Continuous 24-hour assessment of the neural regulation of systemic arterial pressure and RR variabilities in ambulant subjects

In this study, we tested the hypothesis that the neural control of circulation in humans undergoes continuous but in part predictable changes throughout the day and night. Dynamic 24-hour recordings were obtained in two groups of ambulant subjects. In 18 hospitalized patients free to move, direct high-fidelity arterial pressures and electrocardiograms were recorded, and in an additional 28 nonhospitalized subjects, only electrocardiograms were obtained. Spectral analysis of systolic arterial pressure and of RR interval variabilities provided quantitative markers of sympathetic and vagal control of the sinus node and of sympathetic modulation of vasomotor tone. With this approach, the low-frequency (approximately 0.1 Hz) component of RR interval and systolic arterial pressure variabilities is considered a marker primarily of sympathetic activity, whereas the high-frequency (approximately 0.25 Hz) component of RR interval variability, related to respiration, seems to be a marker primarily of vagal activity. We observed a pronounced and consistent reduction in the markers of sympathetic activity and an increase in those of vagal activity during the night. In the invasive studies, while the subjects were still lying in bed after waking up, the markers of sympathetic activity rose rapidly and concomitantly with a simultaneous vagal withdrawal. Noninvasive studies confirmed the early morning rise of the markers of sympathetic activity and the circadian pattern of sympathovagal balance. These data indicate that the ominously increased rate of cardiovascular events in the morning hours may reflect the sudden rise of sympathetic activity and the reduction of vagal tone.

Spectral analysis of R-R and arterial pressure variabilities to assess sympatho-vagal interaction during mental stress in humans

We tested the hypothesis that spectral analysis of the R-R interval and systolic arterial pressure variabilities allows assessment of the dynamic changes in neural control of the cardiovascular system in men undergoing mental stress testing. Mental arithmetic increased the low-frequency components of R-R and systolic arterial pressure, i.e. markers of sympathetic activity to the SA node and the vasculature, respectively; it also decreased the high frequency component of R-R variability, a marker of vagal activity. Spectral analysis of R-R and systolic arterial pressure variabilities may be used in the clinic to test the dynamic effects of mental stress on both sympathetic and vagal activities.

Measurement of mitral valve area in mitral stenosis: four echocardiographic methods compared with direct measurement of anatomic orifices

OBJECTIVES

This study sought to compare the mitral valve areas of patients with rheumatic mitral valve stenoses as determined by means of four echocardiographic and Doppler methods with those obtained by direct anatomic measurements.

BACKGROUND

There has been no systemic comparison between Doppler-determined valve areas and the true anatomic orifice in a single cohort.

METHODS

In 30 patients with mitral stenosis, the mitral valve areas determined by two-dimensional echocardiographic planimetry, pressure half-time, flow convergence region and flow area were compared with the values directly measured on the corresponding excised specimen by means of a custom-built sizer.

RESULTS

The correlation coefficient was r = 0.95 (SE 0.06, p < 0.0001) for two-dimensional planimetry; r = 0.80 (SE 0.09, p < 0.0001) for pressure half-time; r = 0.87 (SE 0.09, p < 0.0001) for flow convergence region; and r = 0.54 (SD 0.1, p < 0.002) for flow area. Two-dimensional echocardiographic planimetry, pressure half-time, flow convergence region and flow area overestimated the actual anatomic orifice by > 0.3 cm2 in 2, 1, 6 and 0 patients, respectively, and underestimated it by > 0.3 cm2 in 0, 4, 1 and 8 patients, respectively.

CONCLUSIONS

Mitral valve areas determined by two-dimensional planimetry, pressure half-time and proximal flow convergence region reliably correlated with size of the anatomic orifice. The flow area method provided a less reliable correlation.

Assessment of the neural control of the circulation during psychological stress

In this study, we used spectral analysis of short-term R-R and systolic arterial pressure (SAP) variabilities to estimate the changes in neural control of the circulation produced by psychological stress. The 0.1 Hz low-frequency (LF) component of R-R and SAP variabilities provided a quantitative index of the sympathetic activity controlling heart rate and vasomotion. Conversely the high-frequency (HF) respiratory component of R-R variability provided an index of vagal tone. In conscious dogs we used the seemingly stressful situation of being accompanied for the first time to the experimental laboratory as a stimulus. In human subjects we used mental arithmetic. In both cases LF of R-R and SAP variabilities increased significantly suggesting enhanced sympathetic activity both to the SA node and the vasculature. In man, the index alpha, a measure of the overall gain of baroreceptor mechanisms, was found to be reduced during mental arithmetic. Spectral analysis of cardiovascular variabilities thus suggests that in man and in conscious dogs psychological challenges induce a profound re-arrangement of neural control of the circulation, which appears to be characterised by sympathetic predominance and which can be monitored by this technique.

Value of transthoracic two-dimensional echocardiography in predicting viability in patients with healed Q-wave anterior wall myocardial infarction

The role of transthoracic echocardiography as a predictor of recovery after revascularization has not yet been established. Two-dimensional echocardiography was performed in 15 patients with a healed anterior wall myocardial infarction and severe, isolated stenosis of the left anterior descending coronary artery before, and 3 to 6 months after angiographically confirmed successful revascularization. The asynergic segments were classified into 2 groups according to 2 different echocardiographic patterns: those showing a normal acoustic reflectance with normal end-diastolic thickness (pattern A segments) and those showing an increase in acoustic reflectance and reduced end-diastolic thickness (pattern B segments). We hypothesized that pattern A segments were more likely to recover (viable myocardium) and that pattern B segments were consistent with irreversibility. A total of 240 segments in the 15 patients were evaluated before and after revascularization. Sixty-seven segments were asynergic; of these, 52 were judged to have pattern A and 15 pattern B. Of the 52 pattern A segments, 27 were hypokinetic and 25 akinetic. All of the pattern B segments were akinetic (n = 9) or dyskinetic (n = 6). Pattern A was predictive of postoperative recovery in 39 of 52 segments (75%) (p < 0.0001); pattern B was predictive of irreversibly damaged tissue in 13 of 15 segments (87%) (p < 0.0001). Thus, in patients with healed anterior wall myocardial infarction, resting transthoracic echocardiography is a simple and reliable predictor of the behavior of asynergic segments after revascularization.

Preoperative assessment of cardiac risk in noncardiac major vascular surgery

We evaluated whether a preoperative clinical algorithm allows an adequate stratification in cardiac risk and the predictive value of dipyridamole thallium-201 scintigraphy and rest echocardiography for postoperative adverse cardiac outcomes. Three hundred twenty patients undergoing 338 vascular surgery procedures were prospectively stratified into low, intermediate, and high risk. The low- and intermediate-risk patients underwent surgery without further diagnostic evaluation. In 7 high-risk patients the vascular procedure was canceled (1 died of myocardial infarction at 6-month follow-up), 9 underwent presurgical myocardial revascularization (1 died of myocardial infarction), and 49 underwent vascular surgery with perioperative intensive care treatment. Hospital mortality was 3.8%. Cardiac mortality and morbidity were 1.5% and 10.4%, respectively. We observed a significant difference in "hard" (death, myocardial infarction, pulmonary edema, major arrhythmias) and "soft" (myocardial ischemia, minor arrhythmias) events between groups, p <0.001. Previous pulmonary edema was a predictive variable of cardiac outcomes (multiple logistic regression analysis). Ninety-nine of 220 intermediate-risk patients randomly underwent dipyridamole thallium-201 scintigraphy: 37 had redistribution, 10 persistent, and 52 no defects; 7 of 13 soft and hard cardiac events occurred in patients without redistribution defects. Sensitivity, specificity, and positive and negative predictive values of redistribution defects for postoperative adverse outcomes were 38%, 63%, 14%, 87%, respectively. This algorithm may provide a safe and cost-effective approach (average cost saving per patient $1,500) to cardiac risk stratification. These results suggest that routine use of dipyridamole thallium-201 scintigraphy for screening of intermediate-risk patients may not be warranted.

Circadian changes in vascular sympathetic activity in ambulant subjects

In 10 ambulant subjects we studied the circadian changes in sympathetic vasomotor control as assessed by the spectral power of the 0.1-Hz low-frequency component of systolic arterial pressure variability measured with a Millar phi 3F tip transducer. The low-frequency component was higher during the daytime, while the subjects were performing light physical activity, and lower during the night, thus paralleling the circadian systolic blood pressure pattern. However, the morning low-frequency rise preceded the blood pressure increase by about 3 h, suggesting that vasometer control and blood pressure control are at least partly related to different mechanisms.

Relationship of unrecognised myocardial infarction, diabetes mellitus and type of surgery to postoperative cardiac outcomes in vascular surgery

OBJECTIVES

to evaluate preoperative clinical, surgical and instrumental variables as predictors of postoperative cardiac events in patients undergoing different types of elective major vascular surgery.

MATERIAL AND METHODS

on the basis of an algorithm including clinical and test echocardiographic data, we prospectively stratified 604 consecutive patients into low, intermediate and high-risk groups. The value of the variables in predicting postoperative cardiac events was assessed by means of multivariate analysis.

RESULTS

there were 16 major postoperative cardiac events and six of 16 postoperative deaths were cardiac related (1%). Significant predictors of cardiac complications were unrecognised myocardial infarction (odds ratio - (OR) 5.6), coronary artery disease (OR 2.5), severe hypertension (OR 2.1) and peripheral vascular surgery (OR 1.9). In the intermediate-risk group, the best correlates with cardiac complications were unrecognised myocardial infarction (OR 3.3) and diabetes (OR 2.5).

CONCLUSIONS

our results suggest the importance of identifying patients with unrecognised ischaemic heart disease and of using aggressive perioperative protocols for managing diabetic patients undergoing peripheral vascular procedures.

Echocardiographic follow-up in patients with mild to moderate mitral stenosis: is a yearly examination justified?

The result of this study showed that echocardiographic and Doppler parameters in patients with mild to moderate mitral stenosis did not undergo any major changes over a relatively long observation period, reflecting the substantial stability of the valve disease process. Thus, unless such patients experience clinical deterioration, a yearly echocardiographic examination appears to be unjustified.