bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regional control of atrial fibrillation by rapid pacing in conscious dogs.
Authors: Allessie M , Kirchhof C , Scheffer G J , Chorro F , Brugada J 
Published: June 2012

BACKGROUND
In five chronically instrumented conscious dogs, we studied the effects of rapid pacing on sustained electrically induced atrial fibrillation.

METHODS AND RESULTS
Twenty-three unipolar atrial electrograms were recorded simultaneously from the bundle of Bachmann and the lateral wall of the right and left atria. During sustained atrial fibrillation, the surface electrocardiogram showed continuous irregularities of the baseline without P or F waves as well as an irregular ventricular rhythm with narrow QRS complexes. The atrial electrograms showed rapid irregular activity with a median cycle length of 85 +/- 8 msec and a range (P5-95) of 33 +/- 18 msec. Overdrive pacing of atrial fibrillation was performed using symmetric biphasic rectangular stimuli (2-msec duration, sixfold that of threshold) applied to a pair of stimulating electrodes at the left atrial appendage. Stimulation was started at pacing intervals of about 10 msec longer than the local median fibrillation interval and subsequently shortened in steps of 1 msec. At a critical pacing interval slightly shorter than the median fibrillation interval, the atrium around the pacing site was suddenly captured by the electrical stimuli. The area of local capture had a diameter of 6.1 +/- 1.6 cm. The time window of capture was 12 +/- 4 msec.

CONCLUSIONS
These observations show that during electrically induced atrial fibrillation in chronically instrumented conscious dogs, a short excitable gap is present, permitting regional control of the fibrillatory process by rapid pacing.
Evaluation of contractile state by maximal ventricular power divided by the square of end-diastolic volume.
Authors: Kass D A , Beyar R 
Published: June 2012

BACKGROUND
Maximal ventricular power (PWRmax) reflects contractile state and has the potential to be noninvasively determined. However, its sensitivities to preload, afterload resistance, and inotropic state are incompletely defined. The present study determines these dependencies and proposes a novel power-based contractile index that is little altered by load.

METHODS AND RESULTS
Seven open-chest, autonomically blocked dogs were instrumented with a proximal aortic flow probe, central aortic and ventricular micromanometers, and a conductance catheter for ventricular chamber volume. Preload was transiently reduced by left atrial hemorrhage, and afterload was increased by intra-aortic balloon inflation. Inotropic state was pharmacologically altered by lidocaine, dobutamine, propranolol, or verapamil. PWRmax was highly preload sensitive, altering 1.7 +/- 0.1-fold a given percent change in end-diastolic volume (EDV). This preload dependence was reduced by dividing PWRmax by EDV but was virtually eliminated when PWRmax was divided by EDV2. This latter index also displayed little change in response to as much as 60% increases in afterload resistance. PWRmax/EDV2 varied directly with inotropic state, correlating to both the slope (Ees) of the end-systolic pressure-volume relation (PWRmax x 1,000/EDV2 = 0.31 x Ees - 0.04, r = 0.82, p less than 0.001) and the slope (A) of the dP/dtmax-EDV relation (PWRmax x 1,000/EDV2 = 0.025 x A + 0.02, r = 0.86, p less than 0.001). PWRmax values determined from the product of ventricular pressure and flow versus central aortic pressure and flow were nearly identical over a broad loading range, indicating that PWRmax may be noninvasively assessed (i.e., without requiring left ventricular chamber pressure).

CONCLUSIONS
PWRmax divided by EDV2 provides a measure of contractile function that is little influenced by loading conditions and has potential for noninvasive clinical use.
Usefulness of transesophageal echocardiography in assessment of aortic dissection.
Authors: Ballal R S , Nanda N C , Gatewood R , D'Arcy B , Samdarshi T E , Holman W L , Kirklin J K , Pacifico A D 
Published: June 2012

BACKGROUND
The value of transesophageal echocardiography in the assessment of patients with aortic dissection was studied.

METHODS AND RESULTS
Group 1 (34 patients) represented all patients studied at our institution with this technique in whom aortic dissection was proven by aortography, surgery, or autopsy. Group 2 (27 patients) represented all patients studied with this technique at our institution in whom aortic dissection was excluded by aortography. Transesophageal echocardiography made a correct diagnosis of aortic dissection in 33 of 34 patients (sensitivity, 97%; specificity, 100%). It also correctly demonstrated the type of dissection in all 29 patients with aortographic or surgical proof. On the other hand, computed tomography scanning, performed in 24 of 34 patients in group 1, made a correct diagnosis in only 67% of patients and misclassified the type of dissection in 33%. Transesophageal echocardiography correctly identified involvement of the coronary arteries by aortic dissection in six of seven patients as well as absence of both left and right coronary artery involvement in 10 patients with aortic dissection. This technique was also useful in detecting communications between the true and false lumens, presence of thrombi in the false lumen, and, in two patients, localized dissection rupture with formation of a false aneurysm. In both groups 1 and 2, transesophageal echocardiography correctly identified patients with moderate to severe aortic regurgitation.

CONCLUSIONS
Transesophageal echocardiography is very useful in the assessment of aortic dissection.
Skeletal muscle metaboreceptor exercise responses are attenuated in heart failure.
Authors: Sterns D A , Ettinger S M , Gray K S , Whisler S K , Mosher T J , Smith M B , Sinoway L I 
Published: June 2012

BACKGROUND
Resting sympathetic nervous system activity is increased in heart failure. Whether sympathetic nervous system responses during exercise are increased is controversial. Furthermore, the role of muscle metaboreceptors and central command in regulating sympathetic outflow has been largely unexplored.

METHODS AND RESULTS
Muscle sympathetic nerve activity (MSNA, peroneal nerve) was measured in nine heart failure subjects and eight age-matched control subjects during static exercise (30% maximal voluntary contraction) for 2 minutes and during a period of posthandgrip regional circulatory arrest. This maneuver isolates the metaboreceptor contribution to sympathetic nervous system responses. MSNA responses were similar during static exercise in the two groups. During posthandgrip regional circulatory arrest we observed a marked attenuation in MSNA responses in the heart failure subjects (15% increase in heart failure versus 57% increase in control subjects). A cold pressor test demonstrated a normal MSNA response to a potent nonspecific stimulus in the heart failure subjects (heart failure subjects, 141% increase; control subjects, 215% increase; NS). Nuclear magnetic resonance spectroscopy studies in five separate heart failure subjects and five control subjects suggested that the attenuated metaboreceptor response in heart failure was not due to reduced H+ production.

CONCLUSIONS
Skeletal muscle metaboreceptor responses are impaired in heart failure. Because MSNA responses during static exercise are similar in the two groups, mechanisms aside from metaboreceptor stimulation must be important in increasing sympathetic nervous system activity.
Psychosocial factors impair vascular responses of coronary arteries.
Authors: Williams J K , Vita J A , Manuck S B , Selwyn A P , Kaplan J R 
Published: June 2012

BACKGROUND
Four sets of monkeys were used to examine the effect of chronic psychosocial disruption and diet on dilator responses of coronary arteries.

METHODS AND RESULTS
One set consisted of monkeys consuming monkey chow and living in a stable social setting (nonatherosclerotic controls, n = 6). Three sets consumed an atherogenic diet for 14 months followed by one of three treatments for the next 16 months: 1) a high-cholesterol diet and housed in unstable social groups (n = 9); 2) a low-cholesterol diet and housed in unstable (n = 8); or 3) stable groups (n = 10). Quantitative coronary angiography revealed that intracoronary infusion of acetylcholine resulted in a change of diameter (versus infusion of 5% dextrose in water) of +4 +/- 1% in control monkeys and -11 +/- 4% in unstable monkeys consuming a high-cholesterol diet (p less than 0.05). In monkeys consuming the cholesterol-lowering diet, the change in artery diameter was +2 +/- 4% in stable and -10 +/- 4% in unstable social conditions (p less than 0.05) despite a similar plaque size (0.4 +/- 0.2 and 0.5 +/- 0.1 mm2) and total plasma cholesterol concentrations (179 +/- 9 and 172 +/- 6 mg/dl), respectively. The arterial response to nitroglycerin was similar among all groups of monkeys.

CONCLUSIONS
We conclude that chronic social disruption is associated with relative arterial constriction in response to acetylcholine in atherosclerotic monkeys consuming a cholesterol-lowering diet.
Predictors of survival in neonates with critical aortic stenosis.
Authors: Rhodes L A , Colan S D , Perry S B , Jonas R A , Sanders S P 
Published: June 2012

BACKGROUND
Failure of infants with critical aortic stenosis to survive after adequate valvotomy despite a left ventricular size that appears to be adequate indicates that additional preoperative anatomic features may contribute to mortality.

METHODS AND RESULTS
Discriminant analysis was used to determine which of several echocardiographically measured left heart structures were independent predictors of survival after valvotomy for neonatal critical aortic stenosis. It was possible to predict outcome after classic valvotomy (two-ventricle-type repair) with 95% accuracy based on mitral valve area, long-axis dimension of the left ventricle relative to the long-axis dimension of the heart, diameter of the aortic root, and body surface area. Left ventricular volume was not a major determinant in this study, in part because patients who had initial valvotomy had been preselected in favor of an adequately sized left ventricle. Patients with multiple small left ventricular structures were found to have significantly improved survival after initial Norwood operation. In contrast, balloon valvotomy with subsequent Norwood procedure was usually unsuccessful.

CONCLUSIONS
The adverse effects of small inflow, outflow, and/or cavity size of the left ventricle are cumulative. The accuracy of prediction of outcome based only on preoperative anatomy indicates that adequacy of valvotomy is not generally a limiting factor for survival in this group of patients. It is possible to identify subjects whose chance of survival is better after a Norwood procedure rather than valvotomy, even if left ventricular volume is not critically small.
Protection against endocarditis due to Staphylococcus epidermidis by immunization with capsular polysaccharide/adhesin.
Authors: Takeda S , Pier G B , Kojima Y , Tojo M , Muller E , Tosteson T , Goldmann D A 
Published: June 2012

BACKGROUND
Staphylococcus epidermidis is the principal pathogen in prosthetic valve endocarditis. The capsular polysaccharide adhesin (PS/A) has been shown to mediate attachment of bacteria to medical devices. In this study, we investigated the efficacy of active and passive immunization against PS/A in preventing S. epidermidis endocarditis in a rabbit model.

METHODS AND RESULTS
Aortic valve vegetations were produced by inserting a Teflon catheter into the left ventricle through the right carotid artery. Bacteremia and endocarditis were then established by implanting in the left jugular vein a catheter that was attached to an osmotic pump and contaminated with S. epidermidis strain RP62A. During a 3-week study period, of 64 blood cultures taken every second or third day from six nonimmune rabbits, 54 (84%) yielded strain RP62A. In rabbits actively immunized with PS/A, eight of 60 blood cultures (13%) were positive (odds ratio 5.0, 95% CI, 2.0-12.3, p = 0.005). At death, all six nonimmune rabbits had infected vegetations that yielded 10(6)-10(11) colony-forming units (cfu)/g of vegetation, whereas only one PS/A-immunized rabbit had an infected vegetation. Immunization protocols designed to elicit antibody to teichoic acid but not to PS/A afforded no protection against bacteremia or endocarditis. Infusion of monoclonal antibody to PS/A through a catheter in the right jugular vein provided a level of protection against both bacteremia and endocarditis comparable to that produced by active immunization. In vitro, antibody against PS/A was opsonic for S. epidermidis.

CONCLUSIONS
Immunoprophylaxis targeted at staphylococcal PS/A is a promising new approach to the prevention of prosthetic valve endocarditis.
Valvular heart disease in four patients with Maroteaux-Lamy syndrome.
Authors: Tan C T , Schaff H V , Miller F A , Edwards W D , Karnes P S 
Published: June 2012

BACKGROUND
Maroteaux-Lamy syndrome is a lysosomal storage disease of mucopolysaccharide metabolism (MPS type VI) that may involve the mitral and aortic valves. Affected patients have other skeletal and oropharyngeal malformations that complicate anesthetic and surgical management.

METHODS AND RESULTS
The present report describes the clinical, echocardiographic, and pathological findings in four patients with Maroteaux-Lamy syndrome. Two of three siblings underwent successful double-valve replacement for aortic and mitral valve stenoses. The third sibling, whose aortic and mitral valves were thick and fibrotic, died from septicemia after hip surgery. A fourth, unrelated patient also had successful double-valve replacement.

CONCLUSIONS
Our experience emphasizes the potential difficulties in preoperative assessment and surgical treatment as well as the unique problems related to airway management in patients with this syndrome.
Are aortic aneurysms caused by atherosclerosis?
Authors: Reed D , Reed C , Stemmermann G , Hayashi T 
Published: June 2012

BACKGROUND
The emerging controversy concerning the causal role of atherosclerosis in the development of aortic aneurysms was examined using the accumulated clinical and autopsy data obtained during a 20-year follow-up of a cohort of more than 8,000 men of Japanese ancestry in Hawaii.

METHODS AND RESULTS
Analyses of 174 clinical incident events indicated that there were two types of aneurysmal disease, 151 aortic aneurysms and 23 aortic dissections. The baseline risk factors that predicted the clinical aortic aneurysms were the same factors that predicted aortic atherosclerosis in the same cohort, namely, high blood pressure, high serum cholesterol, and cigarette smoking. These same risk factors were also significantly associated with the occurrence of 27 aortic aneurysms among 293 autopsied men. The less common aortic dissections had an age-specific incidence pattern indicative of an innate susceptibility precipitated by an exposure to another factor. This pattern was consistent with the findings that the incidence of aortic dissections was predicted mainly by baseline high blood pressure.

CONCLUSIONS
From the perspective of prevention, it appears that the risk factors for aortic atherosclerosis and probably atherosclerosis itself are necessary elements in the causal pathway for the great majority of aortic aneurysms in this cohort.
Treatment of prolonged ventricular fibrillation. Immediate countershock versus high-dose epinephrine and CPR preceding countershock.
Authors: Niemann J T , Cairns C B , Sharma J , Lewis R J 
Published: June 2012

BACKGROUND
Early countershock of ventricular fibrillation has been shown to improve immediate and long-term outcome of cardiac arrest. However, a number of investigations in the laboratory and in the clinical population indicate that immediate countershock of prolonged ventricular fibrillation most commonly is followed by asystole or a nonperfusing spontaneous cardiac rhythm, neither of which rarely respond to current therapy. The use of epinephrine in doses greater than those currently recommended has recently been shown to improve both cerebral and myocardial perfusion during cardiopulmonary resuscitation (CPR). The purpose of this study was to compare cardiac resuscitation outcome between immediate countershock of prolonged ventricular fibrillation with high-dose epinephrine therapy and conventional CPR before countershock of prolonged ventricular fibrillation in a canine model.

METHODS AND RESULTS
After sedation, intubation, induction of anesthesia, and instrumentation, ventricular fibrillation was electrically induced in 28 dogs. After 7.5 minutes of ventricular fibrillation, animals were randomly allocated to two treatment groups: group 1, immediate countershock followed by recommended advanced cardiac life support (ACLS) interventions, or group 2, 0.08 mg/kg epinephrine and manual closed-chest CPR before countershock and ACLS. In both groups, ACLS was continued until a spontaneous perfusing rhythm was restored or for 20 minutes (total arrest time, 27.5 minutes). A spontaneous perfusing rhythm was restored in three of 14 group 1 animals and in nine of 14 group 2 animals (p = 0.014 by sequential analysis method of Whitehead). Coronary perfusion pressure (aortic minus right atrial pressure during CPR diastole) before countershock was significantly greater in group 2 (21 +/- 7 mm Hg) when compared with mean circulatory pressure in group 1 (9 +/- 8, p less than 0.01).

CONCLUSIONS
The findings of this study suggest that a brief period of myocardial perfusion before countershock improves cardiac resuscitation outcome from prolonged ventricular fibrillation.
Response of high-energy phosphates and lactate release during prolonged regional ischemia in vivo.
Authors: Schaefer S , Schwartz G G , Wisneski J A , Trocha S D , Christoph I , Steinman S K , Garcia J , Massie B M , Weiner M W 
Published: June 2012

BACKGROUND
The functional impairment of persistently ischemic, or "hibernating," myocardium may serve to maintain myocardial cell viability through a reduction of energy requirements. Although previous studies have, in a variety of experimental models, independently shown variable responses in lactate metabolism and intracellular phosphates during prolonged ischemia, the responses of these metabolites under identical flow conditions have not been adequately described.

METHODS AND RESULTS
To examine the responses of high-energy phosphates and lactate metabolism to prolonged ischemia induced by partial coronary artery stenosis, 12 open-chest pigs were studied using 31P nuclear magnetic resonance spectroscopy. Concurrent measurements of blood flow, segment shortening, high-energy phosphates, and lactate release (in nine animals) were made during 2 hours of regional ischemia. Subendocardial blood flow and segment shortening were persistently depressed during ischemia, with parallel reductions in ATP, phosphocreatine (PCr), and the ratio of phosphocreatine to inorganic phosphate (PCr/Pi). Pi was persistently elevated during the ischemic period. In contrast, lactate release increased significantly from 0.23 +/- 0.04 to 1.34 +/- 0.28 mumol/ml after 15 minutes of ischemia (p less than 0.05) but then decreased to 0.73 +/- 0.17 mumol/ml at 2 hours (p less than 0.05 versus 15 minutes, p = NS versus control). Similarly, pH increased significantly from a nadir of 6.82 +/- 0.07 at 30 minutes of ischemia to 6.98 +/- 0.05 at 2 hours.

CONCLUSIONS
Changes in high-energy phosphates parallel changes in blood flow and function during prolonged ischemia, whereas there is a partial amelioration in lactate production and acidosis. These data support the concept that reduction of myocardial energy requirements during prolonged flow reduction results in signs of reduced ischemia.
Joint effects of serum triglyceride and LDL cholesterol and HDL cholesterol concentrations on coronary heart disease risk in the Helsinki Heart Study. Implications for treatment.
Authors: Manninen V , Tenkanen L , Koskinen P , Huttunen J K , Mänttäri M , Heinonen O P , Frick M H 
Published: June 2012

BACKGROUND
We studied the joint effect of baseline triglyceride and lipoprotein cholesterol levels on the incidence of cardiac end points in the trial group (n = 4,081) of the Helsinki Heart Study, a 5-year randomized coronary primary prevention trial among dyslipidemic middle-aged men. The relative risks (RR) were calculated using Cox proportional hazards models with a dummy variable technique that allows simultaneous study of subgroup combinations from the placebo and treatment groups.

METHODS AND RESULTS
In the placebo group (n = 2,045), the low density lipoprotein cholesterol (LDL-C)/high density lipoprotein cholesterol (HDL-C) ratio was the best single predictor of cardiac events. This ratio in combination with the serum triglyceride level revealed a high-risk subgroup: subjects with LDL-C/HDL-C ratio greater than 5 and triglycerides greater than 2.3 mmol/l had a RR of 3.8 (95% CI, 2.2-6.6) compared with those with LDL-C/HDL-C ratio less than or equal to 5 and triglyceride concentration less than or equal to 2.3 mmol/l. In subjects with triglyceride concentration greater than 2.3 mmol/l and LDL-C/HDL-C ratio less than or equal to 5, RR was close to unity (1.1), whereas in those with triglyceride level less than or equal to 2.3 mmol/l and LDL-C/HDL-C ratio greater than 5, RR was 1.2. The high-risk group with LDL-C/HDL-C ratio greater than 5 and triglyceride level greater than 2.3 mmol/l profited most from treatment with gemfibrozil, with a 71% lower incidence of coronary heart disease events than the corresponding placebo subgroup. In all other subgroups, the reduction in CHD incidence was substantially smaller.

CONCLUSIONS
Serum triglyceride concentration has prognostic value, both for assessing coronary heart disease risk and in predicting the effect of gemfibrozil treatment, especially when used in combination with HDL-C and LDL-C.