Selective enhancement of the cardiac sympathetic response to exercise by anginal chest pain in humans

Biochemical Assessment of Pheochromocytoma and Paraganglioma

Pheochromocytoma and paraganglioma (PPGL) require prompt consideration and efficient diagnosis and treatment to minimize associated morbidity and mortality. Once considered, appropriate biochemical testing is key to diagnosis. Advances in understanding catecholamine metabolism have clarified why measurements of the O-methylated catecholamine metabolites rather than the catecholamines themselves are important for effective diagnosis. These metabolites, normetanephrine and metanephrine, produced respectively from norepinephrine and epinephrine, can be measured in plasma or urine, with choice according to available methods or presentation of patients. For patients with signs and symptoms of catecholamine excess, either test will invariably establish the diagnosis, whereas the plasma test provides higher sensitivity than urinary metanephrines for patients screened due to an incidentaloma or genetic predisposition, particularly for small tumors or in patients with an asymptomatic presentation. Additional measurements of plasma methoxytyramine can be important for some tumors, such as paragangliomas, and for surveillance of patients at risk of metastatic disease. Avoidance of false-positive test results is best achieved by plasma measurements with appropriate reference intervals and preanalytical precautions, including sampling blood in the fully supine position. Follow-up of positive results, including optimization of preanalytics for repeat tests or whether to proceed directly to anatomic imaging or confirmatory clonidine tests, depends on the test results, which can also suggest likely size, adrenal vs extra-adrenal location, underlying biology, or even metastatic involvement of a suspected tumor. Modern biochemical testing now makes diagnosis of PPGL relatively simple. Integration of artificial intelligence into the process should make it possible to fine-tune these advances.

Improving myocardial perfusion by percutaneous coronary intervention reduces central sympathetic activity in stable angina

BACKGROUND

By stimulating sympathetic afferents, repetitive myocardial ischemia induces a state of increased sympathetic tone.

HYPOTHESIS

Removing the ischemic trigger by revascularization using percutaneous coronary intervention (PCI) might thus reduce central sympathetic activity in symptomatically stable angina patients.

METHODS

A total of 20 patients with stable angina > or = New York Heart Association (NYHA) class II with persistent symptoms despite maximal pharmacological therapy and a clinical indication for PCI, were included in our study. Sympathetic nervous system activity was measured before and 1 month after PCI by a combination of techniques: direct muscle sympathetic nerve activity (MSNA), neurochemical (plasma catecholamine levels), and heart rate variability (HRV).

RESULTS

All patients completed the study. After PCI there was a significant reduction in MSNA (pre-PCI 72 +/- 4 to post-PCI 53 +/- 4 burst/100 beats, P < .05) and low frequency/high frequency (LF/HF) ratio (3.7 +/- 0.6 vs 2.4 +/- 0.4, P < .05) consistent with a decline in sympathetic activity. Plasma norepinephrine levels were reduced after PCI, but this difference did not reach statistical significance (1.84 +/- 0.17 vs 1.73 +/- 0.13 nmol/L, P = not significant).

CONCLUSION

Coronary revascularization by PCI reduces sympathetic activity in patients with established myocardial ischemia.

Circadian Variation of the Myocardial Ischemic Threshold in Patients with Ischemic Heart Disease

PURPOSE

Circadian variation of the heart rate (HR) at the myocardial ischemic threshold was compared with that of the HR at the sympathetic tone threshold in 16 cases of effort angina pectoris.

METHODS

The high (0.15-0.40 Hz, Hf) and low (0.03-0.15 Hz, Lf) frequency spectral components were extracted every twenty seconds, using frequency domain analysis of the RR interval recorded by a 24-hour Holter ECG with an accelerometer. HR-Hf data collected every five minutes were plotted as the X-Y coordinates, and a two-compartment analysis was performed. The HR at the autonomic tone threshold was then determined at the intersection point of the lines. A loop of the HR-ST segment was drawn during walking to determine the ischemic threshold at which heart rate ischemic ST segment depression began and circadian variation was observed.

RESULTS

The circadian rhythm at the sympathetic tone threshold and the HR at the ischemic threshold were high during the day and low at night. The HR at the ischemic threshold was 15-20% higher than that at the sympathetic tone threshold at night but only 9-13% higher during the day. Also, there was a period during which there was no significant difference between the HR at the two thresholds.

CONCLUSION

In comparing circadian variation between HR at the sympathetic tone threshold and HR at the ischemic threshold, there was a period during which there was no significant difference between the HRs. This might suggest a period in which a high incidence of cardiac ischemic attack is likely. This information could provide a feasible indicator for appropriate exercise training for patients with ischemic heart disease.

Heart rate and catecholamine contribution to QT interval shortening on exercise

BACKGROUND

QT interval shortens with exercise. Some of this shortening is due to an increase in heart rate, and some is due to other effects of exercise, probably mostly neuroendocrine effects. Data from subjects with cardiac transplants have suggested that non-heart rate-related changes in QT interval on exercise are due to the effects of circulating catecholamines.

HYPOTHESIS

We sought to determine whether changes in plasma catecholamine levels with exercise are an important contributor to non-heart rate-related QT interval shortening.

METHODS

Subjects with DDD pacemakers were recruited. Subjects had QT intervals measured at rest, during a low fixed level exercise test designed to increase heart rate to about 110 beats/min, and, after resting, during pacing at a heart rate of 110 beats/min. Catecholamine levels were measured at each stage of the study.

RESULTS

QT interval at rest was 420 +/- 12 ms, during pacing 366 +/- 16 ms, and on exercise 325 +/- 14 ms. This then gave the proportion of QT interval shortening due to heart rate as 68.6 +/- 9.3% of total QT shortening, with the range between 35 and 95.6%. There was no proportionality between the degree of QT interval shortening on exercise that was not due to increases in heart rate and changes in plasma catecholamine levels.

CONCLUSION

Two-thirds of exercise-induced QT interval shortening are due to an increase in heart rate, and one-third to other effects. Changes in plasma catecholamine levels on exercise were not closely related to changes in the QT interval on exercise.

Electrocardiographic exercise stress testing: an update beyond the ST segment

Routine exercise testing is frequently ordered to evaluate a patient's cardiovascular performance. The test is more direct and less expensive than imaging technology, and derives valuable information. New variables such as dyspnea and heart rate recovery, as well as integrated scores, provide incremental value to conventional analysis of exercise-induced angina or electrocardiographic changes. Considerations relating to test accuracy in women need to be weighed. This paper seeks to make physicians aware of the current status of the test, and improve their understanding of and ability to integrate new variables and scores to more effectively manage their patients.

Neurohormonal mechanisms and the role of angiotensin-converting enzyme (ACE) inhibitors in heart failure

Clinical evidence accumulated over the past decade suggests that neurohormonal mechanisms significantly influence the pathogenesis and eventual outcome of congestive heart failure (CHF). Pharmacologic modulation of this neuroendocrine activity can, consequently, be expected to improve patient prognosis. Results of several recent clinical trials--the Studies of Left Ventricular Dysfunction (SOLVD), the second Veterans Administration Cooperative Vasodilator Heart Failure Trial (VH eFT-II), and the Cooperative North Scandinavian Enalapril Survival Study (CONSENSUS)--provide substantial evidence that addition of the angiotensin-converting enzyme (ACE) inhibitor enalapril to conventional therapeutic regimens can significantly reduce mortality and improve prognosis in patients with all grades of heart failure. Moreover, data from all three trials confirm the involvement of neurohormonal systems in the development and progression of CHF and suggest that the beneficial effects of enalapril in heart failure may in part be due to the suppression of this neurohormonal activity. It is now apparent that some form of neurohormonal activation is present early in the course of the disease before the emergence of overt heart failure symptoms. On the basis of such findings, it would seem that early introduction of therapy targeted at neurohormonal influences may well become a central component of any future CHF treatment program.

Clinical application of noradrenaline spillover methodology: delineation of regional human sympathetic nervous responses

The proportionality which in general exists between rates of sympathetic nerve firing and the overflow of noradrenaline into the venous drainage of an organ provides the experimental justification for the use of measurements of noradrenaline in plasma as a biochemical measure of sympathetic nervous function. Static measurements of noradrenaline plasma concentration have several limitations. One is the confounding influence of noradrenaline plasma clearance on plasma concentration. Other drawbacks include the distortion arising from antecubital venous sampling (this represents but one venous drainage, that of the forearm), and the inability to detect regional differentiation of sympathetic responses. Clinical regional noradrenaline spillover measurements, performed with infusions of radiolabelled noradrenaline and sampling from centrally placed catheters, and derived from regional isotope dilution, overcome these deficiencies. The strength of the methodology is that sympathetic nervous function may be studied in the internal organs not accessible to nerve recording with microneurography. Examples of the regionalization of human sympathetic responses disclosed include the preferential activation of the cardiac sympathetic outflow with mental stress, cigarette smoking, aerobic exercise, cardiac failure, coronary insufficiency, essential hypertension and in ventricular arrhythmias, and the preferential stimulation or inhibition of the renal sympathetic nerves with low salt diets and mental stress, and with exercise training, respectively. By application of the same principles, regional release of the sympathetic cotransmitters neuropeptide Y and adrenaline can be studied in humans. Cotransmitter release, however, is detected only with some difficulty. In restricted circumstances we find evidence of regional cotransmitter release to plasma, such as the release of neuropeptide Y from the heart at the very high rates of sympathetic nerve firing occurring with aerobic exercise, and cardiac adrenaline release also with exercise and after loading of the neuronal adrenaline pool by intravenous infusion of adrenaline.

Effects of percutaneous transluminal mitral valvuloplasty on plasma catecholamine levels during exercise

Elevation of plasma catecholamine levels during exercise in patients with mitral stenosis correlated with the severity of the disease. We investigated the plasma norepinephrine changes in six patients before and after percutaneous transluminal mitral valvuloplasty (PTMV) during continuously graded ergometer exercise. Peak exercise intensity was increased from 65.8 W to 87.5 W after PTMV. Plasma norepinephrine level at 60 W workload intensity was decreased from 2308 +/- 864 pg/ml to 841 +/- 233 pg/ml after PTMV (p < 0.05). We concluded that PTMV decreased the plasma norepinephrine level during exercise in the patients with mitral stenosis. Percutaneous transluminal mitral valvuloplasty is a novel procedure for the improvement of symptoms in patients with mitral stenosis.

Comparison of different methods for assessing sympathovagal balance in chronic congestive heart failure secondary to coronary artery disease

Twenty-five patients (aged 62 +/- 2 years) with stable, moderate to severe ischemic congestive heart failure (CHF) (New York Heart Association class II/III: 15/10; ejection fraction 21.6 +/- 2%; and peak oxygen uptake 13.6 +/- 0.7 ml/kg/min) were studied to evaluate the ability of different methods to characterize autonomic tone in chronic CHF. Sympathovagal balance was assessed by: (1) heart rate variability in the time domain, assessed by the SD of RR intervals; (2) heart rate variability in the frequency domain, assessed by low- (0.03 to 0.14 Hz) and high- (0.18 to 0.40 Hz) frequency components of heart rate variability by autoregressive power spectral analysis; (3) 24-hour, daytime and nighttime heart rate; (4) submaximal heart rate during upright bicycle exercise, with respiratory gas analysis to obtain peak oxygen uptake; and (5) radiolabeled norepinephrine spillover. These methods did not correlate, with the exception of day and nighttime heart rate (r = 0.74; p < 0.001) and the expected inverse correlation between low and high frequency (r = -0.92; p < 0.001). No method correlated significantly with peak oxygen uptake, exercise tolerance or ejection fraction. After 8 weeks of physical training at home, all methods showed improvement in autonomic balance: increases in SD of RR intervals (+21%; p < 0.02) and high frequency (+41%; p < 0.007), and decreases in low frequency (-19%; p < 0.002), low-/high-frequency ratio (-48%; p < 0.03), norepinephrine spillover (-28.9%; p < 0.03), 24-hour heart rate (-2.7%; p < 0.005) and submaximal heart rate (-10.8%; p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of sympathoneural activity in clinical research

The assessment of autonomic nervous activity is a frequent and challenging goal of clinical research. The diverse current approaches are reviewed. Direct recording from the sympathetic input to muscle has the advantage of excellent time resolution and directness, but gives no information on the sympathetic input to the internal organs. Plasma noradrenaline concentration has limitations of specificity, some of which are overcome by single isotope radiotracer kinetic techniques. Other chemical markers are less satisfactory. End organ responses are generally limited to cardiovascular and cutaneous autonomic assessment, but sophisticated information is obtainable using power spectral analysis of heart rate variability. Assessment of receptor systems, of first and second messengers and radionuclide imaging of adrenergic nerves all give complimentary information. It is likely that a combination of these diverse techniques will advance understanding of the role of the autonomic nervous system in many disease states.

Plasma noradrenaline as an index of sympathetic tone in coronary arterial disease: the confounding influence of clearance of noradrenaline

Kinetics of [3H]noradrenaline in the plasma were compared with plasma noradrenaline concentration in assessing overall sympathetic activity in six groups totalling 118 subjects. Arterial plasma noradrenaline in 21 control subjects was 204 +/- 14 pg/ml, similar to 20 patients with stable angina not treated with beta-blockers (194 +/- 25 pg/ml) and to 31 patients with stable angina treated with beta-blockers (232 +/- 19 pg/ml). Plasma noradrenaline was increased in 17 patients with unstable angina (366 +/- 50 pg/ml, P less than 0.01), in 14 patients with recent acute myocardial infarction (460 +/- 44 pg/ml, P less than 0.001) and in 15 patients with treated cardiac failure (582 +/- 78 pg/ml, P less than 0.001). Whole body clearance of noradrenaline from plasma was, however, reduced in each of the last three groups compared to controls by 20% (P less than 0.05), by 34% (P less than 0.01) and by 31% (P less than 0.01), respectively. In the 31 patients with stable angina on beta-blockers, clearance of noradrenaline was also reduced by 20% (P less than 0.05). Whole body noradrenaline spillover, a potentially more accurate measure of overall sympathetic activity than concentration of noradrenaline in plasma, was 235 +/- 20 ng min-1 m-2 in controls, was similar in subjects with stable angina (no beta-blockers; 260 +/- 34 ng min-1 m-2, beta-blockers; 200 +/- 17 ng min-1 m-2), but was increased in patients with unstable angina (310 +/- 27 ng min-1 m-2, P less than 0.05), with recent acute myocardial infarction (346 +/- 40 ng min-1 m-2, P less than 0.05) or with heart failure (438 +/- 65 ng min-1 m-2, P less than 0.01). Overall sympathetic activity is unchanged in stable angina, but is progressively increased in patients with unstable angina, recent myocardial infarction or heart failure. Plasma concentration of noradrenaline fails accurately to reflect this as a result of decreased clearance of noradrenaline in these patients. The results show the potential limitations of measurement of noradrenaline in the plasma as an index of overall sympathetic activity and the importance of assessing clearance.