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Biomedical subjects

Thomas H Marwick

Publications and source records attributed to Thomas H Marwick.

At least 55 records · Page 3Linked to original sources
PubMed2005

Screening for heart disease in diabetic subjects.

BACKGROUND: The prevalence of left ventricular hypertrophy (LVH), coronary artery disease, and subclinical cardiomyopathy in diabetic patients without known cardiac disease is unclear. We sought the frequency of these findings to determine whether plasma brain natriuretic peptide (BNP) could be used as an alternative screening tool to identify subclinical LV dysfunction. METHODS: Asymptomatic patients with diabetes mellitus without known cardiac disease (n = 101) underwent clinical evaluation, measurement of BNP, exercise stress testing, and detailed echocardiographic assessment. After exclusion of overt dysfunction or ischemia, subclinical myocardial function was sought on the basis of myocardial systolic (Sm) and diastolic velocity (Em). Association was sought between subclinical dysfunction and clinical, biochemical, exercise, and echocardiographic variables. RESULTS; Of 101 patients, 22 had LVH and 16 had ischemia evidenced by exercise-induced wall motion abnormalities. Only 4 patients had abnormal BNP levels; BNP was significantly increased in patients with LVH. After exclusion of LVH and coronary artery disease, subclinical cardiomyopathy was identified in 24 of 66 patients. Subclinical disease could not be predicted by BNP. CONCLUSIONS: Even after exclusion of asymptomatic ischemia and hypertrophy, subclinical systolic and diastolic dysfunction occurs in a significant number of patients with type 2 diabetes. However, screening approaches, including BNP, do not appear to be sufficiently sensitive to identify subclinical dysfunction, which requires sophisticated echocardiographic analysis.

Aged↗
PubMed2005

Screening for coronary artery disease in patients with diabetes: a Bayesian strategy of clinical risk evaluation and exercise echocardiography.

OBJECTIVE: Screening for coronary artery disease is constrained by its low prevalence in unselected patients. We compared the ability of clinical scores to identify a high-risk group with diabetes mellitus and investigated a Bayesian strategy by combination with exercise echocardiography (ExE). METHODS: The Framingham risk score (FRS), a score based on the American Diabetes Association (ADA) screening guidelines, the United Kingdom Prospective Diabetes Study (UKPDS) risk engine, and a disease-specific diabetic cardiac risk score (DCRS) were calculated in 199 asymptomatic patients with type 2 diabetes mellitus undergoing ExE. The frequency of abnormal ExE and the proportion of these with coronary stenoses were sought in groups designated as high risk on the basis of optimal cutoffs for each score. All patients were followed up for 1 year. RESULTS: High risk was identified in fewer patients with the DCRS (27%) than FRS (38%, P = .02), ADA (41%, P = .004), and UKPDS (43%, P = .001). Exercise echocardiography was positive in 27 (14%); 11 of 23 proceeding to angiography showed significant stenoses. Areas under the receiver operator characteristic curves for prediction of a positive ExE were similar for DCRS, UKPDS, and FRS but less for ADA (P = .04). Positive ExE was uncommon in low-risk patients (8%-11%) and most were false positives (58%-80%). Cardiovascular events (n = 9) were more likely in the high-risk compared with the low-risk UKPDS (9% vs 2%, P = .03) and DCRS (12% vs 2%, P = .01). CONCLUSION: Combination of the UKPDS or DCRS with ExE may optimize detection of coronary artery disease and cardiac events in asymptomatic patients, while minimizing the numbers of ExE and false-positive rate.

Bayes Theorem↗
PubMed2005

Predictors of a sustained response to exercise training in patients with chronic heart failure: a telemonitoring study.

BACKGROUND: Exercise training (ExT) improves exercise capacity in chronic heart failure, but the results of home-based training have been variable. We sought the predictors of favorable outcome using a telemonitoring approach. METHODS: Exercise capacity and quality of life (QOL) were assessed in 30 patients (28 men, age 64 +/- 8 years) with symptomatic chronic heart failure and left ventricular ejection fraction < or = 35% (28% +/- 9%) undergoing 8 months of home ExT. Patients were provided with heart rate monitors and exercise diaries after undergoing 4 months of hospital-based ExT. Weekly telephone contact was established and heart rate data were downloaded bimonthly. Changes in peak oxygen consumption per unit time (V*O2) and QOL were compared between the 15 most and 15 least adherent patients defined by the number of hours per week at > 60% maximum heart rate, observed during heart-rate monitoring. RESULTS: Peak V*O2 increased by 26% (P < .001) after 4 months of hospital ExT, but this increase had fallen to 8% (P = .07) at 12 months; only adherent patients (n = 15) showed persistent improvement of peak V*O2 at 12 months (P = .02). Improvement in peak V*O2 at 12 months was associated with baseline peak V*O2 (r = -0.61, P < .001) and hours logged on the heart rate monitor (r = 0.47, P = .01). Quality of life improvements were sustained at 12 months for the Minnesota Living with Heart Failure Questionnaire and Hare-Davis Depression Questionnaire. Nevertheless, QOL improvements achieved during the outpatient program were lost or attenuated at 12 months in nonadherent patients but were maintained in adherent patients. CONCLUSIONS: Telemonitoring is feasible for following adherence to home ExT. Ongoing adherence is critical in obtaining sustained benefit from ExT in heart failure.

Aged↗
PubMed2005

Use of real-time three-dimensional echocardiography to measure left atrial volume: comparison with other echocardiographic techniques.

OBJECTIVES: Left atrial (LA) volume (LAV) is a prognostically important biomarker for diastolic dysfunction, but its reproducibility on repeated testing is not well defined. LA assessment with 3-dimensional (3D) echocardiography (3DE) has been validated against magnetic resonance imaging, and we sought to assess whether this was superior to existing measurements for sequential echocardiographic follow-up. METHODS: Patients (n = 100; 81 men; age 56 +/- 14 years) presenting for LA evaluation were studied with M-mode (MM) echocardiography, 2-dimensional (2D) echocardiography, and 3DE. Test-retest variation was performed by a complete restudy by a separate sonographer within 1 hour without alteration of hemodynamics or therapy. In all, 20 patients were studied for interobserver and intraobserver variation. LAVs were calculated by using M-mode diameter and planimetered atrial area in the apical 4-chamber view to calculate an assumed sphere, as were prolate ellipsoid, Simpson's biplane, and biplane area-length methods. All were compared with 3DE. RESULTS: The average LAV was 72 +/- 27 mL by 3DE. There was significant underestimation of LAV by M-mode (35 +/- 20 mL, r = 0.66, P < .01). The 3DE and various 2D echocardiographic techniques were well correlated: LA planimetry (85 +/- 38 mL, r = 0.77, P < .01), prolate ellipsoid (73 +/- 36 mL, r = 0.73, P = .04), area-length (64 +/- 30 mL, r = 0.74, P < .01), and Simpson's biplane (69 +/- 31 mL, r = 0.78, P = .06). Test-retest variation for 3DE was most favorable (r = 0.98, P < .01), with the prolate ellipsoid method showing most variation. Interobserver agreement between measurements was best for 3DE (r = 0.99, P < .01), with M-mode the worst (r = 0.89, P < .01). Intraobserver results were similar to interobserver, the best correlation for 3DE (r = 0.99, P < .01), with LA planimetry the worst (r = 0.91, P < .01). CONCLUSIONS: The 2D measurements correlate closely with 3DE. Follow-up assessment in daily practice appears feasible and reliable with both 2D and 3D approaches.

Adult↗
PubMed2005

Myocardial blood volume and perfusion reserve responses to combined dipyridamole and exercise stress: a quantitative approach to contrast stress echocardiography.

BACKGROUND: Qualitative interpretation of myocardial contrast echocardiography (MCE) improves the accuracy of wall-motion analysis for assessment of coronary artery disease (CAD). We examined the feasibility and accuracy of quantitative MCE for diagnosis of CAD. METHODS: Dipyridamole/exercise stress MCE (destruction-replenishment protocol with real-time imaging) was performed in 90 patients undergoing quantitative coronary angiography, 48 of whom had significant (> 50%) stenoses. MCE was repeated with exercise alone in 18 patients. Myocardial blood flow (A*beta) was obtained from blood volume (A) and time to refill (beta). RESULTS: Quantification of flow reserve was feasible in 88%. The mean A*beta reserve in the anterior wall was significantly impaired for patients with left anterior descending coronary artery disease (n = 28) compared with those with no disease (1.6 +/- 1.2 vs 4.0 +/- 2.5, P < or = .001). This reflected impaired beta reserve, with no difference in the A reserve. Applying a receiver operating characteristic curve derived cutoff of 2.0 for A*beta reserve, quantitative MCE was 76% sensitive and 71% specific for the diagnosis of significant left anterior descending coronary artery stenosis. Posterior circulation results were similar, with 78% sensitivity and 59% specificity for detection of posterior CAD. Overall, quantitative MCE was similarly sensitive to qualitative approach for diagnosis of CAD (88% vs 93%), but with lower specificity (52% vs 65%, P = .07). In 18 patients restudied with pure exercise stress, the mean myocardial blood flow reserve was less than after combined stress (2.1 +/- 1.6 vs 3.7 +/- 1.9, P = .01). CONCLUSION: Quantitative MCE is feasible for the diagnosis of CAD with dipyridamole/exercise stress. Dipyridamole prolongs postexercise hyperemia, augmenting the degree of hyperemia at the time of imaging.

Blood Volume Determination↗
PubMed2005

Coronary flow responses to exercise training: further evidence of the benefit of an underutilized therapeutic modality.

Inactivity is associated with endothelial dysfunction and the development of cardiovascular disease. Exercise training has a favourable effect in the management of hypertension, heart failure and ischaemic heart disease. These beneficial effects are probably mediated through improvements of vascular function and, in this issue of Clinical Science, Hägg and co-authors propose a coronary artery effect. The use of a Doppler technique for non-invasive assessment of coronary flow reserve in a small animal model is an exciting aspect of this study. If feasible in the hands of other investigators, the availability of sequential coronary flow measurements in animal models may help improve our understanding of the mechanisms of disorders of the coronary circulation.

Animals↗
PubMed2005

Determinants of exercise capacity in patients with type 2 diabetes.

OBJECTIVE: Type 2 diabetes is associated with reduced exercise capacity, but the cause of this association is unclear. We sought the associations of impaired exercise capacity in type 2 diabetes. RESEARCH DESIGN AND METHODS: Subclinical left ventricular (LV) dysfunction was sought from myocardial strain rate and the basal segmental diastolic velocity (Em) of each wall in 170 patients with type 2 diabetes (aged 56 +/- 10 years, 91 men), good quality echocardiographic images, and negative exercise echocardiograms. The same measurements were made in 56 control subjects (aged 53 +/- 10 years, 29 men). Exercise capacity was calculated in metabolic equivalents, and heart rate recovery (HRR) was measured as the heart rate difference between peak and 1 min after exercise. In subjects with type 2 diabetes, exercise capacity was correlated with clinical, therapeutic, biochemical, and echocardiographic variables, and significant independent associations were sought using a multiple linear regression model. RESULTS: Exercise capacity, strain rate, Em, and HRR were significantly reduced in type 2 diabetes. Exercise capacity was associated with age (r = -0.37, P < 0.001), male sex (r = 0.26, P = 0.001), BMI (r = -0.19, P = 0.012), HbA(1c) (A1C; r = -0.22, P = 0.009), Em (r = 0.43, P < 0.001), HRR (r = 0.42, P < 0.001), diabetes duration (r = -0.18, P = 0.021), and hypertension history (r = -0.28, P < 0.001). Age (P < 0.001), male sex (P = 0.007), BMI (P = 0.001), Em (P = 0.032), HRR (P = 0.013), and A1C (P = 0.0007) were independent predictors of exercise capacity. CONCLUSIONS: Reduced exercise capacity in patients with type 2 diabetes is associated with diabetes control, subclinical LV dysfunction, and impaired HRR.

Blood Glucose↗
PubMed2004

Prediction of subclinical left ventricular dysfunction with strain rate imaging in patients with asymptomatic severe mitral regurgitation.

This study sought the ability of strain rate imaging to detect subclinical left ventricular dysfunction, as evidenced by reduced contractile reserve (CR) in 32 asymptomatic patients with isolated severe mitral regurgitation. Compared with CR- patients (n = 10), CR+ patients (n = 22) had significantly higher end-systolic strain and peak systolic strain rate, but these parameters were not significantly different between CR+ patients and matched normal controls.

Aged↗
PubMed2004

Left ventricular dyssynchrony predicts response and prognosis after cardiac resynchronization therapy.

OBJECTIVES: This study was designed to predict the response and prognosis after cardiac resynchronization therapy (CRT) in patients with end-stage heart failure (HF). BACKGROUND: Cardiac resynchronization therapy improves HF symptoms, exercise capacity, and left ventricular (LV) function. Because not all patients respond, preimplantation identification of responders is needed. In the present study, response to CRT was predicted by the presence of LV dyssynchrony assessed by tissue Doppler imaging. Moreover, the prognostic value of LV dyssynchrony in patients undergoing CRT was assessed. METHODS: Eighty-five patients with end-stage HF, QRS duration >120 ms, and left bundle-branch block were evaluated by tissue Doppler imaging before CRT. At baseline and six months follow-up, New York Heart Association functional class, quality of life and 6-min walking distance, LV volumes, and LV ejection fraction were determined. Events (death, hospitalization for decompensated HF) were obtained during one-year follow-up. RESULTS: Responders (74%) and nonresponders (26%) had comparable baseline characteristics, except for a larger dyssynchrony in responders (87 +/- 49 ms vs. 35 +/- 20 ms, p < 0.01). Receiver-operator characteristic curve analysis demonstrated that an optimal cutoff value of 65 ms for LV dyssynchrony yielded a sensitivity and specificity of 80% to predict clinical improvement and of 92% to predict LV reverse remodeling. Patients with dyssynchrony >/=65 ms had an excellent prognosis (6% event rate) after CRT as compared with a 50% event rate in patients with dyssynchrony <65 ms (p < 0.001). CONCLUSIONS: Patients with LV dyssynchrony >/=65 ms respond to CRT and have an excellent prognosis after CRT.

Aged↗
PubMed2004

Alterations of left ventricular myocardial characteristics associated with obesity.

BACKGROUND: Obesity is associated with heart failure, but an effect of weight, independent of comorbidities, on cardiac structure and function is not well established. We sought whether body mass index (BMI) and insulin levels were associated with subclinical myocardial disturbances. METHODS AND RESULTS: Transthoracic echocardiography, myocardial Doppler-derived systolic (sm) and early diastolic velocity (em), strain and strain rate imaging and tissue characterization with cyclic variation (CVIB), and calibrated integrated backscatter (cIB) were obtained in 109 overweight or obese subjects and 33 referents (BMI <25 kg/m2). BMI correlated with left ventricular (LV) mass and wall thickness (P<0.001). Severely obese subjects (BMI >35) had reduced LV systolic and diastolic function and increased myocardial reflectivity compared with referents, evidenced by lower average long-axis strain, sm, cIB, lower CVIB, and reduced em, whereas LV ejection fraction remained normal. Differences in regional or global strain, sm, and em were identified between the severely obese (BMI >35) and the referent patients (P<0.001). Similar but lesser degrees of reduced function by sm, em, and basal septal strain and increased reflectivity by cIB were present in overweight (BMI, 25 to 29.9) and mildly obese (BMI, 30 to 35) groups (P<0.05). Although tissue Doppler measures were not associated with duration of obesity, they did correlate with fasting insulin levels and reduced exercise capacity. BMI was independently related to average LV strain (beta=0.40, P=0.02), sm (beta=-0.36, P=0.002), and em (beta=-0.41, P<0.001). CONCLUSIONS: Overweight subjects without overt heart disease have subclinical changes of LV structure and function even after adjustment for mean arterial pressure, age, gender, and LV mass.

Adult↗
PubMed2004

Combination of contrast with stress echocardiography: a practical guide to methods and interpretation.

Contrast echocardiography has an established role for enhancement of the right heart Doppler signals, the detection of intra-cardiac shunts, and most recently for left ventricular cavity opacification (LVO). The use of intravenously administered micro-bubbles to traverse the myocardial microcirculation in order to outline myocardial viability and perfusion has been the source of research studies for a number of years. Despite the enthusiasm of investigators, myocardial contrast echocardiography (MCE) has not attained routine clinical use and LV opacification during stress has been less widely adopted than the data would support. The purpose of this review is to facilitate an understanding of the involved imaging technologies that have made this technique more feasible for clinical practice, and to guide its introduction into the practice of the non-expert user.

Contrast Media↗
PubMed2004

Incremental benefit of myocardial contrast to combined dipyridamole-exercise stress echocardiography for the assessment of coronary artery disease.

BACKGROUND: Although assessment of myocardial perfusion by myocardial contrast echocardiography (MCE) is feasible, its incremental benefit to stress echocardiography is not well defined. We examined whether the addition of MCE to combined dipyridamole-exercise echocardiography (DExE) provides incremental benefit for evaluation of coronary artery disease (CAD). METHODS AND RESULTS: MCE was combined with DExE in 85 patients, 70 of whom were undergoing quantitative coronary angiography and 15 patients with a low probability of CAD. MCE was acquired by low-mechanical-index imaging in 3 apical views after acquisition of standard resting and poststress images. Wall motion, left ventricular opacification, and MCE components of the study were interpreted sequentially, blinded to other data. Significant (>50%) stenoses were present in 43 patients and involved 69 coronary territories. The addition of qualitative MCE improved sensitivity for the detection of CAD (91% versus 74%, P=0.02) and accurate recognition of disease extent (87% versus 65% of territories, P=0.003), with a nonsignificant reduction in specificity. CONCLUSIONS: The addition of low-mechanical-index MCE to standard imaging during DExE improves detection of CAD and enables a more accurate determination of disease extent.

Aged↗
PubMed2004

Reproducibility and accuracy of echocardiographic measurements of left ventricular parameters using real-time three-dimensional echocardiography.

OBJECTIVES: We sought to determine whether assessment of left ventricular (LV) function with real-time (RT) three-dimensional echocardiography (3DE) could reduce the variation of sequential LV measurements and provide greater accuracy than two-dimensional echocardiography (2DE). BACKGROUND: Real-time 3DE has become feasible as a standard clinical tool, but its accuracy for LV assessment has not been validated. METHODS: Unselected patients (n = 50; 41 men; age, 64 +/- 8 years) presenting for evaluation of LV function were studied with 2DE and RT-3DE. Test-retest variation was performed by a complete restudy by a separate sonographer within 1 h without alteration of hemodynamics or therapy. Magnetic resonance imaging (MRI) images were obtained during a breath-hold, and measurements were made off-line. RESULTS: The test-retest variation showed similar measurements for volumes but wider scatter of LV mass measurements with M-mode and 2DE than 3DE. The average MRI end-diastolic volume was 172 +/- 53 ml; LV volumes were underestimated by 2DE (mean difference, -54 +/- 33; p < 0.01) but only slightly by RT-3DE (-4 +/- 29; p = 0.31). Similarly, end-systolic volume by MRI (91 +/- 53 ml) was underestimated by 2DE (mean difference, -28 +/- 28; p < 0.01) and by RT-3DE (mean difference, -3 +/- 18; p = 0.23). Ejection fraction by MRI was similar by 2DE (p = 0.76) and RT-3DE (p = 0.74). Left ventricular mass (183 +/- 50 g) was overestimated by M-mode (mean difference, 68 +/- 86 g; p < 0.01) and 2DE (16 +/- 57; p = 0.04) but not RT-3DE (0 +/- 38 g; p = 0.94). There was good inter- and intra-observer correlation between RT-3DE by two sonographers for volumes, ejection fraction, and mass. CONCLUSIONS: Real-time 3DE is a feasible approach to reduce test-retest variation of LV volume, ejection fraction, and mass measurements in follow-up LV assessment in daily practice.

Echocardiography, Three-Dimensional↗
PubMed2004

Effect of aldosterone antagonism on myocardial dysfunction in hypertensive patients with diastolic heart failure.

BACKGROUND: Specific treatments targeting the pathophysiology of hypertensive heart disease are lacking. As aldosterone has been implicated in the genesis of myocardial fibrosis, hypertrophy, and dysfunction, we sought to determine the effects of aldosterone antagonism on myocardial function in hypertensive patients with suspected diastolic heart failure by using sensitive quantitative echocardiographic techniques in a randomized, double-blinded, placebo-controlled study. METHODS AND RESULTS: Thirty medically treated ambulatory hypertensive patients (19 women, age 62+/-6 years) with exertional dyspnea, ejection fraction >50%, and diastolic dysfunction (E/A <1, E deceleration time >250 m/sec) and without ischemia were randomized to spironolactone 25 mg/d or placebo for 6 months. Patients were overweight (31+/-5 kg/m2) with reduced treadmill exercise capacity (6.7+/-2.1 METS). Long-axis strain rate (SR), peak systolic strain, and cyclic variation of integrated backscatter (CVIB) were averaged from 6 walls in 3 standard apical views. Mean 24-hour ambulatory blood pressure at baseline (133+/-17/80+/-7 mm Hg) did not change in either group. Values for SR, peak systolic strain, and CVIB were similar between groups at baseline and remained unchanged with placebo. Spironolactone therapy was associated with increases in SR (baseline: -1.57+/-0.46 s(-1) versus 6-months: -1.91+/-0.36 s(-1), P<0.01), peak systolic strain (-20.3+/-5.0% versus -26.9+/-4.3%, P<0.001), and CVIB (7.4+/-1.7 dB versus 8.6+/-1.7 dB, P=0.08). Each parameter was significantly greater in the spironolactone group compared with placebo at 6 months (P=0.05, P=0.02, and P=0.02, respectively), and the increases remained significant after adjusting for baseline differences. The increase in strain was independent of changes in blood pressure with intervention. The spironolactone group also exhibited reduction in posterior wall thickness (P=0.04) and a trend to reduced left atrial area (P=0.09). CONCLUSIONS: Aldosterone antagonism improves myocardial function in hypertensive heart disease.

Aged↗
PubMed2004

A clinical and echocardiographic score for assigning risk of major events after dobutamine echocardiograms.

OBJECTIVES: We sought to develop and validate a risk score combining both clinical and dobutamine echocardiographic (DbE) features in 4890 patients who underwent DbE at three expert laboratories and were followed for death or myocardial infarction for up to five years. BACKGROUND: In contrast to exercise scores, no score exists to combine clinical, stress, and echocardiographic findings with DbE. METHODS: Dobutamine echocardiography was performed for evaluation of known or suspected coronary artery disease in 3156 patients at two sites in the U.S. After exclusion of patients with incomplete follow-up, 1456 DbEs were randomly selected to develop a multivariate model for prediction of events. After simplification of each model for clinical use, the models were internally validated in the remaining DbE patients in the same series and externally validated in 1733 patients in an independent series. RESULTS: The following score was derived from regression models in the modeling group (160 events): DbE risk = (age.0.02) + (heart failure + rate-pressure product <15000).0.4 + (ischemia + scar).0.6. The presence of each variable was scored as 1 and its absence scored as 0, except for age (continuous variable). Using cutoff values of 1.2 and 2.6, patients were classified into groups with five-year event-free survivals >95%, 75% to 95%, and <75%. Application of the score in the internal validation group (265 events) gave equivalent results, as did its application in the external validation group (494 events, C index = 0.72). CONCLUSIONS: A risk score based on clinical and echocardiographic data may be used to quantify the risk of events in patients undergoing DbE.

Cardiotonic Agents↗