Changes in phasic coronary blood flow velocity profile in relation to changes in hemodynamic parameters during stress in patients with aortic valve stenosis

Comparative assessment of coronary physiology using transthoracic pulsed-wave Doppler and myocardial contrast echocardiography in rats

BACKGROUND

Coronary physiology assessment in rodents by ultrasound is an excellent noninvasive and easy to perform technique, including pulsed-wave Doppler (PWD) and myocardial contrast echocardiography (MCE). Both techniques and the corresponding calculated parameters were investigated in this study at rest as well as their response to pharmacologically induced stress.

METHODS

Left ventricular myocardial function was assessed in eight anaesthetised rats using transthoracic echocardiography. Coronary physiology was assessed by both PWD of the left coronary artery and MCE using a bolus method. Measurements were performed at rest and under stimulation with adenosine and dobutamine. Effects of stimulation on the calculated parameters were evaluated and rated by effect size (η²).

RESULTS

Changes could be demonstrated by selected parameters of PWD and MCE. The clearest effect in PWD was found for diastolic peak velocity (η² = 0.58). It increased from 528 ± 110 mm/s (mean ± standard deviation) at rest to 839 ± 342 mm/s (p = 0.001) with adenosine and 1093 ± 302 mm/s with dobutamine (p = 0.001). The most distinct effect from MCE was found for the normalised wash-in rate (η² = 0.58). It increased from 1.95 ± 0.35% at rest to 3.87 ± 0.85% with adenosine (p = 0.001) and 3.72 ± 1.03% with dobutamine (p = 0.001).

CONCLUSION

Induced changes in coronary physiology by adenosine and dobutamine could successfully be monitored using MCE and PWD in anaesthetised rats. Due to the low invasiveness of the measurements, this protocol could be used for longitudinal animal studies.

The Contribution of Whole Blood Viscosity to the Process of Aortic Valve Sclerosis

OBJECTIVE

We aimed to investigate whether increased whole blood viscosity (WBV) could be an important factor for the occurrence of aortic valve sclerosis (AVS).

SUBJECTS AND METHODS

A total of 209 patients were enrolled in the study. WBV was calculated using the hematocrit and total plasma protein at a low shear rate (LSR) and a high shear rate (HSR). AVS was defined as irregular valve thickening and calcification (without evidence of outflow obstruction) documented by a peak transvalvular velocity < 2.5 m/s on echocardiographic examination. The patient group consisted of 109 patients with AVS (77 females, 32 males), and 100 subjects without AVS (65 females, 35 males) were assigned to the control group.

RESULTS

In the AVS group, WBV values were significantly higher for HSR (17.4 ± 0.5 vs. 17.1 ± 0.7 208 s-1, p < 0.001) and LSR (65.9 ± 12.5 vs. 59.7 ± 16.7 0.5 s-1, p = 0.002). In multivariate logistic regression analysis, WBV at HSR and LSR were independent predictors of AVS (odds ratio, OR: 2.24, 95% confidence interval, CI: 1.38-3.64, p = 0.001; OR: 1.026, 95% CI: 1.006-1.046, p = 0.01, respectively). Receiver-operating characteristic (ROC) curve analysis indicated that a WBV cutoff value of 65.4 at LSR had a sensitivity of 46.8% and a specificity of 60.0% (area under the ROC curve, AUC: 0.615, 95% CI: 0.535-0.696, p = 0.004), and a WBV cutoff value of 17.1 at HSR had a sensitivity of 61.5% and specificity of 53% (AUC: 0.648, 95% CI: 0.571-0.725, p < 0.001) for the prediction of AVS.

CONCLUSION

This study demonstrated that WBV was independently associated with AVS. WBV could be an indicator of inflammation and vessel remodeling without evidence of outflow obstruction.

[Coronary microvascular dysfunction and aortic stenosis: an update]

The coronary microcirculatory impairment is a key feature of the pathophysiology of aortic stenosis (AS), the most operated valvular disease over the world. Several studies showed this coronary microcirculatory impairment in AS, using different tools and protocols, in various patient population of AS. This article will review the impairment of the coronary microcirculation in AS underlining its multifactorial origin, its functional part related to the hemodynamic consequences of AS, its complex relationship with left ventricular hypertrophy, and its potential diagnostic and prognostic value.

In Vitro Investigation of the Impact of Aortic Valve Stenosis Severity on Left Coronary Artery Flow

Patients with aortic valve stenosis (AS) may experience angina pectoris even if they have angiographically normal coronary arteries. Angina is associated with a marked increase in the risk of sudden death in AS patients. Only a few in vitro models describing the interaction between the left ventricular and aortic pressures, and the coronary circulation have been reported. These models were designed for specific research studies and they need to be improved or modified when other specific studies are required. Consequently, we have developed an in vitro model that is able to mimic the coronary circulation in presence of aortic stenosis. First, we have validated the model under physiological conditions. Then, we have examined and quantified the hemodynamic effects of different degrees of AS (from normal to severe AS) on the coronary flow using a model of the normal left coronary artery. In the coronary in vitro model without AS (normal valve), the amplitude and shape of coronary flow were similar to those observed in in vivo measurements obtained under physiological conditions, as described by Hozumi et al. (1998, “Noninvasive Assessment of Significant Left Anterior Descending Coronary Artery Stenosis by Coronary Flow Velocity Reserve With Transthoracic Color Doppler Echocardiography,” Circulation, 97, pp. 1557–1562). The presence of an AS induced an increase in the maximum and mean coronary flow rates (97% and 73%, respectively, for a very severe AS). Furthermore, when AS was very severe, a retrograde flow occurred during systole. This study allowed us to validate our coronary in vitro model under physiological conditions, both in the absence and presence of AS. These changes could explain the fact that even if patients have angiographically normal epicardial coronary arteries, we can observe the occurrence of angina pectoris in these patients in the presence of an AS.

Impairment of coronary flow reserve in aortic stenosis

Coronary flow reserve (CFR) is markedly reduced in patients with severe aortic valve stenosis (AS), but the exact mechanisms underlying this impairment of CFR in AS remain unclear. Reduced CFR is the key mechanism leading to myocardial ischemia symptoms and adverse outcomes in AS patients. The objective of this study was to develop an explicit mathematical model formulated with a limited number of parameters that describes the effect of AS on left coronary inflow patterns and CFR. We combined the mathematical V3 (ventricular-valvular-vascular) model with a new lumped-parameter model of coronary inflow. One thousand Monte-Carlo computational simulations with AS graded from mild up to very severe were performed within a wide range of physiological conditions. There was a good agreement between the CFR values computed with this new model and those measured in 24 patients with isolated AS ( r = 0.77, P < 10−4). A global sensitivity analysis showed that the valve effective orifice area (EOA) was the major physiological determinant of CFR (total sensitivity index = 0.87). CFR was markedly reduced when AS became severe, i.e., when EOA was <1.0 cm2, and was generally exhausted when the EOA was <0.5–0.6 cm2. The reduction of CFR that is associated with AS can be explained by the concomitance of 1) reduced myocardial supply as a result of decreased coronary perfusion pressure, and 2) increased myocardial metabolic demand as a result of increased left ventricular workload.

Cross-Talk Between Cardiac Muscle and Coronary Vasculature

The cardiac muscle and the coronary vasculature are in close proximity to each other, and a two-way interaction, called cross-talk, exists. Here we focus on the mechanical aspects of cross-talk including the role of the extracellular matrix. Cardiac muscle affects the coronary vasculature. In diastole, the effect of the cardiac muscle on the coronary vasculature depends on the (changes in) muscle length but appears to be small. In systole, coronary artery inflow is impeded, or even reversed, and venous outflow is augmented. These systolic effects are explained by two mechanisms. The waterfall model and the intramyocardial pump model are based on an intramyocardial pressure, assumed to be proportional to ventricular pressure. They explain the global effects of contraction on coronary flow and the effects of contraction in the layers of the heart wall. The varying elastance model, the muscle shortening and thickening model, and the vascular deformation model are based on direct contact between muscles and vessels. They predict global effects as well as differences on flow in layers and flow heterogeneity due to contraction. The relative contributions of these two mechanisms depend on the wall layer (epi- or endocardial) and type of contraction (isovolumic or shortening). Intramyocardial pressure results from (local) muscle contraction and to what extent the interstitial cavity contracts isovolumically. This explains why small arterioles and venules do not collapse in systole. Coronary vasculature affects the cardiac muscle. In diastole, at physiological ventricular volumes, an increase in coronary perfusion pressure increases ventricular stiffness, but the effect is small. In systole, there are two mechanisms by which coronary perfusion affects cardiac contractility. Increased perfusion pressure increases microvascular volume, thereby opening stretch-activated ion channels, resulting in an increased intracellular Ca2+transient, which is followed by an increase in Ca2+sensitivity and higher muscle contractility (Gregg effect). Thickening of the shortening cardiac muscle takes place at the expense of the vascular volume, which causes build-up of intracellular pressure. The intracellular pressure counteracts the tension generated by the contractile apparatus, leading to lower net force. Therefore, cardiac muscle contraction is augmented when vascular emptying is facilitated. During autoregulation, the microvasculature is protected against volume changes, and the Gregg effect is negligible. However, the effect is present in the right ventricle, as well as in pathological conditions with ineffective autoregulation. The beneficial effect of vascular emptying may be reduced in the presence of a stenosis. Thus cardiac contraction affects vascular diameters thereby reducing coronary inflow and enhancing venous outflow. Emptying of the vasculature, however, enhances muscle contraction. The extracellular matrix exerts its effect mainly on cardiac properties rather than on the cross-talk between cardiac muscle and coronary circulation.

Impact of intraventricular conduction delay on coronary haemodynamics: a study with intracoronary Doppler in patients with bundle branch blocks and normal coronary arteries

AIMS

The impact of right bundle branch block (RBBB) and left bundle branch block (LBBB) on myocardial perfusion is not completely understood as data are often blurred by underlying cardiac disease. The present study investigates whether conduction delays per se affect coronary perfusion-an indirect measure of myocardial oxygen demand.

METHODS AND RESULTS

Intracoronary Doppler and ultrasound were performed in 8 patients with RBBB, 10 patients with LBBB, and 10 control subjects. All patients had angiographically normal coronary arteries and normal left ventricular function. Baseline (bAPV) and adenosine-induced hyperaemic average flow velocity and coronary flow velocity reserve (CFVR) were measured in left anterior descending arteries. Intravascular ultrasound showed no difference in lumen cross-sectional area and plaque burden between groups. Patients with RBBB and LBBB had higher bAPV values than controls (19.0 +/- 4.9, 21.9 +/- 5.1, and 14.6 +/- 2.4 cm/s, respectively; ANOVA P = 0.003). There was no difference between patients with LBBB and RBBB compared with controls in CFVR (2.8 +/- 0.5, 3.0 +/- 1.0, and 3.4 +/- 0.7, respectively; ANOVA P = 0.21).

CONCLUSION

Bundle branch blocks, in particular LBBB, are associated with an increased coronary flow velocity, which indicates enhanced myocardial oxygen demand on the basis of mechanoenergetic disturbance. This may contribute to the unfavourable outcome of patients with intraventricular conduction delay.

The sensitivity of the heart to static magnetic fields

Static magnetic fields induce flow potentials in arterial flows in and around the heart, that have been detected as distortions in the ECG. The resultant currents flowing through the myocardium could alter the rate or rhythm of the heart. No such changes have been seen in animal experiments, or with humans, in static fields up to 8 T. The possible effects of such currents induced by fields larger than 8 T on cardiac pacemaker rate, and arrhythmogenesis are reviewed, using virtual cardiac tissues-computational models of cardiac electrophysiology. Arrhythmogenesis can be by the initiation of ectopic beats, or by re-entry, whose probability of occurrence is increased by any increase in the electrical heterogeneity, in particular, the action potential duration heterogeneity of the ventricle. Focal ectopic activity would be readily detectable, but since re-entrant arrhythmias are very rare events, even a large increase in their probability of occurrence still leaves them unlikely to be observed. Both of these two arrhythmogenic mechanisms would show a steep sigmoidal, or threshold dependence on induced current intensity, with the threshold for increasing the vulnerability to re-entry less than the threshold for initiating activity. Failure to observe them at fields less than 8 T provides only a lower bound for any threshold for arrhythmogenesis.

Determinants of coronary blood flow in humans: quantification by intracoronary Doppler and ultrasound

The direct determinants of coronary flow are lumen area and blood flow velocity; however, the precise mechanisms that control these factors are not fully understood. The aim of the present study was to assess by which mechanisms lumen area and coronary flow velocity interact with hemodynamic and morphometric factors, thereby influencing coronary flow. Intracoronary Doppler and ultrasound measurements were performed in 28 patients without coronary lumen irregularities. Flow velocity and lumen cross-sectional area were measured in the proximal segments of all three coronary arteries. Global lumen cross-sectional area and global flow were obtained by adding up the values of all three coronary arteries. Left ventricular mass was assessed by echocardiography. Stress-mass-heart rate and pressure-rate products reflecting myocardial oxygen demand were calculated. Global coronary flow increased during adenosine-induced hyperemia from 197 +/- 72 to 637 +/- 204 ml/min (P < 0.001). Global coronary flow closely correlated with the stress-mass-heart rate product (r = 0.62; P < 0.001). Looking at the two constituents of flow separately, global coronary cross-sectional area was closely related to left ventricular muscle mass (r = 0.61; P < 0.001), whereas mean coronary flow velocity at rest showed a strong linear relation with the pressure-rate product (r = 0.64; P < 0.001). There was no interaction between cross-sectional area and blood flow velocity in any of the coronary vessels. Coronary lumen size and flow velocity, the two determinants of coronary flow, are principally determined by different physiological factors. Long-term flow adaptation is achieved by an increase in coronary lumen size, whereas short-term myocardial oxygen requirements are met by changes in resting flow velocity.

Determinants of coronary flow abnormalities in obstructive type hypertrophic cardiomyopathy: noninvasive assessment by transthoracic Doppler echocardiography

We aimed to visualize the coronary flow velocities (CFV) of patients with hypertrophic obstructive cardiomyopathy by using transthoracic Doppler echocardiography, and to determine the relationship between abnormal CFV patterns and conventional echocardiography indices. Guided by 2-dimensional echocardiography and Doppler color flow mapping, CFV in the distal left anterior descending coronary artery were measured in 21 patients with hypertrophic obstructive cardiomyopathy using a 3.5-MHz transducer. The results were compared with those of 18 control subjects. Abnormal systolic flow patterns were observed in 15 (71%) patients (11 systolic-reversal flow and 4 no systolic flow). For patients and control subjects, peak diastolic velocity and velocity-time integral obtained from distal left anterior descending coronary artery were higher (63 +/- 21 cm/s and 18.5 +/- 4 cm vs 41 +/- 11 cm/s and 14.2 +/- 5 cm, respectively; P <.01 for both) whereas peak systolic velocity and velocity-time integral were significantly lower (-17 +/- 10 cm/s and 4.5 +/- 6 cm vs 24 +/- 9 cm/s and 9.5 +/- 4 cm, respectively; P <.001 for both). Significant positive and negative correlations between diastolic CFV and septal thickness index (r = 0.79, P <.0001), and between systolic CFV and septal thickness index (r = -0.65, P <.005), have been observed. CFV abnormalities that could easily be recorded by a standard Doppler echocardiographic study seem to be related to septal thickness rather than the degree of obstruction in hypertrophic obstructive cardiomyopathy.

Doppler echocardiographic effects of medetomidine on dynamic left ventricular outflow tract obstruction in cats

OBJECTIVE

To evaluate the effects of medetomidine on dynamic left ventricular outflow tract (LVOT) obstruction in cats with left ventricular hypertrophy.

DESIGN

Clinical trial.

ANIMALS

6 domestic shorthair cats with echocardiographic evidence of dynamic LVOT obstruction.

PROCEDURE

Cats were restrained in lateral recumbency, and baseline M-mode and Doppler echocardiographic examinations were performed. An ECG was recorded continuously, and blood pressure was measured indirectly with Doppler instrumentation. Medetomidine (20 microg/kg 19.1 microg/lb]) was then administered i.m., and examinations were repeated 15 minutes later.

RESULTS

Significant decreases in heart rate, LVOT velocity, and the LVOT pressure gradient were documented following medetomidine administration. After adjusting for the effects of heart rate by ANCOVA, there were no significant differences in any other systolic or diastolic indices of left ventricular function.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that administration of medetomidine to cats with dynamic LVOT obstruction may result in elimination of outflow tract obstruction; medetomidine may be a suitable sedative and analgesic agent in this subpopulation of cats.

Intracoronary flow velocity measurements in adjacent stenotic and normal coronary arteries during incremental intravenous dobutamine stress and intracoronary adenosine injection

To investigate the concomitant coronary flow and hemodynamic changes induced by dobutamine and adenosine in the catheterization laboratory, we studied stenotic and adjacent normal coronary arteries in 20 patients using paired Doppler Flowires. Coronary flow velocity and hemodynamics were measured sequentially after intracoronary (ic) adenosine, during incremental iv dobutamine infusion, and after the addition of ic adenosine during sustained peak dobutamine stress (adenosine on dobutamine). Distal to stenotic arteries, average peak velocity (APV) increased significantly (from 11 +/- 5 to 16 +/- 7 cm/sec, P < 0.001) at an intermediate dose of dobutamine (20 microg/kg/min, Dobutamine20) but did not change further thereafter to peak dobutamine stress (17 +/- 7 cm/sec), despite the significant further increase in rate-pressure product (RPP). Peak stress APV did not change with adenosine on dobutamine (to 18 +/- 7 cm/sec). In normal arteries, APV increased at Dobutamine20 (from 20 +/- 7.5 to 30 +/- 12 cm/sec, P < 0.01) and further at peak dobutamine stress (to 42 +/- 10 cm/sec, P < 0.0001) always exceeding the concomitant significant increases in RPP. Peak stress APV increased further with adenosine on dobutamine (to 53 +/- 13 cm/sec, P < 0.001). Our data demonstrate that at peak dobutamine stress there is supply/demand mismatch only in stenotic arteries where coronary flow reserve is exhausted at an intermediate dobutamine dose. Furthermore, adenosine on dobutamine potentiates coronary flow heterogeneity between stenotic and normal adjacent arteries. Cathet. Cardiovasc. Intervent. 48:1-9, 1999.

Association of aortic-valve sclerosis with cardiovascular mortality and morbidity in the elderly

BACKGROUND

Although aortic-valve stenosis is clearly associated with adverse cardiovascular outcomes, it is unclear whether valve sclerosis increases the risk of cardiovascular events.

METHODS

We assessed echocardiograms obtained at base line from 5621 men and women 65 years of age or older who were enrolled in a population-based prospective study. On echocardiography, the aortic valve was normal in 70 percent (3919 subjects), sclerotic without outflow obstruction in 29 percent (1610), and stenotic in 2 percent (92). The subjects were followed for a mean of 5.0 years to assess the risk of death from any cause and of death from cardiovascular causes. Cardiovascular morbidity was defined as new episodes of myocardial infarction, angina pectoris, congestive heart failure, or stroke.

RESULTS

There was a stepwise increase in deaths from any cause (P for trend, <0.001) and deaths from cardiovascular causes (P for trend, <0.001) with increasing aortic-valve abnormality; the respective rates were 14.9 and 6.1 percent in the group with normal aortic valves, 21.9 and 10.1 percent in the group with aortic sclerosis, and 41.3 and 19.6 percent in the group with aortic stenosis. The relative risk of death from cardiovascular causes among subjects without coronary heart disease at base line was 1.66 (95 percent confidence interval, 1.23 to 2.23) for those with sclerotic valves as compared with those with normal valves, after adjustment for age and sex. The relative risk remained elevated after further adjustment for clinical factors associated with sclerosis (relative risk, 1.52; 95 percent confidence interval, 1.12 to 2.05). The relative risk of myocardial infarction was 1.40 (95 percent confidence interval, 1.07 to 1.83) among subjects with aortic sclerosis, as compared with those with normal aortic valves.

CONCLUSIONS

Aortic sclerosis is common in the elderly and is associated with an increase of approximately 50 percent in the risk of death from cardiovascular causes and the risk of myocardial infarction, even in the absence of hemodynamically significant obstruction of left ventricular outflow.

Aortic stenosis. Clinical evaluation and optimal timing of surgery

Aortic valve disease is common in the elderly with recent data suggesting that aortic sclerosis and stenosis are the end-stage of an active disease process. Aortic atenosis may be diagnosed at symptom onset (angina, heart failure or syncope) but often the diagnosis is suspected in an asymptomatic patient with a systolic murmur. The diagnosis can be confirmed and disease severity evaluated reliably using Doppler echocardiography. Symptomatic severe aortic stenosis is treated with valve replacement, even in the elderly, due to the extremely poor prognosis without relief of outflow obstruction. Management is controversial when there is coexisting moderate aortic stenosis and left ventricular systolic dysfunction.

Effect of aortic valve replacement on coronary flow velocity during metabolic stress in a patient with aortic stenosis

The effect of aortic valve replacement on coronary flow velocity during atrial pacing and papaverine-induced-resistance vessel dilatation was tested in a patient with aortic stenosis. Although systolic flow reversal disappeared early after the valve replacement, rapid atrial pacing caused myocardial ischemia with lactate production. The coronary flow reserve also remained depressed. These results suggest that the alteration in the coronary flow profile early after the aortic valve replacement does not reflect an improvement in the flow increase during metabolic stress in a patient with aortic stenosis.

Effect of dual chamber atrioventricular sequential pacing on coronary flow velocity in a patient with hypertrophic obstructive cardiomyopathy

Effects of dual chamber AV sequential pacing on coronary flow velocity, especially systolic reversal flow, were tested in a patient with hypertrophic obstructive cardiomyopathy. AV sequential pacing with shorter AV delays reduced the systolic reversal flow in the coronary artery, and improved the pressure gradient of the left ventricular outflow tract.

Influences of aortic pressure gradient and ventricular septal thickness with systolic coronary flow in aortic valve stenosis

This study evaluates flow patterns of the left anterior descending and circumflex coronary arteries by multiplane transesophageal echocardiography in 25 patients with aortic valve stenosis, and assesses the relation between coronary flow characteristics and anatomic and hemodynamic parameters.