Biomedical subjects

Gabriel Yip

Publications and source records attributed to Gabriel Yip.

4 recordsLinked to original sources

PubMed2005

Independent and incremental prognostic value of early mitral annulus velocity in patients with impaired left ventricular systolic function.

OBJECTIVES: This study sought to investigate the incremental prognostic value of non-invasive measures of early myocardial relaxation and left ventricular diastolic pressure (LVDP) in patients with impaired left ventricular (LV) systolic function. BACKGROUND: The early diastolic mitral annulus velocity (Em) reflects myocardial relaxation, and the combined ratio of the early transmitral flow velocity (E) to Em (E/Em) >15 correlates well with elevated mean LVDP. It is unknown if these new indexes will predict poorer survival in patients with LV systolic dysfunction. METHODS: Echocardiograms were prospectively obtained in 182 patients with impaired LV systolic function, defined as an LV ejection fraction <0.50. The end point was cardiac mortality. The majority of this patient sample (80%) has been reported on in a previous publication. RESULTS: After a median 48 months' follow-up, Em emerged as an independent predictor of survival (hazard ratio 0.61, 95% confidence interval 0.45 to 0.82). An Em <3 cm/s was associated with a significantly excess mortality (log-rank statistic 9.36, p = 0.002), and this measurement added incremental prognostic value to standard indexes of systolic or diastolic function, including a deceleration time <140 ms and an E/Em >15 (p = 0.038). CONCLUSIONS: Early diastolic mitral annulus velocity is a powerful predictor of cardiac mortality in patients with LV systolic impairment; Em <3 cm/s emerged as the best prognosticator in long-term follow-up, incremental to other clinical or echocardiographic variables, including the ratio E/Em.

Aged↗

PubMed2004

Strain echocardiography tracks dobutamine-induced decrease in regional myocardial perfusion in nonocclusive coronary stenosis.

OBJECTIVES: This study was designed to determine whether strain echocardiography parameters reflect changes in regional myocardial perfusion during dobutamine stress. BACKGROUND: Strain echocardiography depicts regional myocardial mechanical activity. Ischemia has been shown to reduce systolic strain rate (sSR) and prolong the time to regional lengthening (T(RL)). In an experimental model, we tested whether sSR and T(RL) tracked dobutamine-induced changes in regional myocardial perfusion (regional myocardial blood flow [RMBF]), as measured by colored microspheres. METHODS: We used a closed-chest pig model of nonocclusive coronary stenosis (n = 14) created by inflating an angioplasty balloon in the proximal left anterior descending artery. Invasive hemodynamics, RMBF, and strain parameters were measured at baseline and peak dobutamine stimulation before and during the coronary stenosis. We compared segments with reduced RMBF versus those with preserved RMBF at peak dobutamine stimulation. RESULTS: Peak sSR correlated with RMBF (r = 0.70). In the absence of coronary stenosis, dobutamine stimulation caused a significant increase in RMBF and sSR and a decrease in T(RL). This response was blunted during coronary stenosis. Using the "best cutoff" method, the sensitivity and specificity for prediction of reduced RMBF (ischemia) was 81% and 91% for sSR and 65% and 91% for T(RL), respectively. These changes occurred in the absence of any change in global systolic and diastolic function (dP/dT(max), dP/dT(min), and tau). CONCLUSIONS: Novel strain parameters that depict regional myocardial mechanics are able to predict changes in RMBF during dobutamine stress. Quantitative strain parameters may complement current echocardiographic techniques for ischemia detection and potentially improve the accuracy and reproducibility of stress echocardiography.

Animals↗

PubMed2003

Effect of beta blockade (carvedilol or metoprolol) on activation of the renin-angiotensin-aldosterone system and natriuretic peptides in chronic heart failure.

Beta blockers are known to suppress renin release in hypertension and in patients taking angiotensin-converting enzyme (ACE) inhibitors. This study sought to explore the effect of additional beta blockade on neurohumoral modulation in patients with severe heart failure (HF) who received ACE inhibitors. Forty-nine patients with chronic HF who received ACE inhibitors were given metoprolol 50 mg or carvedilol 25 mg twice daily after a 4-week dose titration period in addition to standard therapy in a prospective trial. Samples of plasma renin activity (PRA), aldosterone, aminoterminal B-type natriuretic peptide (N-BNP), and atrial natriuretic peptide (ANP) were taken at baseline and at 4, 12, and 52 weeks after starting therapy. Treatment with either beta blocker significantly lowered PRA at 4 weeks compared with baseline (-2.0 +/- 0.6 nmol/L/hour, p = 0.006), but at 12 weeks, PRA had reduced to -1.1 +/- 0.6 nmol/L/hour (p = 0.08), but at 52 weeks, it was not significantly different from baseline (+1.05 +/- 0.6 nmol/L/hour, p = 0.13). Aldosterone levels did not change significantly from baseline at 4 or 12 weeks, although there was a nonsignificant trend for lower levels at 52 weeks (baseline 232 +/- 154 pmol/L, 52 weeks 192 +/- 100 pmol/L, p = 0.09). There was significant reduction in N-BNP and ANP together with an improvement in symptom and left ventricular systolic function at 1-year follow-up. These results indicate that the suppressive effect of beta blockers on PRA in patients with HF taking ACE inhibitors is temporary, and that there is no significant effect on serum aldosterone levels.

Adrenergic beta-Antagonists↗

PubMed2003

Clinical applications of strain rate imaging.

Myocardial strain (epsilon) is a dimensionless index of change in myocardial length in response to an applied force. epsilon Rate (SR) is the rate of change of length and is usually obtained as the time derivative of the epsilon signal. In echocardiography, SR is calculated as the difference between 2 velocities normalized to the distance between the 2 velocities. SR imaging (SRI) has a theoretic advantage over Doppler tissue imaging in that SRI is relatively immune to cardiac translational motion and tethering. Therefore, SRI may be superior to Doppler tissue imaging in quantitative assessment of regional myocardial function and may find clinical application in the interrogation of coronary artery disease. The high frame rates of SRI have also renewed interest in timings of global and regional mechanical events, and their potential clinical applications. The high temporal resolution allows SRI to depict regional systolic and diastolic asynchrony. Ongoing clinical trials will determine the sensitivity, specificity, and accuracy of SRI parameters for a variety of clinical conditions. Potential clinical applications include investigation of ischemia (at rest and with stress), myocardial viability, and altered global and regional systolic and diastolic function in cardiomyopathies. Suboptimal signal quality remains a major limitation of strain imaging, and advances in data acquisition and postprocessing capabilities will help determine its future incorporation into standard regional myocardial assessment.

Blood Flow Velocity↗