Use of exercise Doppler echocardiography to evaluate cardiac drugs: effects of propranolol and verapamil on aortic blood flow velocity and acceleration

Comparative effects of ivabradine, a selective heart rate-lowering agent, and propranolol on systemic and cardiac haemodynamics at rest and during exercise

AIM

To compare in humans the effects of ivabradine and propranolol on cardiac and systemic haemodynamics at rest, during tilt and exercise.

METHODS

Nine healthy volunteers randomly received single oral doses of ivabradine (Iva, 30 mg), propranolol (Propra, 40 mg) or placebo (Plac) during a double-blind cross-over study. Doses were selected to be equipotent in heart rate (HR) reduction. HR, systolic and diastolic blood pressure (SBP, DBP), cardiac index (CI, bioimpedance), rate pressure product (RPP), plasma epinephrine (E) and norepinephrine (NE), were measured at rest at baseline, before and after two tilt and exercise tests, started 2 and 5 h after drug intake. Heart rate variability (low to high frequency ratio LF/HF) was evaluated at rest and at 5 th minute of tilt.

RESULTS

At rest, HR and RPP decreased similarly with Iva and Propra (both P < 0.01). During tilt, HR increased less with Iva than Propra (P < 0.01), LF/HF decreased after Iva (P < 0.03), SBP and mean blood pressure decreased after Propra (both P < 0.01), RPP decreased similarly after Iva and Propra (both P < 0.01) and CI decreased to a greater extent with Propra than with Iva or Plac (both P < 0.04). During exercise, Iva and Propra similarly decreased HR (both P < 0.01) and RPP (P < 0.01).

CONCLUSIONS

These results demonstrate that for a similar decrease in HR at rest and during sympathetic stimulation, acute administration of ivabradine, a selective heart rate-lowering agent, decreased myocardial oxygen demand to the same extent as a reference beta-blocker, propranolol, but without evidence of depressant effect on cardiac function.

Quantitative Echoca rdiograpy Part III

A comprehensive two-dimensional echocardiographic examination provides useful information that is superior to MT-mode regarding left ventricular chamber sizes and systolic performance, including ejection fraction. Although we rely on visual estimates, quantitative measurements can be particularly valuable in patients with mild or moderate left ventricular systolic dysfunction. Measurements of left ventricular mass by two-dimensional echocardiography is supenror to Ml-mode to detect left ventricular hypertrophy. Two-dimensional echocardiography combined with pulsed Doppler echocardiography can be used to accurately measure stroke volume and to assess changes during medical therapy or after interventions. Future work is needed to assess the significance of continuous-wave Doppler-derived rate of pressure change in patients with mitral regurgitation.

Pulsed wave Doppler echocardiography in normal horses

Reference values were established for selected Doppler derived variables from a group of 40 normal Thoroughbred and Thoroughbred cross horses. Standard two-dimensional (2-D) images used for guiding the Doppler sampling site allowed accurate alignment with flow. Tricuspid inflow velocities during rapid filling (E) and atrial contraction (A) were significantly higher when recorded from a right parasternal angled view than from a right parasternal long-axis view. In 8 horses the tricuspid inflow peak A velocity was higher than the peak E velocity. The peak acceleration of blood flow was higher (P = 0.000) in the aorta (mean 8.01 m/s/s) than in the pulmonary artery (4.45 m/s/s). Significant differences were also noted in the pre-ejection period, ejection time and acceleration time between the 2 vessels. Horses with functional ejection murmurs had lower peak aortic acceleration and a longer acceleration time than horses without flow murmurs. Horses with filling murmurs over the left hemithorax had a significantly higher peak mitral E velocity than horses without such murmurs. Measurements from Doppler waveforms were repeatable and may prove useful in assessing ventricular function in this species.

Doppler determined aortic acceleration after dipyridamole in the prediction of coronary artery disease

Change in the acceleration of aortic blood flow with stress testing is reported to reflect the presence of myocardial ischaemia. We studied its clinical usefulness when compared with dipyridamole thallium scintigraphy in 101 patients, of whom 64 had coronary angiography. Maximum aortic acceleration increased after dipyridamole (P < 0.0001), although no correlation existed between the aortic acceleration and evidence of thallium perfusion abnormalities. For the patients who had angiography, the increase in aortic acceleration was similar for those with no significant coronary stenoses, single vessel or multi-vessel disease. Compared with coronary angiography, Doppler measurement of maximum aortic acceleration had a sensitivity of 92% and a specificity of 37% for the detection of coronary artery disease. When patients with previous myocardial infarction or left ventricular dysfunction were excluded, there was still no relationship between the maximum aortic acceleration and the presence of coronary artery disease. We conclude that changes in the acceleration of aortic blood flow after dipyridamole stressing do not predict the presence or severity of coronary artery disease as measured from perfusion defects at thallium scintigraphy or by coronary angiography. We have observed a wide variability of aortic maximum acceleration in the evaluation of myocardial ischaemia, which we feel introduces serious limitations to its use in routine clinical practice.

A placebo controlled comparison of the effects of metoprolol and celiprolol on echo-Doppler measurements of cardiovascular function in normal volunteers

1. This study used a continuous-wave echo-Doppler method (Exerdrop) to investigate the effects of beta-adrenoceptor antagonism and partial agonism on cardiovascular responses at rest and during dynamic exercise. 2. A double-blind, randomised, placebo controlled comparison of metoprolol (50 mg) and celiprolol (200 mg) was undertaken in nine normal volunteers; single oral doses of medication were administered at weekly intervals. Rest and exercise (supine bicycle) haemodynamics were assessed at 0, 2, 4, 6 and 8 h following dosing. 3. Before dosing and after placebo, the aortic flow velocity, acceleration and velocity integral increased progressively during exercise, as did heart rate, blood pressure and cardiac output. 4. Following metoprolol 50 mg, heart rate was significantly reduced without change in systolic or diastolic blood pressure. Echo-Doppler peak acceleration and velocity decreased at rest. On exercise, heart rate and systolic blood pressure fell significantly; the increase in acceleration was significantly blunted compared with placebo (a decrease of 15.2% at rest and 22.9% at 75 watts; P < 0.01 vs placebo). Peak velocity fell significantly by 75 watts exercise. 5. Celiprolol 200 mg at rest significantly increased systolic blood pressure, peak acceleration and velocity. On exercise celiprolol, in contrast to metoprolol, did not reduce peak acceleration or peak velocity; however exercise heart rate and systolic blood pressure were significantly reduced. The difference between celiprolol and metoprolol in respect of peak acceleration persisted over the 8 h of the study. 6. These differences between metoprolol and celiprolol are compatible with the partial agonism of celiprolol.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal left ventricular early diastolic filling during dobutamine stress Doppler echocardiography is a sensitive indicator of significant coronary artery disease

OBJECTIVES

This study was designed to assess changes in Doppler indexes of left ventricular ejection and filling in response to high dose (40 micrograms/kg body weight per min) dobutamine stress and their utility in detection of coronary artery disease compared with that of new wall motion abnormalities.

METHODS

Ten patients with a low likelihood of coronary artery disease served as a control group, and 23 patients with documented single-vessel coronary artery disease underwent baseline and peak dobutamine echocardiographic and Doppler studies.

RESULTS

In both groups dobutamine induced similar increases in heart rate and systolic blood pressure. During the test, 14 patients had new wall motion abnormalities, 13 had angina, and 7 had electrocardiographic ST segment changes. No markers of ischemia occurred in the control subjects. Dobutamine induced qualitatively similar changes from baseline to peak dobutamine stress in control subjects and patients in peak aortic velocity (46% vs. 42%, p = NS), average aortic acceleration (61% vs. 43%, p = 0.03) and systolic time-velocity integral (7% vs. 2%, p = NS). Dobutamine caused marked increases in control subjects and decreases in patients in peak early filling velocity (E) (33% vs. -22%, p < 0.0001) and average E acceleration (76% vs. -28%, p < 0.0001). The response of Doppler early filling indexes to dobutamine stress was abnormal in all patients. There was no overlap in the percent change from baseline to peak dobutamine stress between control subjects and patients for E and E acceleration.

CONCLUSIONS

During dobutamine stress testing, an abnormal response of Doppler indexes of left ventricular early filling is a more sensitive marker of significant single-vessel coronary disease than are new wall motion abnormalities, and it is far superior to the response of Doppler ejection variables as a predictor of coronary artery disease.

Pharmacodynamics of racemic and S(-)-atenolol in humans

The cardiovascular actions of racemic atenolol (RSATN) have been well characterized in humans, but the actions of S(-)-atenolol (SATN) when administered alone are unknown. In this study, responses of heart rate (HR) and Doppler-derived aortic blood flow profiles to upright treadmill exercise were compared after oral administration of 50 mg SATN and 100 mg RSATN in eight healthy, adult, male volunteers. After a single-blind, placebo run-in period, subjects were randomly allocated in a double-blind, crossover fashion to receive SATN and RSATN. Each study period was separated by a 7-day washout period. Multiple submaximal exercise tests were performed and data were collected over the 24 hours after each treatment. Both SATN and RSATN significantly (P < .05) blunted peak exercise HR by 38 +/- 3 and 37 +/- 3 beats/min, respectively. Aortic blood flow acceleration measured during peak exercise decreased after SATN and RSATN, by 13 +/- 4 and 13 +/- 3 m/sec2, respectively (P < .05). No difference in hemodynamic effect was observed between treatments. Pharmacodynamic parameters derived from plasma S(-)-atenolol concentration-effect (HR) curves after SATN, RSATN, and total atenolol plasma concentrations after RSATN did not differ significantly. Predicted maximum reductions in heart rate (Emax) and EC50 for S(-)-atenolol after SATN were 39.6 +/- 5.8 beats/min and 38.4 +/- 40.9 ng/ml versus 34.5 +/- 8 beats/min and 25.9 +/- 29.9 ng/ml for RSATN, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of rider position on continuous wave Doppler responses to maximal cycle ergometry

Using 10 well-trained (VO2peak = 60.6 ml kg-1min-1) college age cyclists and continuous wave Doppler echocardiography, peak acceleration (PkA) and velocity (PkV) of blood flow in the ascending aorta, and the stroke velocity integral (SVI) were assessed to determine if rider position influenced the central haemodynamic responses to graded maximal cycle ergometry. Cyclist position was determined by hand placement on the uprights (UPRI) or drops (DROP) of conventional handlebars or using aerodynamic handlebars (AHB). All subjects consistently achieved a peak workload of 300 W. The Doppler variables did not differ significantly between rider positions at each stage of the maximal exercise tests but did change in response to increasing workloads. PkA was significantly (P < 0.05) greater at workloads > or = 240 W versus < or = 120 W. PkV increased significantly (P < 0.05) up to 180 W and then reached a plateau. SVI increased to a workload of 120 W and then progressively declined, becoming significantly (P < 0.05) less at 300 W. For each stage, neither submaximal VO2, VI nor heart rate (HR) differed significantly between each trial. These results suggest that rider position does not affect the physiological response to maximal bicycle ergometry as responses to each position are similar.

Vascular characteristics influence the aortic ultrasound Doppler signal: computer and hydraulic model simulations

There is an increasing demand for non-invasive methods for the assessment of left ventricular function. Ultrasound Doppler methods are promising, and the early systolic flow velocity signal immediately distal to the aortic valve has been used clinically for this purpose. However, the signal is influenced not only by left ventricular ejection but also by systemic vascular characteristics. Their relative contribution to the time-velocity signal has not been analysed in depth previously. A theoretical analysis, based on a three-element Windkessel model, neglecting peripheral outflow in early systole and assuming linear pressure rise, was therefore tested in computer and hydraulic model simulations where peripheral outflow was included. Significant changes in early aortic flow velocity parameters were found when vascular characteristics were altered. As predicted by the theory, with a standardized aortic valve area and aortic pressure change, the simulations confirmed that maximal flow velocity is related to compliance of the aorta and the large arteries, and that maximal acceleration is inversely related to the characteristic impedance of the aorta. Therefore, maximal velocity and acceleration can be used for assessment of left ventricular function only in situations where vascular characteristics can be considered relatively constant or where they can be estimated.

Exercise Doppler: functional evaluation of right heart dynamics

Exercise echocardiography is a versatile technique that includes not only two-dimensional imaging, but also Doppler of aortic, mitral, and tricuspid valves. Doppler echocardiography can be useful in the evaluation of global left ventricular systolic and diastolic function, valvular function, transvalvular gradients, and pulmonary artery pressure. The technique lends itself to the study of the cardiac response to exercise in a variety of disease states, including pulmonary, coronary artery, valvular, and congenital heart disease. We review our experience using agitated saline-enhanced Doppler of tricuspid insufficiency to determine pulmonary artery pressure throughout exercise in chronic lung disease.

Stress Doppler echocardiography in the evaluation of ischemic heart disease

Doppler echocardiography enables convenient, noninvasive evaluation of global, systolic performance at rest and during exercise. Early studies suggested that Doppler parameters of systolic function were sensitive to exercise-induced myocardial ischemia and could identify patients with severe coronary artery disease. Subsequent investigation, however, has identified several factors in addition to myocardial ischemia that can significantly influence exercise Doppler study results. Thus, in order to obtain reliable information, the many factors that can influence Doppler measurements of aortic flow velocity and acceleration must be accounted for. Further work in this area is likely to produce results that encourage greater application of this technique in experimental and clinical research. At present, the role of stress Doppler echocardiography in the evaluation of ischemic heart disease remains uncertain.

The relation between radionuclide angiography and Doppler echocardiography during contractile changes with infusions of epinephrine

To define the quantitative relations between radionuclide and Doppler measures of systole during sympathetic activation with epinephrine, 10 young normal men were studied with simultaneous radionuclide angiography and M-mode and Doppler echocardiography during graded infusions of epinephrine (10, 25 and 50 ng/kg/min for 12 minutes each). During a nine-fold increase in circulating levels of epinephrine in arterialized plasma (94 +/- 59 to 879 +/- 310 pg/ml, P less than 0.001), the heart rate increased from 58 +/- 8 to 73 +/- 7 beats/min (P less than 0.01), whereas the mean arterial pressure fell from 82 +/- 3 to 75 +/- 6 mmHg (NS) and end-systolic wall stress decreased from 97 +/- 6 to 67 +/- 10 dynes/sec (P less than 0.01). The ejection fraction as estimated using radionuclide techniques increased from 68 +/- 6 to 83 +/- 6%, the peak ejection rate measured in this way increased from -3.36 +/- 0.3 to -5.10 +/- 0.5 end-diastolic volumes/sec, the ejection fraction as estimated with M-mode echocardiography increased from 66 +/- 5 to 83 +/- 5%, the echocardiographic ventricular dimension shortening increased from -1.78 +/- 0.2 to -2.7 +/- 0.4 sec-1, the peak aortic outflow velocity as measured with Doppler techniques increased from 98 +/- 13 to 147 +/- 25 cm/sec, and the aortic outflow acceleration velocity increased from 11 +/- 3 to 27 +/- 7 m/sec2 (all P less than 0.001). There was a significant correlation between the changes in radionuclide and M-mode estimations of ejection fractions (r = 0.82), between the radionuclide peak ejection rate and M-mode peak dimension shortening (r = 0.80) and between the radionuclide peak ejection rate and the Doppler peak aortic outflow velocity (r = 0.90) (all P less than 0.01). We conclude that corresponding radionuclide and Doppler echocardiographic measurements of systolic function are altered similarly during increased sympathetic activation with epinephrine.

Pronounced reduction of aortic flow velocity and acceleration during heavy isometric exercise in coronary artery disease

Doppler-derived parameters of aortic flow were examined during heavy isometric exercise in 48 men with coronary artery disease (CAD) and in 48 gender- and age-matched healthy controls. The aim was to determine which parameters best separated the groups and to look for a possible relation between exercise-induced Doppler patterns and the extent of CAD. Isometric exercise was performed with a 2-hand bar dynamometer, and the subjects were required to perform 50% of maximal voluntary contraction for 2 minutes. Examination was performed with a pulsed Doppler transducer positioned at the suprasternal notch. Resting peak flow velocity, acceleration time, stroke volume index and cardiac index did not show significant differences between the groups. However, mean acceleration and stroke work were significantly lower in patients with CAD. In this group, exercise peak flow velocity decreased from 98 +/- 13 to 55 +/- 12 cm/s, flow velocity integral from 14 +/- 3 to 7 +/- 3 cm, mean acceleration from 11 +/- 0.9 to 4.7 +/- 1 m/s/s, and stroke volume index from 41 +/- 6 to 23 +/- 4 ml/m2 (p less than 0.001 for all). Cardiac index decreased from 2.7 +/- 0.4 to 2 +/- 0.2 liters/min/m2 (p less than 0.05). Acceleration time increased from 82 +/- 6 to 116 +/- 7 ms. In most of the indexes, the directional changes induced by isometric exercise were similar in patients with CAD and in normal control subjects. The differences compared with the rest values were significantly greater in the CAD group, and especially in patients presenting with 3-vessel disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic evaluation of bisoprolol after coronary artery surgery in patients with altered left ventricular function

Bisoprolol is a new cardioselective beta1 adrenergic blocking agent without intrinsic sympathomimetic activity but with minimal effects on myocardial contractility. Bisoprolol was compared to propranolol in 24 patients after cardiac surgery for coronary artery bypass graft (CABG). Each patient had been treated preoperatively with beta-blocking agents and had a cineangiographic left ventricular ejection fraction between 35% and 55%. Patients were randomized to receive orally either 10 mg of propranolol three times a day or 5 mg of bisoprolol once a day. Both drugs resulted in a significant and similar decrease in heart rate. This was associated with significant decreases in cardiac index, stroke index, and thermodilution right ventricular ejection fraction 6 hours after administration of propranolol, but not after bisoprolol. Systolic function measured by Doppler techniques significantly increased in the 10 postoperative days in patients under bisoprolol but not significantly after propranolol. Each drug was well tolerated during the 10 postoperative days, and the recovery was uneventful in each patient. These results indicate that in patients with altered systolic function after CABG, bisoprolol is susceptible to reduce heart rate with less cardiovascular alteration than propranolol.

Influence of sympathetic stimulation and parasympathetic withdrawal on Doppler echocardiographic left ventricular diastolic filling velocities in young normal subjects

To determine the effects of parasympathetic withdrawal or sympathetic stimulation on Doppler echocardiographic measures of left ventricular diastolic filling, we studied 10 young normal subjects aged 21 to 29 years during separate infusions of atropine (0.8 mg followed by 0.4 mg every 10 minutes until heart rate greater than 110 beats/min or a total dose of 2 mg was attained) and epinephrine (10, 25 and 50 ng/kg/min for 12 minutes each). At the highest atropine dose, heart rate increased from 60 +/- 9 to 105 +/- 8 beats/min (mean +/- standard deviation), the diastolic filling period decreased by 61% (573 +/- 141 to 222 +/- 34 ms), the peak early (E) filling decreased 23% (77 +/- 12 to 61 +/- 11 cm/s), the peak atrial (A) filling increased 103% (40 +/- 6 to 81 +/- 17 cm/s), and the E/A ratio decreased by 60% (2.0 +/- 0.5 to 0.8 +/- 0.3) (all p less than 0.001). These alterations were not correlated to changes in systolic function, preload, blood pressure or plasma catecholamines, all of which were unchanged. However, atropine-induced changes in diastolic filling period were highly correlated to changes in E peak (r = 0.64, p less than 0.01), A peak (r = -0.95, p less than 0.001) and the E/A ratio (r = 0.93, p less than 0.001). The effects of atropine on the E/A ratio were normalized by dividing the E/A ratio by the diastolic filling period (E/A/diastolic filling period).(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic effects of calcium channel and beta-receptor antagonists: evaluation by Doppler echocardiography

To evaluate the ability of Doppler echocardiography to identify hemodynamic changes due to cardiac medications, 10 volunteers underwent Doppler examination at rest and immediately following vigorous treadmill exercise. Upon completion of the control test, each subject received moderate oral doses of propranolol, verapamil, pindolol, or nifedipine, and the same exercise protocol was repeated. During four control tests, values for peak acceleration and flow velocity integral were similar for each subject at rest and exercise. Following propranolol and pindolol, resting acceleration fell by 4.5 and 2 m/sec2, respectively p less than 0.05. Resting acceleration was unchanged by verapamil and increased following nifedipine by 1.7 m/sec2 (p less than 0.0001), but neither verapamil nor nifedipine altered either Doppler parameter. Flow velocity integral was increased by nifedipine at rest and by each of the beta-blockers during exercise (p less than 0.05). We conclude that (1) rest and exercise Doppler measurements are stable and reproducible, given stable cardiovascular status; (2) pindolol produced less hemodynamic depression as measured by Doppler echocardiography at rest relative to propranolol, but showed similar potency at maximal exertion; (3) nifedipine enhanced global cardiac performance at rest, but neither calcium antagonist affected Doppler measurements during exercise; and (4) Doppler echocardiography is a useful, noninvasive technique for evaluating hemodynamic effects of medication at rest and during vigorous exercise.

Noninvasive assessment of intrinsic ventricular load dynamics in dilated cardiomyopathy

On the basis of hemodynamic theory, a new noninvasive method is developed to provide improved insights into the significance of depressed Doppler left ventricular ejection variables in patients with dilated cardiomyopathy. The net force (F) associated with intraventricular flow throughout ejection can be written as: F = A.dv/dt + B.v2, where v is the ejection velocity and A and B are variables related to the geometry of the ventricle and its outflow tract. Instantaneous levels of this force were calculated in 9 normal subjects and 10 patients with dilated cardiomyopathy using Doppler, M-mode and two-dimensional echocardiography. The maximal ejection force (Fmax) was 47.5 +/- 8.5 kdyn in normal subjects and 25.5 +/- 6.2 kdyn in those with dilated cardiomyopathy (p = 0.0001). Peak local acceleration and outflow velocity were severely depressed in those with cardiomyopathy compared with normal subjects (1,260 +/- 129 versus 2,671 +/- 430 cm/s2 and 71 +/- 14 versus 109 +/- 7 cm/s, respectively; p = 0.0001). Maximal ejection force was attained very early in ejection. A significant linear correlation was found between peak outflow acceleration and maximal ejection force (n = 19; r = 0.91, p = 0.0001). At the time of peak ejection velocity, the net force had decreased to 64% of its peak value in those with cardiomyopathy, whereas in normal subjects, it had decreased to only 84% of its peak value (p = 0.008). In normal subjects, the ejection force was positive during the first 75% of ejection, but in those with cardiomyopathy, it was positive only during the first 54% (p = 0.0003). Once its peak value was attained, total left ventricular systolic wall stress declined rapidly during ejection in normal subjects (to 33% of its peak value by end-ejection), whereas it remained elevated throughout ejection in patients with cardiomyopathy (at 60% of its peak value by end-ejection, p = 0.0001 versus normal). The maximal ejection force corresponded to a calculated intraventricular peak pressure gradient of 9.8 +/- 1.6 mm Hg in normal subjects and 6 +/- 1.2 mm Hg in those with cardiomyopathy (p = 0.0001). The average contribution of the intrinsic component of the left ventricular systolic load (that is, wall stress associated with the ventricular to aortic pressure gradient) to the total myocardial load was 9.1% (range 7.3% to 11.2%) in normal subjects and 6.2% (range 3.9% to 7.5%) in those with cardiomyopathy (p = 0.0001).(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of beta-adrenergic blockade upon hemodynamic response to exercise assessed by Doppler echocardiography

Peak aortic blood flow acceleration and velocity measured by Doppler echocardiography have been documented to be accurate descriptors of left ventricular systolic function. Both acceleration and velocity are reduced in the presence of beta-blockade at rest and during exercise. Whether and to what extent the simultaneous alterations in heart rate (HR) due to beta-blockade affect these parameters has received little study. In order to determine the influence of alterations in HR on Doppler measurements of velocity and acceleration, 10 healthy men were studied during upright exercise under control conditions, following propranolol administration, and following propranolol plus transesophageal atrial pacing. In addition, we assessed the response of stroke volume (measured as flow velocity integral) during beta-blocked and control exercise. Propranolol significantly reduced acceleration and velocity during all stages of exercise compared with control values (p less than 0.05). Increasing the HR during exercise via pacing had no effect on acceleration or velocity compared with propranolol administration alone, thus demonstrating that during upright exercise, changes in acceleration and velocity are independent of alterations in HR. At low levels of exercise, propranolol significantly reduced flow velocity integral (FVI) compared with control (-1.14 cm, p less than 0.05.). At high levels of exertion, however, FVI exceeded values obtained during control conditions (1.2 cm at stage 4). Pacing during beta-blockade reduced FVI at high levels of exercise but had no effect at lower levels. Our results suggest that during low levels of exercise stroke volume is increased as a consequence of both increased contractility and augmented left ventricular filling.(ABSTRACT TRUNCATED AT 250 WORDS)

A simplified normalized ejection phase index measured by Doppler echocardiography for the assessment of left ventricular performance

Although useful for the assessment of directional changes in contractility in individual patients, resting peak aortic blood velocity is of limited value for differentiating among patients with different levels of basal cardiac function. A dimensional analysis based on fluid dynamics shows that peak aortic blood velocity is not only generated by the contracting myocardium but also reflects the convective acceleration of blood from the left ventricle to the aorta. The reduction of cross-sectional area from the midleft ventricle to the aorta at the time of peak aortic blood velocity generates the convective acceleration. Accordingly, a higher convective acceleration due to left ventricular (LV) enlargement as observed in cardiomyopathy may explain why peak aortic blood velocity can be maintained as normal although myocardial contractility is depressed. This study tested the hypothesis that peak aortic blood velocity normalized by the ratio of midleft ventricle to aortic cross-sectional areas might provide a reliable index of LV performance. Nine normal control subjects and 25 patients undergoing catheterization were studied by M-mode, 2-dimensional and Doppler echocardiography. The normalized peak velocity measured noninvasively showed a high correlation with angiographic ejection fraction (r = 0.90, p less than 0.0001). Peak aortic blood velocity and the ratio of midleft ventricle to aortic cross-sectional areas alone correlated less well with ejection fraction (r = 0.76 and r = 0.75, p less than 0.0001, respectively). Furthermore, peak aortic blood velocity showed a significant overlap between patients with normal and those with abnormal LV function, whereas normalized peak aortic blood velocity was a better discriminator.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise responses in patients with congenital heart disease after Fontan repair: patterns and determinants of performance

After a Fontan repair for congenital heart disease, 42 patients underwent graded supine bicycle exercise tests at levels relevant to normal daily activities. Results were compared with those of 28 age-matched normal control subjects. At rest, the cardiac index, stroke index and systolic blood pressure were comparable in both groups, but increases with exercise were smaller in the patients with a Fontan circulation. The heart rate at rest was higher in the Fontan group, but this difference disappeared as soon as exercise started. To determine whether there are limitations intrinsic to the Fontan circulation at these levels of exercise, the 10 best performers were compared with 10 age-matched control subjects; no differences were found in cardiac index, stroke index, heart rate or blood pressure at any exercise level. Analysis of the determinants of cardiac output showed that at the other end of the spectrum poor performance after a Fontan operation did not result from inadequate levels of heart rate, but from an inability to increase or maintain stroke volume. Multivariate analysis demonstrated that impairment of ventricular contractility, only when severe, predicted limited performance. There was no evidence of increased afterload, particularly in the poor performers. Therefore, ventricular filling, which is determined primarily by the pulmonary vascular bed, appears to be a major determinant of functional result after a Fontan repair.

Influence of alterations in loading produced by lower body negative pressure on aortic blood flow acceleration

The objectives of this study were to evaluate the effects of alterations in loading induced by lower body negative pressure on aortic blood flow velocity and acceleration. Twenty-seven normal men were studied during various levels of lower body negative pressure (0 to -60 mm Hg) during which echocardiographic, Doppler and hormonal measurements were obtained. Lower body negative pressure induced a decrease in left ventricular diastolic diameter from 5.18 +/- 0.08 to 4.41 +/- 0.1 cm (p less than 0.0001) and in left ventricular systolic diameter from 3.33 +/- 0.09 to 2.84 +/- 0.1 cm (p less than 0.0001). Shortening fraction remained unchanged. The decrease in diastolic diameter resulted in a reduction in flow velocity integral from 13.8 +/- 0.8 to 7.5 +/- 0.4 cm (p less than 0.0001) and, therefore, in stroke volume from 89.6 +/- 4.7 to 49.5 +/- 2.8 ml (p less than 0.0001). Heart rate reflexly increased from 62.5 +/- 1.9 to 82.2 +/- 2.3 beats/min (p less than 0.0001) as did systemic vascular resistance from 1,280.8 +/- 69.5 to 1,863.4 +/- 121.4 dyne.s.cm-5 (p less than 0.0001). The increase in heart rate was insufficient to maintain cardiac output, which decreased from 5.53 +/- 0.29 to 3.99 +/- 0.21 liters/min (p less than 0.0001). Systolic, diastolic and mean arterial blood pressure was maintained. The negative pressure resulted in a concomitant significant increase in norepinephrine levels from 1.46 +/- 0.09 to 2.056 +/- 0.2 nmol/liter (p = 0.0019) but no change in plasma epinephrine: 0.845 +/- 0.22 to 0.78 +/- 0.11 nmol/liter (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of heart rate on Doppler indexes of systolic function in humans

Recent investigations have shown Doppler echocardiography to be useful in the noninvasive assessment of left ventricular systolic function. No data exist, however, regarding the influence of heart rate on Doppler measurements of aortic blood flow velocity and acceleration in humans. Thus, 12 normal volunteers underwent continuous wave Doppler ultrasound recording from the suprasternal notch at baseline and during progressive transesophageal atrial pacing at intervals of 10 beats/min between 90 and 140 beats/min while 100% atrial capture and 1:1 atrioventricular conduction were maintained. Subjects were studied both upright (n = 12) and supine (n = 10). With the subject upright at baseline (mean heart rate 77.8 +/- 10.6 beats/min), peak acceleration averaged to 16.8 +/- 3.4 m/s2, and peak modal velocity and flow velocity integral averaged 0.72 +/- 0.14 m/s and 8.4 +/- 2.1 cm, respectively. With pacing at 90 beats/min, peak acceleration decreased to 15.6 +/- 3.6 m/s2, a significant decline from baseline values (p less than 0.005). Similar declines were seen during pacing at 90 beats/min for peak modal velocity and flow velocity integral (0.64 +/- 0.16 m/s and 7.1 +/- 1.9 cm, respectively; both p less than 0.005 versus baseline values). At the peak pacing rate of 140 beats/min, average peak acceleration decreased to 12.8 +/- 3.1 m/s2, and peak modal velocity and flow velocity integral decreased to 0.52 +/- 0.11 m/s and 5.02 +/- 1.25 cm, respectively. A significant linear correlation (r greater than or equal to 0.97, p less than 0.0001) was obtained for the relation between heart rate and peak acceleration, peak modal velocity and flow velocity integral.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of dipyridamole-Doppler echocardiography to thallium-201 imaging and quantitative coronary arteriography in the assessment of coronary artery disease

This study was undertaken to determine whether Doppler measurements of systolic aortic and diastolic mitral blood flow velocities could reliably detect the presence of reversible myocardial perfusion defects during intravenous dipyridamole-thallium-201 imaging. In addition, the ability of dipyridamole-Doppler echocardiography to predict the presence of significant coronary artery disease (CAD) was evaluated. Baseline and post-dipyridamole Doppler studies were performed in 10 normal control subjects and 23 patients with CAD. Aortic peak velocity and acceleration increased from baseline to post-dipyridamole in normal subjects by 0.07 +/- 0.07 m/s (p = 0.016) and 2.1 +/- 2.0 m/s2 (p = 0.009), respectively. The ratio of early to late peak transmitral velocities decreased slightly in normal subjects, by 0.18 +/- 0.72 (difference not significant), whereas the ratio of early to late transmitral velocity-time integrals increased by 0.07 +/- 0.93 (difference not significant). The response of aortic velocity and acceleration to intravenous dipyridamole was not significantly different between normal subjects, patients without reversible thallium-201 perfusion defects and patients with reversible thallium-201 perfusion defects. Furthermore, only 3 of 14 subjects with reversible thallium-201 perfusion defects had abnormal (greater than 2 standard deviations from the mean) responses of aortic velocity or acceleration to intravenous dipyridamole. No patient had an abnormal response of the early to late mitral peak velocity ratio. In addition, the response of Doppler aortic and mitral indexes to intravenous dipyridamole was not able to identify the presence of significant CAD as assessed by quantitative coronary arteriography.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the Frank-Starling mechanism in maintaining cardiac output during increasing levels of treadmill exercise in beta-blocked normal men

To determine the effects of beta blockade on hemodynamics during increasing levels of treadmill exercise, 10 healthy volunteers were studied after 1 week of placebo, and then after 1 week of treatment with oral propranolol, 80 mg twice daily, or dilevalol, 400 mg once daily. The study was randomized and double-blind, with a crossover sequence. Hemodynamics were measured by CO2 rebreathing at rest and at 25, 50, 75 and 100% of VO2 max. After placebo, cardiac output increased from 5.8 +/- 2.1 (rest), to 19.4 +/- 6.4 liters/min (100% VO2 max), mainly due to an increase in heart rate from 84 +/- 6 to 169 +/- 15 beats/min. Stroke volume increased from 70 +/- 27 (rest), to 137 +/- 65 ml (25% VO2 max), and then leveled off to 116 +/- 41 at 100% VO2 max. After both beta blockers, exercise cardiac output was maintained at 100% VO2 max: 20.1 +/- 9.3 liters/min with propranolol and 19.1 +/- 8.6 with dilevalol. However, a significant reduction versus placebo values was observed for cardiac output at 25% VO2 max, from 13.7 +/- 5.9 during placebo, to 9.4 +/- 2.5 during propranolol, and to 9.6 +/- 2.3 during dilevalol (both p less than 0.01 vs placebo). Maintenance of cardiac output with both beta blockers at higher levels of exercise came from an increased stroke volume (p less than 0.05 vs placebo), while heart rate (in beats/min) was greatly reduced (propranolol 61.6 +/- 9.4 rest, 90.1 +/- 10.7 at 100% VO2 max; dilevalol 70.8 +/- 6.4 rest, 99.2 +/- 11.8 at 100% VO2 max, p less than 0.01 vs placebo for each).(ABSTRACT TRUNCATED AT 250 WORDS)