 30, young; 7.9 +/- 0.5%, n-28, aged and 5.5 +/- 1.1%, n = 6, senescent; P < 0.001), velocities of contraction (P < 0.001) and relaxation (P < 0.001), and normalized velocities of contraction (P < 0.001) and relaxation (P < 0.01) at maximum isoproterenol, as well as in ISO EC50 (P < 0.001) and isoproterenol/Ca2+ ratio (P < 0.02). A general decrease in contractility of the myocyte occurs as the animal ages, with maximum contraction amplitude being reduced and velocity of contraction and relaxation slowed. The effect was more pronounced for beta-adrenoceptor stimulation than for high Ca2+, suggesting a specific lesion in the adenylate cyclase related pathway. Much of the change occurred between the young adult (< or = 4 weeks) and the aged adult (> or = 8 weeks), although the trend was continued in senescent animals (> 52 weeks).

Syndrome X in women is associated with oestrogen deficiency

This study was undertaken to ascertain whether gynaecological history or a reduction in ovarian hormones are triggers of angina in menopausal women with a positive exercise test and normal coronary arteries. The majority of patients with angina pectoris, a positive exercise test and normal coronary arteries are female, suggesting that the female gender may be important in the aetiology. We studied the gynaecological features of 107 women (age 53 +/- 9 years) with syndrome X, taken from a population of 134 patients including 27 males. Cardiological investigations were undertaken and detailed gynaecological history obtained from all the female patients. Menopausal status was confirmed by plasma levels of oestradiol-17 beta < or = 100 pmol.l-1. In 95 of the 107 female patients, chest pain began either during the perimenopausal period (32) or after the menopause (63). Of the 63 menopausal patients, 43 had undergone hysterectomy at an average of 8 +/- 6 years prior to the onset of chest pain. The incidence of hysterectomy in the study population (40%) was four times greater than that of an age-matched population. These findings confirm that the majority of patients with syndrome X are women in whom the chest pain began after the onset of menopause. Ovarian hormone deficiency may, therefore, play a role in the onset of syndrome X in female patients.

Angiotensin-converting enzyme inhibitors and calcium antagonists after acute myocardial infarction

This article examines trials of the use of two types of drugs in the treatment of myocardial infarction: angiotensin-converting enzyme (ACE) inhibitors and calcium antagonists. ACE inhibitors are an established treatment for hypertension and heart failure and have been shown to reduce mortality from heart failure and after myocardial infarction. Six large studies have been carried out. In 1 in which an ACE inhibitor was given 3-16 days after infarction in patients with an ejection fraction < 40%, mortality was reduced by 17%. In a second study of patients who had evidence of heart failure and were followed up for 15 months, treatment with ACE inhibitors was given 3-10 days after myocardial infarction and mortality was reduced by 27%. Two other studies of 11,000 and 50,000 unselected patients with myocardial infarction showed only marginal clinical benefit. Calcium antagonists were introduced to treat hypertension and angina pectoris. In trials with patients with heart failure, the results have not been encouraging, and in some patients these agents seem to be harmful. Recently, long-acting calcium antagonists have become available, and these may avoid the deleterious effects of short-acting drugs. Since calcium antagonists act on smooth muscle, they may increase myocardial blood flow to improve function after "stunning" or "hibernation." This idea was investigated with a long-acting dihydroyridine calcium, antagonist in a randomized double-blind, placebo-controlled study (Doppler Flow, Echocardiography, and Functional Improvement Assessment of Nisoldipine Therapy-I--DEFIANT I), and a further study is being carried out. At present the widespread use of calcium antagonists after infarction is not recommended.

Cardiac syndrome X: clinical characteristics and left ventricular function. Long-term follow-up study

OBJECTIVES

Our aim was to study the clinical characteristics and evolution of symptoms and left ventricular function in a clinically homogeneous group of patients with syndrome X (angina pectoris, positive exercise test results and normal coronary arteriograms).

BACKGROUND

The syndrome of angina with normal coronary arteriograms is heterogeneous and encompasses different pathogenetic entities. These characteristics may contribute to the existing controversy concerning the cause of syndrome X.

METHODS

We studied 99 patients with syndrome X (78 women, 21 men; mean age +/- SD 48.5 +/- 8 years). All underwent clinical characterization, ambulatory electrocardiographic (ECG) monitoring and echocardiographic assessment of left ventricular function during a follow-up period of 7 +/- 4 years.

RESULTS

The syndrome was more common in women than in men. Of the women, 61.5% were postmenopausal before the onset of chest pain. All 99 patients had exertional angina, and 41 also had rest angina. The average duration of episodes of chest pain was > 10 min in 53% of patients. Sublingual nitrate was effective for relief of pain in 42% of patients. Transient ST segment depression was observed during ambulatory ECG monitoring in 64 patients and myocardial perfusion abnormalities in 22. During the first stage of the exercise test, 32 patients had an increase > 20 mm Hg in systolic blood pressure and showed an earlier onset of ST depression and shorter exercise time than did patients whose blood pressure increased < or = 20%. During follow-up, no deaths or myocardial infarctions occurred, ventricular function was unchanged (shortening fraction 35.4 +/- 4% vs. 35.6 +/- 3%; heart failure developed in only one patient), systemic hypertension occurred in eight patients and conduction disturbances in four. Symptoms lessened in 11 patients, were variable or unchanged in 64 and worsened in 24.

CONCLUSIONS

Syndrome X, as defined in this study, occurs predominantly in postmenopausal women. Patients usually have chest pain typical for angina, but conventional antianginal treatment is not often successful. Myocardial perfusion abnormalities occur in a small proportion of patients. Long-term survival is not adversely affected, and deterioration of cardiac function rarely occurs.

Relationship between arterial potassium and ventilation during exercise in patients with chronic heart failure

The mechanisms underlying the increased ventilatory response to exercise seen in patients with chronic heart failure are not clearly understood. Arterial potassium has been suggested as an important ventilatory stimulant. The authors have investigated the arterial potassium response in patients with heart failure. Although arterial potassium rises during exercise, no evidence was found to suggest a greater potassium response in patients with heart failure compared to normal subjects. There was no direct correlation between the rise in ventilation and the rise in arterial potassium. It remains possible that there is an increased sensitivity to arterial potassium in patients with heart failure, but it would need to be three times greater than in normal subjects.

Testosterone relaxes rabbit coronary arteries and aorta

BACKGROUND

Until menopause, women appear to be protected from coronary heart disease. Evidence suggests that estrogen may play a role in the protection of the cardiovascular system by exerting a beneficial effect on risk factors such as cholesterol metabolism and by a direct effect on the coronary arteries. To date there has been no evidence linking testosterone with the occurrence of coronary heart disease. Testosterone may affect the cardiovascular system directly, thus partially explaining the difference in the incidence of coronary artery disease in men and premenopausal women. The purpose of this study was to assess the direct effect of testosterone and a number of testosterone analogues on rabbit coronary arteries and aorta in vitro.

METHODS AND RESULTS

Rings of coronary artery and aorta of adult male or nonpregnant female New Zealand White rabbits were suspended in organ baths containing Krebs solution; isometric tension then was measured. The response to testosterone was investigated in prostaglandin F2 alpha (PGF 2 alpha)- and KCl-contracted rings. The effects of endothelium and nitric oxide synthase, prostaglandin synthetase, and guanylate cyclase inhibition on testosterone-induced relaxation were investigated. The effects of ATP-sensitive potassium channels and potassium conductance were also assessed. Relaxing responses in the presence of aromatase inhibition and testosterone receptor blockade were performed. The relaxing responses to the testosterone analogues etiocholan-3 beta-ol-17-one, epiandrosterone, 17 beta-hydroxy-5 alpha-androst-1-en-3-one, androst-16-en-3-ol, and testosterone enanthanate were measured. Testosterone relaxed rabbit coronary arteries and aorta. There was no significant difference between the relaxation effect of testosterone with or without endothelium. Similar results were obtained from male and nonpregnant female rabbits. The relaxing response of testosterone in the coronary artery was significantly greater than in the aorta. The relaxing response of testosterone in the coronary artery was significantly reduced by the potassium channel inhibitor barium chloride but not by the ATP-sensitive potassium channel inhibitor glibenclamide. The relaxing response to testosterone was greater in PGF 2 alpha-contracted rings compared with KCl-contracted rings. Inhibitors of nitric oxide synthase, prostaglandin synthetase, and guanylate cyclase did not affect relaxation induced by testosterone. Inhibition of aromatase and testosterone receptors did not affect relaxation. Testosterone did not shift the rabbit coronary arterial calcium concentration-dependent contraction curves, whereas verapamil did. There were, however, significant differences in the relaxing response to testosterone compared with testosterone analogues. Testosterone was the most potent relaxing agent, suggesting that there may be a structure-function relation in the relaxing response.

CONCLUSIONS

Testosterone induces endothelium-independent relaxation in isolated rabbit coronary artery and aorta, which is neither mediated by prostaglandin I2 or cyclic GMP. Potassium conductance and potassium channels but not ATP-sensitive potassium channels may be involved partially in the mechanism of testosterone-induced relaxation. The in vitro relaxation is independent of sex and of a classic receptor. The coronary artery is significantly more sensitive to relaxation by testosterone than the aorta. Testosterone is a more potent relaxing agent of rabbit coronary artery than other testosterone analogues.

Contractile function and response to agonists in myocytes from failing human heart

Ventricular myocytes from failing human hearts have a similar maximum contraction amplitude in high Ca2+ to those from non-failing heart at low stimulation rates (0.2 Hz, 32 degrees C), but do not exhibit the same positive frequency-interval relationship. At higher stimulation rates (1 Hz) therefore, the amplitude is depressed in cells from failing hearts compared to controls. Slow relaxation is seen in myocytes from failing ventricle at all stimulation rates, and contraction velocity is also slightly reduced. beta-adrenoceptor desensitization is evident, and increases with severity of disease. There is also a post-receptor defect in myocytes from failing heart since responses to forskolin and cyclic AMP analogues are reduced, and this is accompanied by decreased cyclic AMP levels in myocardium from patients in end-stage disease. Pertussis toxin treatment, which inactivates Gi, reverses most of the alterations in the beta-adrenoceptor pathway. The role of the sympathetic system is indicated by the parallels between myocytes from failing human heart and those from the noradrenaline-treated guinea-pig, which show beta-adrenoceptor desensitization, a post-receptor defect and reduced basal cyclic AMP levels. However, relaxation velocities are not slowed in these guinea-pig myocytes, indicating that basal cyclic AMP does not have a tonic role in speeding relaxation.

The effects of intracoronary substance P and acetylcholine on coronary blood flow in patients with idiopathic dilated cardiomyopathy

Attenuation of the increase in blood flow caused by acetylcholine in the peripheral vasculature and coronary circulation of patients with heart failure has been interpreted as an impairment of endothelium-dependent vasodilation. The aim of this study was to compare in man the effects of acetylcholine, which also has endothelium-independent actions, with substance P, which appears to be a pure endothelium-dependent vasodilator, on epicardial and resistance coronary arteries in patients with idiopathic dilated cardiomyopathy. The effects of intracoronary acetylcholine (10(-7) M and 10(-6) M) and substance P (5, 10 and 25 pmol.min-1) on epicardial coronary artery diameter and coronary blood flow velocity were measured with an intracoronary Doppler flow probe and quantitative coronary angiography in 11 patients with idiopathic dilated cardiomyopathy and 10 control subjects. Epicardial coronary artery diameter did not change with acetylcholine but increased significantly with substance P in both groups (cardiomyopathy patients: 3.3 +/- 0.2 mm (mean +/- SEM) at baseline vs 3.9 +/- 0.2 mm with substance P25 pmol.min-1, P < 0.01; controls: 3.1 +/- 0.2 mm at baseline vs 3.9 +/- 0.3 mm with substance P25 pmol.min-1, P < 0.05). Coronary flow ratios with acetylcholine were lower in cardiomyopathy patients (10(-7) M: 1.4 +/- 0.1 vs 2.3 +/- 0.4, P = 0.05; 10(-6) M: 1.8 +/- 0.2 vs 3.2 +/- 0.5, P = 0.05 vs controls).(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural analysis of skeletal muscle. Microvascular dimensions and basement membrane thickness in chronic heart failure

Chronic heart failure (CHF) is characterized by increased systemic vascular resistance and diminished blood flow to exercising skeletal muscle. The pathogenesis of the increased resistance is not known, and may be due to muscle atrophy, functional abnormalities of resistance vessels or to structural changes in the microcirculation such as endothelial cell swelling. We have compared the ultrastructure of the microvasculature in needle biopsies of the quadriceps muscle from seven control subjects with normal left ventricular function to 10 patients with moderate or severe heart failure, optimally treated and without evidence of fluid overload. Samples were processed for ultrathin sectioning using ruthenium red as a specific basement membrane (BM) stain. Electron micrographs were taken of 10 transversely cut capillaries from each specimen. The total cross-sectional area of the vessels and the area of the endothelium was determined, and the short axis diameter was measured as an index of vessel diameter. The BM thickness was calculated from the mean of six readings around the periphery of the vessel. The short axis diameter in the two groups was not significantly different (controls 3.37 +/- 0.21 microns, CHF 3.56 +/- 0.37 microns, mean +/- 1SD). No difference in total cross-sectional area (controls 11.64 +/- 1.86 microns 2, CHF 13.56 +/- 2.78 microns 2) or area of the endothelium (controls 4.90 +/- 1.18 microns 2, CHF 6.00 +/- 1.58 microns 2) was observed. The thickness of the BM was marginally increased in subjects with CHF when compared to control subjects (0.31 +/- 0.077 microns vs 0.246 +/- 0.047 microns, P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal autonomic control of the cardiovascular system in syndrome X

Anomalies of autonomic control of the coronary circulation may play a role in the development of syndrome X (angina pectoris, ischemic-appearing results on exercise test, and normal coronary arteriograms). Twenty-six patients with syndrome X and 20 healthy sex- and age-matched control subjects were studied by means of analysis of heart rate variability during 24-hour Holter monitoring. Spectral and nonspectral parameters of heart rate variability were investigated. Mean heart rate was similar in patients with syndrome X and in control subjects. Patients with syndrome X had significantly lower standard deviation of all normal RR intervals, a lower percentage of adjacent normal RR intervals > 50 ms in difference (126.4 +/- 22 vs 149 +/- 43 ms, p < 0.05; 6.3 +/- 4 vs 11.2 +/- 7%, p < 0.05; respectively), and a trend toward lower values of time-domain parameters. Lower values of total power and low frequency were also observed in patients with syndrome X (1273 +/- 693 vs 1790 +/- 989 ms2, p < 0.05; 406 +/- 176 vs 729 +/- 455 ms2, p < 0.01, respectively). An inverse correlation between heart rate and measures of heart rate variability was found in syndrome X but not in control subjects. High- and low-frequency power showed a similar circadian pattern in syndrome X patients and control subjects. Patients and control subjects were then allocated into 2 groups according to the median RR duration: syndrome X1 and control 1 with high mean heart rate, and syndrome X2 and control 2 with low mean heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Relations between resting ventricular long axis function, the electrocardiogram, and myocardial perfusion imaging in syndrome X

OBJECTIVE

To investigate interrelations between ventricular long axis function, resting electrocardiogram, and myocardial perfusion imaging in a group of patients with syndrome X in order to define possible underlying mechanisms.

DESIGN

Prospective echocardiographic, electrocardiographic, and myocardial perfusion imaging.

SETTING

A tertiary referral centre for cardiac diseases with invasive and non-invasive facilities.

PATIENTS

50 consecutive patients with syndrome X selected on the basis of a history of angina, ST segment depression on exercise, and normal coronary arteriograms and 21 controls of similar age.

RESULTS

Long axis motion of one or both ventricles assessed by echocardiography was abnormal in 37 patients. The onset of systolic shortening was delayed by > 130 ms (upper limit of normal 95% confidence interval) in eight patients, and was associated with prolonged shortening during the isovolumic relaxation period in seven (p < 0.01) (systolic abnormalities). The onset of diastolic lengthening was delayed by > 80 ms in 20. Early diastolic peak lengthening rate was < 4.5 cm.s-1 in 13 patients, and the relative amplitude of lengthening during atrial systole was > 45% in 18. On the resting electrocardiogram septal q waves were absent in 12 patients. This was associated with long axis systolic disturbances in seven patients (p < 0.05). T waves were abnormal in 10 and associated with delayed onset of early diastolic lengthening in all (p < 0.001). Late diastolic long axis disturbances were not associated with any consistent electrocardiographic abnormality. Myocardial perfusion imaging was abnormal in six of 33 patients, four of whom had systolic abnormalities (p < 0.03). Imaging was normal in the rest, but in 13 of them long axis function was abnormal in the left side and in four it was abnormal on the right ventricle. Both electrocardiography and imaging were normal in 10 patients. No patient with an abnormal electrocardiogram or myocardial perfusion had normal long axis motion on echocardiography.

CONCLUSION

The function of the left and right ventricular long axes was abnormal in about 70% of a sample of patients with syndrome X. Systolic disturbances were consistently associated with absent septal q wave and abnormal myocardial perfusion imaging, while early diastolic disturbances correlated with T wave abnormalities. These associations suggest that the three different investigations detect related objective abnormalities in one or more subgroups of patients with syndrome X.

Effect of lemakalim on action potentials, intracellular calcium, and contraction in guinea pig and human cardiac myocytes

OBJECTIVE

The aim was to investigate the effects of lemakalim on action potential duration, intracellular free calcium ([free Ca2+]i), and cell contraction in human and guinea pig cardiac myocytes. In addition, the possible modulation by pH of lemakalim induced activation of ATP sensitive potassium (KATP) channels was assessed.

METHODS

Single ventricular myocytes were enzymatically dissociated from adult male guinea pigs (300-600 g). Single myocytes were isolated from human ventricular tissues. Cells were loaded with the acetoxymethyl ester form of fura-2 to monitor changes in [free Ca2+]i and subjected to conventional electrophysiological techniques.

RESULTS

In guinea pig cells, lemakalim (3, 10, 30 microM) reduced action potential duration in a concentration dependent manner. This decrease was accompanied by hyperpolarisation of the resting membrane potential. Lemakalim (3, 10, 30 microM) reduced the systolic fura-2 fluorescence ratio without having a significant effect on diastolic fluorescence and also reduced the cell contraction in concentration dependent manner. Glibenclamide (1 microM), a specific inhibitor of KATP channels, did not affect action potential duration, fura-2 fluorescence ratio, or cell contraction in the absence of lemakalim. However, the same dose of glibenclamide markedly inhibited the lemakalim induced decrease in action potential duration, fura-2 fluorescence ratio, and cell contraction. Reducing extracellular pH enhanced the decrease in action potential duration induced by lemakalim. In human ventricular myocytes, lemakalim (3, 10 and 30 microM) caused a decrease in action potential duration and systolic fura-2 fluorescence ratio. The reduction in action potential duration and fura-2 fluorescence ratio was also reversed by glibenclamide (1 microM).

CONCLUSIONS

These results suggest that lemakalim reduces systolic [free Ca2+]i by activating ATP sensitive potassium channels which results in a decrease of action potential duration in guinea pig and human ventricular myocytes. The reduction in [free Ca2+]i mediates the negative inotropic effect induced by lemakalim. In addition, pH may modulate the KATP channel activation by the channel opener.

The DEFIANT study of left ventricular function and exercise performance after acute myocardial infarction. Doppler Flow and Echocardiology in Functional Cardiac Insufficiency: Assessment of Nisoldipine Therapy Study Group

The DEFIANT-I study (Doppler Flow and Echocardiography in Functional cardiac Insufficiency: Assessment of Nisoldipine Therapy) was a multicenter, multinational double-blind randomized study of the effects of the new calcium channel blocking drug nisoldipine on left ventricular (LV) size and function after acute myocardial infarction. Randomization to placebo or to long-acting nisoldipine core coat (20 mg once daily) was performed in 135 eligible patients with mild to moderate systolic LV dysfunction (LV ejection fraction < or = 50%) 20 days (range 7-35) after infarction, with serial clinical, echocardiographic, and Doppler cardiographic measurements during a 4 week follow-up period. At the end of the follow-up period, exercise capacity was determined by bicycle ergometry. Nisoldipine improved indices of diastolic LV function. Early diastolic transmitral blood flow velocity increased, with an increase in peak E wave of 0.06 m/sec (95% confidence intervals [CI], 0.01, 0.11) and an increase in time velocity integral of 1.2 cm (95% CI, 0.16, 2.27). Isovolumic relaxation time was reduced by 14.7 msec (95% CI, -22.5, -6.9), a change not explained by the very small (and not significant) changes in systemic arterial pressure, heart rate, or cardiac output. There was no change in systolic and diastolic LV volume, nor in LV ejection fraction. Exercise capacity was greater by 12 watts (95% CI, 0.8, 23.3) in patients receiving nisoldipine, while the incidence of > or = 1 mm ST-segment depression (relative occurrence 0.54, 95% CI, 0.30-0.97) and the incidence of angina pectoris (relative occurrence 0.67, 95% CI, 0.42-1.08) during exercise testing tended to be lower in this group. Although the relations were not exact, peak exercise workload 7 weeks after infarction correlated with resting measurements of diastolic LV function. Exercise workload was inversely related to peak late diastolic transmitral blood flow velocity (A wave, slope, -86.6; 95% CI, -120.9, -52.2) and directly to the E/A ratio (slope, 20.5, 95% CI, 6.0, 35.1). The relations between exercise workload and peak late diastolic flow velocity remained significant after correction for age, sex, resting heart rate, and usage of beta-blocking drugs or nisoldipine. Exercise capacity was not related to measurements of systolic LV function (LV end-diastolic and end-systolic volume, LV ejection fraction, stroke volume, cardiac index). In summary, the calcium channel blocker nisoldipine improved measurements of diastolic LV function in patients recovering from acute myocardial infarction. Exercise capacity was higher in patients receiving the drug, and there was less exercise induced ischemia.(ABSTRACT TRUNCATED AT 400 WORDS)

Assessment of functional capacity in chronic heart failure: time-limited exercise on a self-powered treadmill

OBJECTIVES

To assess the efficacy of a 9-minute walking test on a self-powered treadmill in a group of patients with various degrees of heart failure, to investigate the reproducibility of the technique, and to establish the safety of the technique.

PATIENTS AND METHODS

24 controls and 37 patients with various grades of heart failure were studied. Peak oxygen consumption was measured in patients and controls. The distance walked in 9 minutes on a self-powered treadmill was measured in all groups and the test was repeated to assess reproducibility.

RESULTS

The distance walked in 9 minutes correlated with peak oxygen consumption in patients, controls, and both groups combined. There was a significant difference in the distance walked by controls and patients and in the distance walked by patients with severe rather than with mild or moderate heart failure. There was no significant difference between the results of successive 9-minute walking tests in any group. No serious adverse reaction was seen in any patient during or after the test.

CONCLUSION

The 9-minute walking test on a self-powered treadmill is a sensitive, reproducible, safe, and inexpensive method of assessing functional capacity in patients with all grades of heart failure.

Effects of motivation of the patient on indices of exercise capacity in chronic heart failure

BACKGROUND

Measurement of variables of metabolic gas exchange during exercise is widely used to assess the severity of heart failure. The variables derived however, are potentially dependent on motivation of the patient and duration of exercise.

METHODS

The data from exercise tests in 23 patients with exertional breathlessness were analysed to derive the following three common indices of exercise tolerance: anaerobic threshold, extrapolated maximum oxygen consumption, and the ventilation to carbon dioxide production slope. The data were reanalysed with the data points from the first 90% of subsequent exercise, the first 75%, and finally the data up to the point where a respiratory gas exchange ratio of 1 was reached.

RESULTS

The mean (SEM) anaerobic threshold was lower when computed from 90% of the data points than from 100% (13.2 (1.0) ml/kg/min v 12.5 (1.0), p < 0.001) and lower still from 75% (11.4 (0.7), p = 0.006 v 90%). Extrapolated maximum oxygen consumption was unchanged when computed from 90% of the data, but higher when computed from 75% (25.4 (2.1) ml/kg/min at 100% v 28.6 (2.1) at 75%, p < 0.001). The slope of the ventilation to carbon dioxide production ratio became progressively shallower measured from 90% and 75% of eventual exercise: 32.3 (1.5) from 100% v 30.0 (1.5) from 90%, p < 0.001; and 28.3 from 75%, p < 0.001 v 90%. At a respiratory gas exchange ratio of 1, extrapolated oxygen consumption was unchanged from the final calculation, anaerobic threshold was lower than at 100% of exercise (11.8 (0.9), p = 0.005) and the ventilation to carbon dioxide production slope was shallower (27.5 (1.4), p < 0.001).

CONCLUSIONS

Anaerobic threshold tends to overestimate severity of exercise limitation and extrapolated maximum oxygen consumption and the ventilation to carbon dioxide production slope tend to underestimate severity. Extrapolated maximum oxygen consumption is the most reliable of the three measures, and is independent of effort provided that patients are encouraged to exercise to the point where the respiratory gas exchange ratio exceeds 1.

Coronary flow reserve in patients with chest pain and normal coronary arteries

BACKGROUND

Many studies have shown that coronary flow reserve is reduced in patients with chest pain and angiographically normal coronary arteries. The methods used to assess coronary blood flow have varied, but in nearly all reports dipyridamole has been used to bring about vasodilatation. This study was designed to assess whether the apparent impairment of coronary flow reserve seen with dipyridamole could be reproduced with either papaverine or adenosine, which induce maximum coronary blood flow by different mechanisms.

METHODS

25 patients with chest pain and angiographically normal coronary arteries were studied with an intracoronary Doppler flow probe and quantitative angiography to determine epicardial coronary artery area, coronary blood flow velocity, coronary flow reserve, and coronary vascular resistance index (CVRI, the ratio of resistance after intervention to basal resistance). All patients received papaverine 8 mg. Eight patients with positive exercise tests received intracoronary papaverine (8 and 10 mg), intracoronary adenosine (6, 20, 60 micrograms), and high-dose intravenous dipyridamole (0.84 mg/kg).

RESULTS

The velocity ratio (peak after intervention: baseline) (mean (SEM)) after 8 mg papaverine was 3.3 (0.2) (n = 25) and the coronary flow reserve was 4.1 (0.3) (n = 25). There were no differences between patients with a positive (n = 16) or negative (n = 9) exercise test. In eight patients coronary flow reserve was measured after increasing doses of papaverine, adenosine, and dipyridamole. Coronary flow reserve was 4.5 (0.3) with papaverine, 4.8 (0.3) with adenosine, and 3.5 (0.4) with dipyridamole (p = 0.08 v papaverine and adenosine). CVRI was 0.22 (0.01) with papaverine, 0.21 (0.02) with adenosine, and 0.29 (0.03) with dipyridamole (p < 0.05 v papaverine, p = 0.09 v adenosine).

CONCLUSIONS

These results indicate that measurement of coronary flow reserve and CVRI in patients with chest pain and normal coronary arteries depends on the pharmacological stimulus. Normal values were obtained with papaverine in all patients, irrespective of the exercise test response. In patients with a positive exercise test significantly lower values were obtained with dipyridamole than with papaverine, or adenosine. The reported impairment of coronary flow reserve in patients with angina and normal coronary arteries may reflect the variability in response to different pharmacological agents. The mechanism underlying this variability is unknown, but may involve an abnormality of adenosine metabolism in the myocardium.

Validation of measurement of regional myocardial perfusion in humans by ultrafast x-ray computed tomography

The objective was to validate the measurement of myocardial perfusion in humans by ultrafast computed tomography (CT), by comparing measurements with those from single photon emission computed tomography (SPECT). Measurement of myocardial perfusion with high spatial resolution (including the differentiation of subendocardial and subepicardial perfusion) may be possible by ultrafast CT in humans. Although there are encouraging data from experiments with dogs, the technique has not been validated in humans. In 11 patients, ultrafast CT measurement of regional perfusion in a single short-axis slice was compared with that obtained by SPECT, and in 14, reproducibility of ultrafast CT was evaluated. The ultrafast CT scanner was set to acquire 20 images, gated to end-diastole. The images were divided into 32 equal segments, and the time course and extent of opacification of the left ventricular cavity and myocardium were analyzed to calculate absolute perfusion. The thallium tomograms were also divided into 32 segments for comparison. The pattern of relative perfusion by segment was represented as a curve. In 18 of 22 paired scans, the mean difference of the position of the minimum and maximum points of the curves was less than 4, indicating close agreement between the two techniques. When scoring segmental perfusion as normal or abnormal, there was agreement between the methods in 129 of 176 segments ([symbol: see text] 0.41). Reproducibility (mean difference +/- 1 SD) of basal scans was 0.005 +/- 0.2 mL/min/mL, and during adenosine vasodilation was 0.05 +/- 0.32 mL/min/mL. Absolute perfusion (mean +/- 1 SD) at rest was 0.52 +/- 0.21 mL/min/mL. During adenosine infusion, perfusion increased to a mean of 0.84 +/- 0.42 mL/min/mL. Ultrafast CT and intravenous contrast can be used to assess relative myocardial perfusion in humans, at rest and during adenosine vasodilatation, although it may underestimate absolute perfusion, particularly at high flow.