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Multiple ablation technologies are used to treat atrial fibrillation during cardiac operations. All such ablation technologies use locally induced temperature extremes (>50°C or −20°C) to kill tissue and create a lesion pattern in the atria which blocks activation pathways that initiate and sustain atrial fibrillation. The technologies used to heat tissue have included radiofrequency (RF), microwave, high-intensity focused ultrasound, and infrared laser. RF accounts for more than 95% of the heating-based ablation technology used by cardiac surgeons. Energy delivery with RF is easier to control than with some other technologies, the heating produced by the energy source is well understood, and manufacturing costs are not excessive. Whichever heating technology is used, control of energy delivery is required to ensure both safe and effective heating of the targeted tissue. All targeted tissue needs to be heated above 50°C to achieve cell death. However, the targeted tissue should not be heated above 100°C, as this can cause perforation due to a steam pop. In addition, adjacent noncardiac tissues must not be damaged during the ablation procedure. The best method to achieve this control uses direct measurement of tissue temperature, because the tissue temperature defines both the safe and effective limits for the ablative process.

Background Endocardial mapping using standard electrode catheters is often technically limited in ventricular tachycardia and constitutes a major obstacle to successful ablation. We wished to examine the utility of a basket-shaped multielectrode mapping catheter (MMC) in the mapping and ablation of ventricular tachycardia. Methods and Results This study of sustained monomorphic ventricular tachycardia (SMVT) was conducted in two phases in the postinfarction pig model. In the first phase, the utility of the MMC in providing adequate localization of potential ablation site(s) of SMVT by different techniques (presystolic potentials, pace mapping, and concealed entrainment) was assessed in 21 pigs. In the second phase, ablation of induced SMVT was attempted in 10 pigs. Mapping of SMVT was performed after percutaneous introduction of the MMC to the LV. Comprehensive mapping was performed in 90 episodes of SMVT and required 2.0 to 25 seconds. Diastolic potentials were recorded during 86 episodes; good or identical pace maps (≥9 of 12 paced surface ECG leads identical to ventricular tachycardia surface ECG leads) were obtained in 25 of 31 maps, and entrainment was achieved during 28 of 42 SMVTs. In 10 pigs, 10 SMVTs were recorded at least twice and were considered for radiofrequency ablation. An 8-mm tip ablation catheter was advanced to potential ablation sites with a specially designed “homing” device, requiring a median time of 120 seconds. In these 10 pigs, either identical pace map (≥11 of 12, 6 SMVTs) or concealed entrainment (4 SMVTs) guided the ablation procedure. After ablation, 8 of 10 SMVTs were rendered noninducible, while 2 pigs died during energy application of degeneration of SMVT to ventricular fibrillation. Conclusions The MMC allows rapid, comprehensive, and reliable endocardial mapping during SMVTs, which facilitates successful ablation in the porcine post–myocardial infarction model.

Ablation of typical atrial flutter using radiofrequency energy is limitted by difficulties in creating a continuous line of block across the istmus between the tricuspid anulus and the inferior vena cava. Recent studies from our laboratory have shown that a novel infusion ablation technique can create large endocardial lesions in a safe and predictable fashion. The purpose of our study was to assess the feasibility of transcatheter subendocardial infusion of a mixture of 95% enthanol, iodinated contrast and glycerin to create atrial lesions resulting in complete ablation of the critical isthmus mediating typical atrial flutter.

Background Identification of critical areas within the ventricular tachycardia circuit is a prerequisite for catheter ablation. Currently, mapping during ventricular tachycardia, usually performed with standard catheters, is difficult and time-consuming and can be used only in patients with hemodynamically stable tachycardia. Methods and Results A total of 43 pigs underwent closed-chest induction of myocardial infarction. A basket-shaped catheter carrying 64 electrodes was deployed in the left ventricle during normal sinus rhythm. Unipolar pacing at 3 mA was successful in 78% of the basket catheter electrodes, demonstrating good electrode-tissue contact. Hemodynamic and echocardiographic measurements did not reveal any significant interference with myocardial or valvular function during or after catheter deployment. One hundred eighteen episodes of monomorphic ventricular tachycardia were induced in 28 pigs through right ventricular stimulation, 81 of which were mapped and analyzed. Ventricular tachycardia mapping was rapid, requiring only several beats and Conclusions The multielectrode catheter enables rapid and safe percutaneous endocardial mapping of ventricular tachycardia in the swine model. Exploration of the clinical potential of the multielectrode catheter seems warranted.

This study analyzed the influence of electrode geometry, tissue-electrode angle, and blood flow on current density and temperature distribution, lesion size, and power requirements during radio-frequency ablation. The authors used validated three-dimensional finite element models to perform these analyses. They found that the use of an electrically insulating layer over the junction between electrode and catheter body reduced the chances of charring and coagulation. The use of a thermistor at the tip of the ablation electrodes did not affect the current density distribution. For longer electrodes, the lateral current density decreased more slowly with distance from the electrode surface. The authors analyzed the effects of three tissue-electrode angles: 0, 45, and 90/spl deg/. More power was needed to reach a maximal tissue temperature of 95/spl deg/C after 120 s when the electrode-tissue angle was 45/spl deg/. Consequently, the lesions were larger and deeper for a tissue-electrode angle of 45/spl deg/ than for 0 and 90/spl deg/. The lesion depth, volume, and required power increased with blood flow rate regardless of the tissue-electrode angle. The significant changes in power with the tissue-electrode angle suggest that it is safer and more efficient to ablate using temperature-controlled RF generators. The maximal temperature was reached at locations within the tissue, a fraction of a millimeter away from the electrode surface. These locations did not always coincide with the local current density maxima. The locations of these hottest spots and the difference between their temperature and the temperature read by a sensor placed at the electrode tip changed with blood flow rate and tissue-electrode angle. >

Radiolabeled deoxyglucose (FDG) has been advocated as a marker of viability of reperfused myocardium during acute infarction. However, data for such recommendation are few. We investigated cardiac deposition of C-14 deoxyglucose (C-14 DG) and of Thallium -201 (T1–201) in rabbits subjected to coronary occlusion (15, 30, 60 or > 100 min) and reperfusion (75 min and 24 h). Measured myocardial concentrations of C-14 DG and T1–201 in macroautoradiograms were quantitatively correlated in a 24 h reperfusion group with presence of myocardial necrosis evaluated by light microscopy. The major finding in this investigation was that with 30 min or 60 min of ischemia followed by reperfusion there were myocardial regions with significant hypoperfusion (T1–201) and histologic necrosis. However, in the same myocardial areas, the deposition of C-14 DG was not correlated with the extent of necrosis (r = 0.27). Also, the deposition of C-14 DG in acute myocardial infarction was higher than that of T1–201 (P = 0.05 by paired T test and by nonparametric Wilcoxon's test). It was also demonstrated that when the occlusion time was varied (15–130 min) and early reperfusion was provided for 75 min or omitted altogether, the myocardial accumulation of T1–201 was variable and that myocardial sequestration of C-14 DG was higher than perfusion in central and peripheral portions of the areaat-risk. These observations do not support a role for the use of radiolabeled deoxyglucose for the detection of myocardial viability in recently infarcted cardiac muscle.

We tested the performance of a multielectrode RF ablation system during in vivo procedures in the right atrium. A total of 75% of the RF applications resulted in complete lesions at the gaps between electrodes and 90% of them were considered potentially therapeutic, as they were transmural and expended along the intended contour. The average total procedure and fluoroscopy times were 83.4 and 5.9 min, respectively. Average power varied between 15 and 114 W. No sudden impedance rise occurred and no char was found by post-ablation inspection. The average impedance was 105/spl plusmn/16 /spl Omega/, with one electrode on, and 75/spl plusmn/12 /spl Omega/ when two electrodes were simultaneously on. The average maximal lesion length and width were 59.2/spl plusmn/11.7 and 7.1/spl plusmn/1.2-mm.

Background Catheter ablation with radiofrequency energy is feasible in a limited subset of patients with ventricular tachycardia. The purpose of this study was to evaluate a technique for mapping and ablation of ventricular myocardium with the use of transcatheter subendocardial infusion. Methods and Results A needle-tipped deflectable electrode catheter was used to deliver reagents to endocardial target sites. This was equipped with two central lumens to allow sequential administration of mapping and ablation injectants with minimal admixture. The mapping injectant consisted of a mixture of lidocaine, iohexal, and glycerin; the ablation injectant contained ethanol, iohexal, and glycerin. Infusion of the mapping injectant (1 cm 3 over 3 or 5 seconds, n=14) produced a stain on fluoroscopy and increased local capture threshold by 61%. No lesions resulted from mapping infusions. Infusion of the ethanol-containing injectant (n=48) produced discrete lesions, with a mean volume ranging from 0.6 to 1.5 cm 3 . There was a direct relationship between infusion volume, infusion duration, and resultant lesion volume. Fibrosis in a region of healed myocardial infarction did not impair diffusion of the injectant or affect lesion dimensions. Microscopic analysis of chronic lesions showed a sharply demarcated border zone between fibrotic and normal myocardium. Conclusions Transcatheter subendocardial infusion can be used to reversibly impair local excitability and mark an injection site fluoroscopically. Subendocardial injection of ethanol can predictably ablate a large volume of ventricular myocardium. Additional study of this system in an arrhythmia model will help to define its potential for mapping and ablation of hypotensive ventricular tachycardia.

Minimum squared error (MinSE) testing protocols and a MinSE estimator are presented which accurately estimate the voltage that defibrillates 95% of the time (the ED95). The MinSE experimental procedures, presented in the form of lookup tables, detail the response to successful and unsuccessful trials. The lookup tables also show the ED95 estimates calculated from the observed results using the MinSE estimator. Two assumptions are required to develop the look-up tables: 1) the dose-response curve, chosen using a statistical analysis of a retrospective sample, and 2) the distribution of the ED95's in the population. The MinSE estimator and experimental procedure are examined in a prospective study of five dogs (19-25 kg, heart weights 139.3-236.9 gm) using nonthoracotomy implantable defibrillator electrodes and a biphasic defibrillation waveform (3.5 ms first phase, 2.0 ms second phase). Employing an ED95 population distribution assumption applicable to most implantable defibrillator electrodes and waveforms, e.g., the ED95 is between 0.0 and 800.0 V, the measured rms error was 15% of the mean measured ED95 for the MinSE, four test shock, ED95 estimates. If the protocols are designed with an ED95 population distribution assumption for animals of the same species and size, and defibrillation is constrained to one electrode configuration and waveform, the estimates improve by 3.8%. Using techniques from the Bayesian statistics literature, the MinSE approach can be extended to a variety of defibrillation parameter estimation problems.

A bistatic active ultrasonic sensor is used to detect and identify an insect attracted to a pheromone lure in the beam intersection. The ultrasound beam is a continuous waveform (CW) of approximately 200 kHz to avoid detection by the insect auditory system, which is very sensitive near 40 kHz and below to detect predatory bats. Both amplitude modulation (AM) and frequency modulation (FM) of the CW beam are examined. The reflection factor of the wing material is measured using ultrasonic pulses. The near‐field interference nulls of the transmitting beam are modeled and measured to ensure that the lure is not placed in one of these zones. While good AM and FM signals are seen in the received waveform, the pivoting and flapping motions of the wings along with the insect movements create a complex pulse‐train like waveform. This is seen to be inherently due to the narrow beam‐width for the transducers and a lack of nonspecular scattering from the moving wings. The data show that a simple AM detector can be us...

Fixed-rate pulsatile cardiopulmonary bypass may improve subendocardial perfusion during ventricular fibrillation and has been employed during intermittent aortic cross-clamping. Variable-rate pulsatile left heart bypass that is governed by venous inflow and is asynchronous to the electrical activity of the heart is currently used in clinical practice. To study the effect of fixed-rate pulsation on myocardial metabolism during left heart bypass, six adult pigs underwent alternating periods of pulsatile (PLS) and nonpulsatile (NPLS) centrifugal pump left atrial-to-aortic bypass in randomized block design. Coronary sinus, aortic, and bypass circuit flows were recorded. Oxygen content and lactate concentration of coronary sinus and aortic blood were measured. Pulsatility index and pulse power index during pulsatile bypass were 4.4 and 4.7 (cycles/s)2, respectively. Percent bypass was maximal at a mean pulsation rate of 41.3 and averaged 92.2 and 91.3 for PLS and NPLS, respectively. Myocardial oxygen consumption per minute was reduced 14.3% during NPLS but was unchanged during PLS compared to control (CTRL). Percent lactate extraction was significantly lower than CTRL during NPLS only. Competition for inflow with the ejecting heart appeared to limit circuit pulsation rate and pulse power index. Fixed-rate pulsation is ineffective in reducing myocardial metabolism and should be avoided in left heart bypass.

Both intravenous and intra-arterial DSA have widespread applications in the field of cardiovascular diagnosis. The definition of carotid artery stenosis or severe peripheral vascular disease in the patient undergoing coronary artery bypass surgery might dictate the need for simultaneous carotid and coronary artery surgery or demonstrate the best route for insertion of an intra-aortic balloon. DSA also might find further application in the definition of thoracic aortic dissection, thoracic aortic trauma, and coarctation of the thoracic aorta, as well as in showing the adequacy of repair of thoracic coarctation in patients who remain hypertensive postoperatively. Left ventricular imaging using intravenous or intraventricular injections of contrast material provides an accurate method of calculating ejection fraction and an excellent picture of left ventricular wall motion. In addition, because smaller amounts of contrast material may be used for intraventricular infections, patients with renal failure or severe impairment of the left ventricle might fare better with the reduced contrast load. Multiple ventriculograms can be performed following interventions such as pacing or exercise to allow a more adequate definition of left ventricular performance. Intravenous DSA still has not achieved satisfactory visualization of the coronary arteries or coronary artery bypass grafts. However, aortic root injections of contrast material can provide adequate definition of these structures and has been recommended as a screening technique for coronary disease in patients undergoing arteriography for other vascular disease. Current work on the development of DSA techniques for the quantitation of coronary artery blood flow and myocardial perfusion is quite promising. Accurate, reproducible measurement of coronary artery blood flow, patterns of myocardial perfusion, and areas of myocardium supplied by specific coronary vessels with obstructions may soon provide physiologic information about anatomically defined coronary artery disease. A variety of congenital heart defects have been defined by intravenous DSA. Shunt lesions such as atrial septal defects, ventricular septal defects, and patent ductus arteriosus have been defined anatomically, and the severity of their shunts has been estimated by placing windows of interest over the various cardiac chambers. It is possible that certain congenital malformations might be studied adequately by intravenous DSA, eliminating the need for cardiac catheterization.(ABSTRACT TRUNCATED AT 400 WORDS)

Various methods have been used to provide mechanical circulatory support for patients in cardiogenic shock following myocardial infarction or cardiac surgery. The most commonly used device currently is the intraaortic balloon pump (IABP) . Left ventricular (LV) bypass has also been used clinically, with devices varying from a simple roller pump to a gas-powered pulsatile left ventricular assist device. An important function of circulatory support devices is reduction of metabolic need to promote recovery of “stunned” myocardium. Studies on isolated cat papillary muscle show myocardial oxygen consumption (MV02) to be a function of developed tension and the velocity of shortening of the unloaded muscle [l]. Moreover, MVO2 has been shown to be directly proportional to LV wall stress in intact hearts [2]. LaPlace’s law states that T = PR/2, where T = wall stress in a sphere, P = transmural pressure, and R = radius. An LV assist device therefore should decrease wall stress and MV02 in proportion to its ability to decrease LV pressure and/or radius. Virtually all clinically proposed methods of LV bypass use left atrial-to-aortic rather than LV apical-to-aortic bypass, despite canine studies showing that LV cannulation provides more complete decompression of the heart than left atria1 cannulation [3]. It is unclear whether or not the technical ease of inserting an atria1 cannula is an adequate rationale for using left atrial-to-aortic bypass in patients with reversible LV dysfunction. The aim of this study is to determine the effect of cannulation site on myocardial oxygen consumption and on the three primary determinants of MV02 during left heart bypass: wall tension, contractile state, and heart rate. Previous studies which have compared the effect of cannulation site on MV02 used noninfarcted paced canine models. Canine hearts are small and collateral coronary flow is greater than in humans. To study MV02 in both the noninfarcted

Four methods of protecting the heart during implantation were compared. All hearts were arrested in situ by perfusing 4° C cardioplegic solution into the aortic root and were stored by a nonperfused cold storage technique for 5 hours at 4° C. The hearts were then transplanted orthotopically with the use of topical iced slush alone or with infusions of either blood cardioplegic solution or one of two crystalloid cardioplegic solutions after each atrial anastomosis. Five dog hearts were included in each group. Biopsy samples to test for adenylates were taken before the arrest, at the end of storage, before cross-clamp removal, and 3.5 hours after cross-clamp removal. The dogs were removed from cardiopulmonary bypass, and with the chest open, left ventricular function curves were measured at 1, 2, and 3 hours after cross-clamp removal. At 3.5 hours of reperfusion time, a full-width section was obtained from the left ventricle for measurement of tissue sodium and water content No differences in tissue water, sodium, or potassium content were found among the groups. Left ventricular function was significantly better in the blood cardioplegia group than in any other groups. Adenosine triphosphate levels were significantly reduced 3.5 hours after reperfusion in the crystalloid cardioplegia groups but were not significantly depressed at any other measurement time. Excellent early graft function was observed after crystalloid cardioplegic arrest and blood cardioplegic reperfusion during graft implantation.

Heart and kidney allografts showed markedly prolonged survival in unrelated mongrel dogs following total lymphoid irradiation (TLI) and donor bone marrow without any other immunosuppression. In every animal the heart survived longer than the kidney; genetic disparity was ruled out, since the heart and kidney from the same donor were placed into one recipient. Placing the kidney allograft in the abdomen with the bone marrow given intraperitoneally doubled kidney survival over placement in the neck, but heart survival was equally prolonged in the abdomen or neck. Splenectomy before TLI or after TLI, but just before transplantation, almost completely eliminated the prolonged survival of both heart and kidney allografts. Thus there is suggestive evidence from the work of Slavin and his colleagues and from our study that TLI plus bone marrow from the donor may be valuable for transplantation in man, particularly heart transplantation.

A computerized fluoroscopy system has been developed on the basis of real-time digital processing of x-ray transmission data from traditional image-intensified fluoroscopy equipment. High-quality visualization of any part of the arterial system is obtained following intravenous injection of 0.5 to 0.75 ml/kg of iodinated contrast materials. This report describes the use of this technique to evaluate the aortic arch, left ventricular function, and coronary artery bypass graft patency. Fifty intravenous studies were performed in 25 patients. Among 20 patients with coronary artery bypass grafts, computerized fluoroscopy correctly identified 11 of 15 patent grafts and 11 of 11 occluded grafts as confirmed by standard coronary arteriography in 11 of these patients. Unlike computerized tomography, our technique gives a longitudinal view of the bypass graft much like direct coronary angiography. Aortic arch studies included demonstration of a right aortic arch with a small left subclavian artery, a coarctation, and a normal aortic arch in a trauma patient with a wide mediastinum. Segmental wall motion abnormalities were clearly identified by a modification of the technique which produces a negative outline on the ventriculogram in dyskinetic segments. Ejection fractions may be calculated by determining the amount of iodine in the ventricle in systole and diastole. This technique may also be used to evaluate carotid disease and peripheral vascular disease in patients undergoing coronary artery bypass procedures. Computerized fluoroscopy, therefore, allows evaluation of the entire cardiovascular system by the relatively noninvasive technique of intravenous angiography.

Hearts preserved for 2 hours at 15 degrees C were evaluated for maximum function with the use of an isolated working dog heart subjected to stress. We determined left ventricular function by controlling aortic flow resistance and flow into the left atrium. Groups studied were hypothermia alone (H), hypothermia with a modified extracellular solution (H + DKS), hypothermia with a modified Collins solution (H + C), six periods of 20 minutes of hypoxic hypothermia followed by 10 minutes of blood reperfusion (H20 + R10) and blood cardiplegia (BC). Hypothermia alone for 1 hour was also evaluated. Functions were studied for 2 1/2 hours following reperfusion by determining Starling's curves for each heart. Our data show that H alone gave adequate myocardial protection for only 1 hour but not for 2 hours. H20 + R10 was better than H, but function was depressed. Use of H + C provided protection equal to H20 + R10, but the hearts recovered function slowly. Only hearts preserved by H + DKS and BC for 2 hours had normal function. Hearts from all groups except H + DKS and BC became edematous. Excellent function was obtained with DKS or BC following 2 hours of ischemia at 15 degrees C. Initial clinical use of BC supported these laboratory findings.

A retrospective analysis of 38 patients undergoing cardiac catheterization with the diagnoses of hypothyroidism and chest pain revealed 23 to be euthyroid while receiving replacement therapy and 15 to be hypothyroid. Cardiac index was significantly reduced (p less than 0.01) in hypothyroid and euthyroid patients with thyroxine values between 4 and 7 micrograms/dl (2.8 +/- 0.7 and 3.0 +/- 0.9 L/min/m2, respectively), compared to euthyroid patients with thyroxine values greater than 7 micrograms/dl with or without coronary artery disease (4.0 +/- 1.2 and 4.0 +/- 0.7 L/min/m2, respectively). Ten hypothyroid patients underwent coronary artery bypass. There were no deaths, and only one patient required prolonged postoperative intubation. With a mean follow-up of 36 months, there have been no myocardial infarctions and one late death, which occurred at 7 years secondary to stroke. We conclude that preoperative thyroid replacement therapy is theoretically dangerous and may not significantly improve hemodynamics until full replacement is achieved. Coronary bypass grafting can be performed safely despite hypothyroidism with excellent early results.

Reperfusion conditions significantly affect recovery following global myocardial ischemia. Using an isolated dog heart model, we investigated the effect of initial (first 10 minutes) reperfusion temperature and pressure on the metabolic and functional recovery of the preserved heart. Four groups of five or six dogs each underwent 2 hours of ischemic cardioplegic arrest at 15 degrees C following single-dose crystalloid cardioplegia. Hearts were initially reperfused at 37 degrees C (high temperature) or 28 degrees C (low temperature) and at 50 mm Hg (low pressure) or 80 mm Hg (high pressure), giving four groups: (1) high-temperature, high-pressure; (2) high-temperature, low-pressure; (3) low-temperature, high-pressure; and (4) low-temperature, low-pressure. Septal temperatures were continuously recorded. Ventricular function curves 1 and 2 hours following reperfusion were significantly depressed in the high-temperature, high-pressure group (70%, p less than 0.01, and 83%, p less than 0.02) and the low-temperature, high-pressure group (78%, p less than 0.03, and 85%, p less than 0.03) but were normal in the low-temperature, low-pressure and the high-temperature, low-pressure groups. All groups showed edema 1/2 hour after reperfusion as measured by water and sodium content in myocardial biopsy specimens but only the high-temperature, high-pressure and the low-temperature, high-pressure groups showed persistent edema at 3 hours (3.95 +/- 0.2 ml H2O/gm dry weight, p less than 0.03 and 3.99 +/- 0.16 ml/gm, p less than 0.02, respectively). Only low-temperature, high-pressure reperfusion resulted in statistically significant reductions in adenosine triphosphate (ATP) 1/2 hour and 2 hours following reperfusion (a 15% reduction from baseline). Maximum rewarming rates were measured for each group. High-temperature, high-pressure = 2 degrees C per second; low-temperature, high-pressure = 1 degree C per second; high-temperature, low-pressure = 0.75 degrees C per second; and low-temperature, low-pressure = 0.4 degrees C per second. High-pressure reperfusion following global myocardial ischemia results in rapid rewarming and is associated with prolonged myocardial edema, depressed ATP levels, and delayed functional recovery. Therefore, we employ 10 minutes of low-pressure reperfusion in our patients undergoing potassium cardioplegic arrest.

With a new radiographic method to determine the pulsatile flow pattern in an imaged artery, flow velocity is determined by tracking the movement of contrast material along the artery over time. Flow velocity is multiplied by an automatically determined cross-sectional area of the artery to determine blood flow. Pulsatile blood-flow waveforms were determined by radiographic and electromagnetic techniques in each femoral artery of four dogs while flow conditions were varied. Peak and average blood flows measured by the two techniques were highly correlated (r = .97 and .95, respectively). The closest agreement between the flow waveforms measured by the electromagnetic and radiographic techniques was found under normal flow conditions. The radiographically derived flow waveforms tended to be noisy at low blood-flow rates, and instantaneous blood-flow rates exceeding 700 ml/min were underestimated.

Left ventricular ejection fractions were determined following eight intravenous injections in three dogs using area/length and digital videodensitometric techniques. Ejection fractions were measured by both techniques for all beats during left ventricular opacification. Even after noniodinated background corrections, tissue iodine accumulation produced large errors in measured iodine content late in the contrast material curve. By using a model for tissue iodine accumulation, an algorithm was developed that appears to reduce these errors. The measured ejection fraction for ten beats following the peak of the contrast material curve declined an average of 1.8% following correction, compared with 14% prior to correction. Following correction for tissue iodine accumulation, correlation between area/length and video-densitometric ejection fractions was 0.94. By correcting for tissue iodine accumulation, much more of the contrast material curve provides usable data for estimating ejection fractions.

Multiple ablation technologies are used to provide atrial fibrillation therapy during cardiac surgery. A rigorous search was performed to identify all peer-reviewed papers that provided clinical outcome data following ablation therapy. A META analysis showed significant differences in clinical outcome by ablation technology: clinicians, using temperature-controlled RF power delivery, achieved higher rates of normal sinus rhythm at follow-up, and patients ablated with microwave ablation had lower rates of normal sinus rhythm than the average of all ablation-treated patients. Permanent pacemaker implantation rates were higher than average for patients treated with microwave or argon-based cryoablation technologies, but were lower than the average for patients treated using temperature-controlled RF.

Preservation of the myocardium in vitro is more effective than preservation in vitro when preservation conditions are apparently the same. The washout of cardioplegia from the myocardium by noncoronary blood flow has been implicated as a probable cause of the poorer myocardial preservation seen in vivo. Isolated dog hearts were used to study the effects of cardioplegia washout by low flow perfusion (0.05 ml/min/g LV weight) during a 2-hr preservation period. Six experimental groups of five hearts each underwent 2 hr of myocardial preservation at temperatures of 20 degrees C (three groups) or 30 degrees C (three groups). The three groups for each temperature consisted of retrograde coronary sinus perfusion (to simulate cardioplegia washout by collateral flow) with blood cardioplegia (BC), normal blood (NB), or no perfusion at all (No CSP). The quality of preservation in each group was assessed by measuring recovery of left ventricular function, tissue water and electrolyte content, and myocardial high-energy phosphate and adenylate content prior to, during, and following preservation. In hearts maintained at 20 degrees C, cardioplegia washout did not significantly affect left ventricular function or myocardial levels of H2O, Na, K, ATP, or total adenylates. When myocardial temperature was allowed to increase to 30 degrees C, preservation was better with low flow perfusion during the preservation period. Hearts warmed to 30 degrees C with no cardioplegia washout experienced a 50% loss of tissue ATP levels and recovered less than 30% of normal left ventricular function during a 150-min reperfusion period. In contrast, hearts slowly perfused during the preservation period maintained nearly normal levels of ATP and returned to normal function by 150 min of reperfusion. Although myocardial warming by noncoronary perfusion has a detrimental effect on myocardial preservation, the slow washout of cardioplegia per se has no apparent detrimental effect on preservation.

Standard angiography demonstrates the anatomy of arterial occlusive disease but does not define its physiological significance. However, measurement of flow in a compromised vessel at rest and following peripheral dilatation provides important physiological information. Using digital subtraction angiography, femoral arterial flows determined by the cross-correlation transit time technique were compared to measurements by electromagnetic flowmeter. Thirty-five femoral arterial flow measurements were obtained in nine dogs instrumented with an electromagnetic flow probe and balloon occluder. Renografin 76 (7 cc) was power-injected at 14 cc/sec into the distal abdominal aorta. Angiographic flow measurements correlated well with electromagnetic flowmeter measurements ( r = 0.94, standard deviation of the difference (SDD) = 15 ml/min). Intravenous studies provided somewhat poorer correlation due to difficulties in defining dimensions ( r = 0.72, SDD = 36). Paired contrast injections (2 injections in succession) in 11 studies increased flow from an average of 80 to 250 ml/min (a 210 ± 100% increase), providing an estimate of a vessel's capacity to provide increased flow during peripheral dilatation. Thus, reliable angiographic flow determinations may be obtained by arterial and intravenous contrast injections, adding physiological information to anatomical definition.

Coronary angiography defines the location and size of obstructive lesions, but does not assess their physiological significance. To assess a new method to measure the blood-flow waveform, reversed saphenous vein grafts from the left subclavian artery to the left anterior descending coronary artery were placed in five mongrel dogs. Contrast material was injected selectively into the vein graft while obtaining fluoroscopic images from AP and 45° LAO projections. Blood flow was measured under baseline, low-flow, and hyperemic conditions using an electromagnetic flow probe (EM). Seventeen radiographic determinations of mean blood flow (range 18–130 ml/min) were linearly correlated to simultaneous EM measurements ( r = 0.91 and 0.88, respectively). Contrast material injections changed EM flow measurements by an average of 35%, which though large, is less than with other radiographic methods. The computed blood-flow waveforms had a time resolution of 1 30 sec and were in good agreement with EM waveforms measured simultaneously. Clinical application of this radiographic method for determining the blood-flow waveform may allow early prediction of coronary artery bypass graft closure.

Standard angiography demonstrates the anatomy of arterial occlusive disease but not its physiological signficance. Using intravenous digital subtraction angiography (DSA), we investigated transit-time videodensitometric techniques in measuring femoral arterial flows in dogs. These methods have been successfully applied to intraarterial DSA but not to intravenous DSA. Eight 20 kg dogs were instrumented with an electromagnetic flow probe and a balloon occluder above an imaged segment of femoral artery. 20 cc of Renografin 76 was power injected at 15 cc/sec into the right atrium. Flow in the femoral artery was varied by partial balloon occlusion or peripheral dilatation following induced ischemia resulting in 51 flow measurements varying from 15 to 270 cc/min. Three different transit-time techniques were studied: crosscorrelation, mean square error, and two leading edge methods. Correlation between videodensitometry and flowmeter measurements using these different techniques ranged from 0.78 to 0.88 with a mean square error of 29 to 37 cc/min. Blood flow information using several different transit-time techniques can be obtained with intravenous DSA.