Computational modeling of three-dimensional microwave tomography of breast cancer.

Microwave tomographic approach is proposed to detect and image breast cancers. Taking into account the big difference in dielectrical properties between normal and malignant tissues, we have proposed using the microwave tomographic method to image a human breast. Because of the anatomical features of the objects, this case has to be referred to the tomography with a limited angle of observation. As a result of computer experiments we have established that multiview cylindrical configurations are able to provide microwave tomograms of the breast with a small size tumor inside. Using the gradient method, we have developed a computer code to create images of the three-dimensional objects in dielectrical properties on microwave frequencies.

Dielectrical model of cellular structures in radio frequency and microwave spectrum. Electrically interacting versus noninteracting cells.

A model of dielectrical properties of cellular structures of a tissue has been proposed. Cellular structures were presented as a composition of membrane covered spheres and cylinders that do not interact with each other. No restrictions were applied to the thickness of cellular membranes. The model was further generalized into a case of electrically interacting cells. The difference in dielectrical properties calculated with the model of electrically noninteracting versus interacting cells is inversely dependent on frequency. At biological values of cellular volume fraction near 0.7 (packed configuration) the difference is about 10%-15% in resistance and in epsilon' for frequencies near 0.1 MHz. Experimental data for myocardial tissue and theoretical data, for both interacting and noninteracting models, reasonably agree at frequencies of 1-100 MHz.

Brugada-type electrocardiographic pattern induced by cocaine.

Right bundle branch block with coved ST-segment elevation in leads V1 through V3 is the electrocardiographic (ECG) marker of the Brugada syndrome. We describe a healthy young man with a normal baseline ECG in whom a transient Brugada pattern was observed repeatedly after recreational cocaine use. Intravenous administration of procainamide and subsequent intravenous propranolol followed by noradrenaline failed to reproduce the Brugada sign. An electrophysiologic study performed in the presence of the Brugada ECG pattern showed no inducible arrhythmias. This case illustrates that, in susceptible individuals, cocaine may provoke the Brugada sign. The clinical importance of this cocaine-induced ECG abnormality is currently unknown.

Microwave spectroscopy of myocardial ischemia and infarction. 1. Experimental study.

The purpose of this study was to assess whether physiologic changes in canine myocardium due to coronary blood flow reduction, ischemia, and infarction could be detected by changes in dielectrical properties. Measurements were made in the frequency range of 0.2-6.0 GHz. Percent coronary blood flow reduction was linearly related to the decrease in epsilon" at frequencies of 0.2 GHz(R =-0.997) and 1.1 GHz (R =- 0.9987). In 2 h occlusions, increased conduction time in the infarct area mirrored the temporal changes in dielectrical properties. In 2-week-old infarctions differences, in epsilon' between normal and central infarct zones were statistically significant (P<0.05) for all frequencies. For epsilon" the differences between normal and central infarct zones were also significant for all frequencies (P<0.01). In conclusion, coronary blood flow reduction, ischemia, and infarction can be detected by microwave spectroscopy and potentially can form the basis for a physiologic microwave tomographic imaging system.

Microwave spectroscopy of myocardial ischemia and infarction. 2. Biophysical reconstruction.

The proposed dielectrical relaxation model of the myocardium in the microwave spectrum has been verified both on test solutions and on normal canine myocardium. Furthermore, the model was utilized to reconstruct the changes in tissue properties (including myocardial bulk resistance and water content) following myocardial acute ischemia and chronic infarction. It was shown that the reconstructed myocardial resistance and water content correlate dynamically with the process of the development of acute myocardial ischemic injury. In chronic cases the reconstructed resistance and water content of infarcted myocardium are significantly different from that of normal myocardium: the resistance is lower and water content is higher than in normal myocardium.

Three-dimensional microwave tomography: experimental prototype of the system and vector born reconstruction method.

A method of image reconstruction in three-dimensional (3-D) microwave tomography in a weak dielectric contrast case has been developed. By utilizing only one component of the vector electromagnetic field this method allows successful reconstruction of images of 3-D mathematical phantoms. A prototype of the 3-D microwave tomographic system capable of imaging 3-D objects has been constructed. The system operates at a frequency of 2.36 GHz and utilizes a code-division technique. With dimensions of the cylindrical working chamber z = 40 cm and d = 60 cm, the system allows measurement of an attenuation up to 120 dB having signal-to-noise ratio about 30 dB. The direct problem solutions for different mathematical approaches were compared with an experimentally measured field distribution inside the working chamber. The tomographic system and the reconstruction method were tested in simple experimental imaging.

Laser photoablation of experimental post-infarction ventricular tachycardia guided by three dimensional activation mapping.

BACKGROUND AND OBJECTIVE: The purpose of this study was to evaluate the efficacy of epicardially delivered laser energy to ablate induced ventricular tachycardia in a post-infarction canine model. STUDY DESIGN/MATERIALS AND METHODS: In 13 canines, the left anterior wall myocardial infarction was created. Five days later, 240 plunged electrodes were inserted into the heart. Three-dimensional ventricular activation sequences were analyzed on line by a computerized mapping system. RESULTS: Sixteen sustained monomorphic ventricular tachycardias were reproducibly induced in 10 canines. Epicardially contacted Nd:YAG laser irradiated the areas of the final pathway in macro-reentrant activation and the impulse origin in focal excitation. Linear photocoagulation lesions (11-16 x 50-72 mm) were created. Seven macro-reentrant circuits and six of nine focal origins were eliminated (success rate 81%). Pathology showed that laser photocoagulation involved all surviving subepicardial and intramural fibers. CONCLUSION: Epicardially delivered laser energy in conjunction with electrical activation mapping has a high probability of ablating post-infarction ventricular tachycardia.

Epicardial neodymium. YAG laser photocoagulation of ventricular tachycardia without ventriculotomy in patients after myocardial infarction.

BACKGROUND: Surgical ablation of ventricular tachycardia (VT) after myocardial infarction has been reported by different endocardial approaches. The ventriculotomy may increase mortality of the procedure. METHODS AND RESULTS: We report on nine patients who suffered from recurrent VT in the late post-myocardial infarction period. Significant stenoses were detected in all patients. The mean left ventricular ejection fraction was 43.1 +/- 8.3%. Left ventricular scar (n = 9) was seen. The mean NYHA class was 2.2 +/- 0.4. Sustained VT (mean cycle length, 293 +/- 52 ms) occurred spontaneously (n = 9) and could be induced reproducibly. Catheter mapping detected a prematurity of -42 +/- 13 ms in six patients. Clinical VT was inducible during surgery in seven patients. Middiastolic potentials were detected from the epicardial surface (n = 3), and premature potentials were found (n = 8 with prematurity of -108 +/- 46 ms). Application of neodymium/yttrium/argon/ garnet (Nd:YAG) laser energy to early epicardial activation terminated the arrhythmia (n = 7). Ventriculotomy was not performed. Seven patients have been free of VT for a mean follow-up period of 17 +/- 11 months; one patient relapsed and was treated with an implantable cardioverter-defibrillator, as was a second patient with inducible VT after surgery. CONCLUSIONS: Surgical Nd:YAG laser photocoagulation of VT on the epicardial surface of the heart in post-myocardial infarction patients without ventriculotomy is safe and has a high success rate. At the present time, this method is recommended in patients with sustained and tolerated VT who need bypass surgery. This is the first report on epicardial laser ablation of VT in post-myocardial infarction VT.

Microwave tomography: two-dimensional system for biological imaging.

Microwave tomographic imaging is one of the new technologies which has the potential for important applications in medicine. Microwave tomographically reconstructed images may potentially provide information about the physiological state of tissue as well as the anatomical structure of an organ. A two-dimensional (2-D) prototype of a quasi real-time microwave tomographic system was constructed. It was utilized to reconstruct images of physiologically active biological tissues such as an explanted canine perfused heart. The tomographic system consisted of 64 special antennae, divided into 32 emitters and 32 receivers which were electronically scanned. The cylindrical microwave chamber had an internal diameter of 360 mm and was filled with various solutions, including deionized water. The system operated on a frequency of 2.45 GHz. The polarization of the incident electromagnetic field was linear in the vertical direction. Total acquisition time was less than 500 ms. Both accurate and approximation methods of image reconstruction were used. Images of 2-D phantoms, canine hearts, and beating canine hearts have been achieved. In the worst-case situation when the 2-D diffraction model was used for an attempt to "slice" three-dimensional (3-D) object reconstruction, we still achieved spatial resolution of 1 to 2 cm and contrast resolution of 5%.

Computerized three-dimensional activation mapping study of spontaneous ventricular arrhythmias during acute myocardial ischemia in dogs. Evidence against macroreentrant mechanism.

This study was undertaken to investigate the activation patterns of spontaneous ventricular arrhythmias during acute myocardial ischemia in dogs. In 14 open-chest dogs, the left anterior descending coronary artery was occluded for 2 hours. Three-dimensional activation maps were derived from 240 bipolar sites by insertion of 60 plunge needle electrodes into both ventricles and the septum. Global ventricular activation sequences were displayed in five planes in 10 dogs, whereas the high density regional activation maps of the anterior wall were displayed in four layers in 4 dogs. Three-dimensional activation maps of 95 sinus beats, 82 premature ventricular complexes (PVCs), and 210 beats of ventricular tachycardia (VT) were analyzed. Sinus beats had a uniform activation pattern with total ventricular activation times measuring 42 +/- 4 ms and 67 +/- 8 ms during baseline and ischemia, respectively (P < .05). The PVCs and VTs originated from the subendocardial and intramural layers, and activation patterns invariably suggested focal excitation. Macroeentry was not operative because (1) the breakthrough sites were always remote from the latest activation areas; (2) there was no electrical activity bridging the gap between the termination of a beat and initiation of the subsequent beat; and (3) impulse conduction was not sufficiently delayed to reexcite the area of impulse origin even though functional conduction block was frequently present. In high-density regional activation maps, fragmented activity spanning the diastolic interval was never found. In conclusion, spontaneously occurring PVCs and VTs during acute myocardial ischemia in dogs display focal excitation with no evidence of macroreentry.

Myocardial temperatures during in vivo endocardial Nd:YAG laser irradiation.

To determine safety and efficacy of neodymium:YAG laser irradiation of the endocardium, temperatures at both the epicardium and the endocardium were recorded for thermal damage evaluation. A total of 48 coagulation lesions were created at power settings of 20 and 30 W in 20 open chest dogs by transcatheter endocardial laser irradiation. Tissue temperatures were monitored by epicardial thermography (Tepi), and by endocardial thermocouples at the catheter tip (Tprox) and 4 mm below the endocardial surface (Tdist). In group I the optical fiber extended 1 mm from the catheter and irradiation times ranged from 3 to 60 sec. Tepi reached > or = 57 degrees after a weighted average of 5 sec of laser irradiation (n = 44). In group II the fiber was retracted 1 mm from the catheter tip, and irradiation times were 100 to 150 sec. Tepi reached > or = 57 degrees C after a weighted average of 30 sec (n = 4). Blood vessels were recognized as heat sinks until coagulation occurred. Lesion volume showed a proportional increase with total delivered energy. From the observed timeframes in epicardial temperature rise it is suggested that total direct light absorption at the epicardium was the main contribution to Tepi, and the Nd:YAG laser can efficiently create transmural lesions. The epicardial temperatures remained below 80 degrees C in combination with the constant movement of the epicardial wall suggested safety from thermal damage to the ambient organs.

Selective coagulation necrosis of canine adventitia and media induces extracellular matrix accumulation without neointima formation.

Endothelial cell injury, the disruption of the internal elastic membrane and medial damage represent important stimuli for the development of a neointima. It is unclear whether selective adventitial and medial injury also induce neointima formation. Incremental argon laser energies (11.4-180 J/cm2) were applied to the external surface of dog femoral arteries to evaluate the vascular repair of acute adventitial or medial necrosis without injury of the intima. The animals were sacrificed either one hour after the initial procedure or after an 8 week follow up period for histologic examination. Acute, and mild to moderate necrosis of the arterial wall was found above 50 J/cm2. Ablation of the internal elastic membrane or mural thrombi was not detected. Eight weeks after photocoagulation with laser energies above 50 J/cm2, a significant increase in mean wall thickness of the media was observed. The medial thickening was characterised by an accumulation of extracellular matrix and a loss of smooth muscle cells. Necrosis of adventitia and media resulted in arterial wall thickening without neointima formation. It is concluded that, in dogs, an acute, selective injury of adventitia and media stimulates the production of extracellular matrix and not the proliferation of cells. Smooth muscle cell migration and subsequently neointima formation are induced by viable smooth muscle cells when blood-borne stimuli are available.

Myocardial temperature distribution under cw Nd:YAG laser irradiation in in vitro and in vivo situations: theory and experiment.

Tissue samples ranging from 2 to 16 mm in thickness were irradiated at 1064 nm with energies ranging from 40 to 2400 J. Coagulation lesions of in vitro and in vivo experiments were subjected to temperature profiling and submitted for histology. Irreversible damage was calculated with the damage integral formalism, following the bioheat equation solved with Monte Carlo computer light-distribution simulations. Numerical temperature rise and coagulation depth compared well with the in vitro results. The in vivo data required a change in the optical properties based on integrating sphere measurements for high irradiance to make the experimental and numerical data converge. The computer model has successfully solved several light-tissue interaction situations in which scattering dominates over absorption.

Aminophylline fails to improve the outcome of cardiopulmonary resuscitation from prolonged ventricular fibrillation: a placebo-controlled, randomized, blinded experimental study.

OBJECTIVES: The purpose of this study was to evaluate systematically the effects of the adenosine antagonist aminophylline on resuscitation outcome in a canine model of postcardioversion nonperfusing rhythm. BACKGROUND: Theoretic considerations and experimental studies indicate that myocardial adenosine accumulation during prolonged ventricular fibrillation might play a significant role in postcardioversion asystole and electromechanical dissociation. A recent uncontrolled clinical trial has suggested that the adenosine antagonist aminophylline might improve the outcome of cardiopulmonary resuscitation from refractory bradyasystolic cardiac arrest. METHODS: Two placebo-controlled, randomized, blinded experimental studies were performed. In protocol 1 (20 dogs), ventricular fibrillation was induced and maintained for 7.5 min. Sixty seconds before cardioversion, dogs received 1 mg of epinephrine followed by 250 mg of aminophylline or placebo. In protocol 2 (20 dogs), dogs were cardioverted to electromechanical dissociation after 5 min of unsupported ventricular fibrillation. Sixty seconds later, all dogs received 1 mg of epinephrine followed by 250 mg of aminophylline or placebo. In both experiments, resuscitation efforts were continued until return of spontaneous circulation, or up to 30 min. The primary end point was survival to 1 h. RESULTS: In protocol 1, 4 of 10 dogs survived in the aminophylline group, whereas 7 of 10 dogs survived in the placebo group, a nonsignificant trend toward unfavorable outcome from aminophylline. Pretreatment with aminophylline increased the number of cardioversion applications required to terminate ventricular fibrillation. In protocol 2, 5 of 10 and 6 of 10 dogs survived in the aminophylline and placebo groups, respectively. CONCLUSIONS: The results of this study suggest that aminophylline fails to improve the outcome of resuscitation from prolonged ventricular fibrillation. It does not reverse established electromechanical dissociation and may in fact increase the number of cardioversion applications required to terminate ventricular fibrillation. The rationale for conducting clinical trials with aminophylline during cardiopulmonary resuscitation is questionable.

Ultrasonic characterization of myocardial photocoagulation lesion size in vivo during Nd:YAG laser irradiation.

Endocardial coagulation lesions were created using transcatheter continuous-wave Nd:YAG laser irradiation. Ultrasound monitoring of thermal lesion dimensions was performed using 7.5-MHz and 10-MHz transducers directly from the epicardial surface in short-axis configuration (group A) or through the chest wall (group B). A total of 33 lesions were created in 10 dogs at energy levels ranging from 300 J to 1000 J. Mean histological lesion width (HW) compared with ultrasonically determined mean width (UW) showed that the differences (mean +/- standard deviation) in group A (UW - HW) was = 1.14 +/- 0.8 mm, which was not statistically significantly different from zero. In group B, (UW - HW) = 2.04 mm +/- 0.7 mm (p < .05), which was statistically significantly different from zero. Mean histological depth (HD) differentially related to ultrasound mean depth (UD) for group A and B combined showed (UD - HD) = -0.19 mm +/- 0.46 mm, not statistically significantly different from zero. The frequency distribution for width in group A showed magnitude of UW-HW > 3 mm in 32% of cases. In group B magnitude of UW-HW > 3 mm in 15%, whereas ultrasound width was larger than histology in 75% of the cases. For depth, magnitude of UD-HD > 3 mm in 15% of cases. With further refinement of the technique, ultrasonic tissue characterization may become a useful adjunct to monitoring lesion dimensions during transcatheter laser photocoagulation.

Mobile cardiac catheterization registry: report of the first 1,001 patients.

The purpose of this study was to evaluate prospectively the efficacy and safety of mobile cardiac catheterization. Mobile cardiac catheterization was introduced into clinical practice in 1989, but there has been no systematic study of its performance and safety. A registry was established in 1989 to monitor outcomes with mobile cardiac catheterization and is reported here. Patients were screened for eligibility for mobile cardiac catheterization using the joint AHA/ACC criteria for outpatient angiography. Eligible patients underwent mobile catheterization at eight hospitals within 120 miles of the base tertiary center. Helicopter evacuation services were available at each mobile site. The indications, findings, dispositions, and complications of mobile cardiac catheterization were recorded by means of a checklist, telephone follow-up and chart review. A total of 1,001 consecutive patients were entered into the registry in the first 20 months of operation, including 436 females and 565 males aged 22 to 84 years. Angina (Canadian Classes II-IV) was the most frequent primary indication for catheterization (46.4%), followed by atypical chest pain (36.9%), or a positive exercise stress test (25.6%). Infrequent indications for catheterization included a history of myocardial infarction (5.6%), congestive heart failure (7.1%), arrhythmias (4.1%), and valvular heart disease (0.7%). Catheterization was accomplished in 99.9% of patients. Angiographically normal studies were observed in 22.8%, and mild (< or = 50%) coronary artery disease in 13.6% of patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Mobile cardiac catheterization: comparison with outpatient and inpatient catheterization at tertiary facilities.

The study group included 1,553 consecutive patients from areas serviced by our mobile catheterization laboratories: 719 procedures were performed in the mobile unit at their local hospitals, 277 were performed at a tertiary hospital with less than a 24 hr hospital stay, and 557 were performed at a tertiary hospital as inpatients. The indications for mobile catheterization were predominantly atypical chest pain, angina pectoris, or positive treadmill stress test, whereas patients with less than 24 hr hospitalization at the tertiary center had their catheterization performed for additional reasons. The majority of the inpatient indications were for recent myocardial infarction or unstable angina. Using the American College of Cardiology/American Heart Association (ACC/AHA) criteria for outpatient catheterization, the mobile catheterizations were performed safely with a complication rate of only 0.7% compared to a complication rate of 3.1% for inpatients demonstrating that a low risk group of patients can be prospectively identified and catheterized safely in the mobile setting. An extremely high risk group of patients with ongoing unstable angina and recent myocardial infarction was also identified which should undergo catheterization only at a tertiary center.