[Determining myocardial perfusion--contribution of contrast echocardiography]

There is great demand for a non-radioactive bed-side method for the assessment of myocardial perfusion by contrast echocardiography, which may gain clinical relevance for diagnostic strategies only with i.v. application of the contrast agent as opposed to the intracoronary application used until recently. This has finally become true after many years of developing left heart contrast agents and more adequate ultrasound acquisition methods. This leads to the question: Where are we now? Myocardial contrast echocardiography yields unique information on the pathophysiology of microcirculation in vivo due to the fact that microbubbles remain strictly intravascular. Experimental and clinical studies using intracoronary contrast application have shown that infarct size and area at risk are depicted with high accuracy and furthermore that reflow vs no reflow phenomena are demonstrated after the revascularization procedure. In addition, presence and prognostic implications of collateralization may be assessed. Microvascular integrity plays an important role for functional recovery after revascularization. The breakthrough to a potentially clinical role of contrast echocardiography is mainly due to the development of new acquisition methods, such as pulse inversion technique, which allow differentiation of the microbubble signature from the surrounding myocardium. Initial publications show good diagnostic accuracy for the assessment of infarct size and area at risk as well as for the reflow vs no reflow phenomena and microvascular integrity, in particular also as follow up after protective interventions to improve microcirculation. Now, it is conceivable to assess relative or absolute changes of myocardial perfusion. This may be achieved by using non-video signals for analysis and by understanding attenuation effects and other artifacts. Further intensive and critical evaluation and standardization of imaging and analysis techniques is required before general clinical acceptance. New insight into the dynamic nature of perfusion, however, may already allow progress in some urgent questions of microvascular protection.

Shu 508 A (Levovist)-enhanced Doppler echocardiography improves the assessment of valvular heart disease

OBJECTIVE

To investigate whether intravenous injection of SHU 508 A improves the diagnostic accuracy of Doppler echocardiography in the assessment of valvular pathologies.

METHODS AND RESULTS

One hundred and twenty-five consecutive patients with valvular pathology (aortic stenosis, n = 48; aortic regurgitation, n = 20; mitral stenosis, n = 21; and mitral regurgitation, n = 36) and diagnostically insufficient Doppler signal were enrolled in this multicenter study. The severity of valvular pathology was graded on a four-point scale using unenhanced and contrast-enhanced Doppler echocardiography as well as cardiac catheterization. Agreement with cardiac catheterization findings increased from 63% using the unenhanced examination to 73% using the contrast-enhanced Doppler examination. Grading was possible in all patients using SHU 508 A, whereas the unenhanced Doppler examination remained inconclusive in six patients. The weighted kappa coefficient between contrast-enhanced Doppler and cardiac catheterization for all diagnoses was 0.76 as compared to 0.68 between unenhanced Doppler and cardiac catheterization. Agreement was especially improved in aortic stenosis (kappa 0.69 unenhanced vs 0.81 contrast-enhanced) and in aortic regurgitation (kappa 0.45 unenhanced vs 0.75 contrast-enhanced). Patients with mitral stenosis and mitral regurgitation experienced less improvement.

CONCLUSIONS

In case of an inconclusive unenhanced Doppler echo study, the administration of a left heart contrast agent should be considered. SHU 508 A is especially useful in improving the severity grading of aortic stenosis and aortic regurgitation, while grading of mitral stenosis and mitral regurgitation is less improved.

[New techniques for the quantification of myocardial function: acoustic quantification, color kinesis, tissue Doppler and "strain rate imaging"]

In this article, the authors discuss different semi-quantitative methods for the analysis of global and regional myocardial function. Analysis of endocardial motion and direct measurements of myocardial velocities are the basic principles. The former is a two-dimensional technique which, however, requires good image quality and which is influenced by motion artefacts. The latter technique has a better signal to noise ratio and offers the opportunity to sufficiently quantify diastole. Strain rate imaging is a new and interesting way to display and evaluate regional myocardial deformation.

[Contrast echocardiography]

The intravenous application of an ultrasound contrast agent induces enhanced display of blood in all its pathways. Within cardiology, this principle is mainly utilized for signal enhancement of color Doppler and spectral Doppler in order to improve quantification of congenital and acquired valvular lesions and also for improved endocardial delineation during stress tests and in the evaluation of LV function. The new domaine of myocardial perfusion imaging by contrast echocardiography, however, needed profound technical developments before realization of the clinical potential could even be conceived. These are based on the complex reactions of microbubbbles in the acoustic field in order to allow the sensitive and bubble specific display of intramyocardial contrast effects. The presently available acquisition techniques, second harmonic imaging and harmonic power Doppler, demonstrate significant improvements if compared to traditional fundamental 2-d echocardiography; however, they are still subjected to important limitations. There are many anatomical, physiological, and technical reasons for insufficient display of intramyocardial microbubbles, the most important one being attenuation. It is hoped that the most recently developed imaging modality, pulse inversion technique, allows the necessary diagnostic accuracy and reproducibility in myocardial perfusion imaging.

Regional diastolic function by pulsed Doppler myocardial mapping for the detection of left ventricular ischemia during pharmacologic stress testing: a comparison with stress echocardiography and perfusion scintigraphy

OBJECTIVES

We evaluated regional diastolic function by pulsed Doppler myocardial mapping for the detection of left ventricular ischemia during pharmacologic stress testing.

BACKGROUND

Evaluation and quantification of diastolic myocardial function remain a challenge for imaging techniques in stress tests.

METHODS

A prospective study compared the detection of coronary artery stenosis: 1) by pulsed Doppler myocardial mapping, 2) by two-dimensional echocardiographic dobutamine stress test, and 3) by perfusion scintigraphy in 64 patients using coronary angiography for reference. An age matched subgroup of 10 patients with normal angiograms and two-dimensional echocardiographic stress test served as control group. Peak myocardial contraction velocity (Vc) and lengthening rate during early diastolic left ventricular (LV) filling (VE) were measured in 12 LV segments from three apical views.

RESULTS

In controls, myocardial velocities increased during stress by > or =3.6 cm/s (p < 0.001). In LV segments depending on a stenosed artery (n = 70), VE decreased by > or =1 cm/s and, thus, was different from control segments (n = 112, p < 0.001) and from scar segments (n = 13, p < 0.01), whereas the change of Vc was similar to that in scar segments. A stress induced 2 cm/s reduction of VE discerned the best diagnostic accuracy (sensitivity 84%, specificity 93%) in comparison with two-dimensional echocardiography (78% and 71%) and perfusion scintigraphy (61% and 86%). Using receiver operating curves at incremental levels of luminal narrowing, these relations persisted.

CONCLUSIONS

Quantification of diastolic myocardial function by pulsed Doppler myocardial mapping during dobutamine stress test was shown to be a feasible, accurate, reproducible, noninvasive technique that should be considered to be a sensitive alternative to the present echocardiographic and scintigraphic imaging techniques for stress tests.

[A standardized documentation structure for data documentation in echocardiography. Work Team on Standards and LV Function of the Work Group on Cardiovascular Ultrasound of the German Society of Cardiology, Heart and Circulation Research]

Presently, there are no well-defined standards for documentation of echocardiographic studies. Nevertheless, standards are essential to provide comparability of data and to realize electronic communication, both essential for quality management in echocardiography. Therefore, the working group "Standards and LV function" of the German Society of Cardiology developed a consensus for documentation of echocardiographic studies. In the present paper this consensus is presented and illustrated by typical clinical examples. Additionally, a prototype of a user-oriented software based on this data set is presented. The complete data set for transesophageal and transthoracic echocardiography and the software prototype can be downloaded at http:@echo.ma.uni-heidelberg.de.

Noninvasive localization of accessory pathways in patients with Wolff-Parkinson-White syndrome with the use of myocardial Doppler imaging

This study sought to examine the diagnostic accuracy of noninvasive prediction of accessory pathway localization in patients with manifest Wolff-Parkinson-White syndrome with the use of myocardial Doppler imaging as a new noninvasive mapping procedure. Myocardial Doppler imaging measures myocardial velocities and therefore can determine the site of earliest ventricular activation in patients with accessory bypass tracts. Twenty-five patients with manifest preexcitation were studied with the use of pulsed wave and M-mode myocardial Doppler imaging for the evaluation of the shortest electromechanical time interval in 9 basal myocardial segments. The new diagnostic test was compared with 3 electrocardiographic algorithms. An invasive mapping procedure served as reference standard. Abnormally short electromechanical time intervals were found in preexcited segments (27 +/- 12 ms vs 64 +/- 27 ms). Myocardial Doppler imaging correctly localized 84% of the accessory pathways and electrocardiographic algorithms only 48% to 60% of cases. Noninvasive prediction of accessory pathway localization by myocardial Doppler imaging is accurate and proved to be superior to prediction based on electrocardiographic algorithms.

[Enhancement of Doppler signals in aortic and mitral valve diseases]

Ultrasound contrast media increase backscatter from blood, thus improving the signal-to-noise ratio. Potential clinical applications of intravenous ultrasound contrast are reviewed. Contrast enhancement of continuous wave Doppler is indicated when the native recordings are noisy and no complete envelope of the Doppler spectrum is obtained. In aortic stenosis several investigations showed good agreement between the gradient calculated from Doppler measurements and the results of cardiac catheterization. In mitral insufficiency maximum area of the regurgitant jet is a widely used parameter for estimation of the severity of the regurgitation. However, assessment of the maximum jet area may not be possible because of poor acoustic windows. Contrast enhancement provides complete display of the regurgitant jet in most of the patients. The diagnostic confidence of the Doppler investigation is further improved by the recording of the pulmonary venous flow, which can be recorded in most of the patients following contrast injection. Therefore contrast enhanced transthoracic Doppler is an alternative to transesophageal Doppler investigation in patients with poor transthoracic windows.

Doppler energy: a new acquisition technique for the transthoracic detection of myocardial perfusion defects with the use of a venous contrast agent

AIMS

This animal experiment was designed to study whether the new technique of Doppler energy imaging could display myocardial perfusion abnormalities with the use of a combination of transthoracic imaging and right atrial injection of a myocardial contrast agent.

METHODS AND RESULTS

A series of 11 pigs were studied during (1) normal perfusion, (2) dipyridamole-induced coronary dilatation, and (3) during and after temporary occlusion of the left anterior descending or circumflex artery after a right atrial injection of 8 ml Levovist, 400 mg/ml. Short-axis views were obtained with the four following imaging modes: gray scale imaging (two-dimensional and M-mode), Doppler energy imaging (two-dimensional and M-mode). Visual inspection and off-line video densitometry (results expressed in arbitrary videointensity units 0 to 255) with digital background subtraction were performed. Doppler energy was significantly more sensitive in detecting the presence of contrast than gray scale imaging (background subtracted peak videointensity 32 +/- 17 versus 17 +/- 12, p < 0.001). Mean background-subtracted videointensity increased during dipyridamole-induced coronary hyperemia (40 +/- 14 versus 31 +/- 9, p < 0.003) using Doppler energy technique. Doppler energy imaging consistently detected absent perfusion (background subtracted videointensity -6 +/- 6) and immediate reperfusion (background subtracted peak videointensity 29 +/- 15, p < 0.001).

CONCLUSIONS

With the use of a galactose-based contrast agent, Doppler energy data acquisition was superior to standard gray scale imaging in transthoracic evaluation of regional myocardial perfusion, absence of perfusion, and reperfusion.

Combined use of contrast-enhanced 2-dimensional and color Doppler echocardiography for improved left ventricular endocardial border delineation using Levovist, a new venous echocardiographic contrast agent

Transthoracic echocardiography often provides inadequate endocardial border visualization, particularly of the left ventricular apex. The aim of this study was to determine whether the transpulmonary echocardiographic contrast agent, Levovist, could improve endocardial visualization. Accordingly, 43 patients underwent 2-dimensional echocardiography before and after intravenous administration of Levovist. Definition of the left ventricular septal, apical and lateral borders was graded: 0 = no definition, 1 = partial definition, 2 = complete definition. Color Doppler was performed before and after contrast in 32/43 patients and similarly scored to determine any further benefit in apical border detection. There was significant (p < 0.001) improvement of the average end-diastolic scores of the septal, apical and lateral regions (1.4 +/- 0.5, 0.6 +/- 0.7 and 0.9 +/- 0.5 before and 1.8 +/- 0.4, 1.4 +/- 0.6 and 1.7 +/- 0.5 after Levovist). The average end-systolic score was significantly different (p < 0.001) from end-diastolic values in the apex only (0.3 +/- 0.6 before and 0.8 +/- 0.7 after Levovist). Average apical scores using color Doppler improved from 0.3 +/- 0.6 and 0.1 +/- 0.2 during end-diastole and end-systole to 1.7 +/- 0.5 and 1.2 +/- 0.6, respectively, after Levovist (p < 0.001); the average end-diastolic contrast-enhanced color Doppler score was significantly higher than the corresponding grey scale score (p < 0.001). We conclude that left ventricular endocardial border definition is significantly improved by Levovist. The use of contrast enhanced color Doppler can compensate for limited efficacy of this method in the apex.

Clinical evaluation of left heart Doppler contrast enhancement by a saccharide-based transpulmonary contrast agent. The Levovist Cardiac Working Group

OBJECTIVES

A multicenter study was carried out to evaluate the efficacy with which SHU 508A enhances left heart Doppler signals and improves the clinical quantification of valve disease.

BACKGROUND

Poor signal-to-noise ratio often limits the Doppler interrogation of left heart flows. This problem may be resolved by the enhancement of Doppler signals by an ultrasound contrast agent capable of pulmonary transmission, such as the recently developed SHU 508A.

METHODS

Left heart contrast enhancement was tested for 1) continuous wave Doppler evaluation in 51 patients with aortic stenosis, 2) pulsed Doppler transthoracic evaluation of pulmonary venous flow in 85 patients, and 3) color Doppler evaluation of mitral regurgitation in 60 patients. Studies were performed immediately before and during the intravenous administration of SHU 508A (16 ml of 200 mg/ml) and compared with unenhanced transesophageal data in representative subsets of patients.

RESULTS

SHU 508A had no serious adverse effects. A significant increase in left heart Doppler signal intensity lasted for 30 to 300 s. The continuous wave Doppler velocity envelope was enhanced for all jets, but Doppler peak velocity was not altered in high quality baseline studies. However, Doppler contrast enhancement resulted in higher measured peak gradients (p < 0.001) in 29 patients with aortic stenosis who had poor quality baseline studies. This improved the overall correlation with invasive pressure measurements (r = 0.73 vs. r = 0.89, p < 0.01). The enhanced pulsed Doppler traces of transthoracic pulmonary venous flow allowed quantitative analysis in 92% patients (vs. 27% at baseline) and correlated well with peak velocities and velocity profiles obtained by transesophageal echocardiography (r = 0.91, p < 0.001). The enhanced color Doppler display of regurgitant jets increased jet area with a high interindividual variability (mean 276%), resulting in almost identical jet areas as unenhanced transesophageal values (r = 0.97, p < 0.001).

CONCLUSIONS

SHU 508A is a safe transpulmonary contrast agent that significantly enhances both spectral and color Doppler signals in the left heart. In specific patient subsets, the increase in signal-to-noise ratio improved the quantitative assessment of aortic stenosis, pulmonary venous flow and mitral regurgitation.

Enhancement of mitral regurgitation and normal left atrial color Doppler flow signals with peripheral venous injection of a saccharide-based contrast agent

OBJECTIVES

The saccharide ultrasound contrast agent SHU 508 A was used to test the hypothesis that an intravenous, transpulmonary contrast method can enhance color Doppler flow signals in the left atrium in a clinically useful manner.

BACKGROUND

Color Doppler display of mitral regurgitation may be unreliable because of variable signal to noise ratios that are at times poor. Traditional contrast agents enhance color Doppler flow signals in the right heart chambers. This study describes our observation of a recently developed contrast agent, SHU 508 A, capable of pulmonary transit after peripheral venous injection.

METHODS

Control subjects (n = 10) and patients with suspected mitral regurgitation (n = 23) were studied by color Doppler flow imaging before and after 3-g intravenous doses of SHU 508 A. Reference grading of mitral regurgitation (0 to 3) was formulated from left ventricular angiography. In the four-chamber view of the left atrium, we selected for analysis the systolic frame with the maximal retrograde jet of mitral regurgitation (aliased/blue) and the diastolic frame with the maximal color coding from anterograde pulmonary venous flow (red) for planimetry and for grading the intensity of the color Doppler signal (0 to 5).

RESULTS

The score of the color Doppler signal intensity increased by > or = 2.5 after 3 g of SHU 508 A (p < 0.001). Flow detection improved, as shown by the increased jet area of mitral regurgitation (> or = 170%), after 3 g of SHU 508 A (3 +/- 3 vs. 12 +/- 8 cm2, p < 0.001) and by a > or = 200% increase in normal anterograde flow area (p < 0.001) in both the mitral regurgitation group and the control group. After contrast enhancement, the correlation between angiographic grading and the relation of jet area to the left atrial area increased from r = 0.79 to r = 0.91.

CONCLUSIONS

Contrast-mediated increased echogenicity of the left atrial blood pool improves the signal to noise ratio of Doppler images of mitral regurgitation and anterograde atrial flow. The technique is safe and simple and seems to minimize variability due to instrument design and anatomic signal attenuation.

Limitations of flow detection by color Doppler: in vitro comparison to conventional Doppler

There is little awareness of the limitations of flow detection with the commercially available color Doppler flow mapping system. The influence of flow velocity, ultrasound attenuation, and penetration depth on flow detection in color Doppler (Toshiba SSH 65A) were therefore studied in vitro and compared with conventional Doppler. The flow model had physiological flow volumes and laminar flow with parabolic velocity profile in a horizontal tube of Lucite with less than 3 degrees of coincidence. Conventional Doppler flow velocity measurements correlated highly with laser Doppler anemometry results (r = 0.99, SEE = 3 cm/sec). Signal strength of color Doppler and pulsed Doppler was semi-quantitatively graded using a scale from 0 to 5. Scale 1 (sparse signals) was useless for any assessment in color Doppler but just allowed velocity measurement in pulsed Doppler. Using 19-dB attenuation, flow velocities greater than 100 cm/sec had good scores with moderate gain, 60-100 cm/sec needed increasing gain, and velocities less than 40 cm/sec were not detectable with color Doppler but readily so with pulsed Doppler. With increasing attenuation (1-29 dB) and also with increasing penetration depth, flow detection was reduced significantly (P less than 0.001) more in color Doppler than in the pulsed technique (P less than 0.01). In conclusion, low flow velocities, high attenuation, and greater than 8 cm penetration depth may hamper flow detection in color Doppler and, thus, diagnostic accuracy. Conventional Doppler with its superior accuracy and sensitivity should therefore consolidate diagnostic ultrasound assessment.

[Accuracy of various Doppler technics in recording blood flow velocity. Studies in vitro]

Conventional and color-coded Doppler techniques were studied as to their accuracy in displaying flow and velocity using an in vitro model and a Laser-Doppler-anemometer. Furthermore, the estimation of pressure gradients as determined by Doppler ultrasound was compared to measurements by manometers under a variety of hemodynamic conditions. Pulsed and continuous wave Doppler had good reproducibility. There was an excellent correlation for measurements of flow velocity as determined by Doppler ultrasound and by Laser-Doppler anemometer (r = 0.98, SEE = 3 cm/s). The well-known underestimation of flow velocity due to an increasing angle of incidence (greater than 25 degrees) was confirmed in vitro. However this error was smaller than the actual overestimation resulting from angle correction for the apparent cosine. Doppler gradients correlated strongly with manometer gradients for orifice areas 12-80 mm2 and flow volumes 0.9-12.8 l/min (r = 0.98, SEE = 7 mm Hg) using continuous as well as pulsatile flow. Some overestimation of the Doppler gradient occurred with increasing flow rates (r = 0.66). Color-Doppler has poor spatial resolution. Display of velocities was therefore assessed using a qualitative score (0-5), the variability of which was 13 +/- 30% of the initial value. Display of faintest quality (score 1) was useless for clinical assessment in color-Doppler technique, but allowed quantitative measurement of velocity in conventional Doppler. Reduction of flow velocities limited display in color-Doppler (5-20 cm/s) but not in pulsed-Doppler technique. Thus, conventional Doppler has better sensitivity and accuracy of displaying flow when compared to color-Doppler, particularly in conditions of poor imaging. As reproducibility and accuracy of velocity determination are excellent, this technique should be used in all diagnostic procedures involving ultrasound. The Doppler gradient as derived from the modified Bernoulli equation provides accurate results in vitro which may also be concluded for use in the clinical situation.

[Asymptomatic course of severe tricuspid valve insufficiency with ateroseptal infarct, coronary fistula and ventricular septum defect as a sequela of blunt thoracic trauma]

Traumatic tricuspid valve insufficiency is a rare in vivo finding, especially in combination with other traumatic cardiac injuries like ventricular septal defect, myocardial infarction, and traumatic coronary fistula. Two-dimensional and, more recently, colorcoded Doppler echocardiography have gained importance for the diagnosis of tricuspid insufficiency. Patients with traumatic tricuspid insufficiency who survive the acute trauma, may remain asymptomatic for many years and even decades. If symptoms develop, tricuspid valve replacement appears feasible even after many years.

Diagnosis of constrictive pericarditis by pulsed Doppler echocardiography of the hepatic vein

The diagnostic value of hepatic venous flow patterns was evaluated for constrictive pericarditis by pulsed Doppler. A characteristic flow pattern was assumed to be associated with the well-known atrial pressure curve. Thirteen patients with constrictive pericarditis were compared to 13 control subjects and to 25 patients with right ventricular pressure overload including 13 patients with tricuspid regurgitation. The characteristic finding in constrictive pericarditis was a W-wave pattern of flow velocities in the dilated hepatic veins, with abrupt reversal of flow late in systole and diastole before the A wave (100% specificity, 68% sensitivity). This depends, however, on the absence of tricuspid regurgitation (for its systolic component) or fast sinus rhythm (for its diastolic component). Additional diagnostic markers were systolic deceleration time of forward flow (40 to 130 ms) and systolic integral of flow velocities (4.3 to -4.0 cm) (sensitivity and specificity greater than or equal to 92%). In the presence of tricuspid regurgitation, diastolic deceleration time less than 150 ms and diastolic integral of flow velocities less than 6 cm were useful diagnostic signs. If combined, these criteria had 100% sensitivity and specificity for the diagnosis. Thus, pulsed Doppler assessment of flow velocities in the hepatic vein facilitates the diagnosis of constrictive pericarditis in clinical routine, using an auxiliary site with unlimited diagnostic access to the characteristic flow velocity pattern, which reflects right atrial pressure curve and filling abnormalities.

[Diagnosis of pulmonary hypertension using pulsed Doppler cardiography]

The accuracy of pulsed Doppler cardiography in predicting pulmonary hypertension was assessed in 70 patients (aged 16-72 years) with varying cardiac disease, who had undergone catheterization. Doppler velocity traces were recorded from four sampling sites in the pulmonary outflow tract and from the tricuspid valve. These results were compared to the invasive data. An inverse correlation (r = -0.77) was found between acceleration time (onset of RV ejection to peak pulmonary velocity) and mean pulmonary arterial pressure, with the sampling site in the centre of the pulmonary valves or of the RV outflow tract (r = -0.71). Acceleration time was inversely related to patient age but was not dependent on heart rate or on cardiac output. The sensitivity of the acceleration time was 85-91% for the diagnosis of moderate or severe pulmonary hypertension, and the predictive value was greater than 90%. The following measurements were less helpful in diagnosing pulmonary hypertension: peak velocity of pulmonary arterial blood flow, its mean acceleration, RV isovolumic relaxation time and the qualitative sign of a presystolic pulmonary flow wave induced by atrial contraction. A reversal of systolic flow at the level of the pulmonic valves, measured as time of forward flow in percent of RV ejection time, was found only in patients with moderate or severe pulmonary hypertension. This was a sensitive marker of an elevated pulmonary arterial resistance (greater than or equal to 95%), the mechanism of which is not yet fully understood.

Mitral valve closure and left ventricular filling time in patients with VDD pacemakers. Assessment of the onset of left ventricular systole and the end of diastole

The effect of mitral valve closure on left ventricular filling time and its relation to the onset of systole were assessed from mitral valve echocardiograms and simultaneous apex cardiograms in 21 normal subjects, 11 patients with left bundle branch block, and 19 patients with VDD pacemakers programmed for atrioventricular intervals of 50, 150, and 250 ms. The interval between the electrocardiograph Q wave and the apex cardiogram upstroke was similar in normal subjects and patients with left bundle branch block, but was significantly longer in patients with VDD pacemakers at all atrioventricular intervals. Similarly there was little difference in the time interval between the Q wave and mitral valve closure in normal individuals and patients with left bundle branch block but this was considerably delayed in VDD pacemaker patients with the atrioventricular interval set at 50 ms. With increasing atrioventricular intervals the mitral valve closed significantly earlier, whereas the onset of left ventricular systole and the timing of mitral valve opening remained unchanged. Thus as a result of earlier mitral valve closure left ventricular filling time decreased progressively as the atrioventricular interval was increased. Since the onset of left ventricular systole, with respect to left ventricular stimulation, is considerably delayed in VDD pacemaker patients a short atrioventricular interval is required in these patients to maintain the normal time relations between atrial and ventricular contraction and hence maximise left ventricular filling.

[Physiologic effect of short AV intervals on LV filling time in VDD pacemakers--mitral valve closure in relation to atrial and ventricular contraction]

The effect of mitral valve closure on LV filling time and the onset of LV systole were assessed in 21 normals, 11 patients with left bundle branch block and in 19 patients with VDD pacemakers, which were programmed for the AV intervals 50, 150 and 250 ms, by means of echo-apexcardiography. Mitral valve closure was significantly delayed with increasing delay of intraventricular conduction: 52 +/- 11 ms in normals, 65 +/- 20 ms in LBBB patients and 127 +/- 14 ms in VDD patients. There was a similar distribution of the apexcardiographic upstroke and aortic valve opening in the 3 groups. With increasing AV intervals mitral valve closure was earlier: 127 +/- 14 ms at AV = 50 ms, 83 +/- 38 ms at AV = 150 ms and 20 +/- 75 ms at AV = 250 ms whereas the onset of LV systole and mitral valve opening remained unaltered. Thus filling time expressed in percent of cycle length was reduced from 50 +/- 6% at AV = 50 ms to 45 +/- 9% and to 38 +/- 10% at AV = 250 ms (p less than 0.001). The late onset of LV systole in VDD pacemaker patients therefore reduces LV filling time unless this is compensated by programming a short AV interval in order to maintain the physiological interval between atrial and ventricular contraction.

Prenalterol: a partial beta 1-adrenoceptor agonist or a beta-blocker with intrinsic activity?

Hemodynamic studies have demonstrated a significantly reduced beta 1-adrenoceptor stimulating effect of prenalterol compared to dobutamine suggesting a partial agonism on the receptor. In order to prove this hypothesis we administered 80 micrograms/kg of prenalterol within 5 minutes in 8 healthy volunteers during a continuous infusion of dobutamine (15 micrograms/kg/min). In addition to heart rate, blood pressure and the double product, the systolic time intervals QS2I, PEP and LVET and the echocardiographically determined parameters FS and Vcf were measured for evaluation of ventrical function. The injection of prenalterol caused a distinct attenuation of the cardiostimulating effects of dobutamine: there was a prompt fall in heart rate and systolic blood pressure and a typical negative inotropic effect on the parameters of left ventricular function. In the experimental conditions selected, the effects of prenalterol were those of a beta-sympatholoytic agent. Prenalterol should therefore be classified as a partial beta 1-adrenoceptor agonist or as a beta-blocking agent with pronounced intrinsic sympathomimetic activity. The beta 1-stimulating potency of prenalterol amounts to about 60% of a full agonist.