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Biomedical subjects

N G Pandian

Publications and source records attributed to N G Pandian.

At least 91 records · Page 5Linked to original sources
PubMed1993

Endothelium-dependent pulmonary artery responses in chronic heart failure: influence of pulmonary hypertension.

OBJECTIVES: The purpose of this study was to determine whether pulmonary artery responses to acetylcholine are abnormal in patients with chronic heart failure. BACKGROUND: Defective pulmonary artery endothelium-dependent responses have been observed in chronic heart failure models in animals. However, pulmonary artery endothelial responses in humans with chronic heart failure are unknown. METHODS: Twenty-two patients with chronic treated heart failure (12 with secondary pulmonary hypertension, Group I; 10 with normal pulmonary artery pressure, Group II) and 8 control patients constituted the study groups. Intravascular ultrasound measurements of pulmonary artery area just beyond the tip of an 8F infusion sheath were obtained in response to acetylcholine (10(-6), 10(-5) and 10(-4) mol/liter). The 10(-6) mol/liter infusion was repeated after methylene blue infusion. Indomethacin (5 micrograms/ml) was sequentially added to this combination in 17 patients. RESULTS: There were no significant differences among the three groups in vascular area responses to the lowest concentration (10(-6) and 10(-5) mol/liter) of acetylcholine, but the 10(-4) mol/liter infusion resulted in significant constriction in Group II patients (p < 0.05, analysis of variance [ANOVA]). Pretreatment with methylene blue in Group II also resulted in significant pulmonary artery vasoconstriction to even the 10(-6) mol/liter acetylcholine infusion (10.4 +/- 7.8% in Group II vs. 1.7 +/- 3.9% in the control group and 0.1 +/- 4.3% in Group I, p < 0.05, ANOVA). The addition of indomethacin resulted in reversal of the constriction in Group II patients. CONCLUSIONS: These responses indicate that the pulmonary artery endothelium may play a significant role in inhibiting vasoconstriction in patients with chronic heart failure who maintain normal pulmonary artery pressure.

Acetylcholine↗
PubMed1993

Left ventricular diastolic collapse in regional left heart cardiac tamponade. An experimental echocardiographic and hemodynamic study.

OBJECTIVES: This study was designed to describe the hemodynamic abnormalities associated with the appearance of left ventricular diastolic collapse in the setting of regional left heart cardiac tamponade. BACKGROUND: Cardiac tamponade after heart surgery is frequently associated with localized pericardial effusion. Although right ventricular diastolic collapse and right atrial collapse are reliable echocardiographic findings in patients with circumferential pericardial effusion and tamponade, they are often not present in postoperative patients with localized pericardial effusion and regional left heart tamponade. Left ventricular diastolic collapse has been described in such patients, but the degree of hemodynamic alteration that exists with this finding is not known. METHODS: Acute regional left heart tamponade was produced 14 times in seven spontaneously breathing anesthetized dogs by infusing fluid into an isolated compartment created in the pericardial space adjacent to the left ventricular free wall. Continuous echocardiographic imaging and hemodynamic monitoring of left ventricular, systemic arterial, right atrial, pulmonary capillary wedge and pericardial pressures were performed. Measurements at baseline were compared with those made at the onset of left ventricular diastolic collapse and at decompensated tamponade. RESULTS: Left ventricular diastolic collapse was noted in all 14 episodes of regional tamponade. It occurred when pressure in the left pericardial compartment exceeded left ventricular diastolic pressure by 3.0 +/- 1.9 mm Hg. At the onset of left ventricular diastolic collapse, cardiac output and mean arterial pressure were significantly reduced from the control value (p < 0.05). Systolic hypotension was noted only twice at this stage, respiratory variation in systolic pressure > 10 mm Hg only once. The appearance of this sign was also associated with elevated left heart filling pressures. CONCLUSIONS: Left ventricular diastolic collapse is a reliable sign of regional left ventricular tamponade and is associated with a reduction in cardiac output. This echocardiographic finding usually occurs before the development of arterial hypotension and pulsus paradoxus. Thus, left ventricular diastolic collapse is potentially more reliable than hypotension or pulsus paradoxus in the diagnosis of regional left ventricular tamponade.

Acute Disease↗
PubMed1993

Single, biplane, multiplane, and three-dimensional transesophageal echocardiography. Echocardiographic-anatomic correlations.

Advances in TEE instrumentation have led to the emergence of this modality as a powerful diagnostic tool. Numerous investigations in humans have clearly defined the plethora of clinical applications of TEE in a variety of patient care scenarios. Research in progress in the area of transducer technology and computerized image processing is likely to bring 3-D TEE to the clinical front.

Aorta, Thoracic↗
PubMed1992

Intravascular ultrasound and intracardiac echocardiography: concepts for the future.

Intravascular ultrasound imaging is a catheter-based method that has been shown to be better than contrast angiography in the detailed assessment of coronary and peripheral arterial atherosclerotic lesions, arterial dissections and clots, aortic and pulmonary arterial disorders, and the effects and complications of interventional therapy in various vascular beds. Evaluation of refined ultrasound catheters, combined imaging and therapeutic devices, and off-line 3-dimensional reconstruction capabilities indicates that intravascular ultrasound could provide guidance during various catheter-based therapeutic procedures. Early experience with intracardiac echocardiography suggests that this technique could evolve as a clinically useful method with diagnostic, monitoring, and guidance applications. Future directions for further development include designing of miniaturized imaging devices, "look-forward" imaging devices, low frequency devices for whole heart imaging, multifrequency ultrasound catheters and multifunction ultrasound consoles, and approaches to real-time 3-dimensional imaging, on-line tissue characterization, automated acoustic quantification and tissue characterization, the study of myocardial perfusion, and catheter-based acoustic myocardial biopsy. These developments could lead to the conversion of catheterization laboratories into integrated imaging, monitoring, and therapeutic stations. In addition, continuous monitoring of cardiac function could be possible in the critical care unit and in the operating room as well. Ongoing advances in catheter technology and image processing indicate that these concepts are within the realm of becoming reality.

Arteries↗
PubMed1992

Intracardiac echocardiography during simulated aortic and mitral balloon valvuloplasty: in vivo experimental studies.

The feasibility of intracardiac echocardiography with a low-frequency transducer to assess catheter position and detect complications during experimental aortic and mitral balloon valvuloplasty was studied in 10 dogs. Intracardiac echocardiography was performed with a transesophageal echocardiographic probe placed in the right atrium. In all instances high-quality images of cardiac structures were obtained. The guide wire and balloon catheter were clearly seen as they crossed the valves. With inflation the balloon was seen as a hyperechoic structure. Doppler echocardiography documented aortic regurgitation after inflations. Acute pericardial effusion was instantly detected. It is concluded that intracardiac echocardiography is a potentially useful technique for cardiac imaging, assessing wire and balloon catheter position, evaluating valvular regurgitation, and instantly detecting acute pericardial effusion. Further research in humans with low-frequency, catheter-based transducers needs to be performed.

Animals↗
PubMed1992

Multiplane transesophageal echocardiography. Imaging planes, echocardiographic anatomy, and clinical experience with a prototype phased array OmniPlane probe.

Multiplane transesophageal echocardiography is a new exciting development in echocardiography. We examined the methodology and echo-anatomic correlations of multiplane transesophageal echocardiography and its clinical applications in 100 patients. We used a 5-MHz phased array multiplane (OmniPlane) transesophageal probe. In this instrument, the transducer array can be steered through 180 degrees from any transducer location. This provides a vast assembly of imaging planes, allowing for detailed visualization of all dimensions of cardiac anatomy. This report presents our observations on the echocardiographic anatomy seen in various image planes and the unique clinical potential of multiplane transesophageal echocardiography in the diagnostic assessment of cardiovascular disorders. This technique appears to provide incremental diagnostic information that enhances the interpretative ability. Less esophageal probe manipulation is required with consequent decrease in patient discomfort. We conclude that multiplane transesophageal echocardiography enhances the versatility of transesophageal examination and offers many new avenues for developments such as three-dimensional echocardiography.

Echocardiography↗
PubMed1992

Three-dimensional and four-dimensional transesophageal echocardiographic imaging of the heart and aorta in humans using a computed tomographic imaging probe.

We evaluated the clinical applicability of a prototype tomographic transesophageal echocardiographic (TEE) system, which not only provides conventional TEE images but also three-dimensional tissue reconstruction and four-dimensional display capabilities. The probe was used in 16 patients in the echocardiographic laboratory, intensive care unit, and the operating room. The instrument is a 5-MHz, 64-element, phased array unit mounted on a sliding carriage within a casing. After appropriate probe placement within the esophagus, the probe is straightened, a balloon surrounding the probe is inflated, and data acquisition begun with ECG and respiration gating. With computer controlled transducer movement at 1-mm increments, a complete cardiac cycle is recorded at each tomographic level. These are processed using a dedicated four-dimensional software, and displayed as a dynamic three-dimensional tissue image of the heart. We were able to see the dynamic motion of the ventricles and all the valves in the four-dimensional format. In addition to four-dimensional display, we were able to cut and visualize the heart in dynamic mode in any desired plane and also in multiple planes. Patients tolerated the procedure well. We conclude that this tomographic four-dimensional approach, which does not require tedious off-line processing, can easily be performed in patients and has a strong clinical potential.

Aorta↗
PubMed1991

Intracardiac echocardiography: current developments.

Intracardiac echocardiography refers to the method of imaging cardiac structures from intracardiac locations with the use of ultrasound catheters. Advances in catheter-based interventional cardiologic procedures to treat cardiovascular lesions and the problems encountered during those procedures due to inadequate guidance provided by fluoroscopy have given the impetus to develop other guidance modalities. Experimental explorations with intracardiac ultrasound probes have indicated that detailed visualization of cardiac structures in real-time is possible by intracardiac ultrasound. Recent advances in catheter-based ultrasound technology make it feasible to safely pass small-sized catheters in humans into various intracardiac locations and acquire images of valvular structures and various chambers. Experience with 20 MHz ultrasound catheters indicates that high resolution images of normal and abnormal structures can be obtained if the catheter is manipulated close to the region of interest. The problem of the limited depth of field associated with 20 MHz catheters has led to the fabrication of catheters with lower frequency ultrasound elements. Experimental and clinical experience with 12.5 MHz ultrasound catheters points to the capability and potential of intracardiac echocardiography to not only display normal structures but also aid in the identification of valvular abnormalities, chamber dysfunction and pericardial effusions. In addition, aortic disorders such as acute dissection, coarctation and atherosclerotic disease could be delineated. Similarly, abnormalities involving the pulmonary arteries such as pulmonary embolism, organized thrombi, peripheral pulmonary arterial stenoses, and pulmonary hypertension-induced vascular changes could be recognized. Many modifications in the catheter design are being explored. With further work in the area of catheter technology and ultrasound image processing, intracardiac echocardiography is likely to become a clinical tool.

Animals↗
PubMed1991

Real-time, intracardiac, two-dimensional echocardiography: enhanced depth of field with a low-frequency (12.5 mhz) ultrasound catheter.

Advances in catheter-based ultrasound imaging technology allow for a unique opportunity to develop two-dimensional intracardiac echocardiography, an imaging method that could have significant clinical applications. In this study, we evaluated the potential of a new, percutaneous, 9-Fr prototype intracardiac echocardiographic catheter with a 12.5-MHz rotating crystal in 13 dogs. In all dogs, we were able to easily advance the intracardiac echocardiographic catheter into the right and left hearts percutaneously and obtain dynamic images of cardiac structures in various imaging planes. With the intracardiac echocardiographic catheter in the right atrium, the whole chamber could be visualized. Minor manipulation allowed visualization of the right atrium, right ventricle, and tricuspid valve in a two-chamber view; further maneuvering yielded four-chamber views. With advancement of the catheter into the right ventricle and pulmonary artery, the right ventricular cavity, right ventricular outflow tract, and pulmonary artery could be imaged. The intracardiac echocardiographic catheter in the aortic root allowed visualization of the pulmonary artery and its bifurcation, superior portions of the atria, interatrial septum, aortic valve, and the proximal left coronary artery. With the intracardiac echocardiographic catheter in the left ventricle, short-axis images of the whole left ventricle were obtained. Manipulating the catheter tip within the left ventricle, we could visualize the left ventricle, left atrium (LA), and the mitral valve in the long axis. We were also able to visualize and identify experimentally-induced ischemic regional left ventricular dyskinesis (four of of five dogs), aortic valvular tear (five out of five dogs), and pericardial effusion with right atrial collapse (two out of two dogs). Intracardiac echocardiography was not associated with any complications. We conclude that percutaneous, low-frequency intracardiac echocardiography with a 12.5-MHz, 9-Fr catheter yields cardiac images in many imaging planes with a good depth of field, allows identification of valvular, myocardial, and pericardial abnormalities, and has excellent clinical potential in the assessment of many cardiovascular disorders.

Animals↗
PubMed1991

Panoramic transesophageal echocardiography. Clinical application of real-time, wide-angle, transesophageal two-dimensional echocardiography and color flow imaging.

Panoramic transesophageal echocardiography is a new development in transesophageal echocardiography (TEE) technology, which yields a wide-angle imaging field for real-time two-dimensional and color flow imaging. We report our early experience in patients with the use of an annular-array TEE probe that provides a wide, 270 degrees angle imaging field for two-dimensional echocardiographic imaging. The field of view can, however, be narrowed to 15 degrees . The field of view for color flow imaging can be varied from 180 degrees to 10 degrees . Pulsed-Doppler recordings of flow velocity are also possible. This TEE system provides a panoramic vision of cardiac and paracardiac structures from the esophagus and stomach. Besides cardiovascular structures, other thoracic and upper abdominal organs can be visualized. The wide field of view allows a better comprehension of the cardiac anatomy and its relationship with adjacent structures. The initial experience suggests that this method, besides providing the usually required diagnostic information, may have a number of additional applications. Its clinical potential and directions for future developments are reviewed.

Blood Vessels↗
PubMed1991

Biplane transesophageal echocardiography utilizing transverse and sagittal imaging planes: technique, echo-anatomic correlations, and display approaches.

The recent development of biplane transesophageal probes equipped with both transverse plane and sagittal plane imaging transducers allows a more complete examination of cardiac and aortic anatomy than is possible with conventional single plane transesophageal instruments. While the imaging planes used in transverse plane transesophageal imaging have been standardized, several different approaches have been suggested for the orientation and display of the newer sagittal plane images. An accepted display convention for the transverse and sagittal plane images would ease interpretation of the multiple complex images obtained during the biplane transesophageal examination. In this article, the different transverse plane and sagittal plane echocardiographic images that may be acquired during the biplane transesophageal examination are described and correlated with cardiac anatomy. A method for image display orientation is suggested that is most consistent with that previously used for the single plane transesophageal examination.

Animals↗
PubMed1991

Intracardiac echocardiography. Experimental observations on intracavitary imaging of cardiac structures with 20-MHz ultrasound catheters.

Recently catheter-based ultrasound devices have become available for obtaining high-resolution images of blood vessels. In this study we evaluated the feasibility of imaging cardiac structures using 20-MHz ultrasound catheters. In 25 dogs, the ultrasound catheter was advanced into the right and left heart chambers percutaneously. The intravascular devices yielded images of the right atrial wall, right and left ventricular myocardia, tricuspid, pulmonic, and aortic valves, and the great vessels. Although the small depth of field inherent to the frequency range of 20 MHz limited the visualization to only portions of the cardiac chambers, the images obtained were of high resolution and allowed easy identification of the various cardiac structures. Intracardiac echocardiography was easy to perform and did not result in damage to the cardiac structures. We conclude that intracardiac echocardiography using ultrasound catheters provides a new approach to cardiac imaging and that the development of lower frequency catheters could aid in extending the potential utility of intracardiac echocardiography.

Animals↗