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Biomedical subjects

J V Nixon

Publications and source records attributed to J V Nixon.

At least 19 recordsLinked to original sources
PubMed2006

Lower is better--the contemporary concept of low-density lipoprotein lowering in the preventive management of cardiovascular risk: does this apply to all patients?

The number of multiple outcomes-based clinical trials evaluating the use of statin drugs for lowering cardiovascular risk continues to grow, incorporating patients requiring primary and secondary preventive care. This review surveys the most recently published studies and identifies both the more extensive patient population that may benefit from primary preventive care and the concept of aggressive titration of the statin drug to improve the prognosis of the patient undergoing secondary preventive care. Data on the elderly patient, the female patient, and the diabetic patient are reviewed, as are the possible mechanisms of action of the statins in modifying cardiovascular risk. The pleiotropic effects and anti-inflammatory capabilities of the drugs are also reviewed. Conclusions are drawn regarding the contemporary use of statins in the primary and secondary preventive management of patients to significantly reduce cardiovascular risk.

Age Factors↗
PubMed2004

A comparison of pulmonary vein ostial anatomy by computerized tomography, echocardiography, and venography in patients with atrial fibrillation having radiofrequency catheter ablation.

Accurate assessment of pulmonary vein anatomy is important to procedures that isolate these structures in patients with atrial fibrillation. Various modalities of pulmonary vein (PV) imaging are employed in clinical practice; however, the consistency of findings among the different modalities is unknown. The purpose of this study is to compare PV ostial anatomy by 4 common imaging techniques. Twenty-four patients undergoing catheter-based PV isolation procedures for atrial fibrillation had their PV ostial anatomy determined by cardiac computerized tomography (CT) and transesophageal echocardiography (TEE) before ablation and by intracardiac echocardiography (ICE) and venography during the ablation procedure. The number and maximal dimension of the PV ostia were determined by each imaging modality. In the 24 patients, 98 PV ostia were visualized by CT, 93 by ICE, 81 by TEE, and 71 by venography. The average ostial diameters were similar between CT (1.45 +/- 0.29 cm) and ICE (1.51 +/- 0.22 cm, p = 0.066). Compared with CT or ICE, the ostial diameters were larger with venography (1.67 +/- 0.32 cm) and smaller with TEE (1.16 +/- 0.28 cm, all p <0.001). PV ostial diameters as determined by ICE were significantly correlated with CT measurements (r = 0.57, p <0.001) and venography (r = 0.52, p <0.001). Venography measures of PV diameter were correlated with measures by CT (r = 0.33, p = 0.03). TEE measures were not correlated with any other modality (all p >/=0.43). CT identifies the greatest number of PV ostia followed by ICE. Venography overestimates and TEE underestimates ostial diameters compared with CT or ICE. The PV ostial dimensions obtained by ICE, CT, and venography are all significantly correlated.

Atrial Fibrillation↗
PubMed2004

Cholesterol management and the reduction of cardiovascular risk.

The increasing number of outcomes-based clinical trials addressing cardiovascular risk factor reduction using statin therapy has resulted in a substantial revision of the management of patients at risk for cardiovascular events. The clinical trials involve both primary and secondary preventive care. This review outlines the trials addressing primary and secondary prevention, detailing the more recently published studies, their place in risk-factor management, and their relationship to the National Cholesterol Education Program guidelines. Available data in elderly patients are reviewed, as are the adverse effects of the different statins and the statin drugs undergoing preliminary trials but not yet approved for general clinical use. The underuse of statin therapy is also addressed. Conclusions are drawn regarding the appropriate use of statin therapy in the contemporary primary and secondary preventive management of patients to reduce cardiovascular mortality and morbidity.

Aged↗
PubMed2002

Phased-array intracardiac echocardiography during pulmonary vein isolation and linear ablation for atrial fibrillation.

INTRODUCTION: Fluoroscopic imaging provides limited anatomic guidance for left atrial structures. The aim of this study was to determine the utility of real-time, phased-array intracardiac echocardiography during radiofrequency ablation for atrial fibrillation. METHODS AND RESULTS: In 29 patients undergoing pulmonary vein isolation (n = 16) or linear (n = 13) left atrial radiofrequency ablation for atrial fibrillation, intracardiac phased-array echocardiography was used to visualize left atrial anatomy and the pulmonary veins, as well as ablation and mapping catheters during ablation procedures. In the 16 pulmonary vein isolation patients, the mean pulmonary vein ostial diameters measured by venography and intracardiac echocardiography were similar for all veins positions, except that left common pulmonary vein diameters were larger as measured by echocardiography (2.50 +/- 0.29 cm) than by venography (1.79 +/- 0.50 cm, P = 0.001). The ostial diameters measured by echocardiography and venography were not correlated, however (r = 0.23, P = 0.19). As directed by echocardiography, only 1 of 25 circular mapping catheters (4%) used in 16 patients was replaced due to inappropriate sizing of the pulmonary veins. Mean pulmonary vein Doppler flow velocities increased after ablation for left-sided veins but ostial diameters were unchanged. In the linear ablation patients, the entire extent of the linear electrode array could be visualized in only 3 of 52 of catheter positions (6%) in the 13 patients. A portion of the catheter could be seen in only 50% of all target catheter positions. CONCLUSION: Phased-array intracardiac echocardiography (1) allows sizing and positioning of pulmonary vein mapping catheters, (2) provides measures of pulmonary vein ostial diameters, (3) continuously monitors pulmonary vein Doppler flow velocities, and (4) has limited use in positioning linear ablation catheters in the left atrium.

Alabama↗
PubMed2002

Comparison of 2-dimensional echocardiography and myocardial perfusion imaging for diagnosing myocardial infarction in emergency department patients.

BACKGROUND: Both 2-dimensional echocardiography and myocardial perfusion imaging (MPI) with technetium-99m based agents have been used to identify patients in the emergency department with myocardial infarction (MI). However, the inclusion of small numbers of patients in prior studies limits the accurate assessment of sensitivity of the 2 techniques. METHODS: Gated MPI was used as part of the initial triage process in patients initially considered at low to moderate risk for acute coronary syndromes (no ST elevation or depression). Patients diagnosed with MI also underwent echocardiography. MPI results were considered positive if there was a perfusion defect associated with abnormal wall motion or thickening, and echocardiographic results were considered positive if there were segmental wall motion abnormalities or ejection fraction of less than 40%. RESULTS: Both tests were performed on 141 patients. The sensitivities for MI for echocardiography (91%; 95% CI, 86%-95%) and MPI (89%; 95% CI, 83%-94%) were similar. Patients who had either negative echocardiographic results (peak creatine kinase level [CK], 325 +/- 206 vs 582 +/- 614 U/L; P =.003) or negative MPI results (peak CK, 313 +/- 227 vs 590 +/- 620 U/L; P =.001) had smaller MIs as estimated with peak CK values. Ejection fraction was highly correlated between the 2 techniques (r = 0.82; P <.001). CONCLUSION: Both echocardiography and MPI have a high sensitivity for identifying patients in the emergency department who have MI. False negative studies with either technique were associated with small MIs.

Biomarkers↗
PubMed1998

Comparison between 2-dimensional echocardiography and myocardial perfusion imaging in the emergency department in patients with possible myocardial ischemia.

BACKGROUND: Accurate identification of patients at high risk for acute coronary syndromes among those seen in the emergency department (ED) with possible myocardial ischemia and nonischemic electrocardiograms is problematic. Both 2-dimensional echocardiography and myocardial perfusion imaging with technetium-99m sestamibi can identify patients at low and high risk; however, comparative studies are lacking. METHODS AND RESULTS: Patients initially considered at low or moderate risk for myocardial ischemia on the basis of the presenting history, physical examination, and electrocardiogram underwent both echocardiography and myocardial perfusion imaging within 4 hours of ED presentation. Positive echocardiography was defined as the presence of segmental wall motion abnormalities or moderate to severe global systolic dysfunction; positive perfusion imaging was defined as a perfusion defect in association with abnormal wall motion, thickening, or both. End points included MI, percutaneous transluminal coronary angioplasty, and positive stress perfusion imaging. Both imaging procedures were performed in the ED on 185 patients. Six patients had MI, and an additional 4 patients underwent percutaneous transluminal coronary angioplasty. Echocardiography and perfusion imaging were positive in all 10. Overall agreement between the 2 techniques was high (concordance 89%, kappa coefficient 0.74) in the 27 patients who had MI or underwent coronary angiography. For all patients, concordance was 89%, with a kappa coefficient of 0.66. CONCLUSIONS: Agreement between echocardiography and perfusion imaging with technetium-99m sestamibi is high when used in patients in the ED with possible myocardial ischemia. Both techniques identified patients at high risk who required admission and those who could be safely discharged directly from the ED.

Adult↗
PubMed1998

Early echocardiography can predict cardiac events in emergency department patients with chest pain.

STUDY OBJECTIVE: Accurate diagnosis in emergency department patients with possible myocardial ischemia is problematic. Two-dimensional echocardiography has a high sensitivity for identifying patients with myocardial infarction (MI); however, few studies have investigated its diagnostic ability when used acutely in ED patients with possible myocardial ischemia. Therefore we investigated the ability of ED echocardiography for predicting cardiac events in patients with possible myocardial ischemia. METHODS: Echocardiography was performed within 4 hours of ED presentation in 260 patients with possible myocardial ischemia, and was considered positive if there were segmental wall motion abnormalities or the ejection fraction was less than 40%. ECGs were considered abnormal if there was an ST-segment elevation or depression of greater than or equal to 1 mm, or ischemic T-wave inversion. Cardiac events included MI and revascularization. RESULTS: Of the 260 patients studied, 45 had cardiac events (23 MI, 19 percutaneous transluminal angioplasty, 3 coronary bypass surgery). The sensitivity of echocardiography for predicting cardiac events was 91% (95% confidence interval 79% to 97%]), which was significantly higher than the ECG (40% [95% CI 27% to 55%]: P < .0001), although specificity was lower (75% [95% CI 69% to 81%] versus 94% [95% CI 90% to 97%]; P < .001). Addition of the echocardiography results to baseline clinical variables and the ECG added significant incremental diagnostic value (P < .001). With use of multivariate analysis, only male gender (P < .03, odds ratio [OR] 2.4 [1.1 to 5.3]), and a positive echocardiographic finding (P < .0001, OR 24 [9 to 65]) predicted cardiac events. Excluding patients with abnormal ECGs (N = 30) did not affect sensitivity (85%) or specificity (74%) of echocardiography. CONCLUSION: Echocardiography performed in ED patients with possible myocardial ischemia identifies those who will have cardiac events, is more sensitive than the ECG, and has significant incremental value when added to baseline clinical variables and the ECG.

Aged↗
PubMed1997

Factors associated with elevated impedance with a nonthoracotomy defibrillation lead system.

Peak current flow across the heart determines the success of defibrillation and is inversely dependent on impedance between defibrillation electrodes. Factors associated with elevated impedance in patients with implantable defibrillators using nonthoracotomy lead systems have not been well described. Clinical and echocardiographically derived variables were analyzed in 41 patients in whom implantation of a nonthoracotomy lead system was attempted. Lead impedance was measured at end-expiration with 5-J monophasic shocks. Successful defibrillation with or without addition of a subcutaneous patch with < or = 20 J with a monophasic waveform was required for nonthoracotomy lead placement. Patients were divided into 2 groups based on impedance: low (< or = 47 ohms, n = 30) and high (>47 ohms, n = 11). Twenty-four patients had successful defibrillator implantation using a transvenous lead alone, 13 required placement of a subcutaneous patch, and 4 required epicardial patch placement. The mean left ventricular end-diastolic and end-systolic volumes were significantly smaller (p = 0.01 for both) in patients in the low- versus high-impedance groups and were significantly correlated with impedance (r = 0.44, p <0.005 for both). Impedance was not significantly different between patients with successful defibrillation using a transvenous lead alone compared with those who required either subcutaneous or epicardial patches. Thus, impedance using a nonthoracotomy lead system with monophasic shocks is significantly correlated with both end-systolic and end-diastolic volumes, but elevated impedance does not predict increased defibrillation energy requirements.

Defibrillators, Implantable↗
PubMed1994

Non-Q-wave myocardial infarction. An incomplete cardiac event requiring an aggressive approach.

Evidence that non-Q-wave myocardial infarction (MI) is an unstable or incomplete cardiac syndrome is clear. Morphologic findings, coronary pathoanatomy, in-hospital complication rates, risk-stratification data, postdischarge mortality data, and particularly morbidity data indicate a need for close diagnostic evaluation and careful long-term follow-up. Thrombolytic therapy appears to be ineffective in patients with non-Q-wave MI. Measures to prevent reinfarction during the hospital stay are indicated. Any complication of non-Q-wave MI is an indication for cardiac catheterization. All patients with non-Q-wave MI require predischarge risk stratification. If they cannot be stratified by clinical or electrocardiographic characteristics, exercise stress testing is required, preferably with an imaging study. When stratification indicates high risk, predischarge cardiac catheterization is required.

Creatine Kinase↗
PubMed1993

Usefulness of myocardial contrast echocardiography in detecting the immediate changes in anterograde blood flow reserve after coronary angioplasty.

Myocardial contrast echocardiography has revealed that successful coronary angioplasty results in an immediate decrease in the amount of collateral blood flow to the perfusion bed supplied by the dilated vessel. This information could potentially be used with pharmacologic stress in the catheterization laboratory to also assess the improvement in coronary flow reserve after angioplasty. The immediate changes in area under the time intensity curve produced by a 1 ml slow injection of sonicated albumin immediately proximal to a stenosis before and after 14 angiographically successful angioplasties was studied in 12 patients. Area under the curve was assessed before and after an 8 mg selective injection of papaverine. The changes in area under the curve were correlated with percent improvement in epicardial area stenosis. Visually successful angioplasty resulted in > 30% improvement in area under the curve after papaverine in 9 of 14 studies. There was a significant correlation between improvement in area under the curve after papaverine and percent improvement in epicardial area stenosis (r = 0.75; p < 0.01). No patient had left ventricular wall motion abnormalities after papaverine before or after angioplasty. These changes suggest that quantitatively successful angioplasty results in decreased collateral blood flow to the involved myocardium during pharmacologic stress. These improvements in coronary flow reserve cannot be predicted by visual analysis of angioplasty results.

Aged↗
PubMed1993

Doppler echocardiographic assessment of an impedance-based dual-chamber rate-responsive pacemaker.

Rate-responsive pacing allows patients with chronotropic incompetence to achieve more physiologic heart rate responses to exercise. One sensor currently being investigated uses impedance-derived measurements of changes in right ventricular stroke volume to alter the pacing rate. Correlation of pacemaker-derived measurements of stroke volume with an accepted method of stroke volume measurement has not been performed. The relative changes in impedance-derived stroke volume were compared in 10 patients with an impedance-based dual-chamber rate-responsive pacemaker (Precept DR, Cardiac Pacemakers, Inc.) with simultaneous Doppler echocardiographic measurements of right and left ventricular stroke volume. These comparisons were made during pacing at 2 heart rates (70 and 100 beats/min) and 3 AV intervals (150, 200 and 250 ms) while in a supine resting state, during lower body negative pressure to -30 mm Hg, and while performing 25% maximal handgrip. Pacemaker-derived stroke volume decreased by 7 to 11% and Doppler time-velocity integral measurements decreased by 14 to 19% in response to an increase in pacing rate (p = NS). There was also no significant difference by either technique in the mean stroke volume change when the atrioventricular interval was varied. Both techniques detected a decrease in stroke volume during lower body negative pressure, ranging from -7 to -20% by pacemaker, and -17 to -38% by Doppler. Overall, the pacemaker stroke volume measurements responded in an appropriate direction to each intervention, signaling the pacemaker's ability to detect directional change in stroke volume. The Precept DR may aid in the programming of parameters such as atrioventricular interval and heart rate by allowing for optimization of stroke volume in individual patients.

Adult↗
PubMed1993

Myocardial contrast echocardiography for the assessment of coronary blood flow reserve: validation in humans.

OBJECTIVES: The aim of this study was to validate the use of myocardial contrast echocardiography to determine coronary blood flow reserve in humans. BACKGROUND: Although myocardial contrast echocardiography has been used to accurately quantify coronary flow reserve in animals, validation for its use in humans to measure flow reserve is lacking. METHODS: We analyzed the time-intensity curve from the anteroseptal region of the left ventricular short axis produced after a left main coronary artery injection of sonicated albumin before and after intracoronary administration of papaverine in 16 patients without angiographically significant coronary artery disease. The ratio of half-time of video intensity disappearance from peak intensity, variable of curve width, area under the time-intensity curve and corrected peak contrast intensity after papaverine compared with baseline were correlated with coronary flow reserve measured simultaneously with an intracoronary Doppler probe in the left anterior descending coronary artery. RESULTS: There was a strong inverse correlation with half-time of contrast washout and coronary flow reserve (r = -0.76, p = 0.0007) and a strong positive correlation between the variable of curve width (which is inversely proportional to curve width) and coronary flow reserve (r = 0.71, p = 0.002). There was a weak but significant inverse correlation between area under the time-intensity curve and coronary flow reserve (r = -0.54, p = 0.03) but no correlation between corrected peak contrast intensity and coronary flow reserve (r = -0.36, p = NS). Despite the strong correlation for the ratios for half-time of contrast washout and variable of curve width and actual coronary flow reserve measured with intracoronary Doppler probe, the transit time ratios consistently underestimated coronary flow reserve. CONCLUSIONS: Myocardial contrast echocardiography performed with left main coronary artery injections of sonicated albumin can be utilized to measure coronary flow reserve in humans. Transit time variable ratios (half-time of contrast washout and variable of curve width) derived from the time-intensity curve correlate most strongly with coronary flow reserve.

Adult↗
PubMed1993

Modulation of the QT interval: effects of graded exercise and reflex cardiovascular stimulation.

During exercise, as heart rate (HR) increases, the QT interval of the electrocardiogram shortens. The mechanism(s) involved in this QT shortening has not been clearly defined. To distinguish the influence of increased circulating catecholamines from myocardial efferent stimulation, the relationship between HR and QT interval was investigated during exercise and cardiovascular reflex stimulation in cardiac transplant patients and normal control subjects. Because of cardiac denervation, increases in HR in these patients are solely due to circulating catecholamines and thus allow isolation of their effect on the QT interval. Twenty-one cardiac transplant patients were studied and compared with 16 normal control subjects. The QT-HR relationship was determined according to an exponential model during treadmill exercise in both groups [QT = 0.12 + 0.492e(-0.008.HR) and QT = 0.12 + 0.459e(-0.007.HR) in normal subjects and transplant patients, respectively] and was statistically similar between groups, suggesting similar QT interval shortening in both groups. During cold pressor and Valsalva maneuvers, HR increased significantly in normal subjects only, whereas QT interval changed minimally in both groups. These results suggest that during exercise the QT interval is influenced predominantly by increases in circulating catecholamines rather than by neurally mediated reflex autonomic changes.

Adult↗
PubMed1992

Transesophageal echocardiography to assess mitral valve function and flow during cardiopulmonary resuscitation.

This study further defines the mechanism of blood flow during closed-chest compression using transesophageal Doppler echocardiography. Although the echocardiographic demonstration of mitral valve closure during closed-chest compression has been used as evidence of direct cardiac compression, mitral valve closure has also been documented to occur during resuscitation by selectively increasing intrathoracic pressure. Transesophageal Doppler echocardiography was used to assess mitral valve position and flow in 17 adult patients undergoing cardiopulmonary resuscitation with a mechanical piston compression device. Left and right ventricular fractional shortening, mitral valve position with chest compression, timing and magnitude of transmitral flow, and anteroposterior chest diameter were recorded. In 12 patients (group I), the mitral valve closed during the down-stroke of chest compression; in the remaining 5 (group II), it opened further. Peak transmitral flow occurred during the release phase and was significantly higher (p < 0.05) in group I (39.5 +/- 9.3 cm/s) than the peak flow in group II (21.3 +/- 5.9 cm/s), which occurred during the downstroke of chest compression. Left ventricular fractional shortening inversely correlated (r = -0.68; p = 0.02) with the anteroposterior chest diameter, but did not correlate with peak transmitral flow (r = 0.34; p = not significant). It is concluded that the mitral valve closes during the downstroke of chest compression in most adult patients during resuscitation. The absence of a relation between mitral valve flow and left ventricular fractional shortening supports the hypothesis that other factors such as nonuniform increases in intrathoracic pressure cause the mitral valve to open or close during chest compression.

Blood Flow Velocity↗
PubMed1991

Effects of exercise on left ventricular diastolic performance in trained athletes.

Dynamically trained athletes develop increased left ventricular (LV) wall mass. To determine whether this increased wall mass impaired characteristics of LV diastolic filling, serial Doppler echocardiograms were obtained from 10 trained athletes (mean age 21 years) at rest, during supine graded bicycle exercise and during recovery at heart rates of 80, 120 and 140 beats/min, respectively. Similar studies were obtained in 10 age-matched control subjects. Studies at rest showed significant increases in athletes in LV end-diastolic dimension and indexed LV wall mass. Differences in peak filling rates and in normalized peak lengthening rates between athletes and control subjects were seen at heart rates of 140 beats/min during exercise and recovery. Differences in Doppler-derived variables between athletes and control subjects were seen in total time-velocity integral, early peak filling velocity and E/A ratio. In athletes, time-velocity integral was increased during recovery at heart rates of 120 beats/min and 80 beats/min, early peak filling velocity was increased during exercise at 120 beats/min and during recovery at 120 beats/min and 80 beats/min, and E/A ratio was higher at all heart rates during both exercise and recovery. Although no significant differences were found in LV diastolic filling indexes at rest, a significant enhancement was found in these parameters in dynamically trained athletes during exercise, particularly at higher levels of dynamic exercise.

Adult↗
PubMed1991

Noninvasive estimation of left atrial pressure in patients with congestive heart failure and mitral regurgitation by Doppler echocardiography.

A completely noninvasive method for estimating left atrial pressure in patients with congestive heart failure and mitral regurgitation has been devised with the use of continuous-wave Doppler echocardiography and brachial sphygmomanometry. Of 46 patients studied with mitral regurgitation, 35 (76%) had jets with distinct Doppler spectral envelopes recorded. The peak ventriculoatrial gradient was obtained by measuring peak mitral regurgitant velocity in systole and using the modified Bernoulli equation. This gradient was then subtracted from peak brachial systolic blood pressure, an estimate of left ventricular systolic pressure, to yield left atrial pressure (left atrial pressure = systolic blood pressure - mitral regurgitant pressure gradient). Noninvasive estimates of left atrial pressure from 35 patients were plotted against simultaneous recordings of mean pulmonary capillary wedge pressure resulting in the correlation y = 0.88x + 3.3, r = 0.88, standard error of estimate = +/- 4 mm Hg (p less than 0.001). Therefore, continuous-wave Doppler echocardiography and sphygmomanometry may be used in selected patients with congestive heart failure and mitral regurgitation for noninvasive estimation of left atrial pressure.

Atrial Function, Left↗