Guy Armstrong

Correlation of myocardial doppler velocity response to exercise with independent evidence of myocardial ischemia by dual-isotope single-photon emission computed tomography

Myocardial Doppler velocity (MDV) imaging may provide an objective correlate of ischemia, thereby reducing the expertise needed for interpreting stress echocardiography and improving its reproducibility. This study sought to independently validate the results of exercise MDV imaging with single-photon emission computed tomography (SPECT) perfusion imaging in 116 patients (age 60+/-12 years, 28 women) referred for exercise SPECT for diagnostic or prognostic assessment of coronary artery disease. Two-dimensional echocardiography was performed with simultaneous color MDV data acquisition before and after exercise treadmill testing. MDV data were processed off-line to display myocardial velocity profiles in each segment at rest and peak exercise. SPECT was analyzed using a 16-segment model and segments were classified as normal or showing resting or stress defects. Resting defects within segments showing normal function were attributed to attenuation. Color MDV data were compared with SPECT results, and a multivariate analysis (including exercise and SPECT results) was performed to identify the determinants of the exercise MDV response. Patients exercised maximally (peak rate-pressure product 27.6+/-6.1x10(3), and SPECT was abnormal in 33 patients. Of the 1,333 left ventricular segments evaluable by SPECT and MDV, 1,217 segments were classified as normal, 43 showed a stress defect, and 73 a rest defect. Segmental comparison of thallium findings and MDV showed that segments with a rest defect had a lower velocity at rest and stress than normal segments (p<0.001). Segments with a stress defect had a marked reduction in peak exercise velocity and less increment in velocity than normal segments. Heart rate, functional capacity, and presence of abnormally perfused segments were independent predictors of myocardial velocity at peak exercise. Thus, color MDV correlates with independent evidence of ischemia, although it is also influenced by exercise capacity and left ventricular function. This technique may permit a feasible approach to quantitation of exercise echocardiography.

Influence of dobutamine or exercise stress on the results of pulsed-wave Doppler assessment of myocardial velocity

BACKGROUND Pulsed-wave Doppler assessment of myocardial velocity (MDV) may permit a more quantitative interpretation of stress echocardiography. This technique has been used with dobutamine echo (DbE), but exercise echo (ExE) may be preferred in patients who are able to exercise maximally. The influence of these stressors on the results of MDV are undefined. PURPOSE This study sought to determine whether differences between the physiology of DbE and ExE could influence the MDV responses to stress and whether interpretative criteria should be different with exercise or dobutamine stress. METHODS DbE or ExE was performed in 105 patients tested for known or suspected coronary artery disease. Pulsed-wave MDV was obtained in basal segments of anteroseptal, septal, anterior, posterior, lateral, and inferior walls in the apical views at rest and at peak doses of dobutamine or immediately after exercise. Segments were classified as normal or abnormal (ischemia or scar) according to results of 2-dimensional echocardiography, and MDV obtained at rest and stress was compared by using analysis of variance. RESULTS Resting heart rate was similar before both dobutamine and exercise, but heart rate at peak dobutamine exceeded that after exercise (137 +/- 10 vs 115 +/- 22, P <.01). For both ExE and DbE, MDV was significantly greater at rest and stress in normal than in abnormal segments. Stress MDV in both normal and abnormal segments was greater with DbE than with ExE (17.0 +/- 4.8 cm/s vs 10. 3 +/- 3.4 cm/s, P <.001 for normal segments and 10.7 +/- 4.4 cm/s vs 7.9 +/- 3.3 cm/s, P <.001 for abnormal segments. Increase in MDV/Deltaheart rate induced by DbE was greater than by ExE in normal (0.14 +/- 0.07 cm/s. beat for DbE and 0.09 +/- 0.08 cm/s. beat for ExE; P <.05) but similar in abnormal segments (0.06 +/- 0.07 cm/s. beat for DbE and 0.05 +/- 0.09 cm/s. beat for ExE). MDV correlated better with peak heart rate at ExE (r = 0.56, P <.01) than at DbE (r = 0.28, P <.01). CONCLUSIONS MDV responses to exercise and pharmacologic stress appear to be different, reflecting differences in inotropy, loading, and the timing of imaging. These findings may influence the ability of MDV to differentiate normal from abnormal stress echocardiography responses.

Estimation of cardiac reserve by peak power: validation and initial application of a simplified index

OBJECTIVES To validate a simplified estimate of peak power (SPP) against true (invasively measured) peak instantaneous power (TPP), to assess the feasibility of measuring SPP during exercise and to correlate this with functional capacity. DESIGN Development of a simplified method of measurement and observational study. SETTING Tertiary referral centre for cardiothoracic disease. SUBJECTS For validation of SPP with TPP, seven normal dogs and four dogs with dilated cardiomyopathy were studied. To assess feasibility and clinical significance in humans, 40 subjects were studied (26 patients; 14 normal controls). METHODS In the animal validation study, TPP was derived from ascending aortic pressure and flow probe, and from Doppler measurements of flow. SPP, calculated using the different flow measures, was compared with peak instantaneous power under different loading conditions. For the assessment in humans, SPP was measured at rest and during maximum exercise. Peak aortic flow was measured with transthoracic continuous wave Doppler, and systolic and diastolic blood pressures were derived from brachial sphygmomanometry. The difference between exercise and rest simplified peak power (Δ SPP) was compared with maximum oxygen uptake (V˙O2max), measured from expired gas analysis. RESULTS SPP estimates using peak flow measures correlated well with true peak instantaneous power (r = 0.89 to 0.97), despite marked changes in systemic pressure and flow induced by manipulation of loading conditions. In the human study, V˙O2max correlated with Δ SPP (r = 0.78) better than Δ ejection fraction (r = 0.18) and Δ rate–pressure product (r = 0.59). CONCLUSIONS The simple product of mean arterial pressure and peak aortic flow (simplified peak power, SPP) correlates with peak instantaneous power over a range of loading conditions in dogs. In humans, it can be estimated during exercise echocardiography, and correlates with maximum oxygen uptake better than ejection fraction or rate–pressure product.

Numeric modeling of the cardiovascular system with a left ventricular assist device.

A numeric model consisting of a lump-parameter cardiovascular system (CVS) model and a model for the Cleveland Clinic Implantable Ventricular Assist System (IVAS), a nonpulsatile rotary pump designed to augment the failing left ventricle, are described in this paper. The purposes of this study were to 1) observe the hemodynamic interactions between CVS and IVAS under various physiologic and pathophysiologic conditions running at different speeds; and 2) allow testing and optimization of various IVAS control algorithms. An existing numeric model of CVS (24 coupled differential equations, representing all cardiac chambers and systemic and pulmonary vasculature) was modified to add the IVAS pump as an auxiliary chamber between the left ventricle and aorta with pressure-flow-speed characteristics derived from in vitro testing. Simulations were conducted for ventricles with normal and abnormal systolic and diastolic dysfunction at different exercise levels with the pump running at various speeds. Computer simulations show that 1) numeric modeling is useful for predicting hemodynamic response of CVS to IVAS in various circumstances; 2) IVAS results in normalization of cardiac output, especially in failing hearts, although with reduced pulse pressure; and 3) various control algorithms allowing adaptation of IVAS to physiologic demands of CVS could be developed based on the simulation study.

Intraoperative echocardiographic detection of regurgitant jets after valve replacement.

BACKGROUND Paravalvular jets, documented by intraoperative transesophageal echocardiography, have prompted immediate valve explantation by others, yet the significance of these jets is unknown. METHODS Twenty-seven patients had intraoperative transesophageal two-dimensional color Doppler echocardiography, performed to assess the number and area of regurgitant jets after valve replacement, before and after protamine. Patients were grouped by first time versus redo operation, valve position and type. RESULTS Before protamine, 55 jets were identified (2.04+/-1.4 per patient) versus 29 jets after (1.07+/-1.2 per patient, p = 0.0002). Total jet area improved from 2.0+/-2.2 cm2 to 0.86+/-1.7 cm2 with protamine (p<0.0001). In all patients jet area decreased (average decrease, 70.7%+/-27.0%). First time and redo operations had similar improvements in jet number and area (both p>0.6). Furthermore, mitral and mechanical valves each had more jets and overall greater jet area when compared to aortic and tissue valves, respectively. CONCLUSIONS Following valve replacement, multiple jets are detected by intraoperative transesophageal echocardiography. They are more common and larger in the mitral position and with mechanical valves. Improvement occurs with reversal of anticoagulation.

An evaluation of the use of new Doppler methods for detecting longitudinal function abnormalities in a pacing-induced heart failure model.

BACKGROUND Doppler tissue echocardiography and color M-mode Doppler flow propagation velocity have proven useful in evaluating cross-sections of patients with left ventricular (LV) dysfunction, but experience with serial changes is limited. PURPOSE AND METHODS We tested their use by evaluating the temporal changes of LV function in a pacing-induced congestive heart failure model. Rapid ventricular pacing was initiated and maintained in 20 dogs for 4 weeks. Echocardiography was performed at baseline and weekly during brief pacing cessation. RESULTS With rapid pacing, LV volume significantly increased and ejection fraction (57%-28%), stroke volume (37-18 mL), and mitral annulus systolic velocity (16.1-6.6 cm/s) by Doppler tissue echocardiography significantly decreased, with ejection fraction and mitral annulus systolic velocity closely correlated (r = 0.706, P <.0001). In contrast to the mitral inflow velocities, mitral annulus early diastolic velocity decreased steadily (12.3-7.3 cm/s) resulting in a dramatic decrease in mitral annulus early/late (1.22-0.57) diastolic velocity with no tendency toward pseudonormalization. The color M-mode Doppler flow propagation velocity also showed significant steady decrease (57-24 cm/s) throughout the pacing period. Multiple regression analysis chose mitral annulus systolic velocity (r = 0.895, P <.0001) and propagation velocity (r = 0.782, P <.0001) for the most important factor predicting LV systolic and diastolic function, respectively. CONCLUSIONS Doppler tissue echocardiography and color M-mode Doppler flow could evaluate the serial deterioration in LV dysfunction throughout the pacing period. These were more useful in quantifying progressive LV dysfunction than conventional ehocardiographic techniques, and were probably relatively independent of preload. These techniques could be suitable for longitudinal evaluation in addition to the cross-sectional study.

Reliability of Echocardiographic Indices of Dyssynchrony

Background: Echocardiographic indices of dyssynchrony are increasingly used to select candidates for cardiac resynchronization therapy. For widespread screening of heart failure patients, such variables need to be comparable when evaluated by different operators using different equipment. Objective and Methods: To evaluate the reproducibility and obtainability of echocardiographic indices of mechanical dyssynchrony, we studied 40 subjects stratified according to QRS morphology and systolic function. Two echocardiograms were performed on each patient by different sonographers on different machines and each study was analyzed by two observers. Results: All blood‐pool and tissue Doppler indices of dyssynchrony were obtainable in over 97% of cases. Blood‐pool Doppler measures were the most reproducible indices of intraventricular dyssynchrony (aortic ejection delay) and interventricular dyssynchrony (aortopulmonary difference in ejection delay). For annular tissue Doppler delays, the time to peak velocity was consistently more reproducible than the time to velocity onset. Conclusion: Differences in the reliability of echocardiographic indices may affect their suitability as screening tests for dyssynchrony.

Characteristics and Prognostic Importance of Myocardial Fibrosis in Patients with Dilated Cardiomyopathy Assessed by Contrast-Enhanced Cardiac Magnetic Resonance Imaging

Introduction Dilated cardiomyopathy (DCM) is associated with significant morbidity and mortality. Contrast-enhanced cardiac MRI (CE-CMR) can detect potentially prognostic myocardial fibrosis in DCM. We investigated the role of CE-CMR in New Zealand patients with DCM, both Maori and non-Maori, including the characteristics and prognostic importance of fibrosis. Methods One hundred and three patients (mean age 58 ± 13, 78 male) referred for CMR assessment of DCM were followed for 660 ± 346 days. Major adverse cardiac events (MACE) were defined as death, infarction, ventricular arrhythmias or rehospitalisation. CE-CMR used cines for functional analysis, and delayed enhancement to assess fibrosis. Results Myocardial fibrosis was present in 30% of patients, the majority of which was mid-myocardial (63%). Volumetric parameters were similar in patients with or without fibrosis. At 2 years patients with fibrosis had an increased rate of MACE (HR = 0.77, 95% CI 0.3-2.0). Patients with full thickness or subendocardial fibrosis had the highest MACE, even in the absence of CAD). More Maori had fibrosis on CE-CMR (40% vs. 28% for non-Maori), and the majority (75%) was mid-myocardial. Maori and non-Maori had similar outcomes (25% vs. 24% with events during follow-up). Conclusions DCM patients frequently have myocardial fibrosis detected on CE-CMR, the majority of which is mid-myocardial. Fibrosis is associated with worse outcome in the medium term. The information obtained using CE-CMR in DCM may be of incremental clinical benefit.

Exercise echocardiographic assessment in severe mitral regurgitation.

In chronic severe mitral regurgitation, minimum morbidity and mortality is achieved by applying surgical correction before left ventricular dysfunction becomes irreversible. This requires detection of subtle signs of early ventricular decompensation, for which isotonic stress echocardiography is more accurate than is use of resting indices of contractile function alone. We perform serial 6-monthly stress echocardiography for patients with severe mitral regurgitation, and recommend surgery when the exercise end-systolic volume index or ejection fraction reaches the cutoff values in Table 4 or if there is a clear adverse trend. Exercise echocardiography is more accurate than is exercise electrocardiography for detecting concomitant coronary disease prior to revascularization. Stress testing is also an objective measure of symptoms. Color-Doppler stress echocardiography can detect those patients whose mitral regurgitation worsens (or even develops de novo) with exercise, which can explain unexpected symptoms. Stress echocardiography, therefore, provides a comprehensive and cost-effective evaluation of patients with mitral regurgitation that combines functional, diagnostic, and prognostic information.

Non-invasive characterization of total arterial compliance by simultaneous acquisition of pressure and flow: advantages of the pulse pressure method

The authors compare three proposed indices of total arterial compliance (Ctot) in normal volunteers (n=9) and patients with coronary artery disease (n=14) using a non-invasive approach (echo-Doppler and carotid tonometry): (1) the pulse pressure method (PPM), (2) the area method (AM) and (3) the stroke volume-to-pulse pressure ratio (SV/PP). The best agreement was found between the PPM and SV/PP. Compliance estimates were lower in the patient group (PPM: 1.2/spl plusmn/0.4 vs. 1.6/spl plusmn/0.2; AM: 1.6/spl plusmn/0.6 vs. 2.8/spl plusmn/1.3; SV/PP: 1.8/spl plusmn/0.6 vs. 2.4/spl plusmn/0.4), being older (64/spl plusmn/14 vs. 35/spl plusmn/4 y) and with known atherosclerosis. The best correlation between compliance and age was found with PPM (r/sup 2/=0.52). AM varied with the chosen computation interval in diastole. These preliminary data describing the very first use of the PPM on non-invasive human recordings suggest that PPM could be a more robust estimator of Ctot than the widely used AM, and that SV/PP could be a reasonable simpler surrogate.