bluuebunny/crossref_metadata_2025 huggingface dataset:
Systemic oxygen transport in patients with congenital heart disease.
Authors: Berman W , Wood S C , Yabek S M , Dillon T , Fripp R R , Burstein R
Published: June 2011

The physiology of oxygen delivery was studied in 118 stable patients from 3 months to 20 years old with congenital heart disease. During cardiac catheterization, oxygen consumption (VO2), arterial and venous blood gases and oxygen saturations (range 41% to 98%), hemoglobin concentration, diphosphoglycerate (2,3-DPG), and P50 levels were measured, and then cardiac output, systemic oxygen transport (SOT), arterial and venous oxygen contents, and the VO2/SOT ratio (fractional O2 extraction) were calculated. P50 averaged 31 mm Hg, compared with 27 mm Hg in 10 control children (p less than .01). The composite O2-hemoglobin dissociation curve in vivo was broad: Po2 varied from 37 to 65 mm Hg at 80% saturation. P50, 2,3-DPG, hemoglobin concentrations, and O2 saturation varied widely and inconsistently with Po2 and arterial and venous O2 content, but resulted in clustering of the arterial oxygen content near 165 +/- 23 (SD) ml/liter over a wide range of Po2 and hemoglobin concentrations. SOT varied in direct relation with flow (r = .82, p less than .001), but not with oxygen content, Po2, or P50. VO2 varied widely at normal or high levels of SOT, but decreased linearly at SOT levels below 400 ml/min/m2. Oxygen extraction varied inversely with venous O2 content, rising to about 50% and plateauing below venous contents of 100 ml/liter. O2 extraction did not correlate with Po2, arterial O2 content, or P50. These data suggest that: O2 saturation cannot be predicted or calculated accurately from measured Po2, but must be measured directly, 2,3-DPG, hemoglobin concentration, and P50 fluctuate to stabilize arterial oxygen content, SOT is determined primarily by cardiac output in subjects who are adapted chronically, O2 extraction rises, due to a fall in venous O2 content, to maintain VO2 as transport falls, below a critical level of SOT, O2 extraction ceases to rise and VO2 falls with further reduction in transport.
Demonstration of the presence of slow conduction during sustained ventricular tachycardia in man: use of transient entrainment of the tachycardia.
Authors: Okumura K , Olshansky B , Henthorn R W , Epstein A E , Plumb V J , Waldo A L
Published: June 2011

To test the hypothesis that an area of slow conduction is present during reentrant ventricular tachycardia in man, and that the earliest activation site during ventricular tachycardia is within or orthodromically just distal to the area of slow conduction in the reentry loop, we studied 12 episodes of ventricular tachycardia (mean rate 185 +/- 32 beats/min) that were induced in nine patients with ischemic heart disease. Rapid ventricular pacing was performed at selected sites during ventricular tachycardia while recording electrograms from an early activation site relative to the onset of the QRS complex (site A) and from a site close to the pacing site (site B). Rapid pacing from the right ventricular apex during ventricular tachycardia with a right bundle branch block pattern and from selected left ventricular sites during ventricular tachycardia with a left bundle branch block pattern (mean pacing rate 202 +/- 38 beats/min) resulted in constant ventricular fusion beats on the electrocardiogram except for the last captured beat (i.e., the ventricular tachycardia was entrained) in 11 of 12 episodes. During entrainment: sites A and B were activated at the pacing rate, conduction time from the last pacing impulse to the last captured ventricular electrogram at site A (St-A interval) was 359 +/- 69 msec and spanned the diastolic interval, while that at site B (St-B interval) was only 28 +/- 13 msec, site A had the same ventricular electrogram morphology as that during ventricular tachycardia, while site B had a different electrogram morphology, indicating that site A was activated in the same direction during entrainment as during ventricular tachycardia. Eight episodes of ventricular tachycardia were entrained at two or more different pacing rates. The St-A interval increased during pacing at the faster rate(s) in four of eight episodes, while the St-B interval remained unchanged. Rapid ventricular pacing performed from the same site during sinus rhythm (mean pacing rate 201 +/- 37 beats/min) resulted in an St-A interval of 103 +/- 37 msec (p less than .001 vs the value during entrainment) and an St-B interval of 31 +/- 15 msec (p = NS vs the value during entrainment). It is concluded that an area of slow conduction not demonstrable during sinus rhythm exists during ventricular tachycardia, and that the earliest activation site during ventricular tachycardia is at or orthodromically distal to this area of slow conduction.
Detection and quantitation of constriction of the fetal ductus arteriosus by Doppler echocardiography.
Authors: Huhta J C , Moise K J , Fisher D J , Sharif D S , Wasserstrum N , Martin C
Published: June 2011

Pulmonary hypertension may occur in the fetus in the presence of constriction of the ductus arteriosus. The feasibility of detection and quantitation of fetal ductal constriction by Doppler echocardiography was assessed in an animal preparation in which ductal constriction was created in the fetal lamb with a variable ligature causing varying degrees of fetal pulmonary hypertension (fetal pulmonary arterial systolic pressure 57 to 97 mm Hg and ductal gradient 9 to 42 mm Hg). Comparison of blinded, continuous-wave peak Doppler velocity (V) measurements of the ductal gradient with the modified Bernoulli assumption (gradient = 4V2) compared well with direct catheter measurements of instantaneous peak systolic gradient (r = .99, catheter = 0.95 X Doppler + 0.6), peak-to-peak gradient (r = .97), and mid-diastolic gradient (r = .85). Ductal constriction was characterized by an increase in the peak systolic and diastolic velocities. The normal human fetal ductus arteriosus blood flow velocity pattern was assessed by pulsed Doppler techniques in 25 normal human fetuses after 20 weeks gestation. The peak systolic flow velocity in the ductus arteriosus measured by image-directed pulsed Doppler echocardiography ranged from 50 to 141 cm/sec (mean 80 cm/sec) and increased with gestational age (r = .50). Diastolic velocity in the ductus arteriosus was consistently directed toward the descending aorta and ranged from 6 to 30 cm/sec. The ductal systolic velocities were the highest blood flow velocities in the fetal cardiovascular system. Application of these techniques to fetuses whose mothers were receiving indomethacin for treatment of premature labor at 30 to 31 weeks gestation confirmed this method to be sensitive for detection of fetal ductal constriction, which developed in three fetuses.(ABSTRACT TRUNCATED AT 250 WORDS)
Acute myocardial infarction: diagnostic and prognostic applications of two-dimensional echocardiography.
Authors: Kloner R A , Parisi A F
Published: June 2011

Now that we are entering an era when thrombolytic therapy and early invasive interventions appear to offer significant myocardium-sparing effects, it is important to attempt to exploit techniques that bear directly on the issue of anatomy to obtain an objective measure of infarct size and prognosis. Traditional tests for AMI were developed as diagnostic measures and cannot be expected to measure up to issues raised by modern therapy. Despite its pitfalls, echocardiography can be applied prognostically during the first few hours of AMI evolution to far more patients than can any other imaging technique. We believe that an adequate echocardiographic examination can be an important adjunct that should be used in the early risk assessment of any patient with AMI. Those patients with the greatest potential reversible myocardial damage are clearly the best candidates for aggressive interventions, particularly thrombolysis. For patients with small or no detectable regional wall motion abnormalities, a more conservative initial approach is in order.
In search of afferent pathways of a cardiogenic hypertensive chemoreflex.
Authors: Thames M D , Johannsen U J , Mark A L
Published: June 2011

Injection of serotonin (5-HT) into the left atrium or ventricle activates a hypertensive chemoreflex. The primary purpose of our study was to determine the afferent pathway(s) that mediates this response. A secondary goal was to localize the receptive sites of this reflex. We measured changes in arterial pressure, reflex vascular responses in skeletal muscle and paw, and changes in renal nerve traffic that occurred after the left atrial or left ventricular injection of 5-HT. Injection of 5-HT (100 to 600 micrograms) into left atrium or ventricle produced large reflex increases in vascular resistance and sympathetic outflow. These responses were not reduced after bilateral cervical vagotomy. In separate experiments, increases in renal nerve traffic with left ventricular injection of 5-HT were assessed before and after cardiac sympathetic deafferentation. Interruption of cardiac sympathetic afferent pathways did not significantly attenuate increases in renal nerve activity with 5-HT. Injection of 5-HT (300 micrograms) into the aortic root produced large increases in arterial pressure but this was not observed after injections into the vertebral or common carotid arteries or descending aorta. Injection of 5-HT (100 micrograms) into the left main coronary artery (perfused via a Gregg cannula from an external reservoir) resulted in a depressor reflex (Bezold-Jarisch). In contrast, injection of 5-HT (200 micrograms) into the left ventricle when the drug was prevented from reaching the left coronary artery produced a large pressor response.(ABSTRACT TRUNCATED AT 250 WORDS)
Pathologic features of myocardial hamartomas causing childhood tachyarrhythmias.
Authors: Kearney D L , Titus J L , Hawkins E P , Ott D A , Garson A
Published: June 2011

We have observed in 11 infants, aged 2 years or less, a distinct clinicopathologic lesion responsible for tachyarrhythmias that were fatal in 96% (25/26) of previously reported cases. Nine of the 11 patients, who underwent electrophysiologic mapping and surgical excision of the lesion, have survived, with follow-up periods ranging from 1 month to 6 years. The morphologic findings in these 11 patients and in the 26 cases cited in the literature are reviewed. Pathogenic considerations have included viral-induced lesion, cardiomyopathy, neoplasm, and developmental disorder of Purkinje cells. We believe this lesion to be a myocardial hamartoma. Supportive evidence includes prevalence in infants, tumorlike growth pattern without mitotic figures, and association of other developmental abnormalities. Through electrophysiologic mapping, this myocardial hamartoma is potentially accessible to surgical excision and long-term cure.
Antiarrhythmic efficacy and hemodynamic effects of cibenzoline in patients with nonsustained ventricular tachycardia and left ventricular dysfunction.
Authors: Seals A A , Haider R , Leon C , Francis M , Young J B , Roberts R , Pratt C M
Published: June 2011

This was a prospective single-blind, placebo-controlled study of cibenzoline in 21 patients with five or more runs of nonsustained ventricular tachycardia (VT) and left ventricular dysfunction (mean left ventricular ejection fraction 36 +/- 24%). Ambulatory electrocardiographic monitoring revealed a baseline of 616 +/- 431 runs of VT/day on placebo. Of the 18 patients tolerating the drug, 14 (77%) patients initially had a 75% or greater reduction in VT (177 +/- 164 runs of VT/day, p less than .05). A repeat ambulatory electrocardiogram documented long-term suppression of VT in 13 of 14 patients at 1 month (2.1 +/- 1.3 runs VT/day, p less than .01), in 10 of 14 patients at 3 months (2.5 +/- 1.9 runs VT/day, p less than .01), and in nine of 14 patients at 6 months (1.5 +/- 0.8 runs VT/day, p less than .01). Aggravation of arrhythmia or drug failure was seen in four of 18 (22%) patients (new onset of sudden cardiac death, two patients; sustained VT, two patients). Hemodynamic measurements were obtained with the use of right heart catheterization in patients at rest and exercising during the placebo phase and after 60 hr of oral cibenzoline. Group hemodynamic variables, both measured and derived, showed no detrimental effect of cibenzoline. However, in three of 21 patients (mean ejection fraction 21%), cibenzoline was discontinued due to severe depression of left ventricular function. Caution is recommended in the use of cibenzoline in patients with left ventricular ejection fractions of less than 25%.
Results of sympathetic denervation in the canine heart: supersensitivity that may be arrhythmogenic.
Authors: Inoue H , Zipes D P
Published: June 2011

Latex-induced transmural myocardial infarction or epicardial application of phenol interrupts sympathetic fibers innervating myocardium apical to the infarction or to the phenol-painted area. These denervated regions subsequently show supersensitive shortening of effective refractory period (ERP) in response to the infusion of norepinephrine (denervation supersensitivity). The purpose of this study was to test the hypothesis that such denervation supersensitivity is arrhythmogenic. Ventricular arrhythmias were elicited by programmed ventricular stimulation (PVS) during a control period, during bilateral stimulation of the ansae subclaviae (4 msec pulses, 4 Hz and 3 mA), and during the infusion of norepinephrine (0.5 microgram/kg/min). Study groups consisted of 14 sham-operated dogs, 16 dogs with phenol painted over a diagonal branch, 13 dogs with latex embolization of a diagonal branch that resulted in transmural myocardial infarction, 14 dogs with a one-stage ligation of a diagonal branch producing nontransmural myocardial infarction, and 12 dogs undergoing both phenol painting and one-stage ligation of a diagonal branch. Four to 22 days after the first operation, PVS was performed in anesthetized, open-chest dogs after neural decentralization of the heart. Dogs with phenol painting on the epicardium and dogs in which latex was injected into a diagonal branch showed supersensitive shortening of ERP to infused norepinephrine at apical sites. PVS resulted in ventricular fibrillation more often during stimulation of the ansae subclaviae (p less than .001) and infusion of norepinephrine (p less than .001) than during the control state in dogs treated with phenol alone. The incidence of ventricular fibrillation was highest in dogs with ligation-induced infarction that received phenol compared with all other groups during control (p less than .001), stimulation of the ansae subclaviae (p less than .002), and the infusion of norepinephrine (p less than .01). Propranolol (0.5 mg/kg or 10 mg iv at maximum) attenuated supersensitive shortening of ERP and decreased the incidence of induction of ventricular fibrillation.(ABSTRACT TRUNCATED AT 400 WORDS)
Inhibition of prostacyclin and thromboxane A2 generation by low-dose aspirin at the site of plug formation in man in vivo.
Authors: Kyrle P A , Eichler H G , Jäger U , Lechner K
Published: June 2011

In a double-blind placebo-controlled crossover study, we investigated in seven healthy male volunteers the effect of a low-dose aspirin regimen (35 mg acetylsalicylate per day for 7 days) on the formation of thromboxane A2 (TxA2) and prostacyclin (PGI2) in blood emerging from a standardized injury of the microvasculature made to determine skin bleeding time. When subjects were treated with placebo, there was rapid and substantial generation of TxA2 and PGI2 at the site of platelet-vessel wall interaction within the first 2 min after vascular injury. This was reflected by a greater than 100-fold and greater than 10-fold increase in thromboxane B2 (TxB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) in blood obtained from incisions made to determine bleeding time as compared with the corresponding plasma values. Low-dose aspirin caused a significant inhibition of both TxA2 and PGI2 generation in blood sampled from the skin incisions, represented by a 85% and 92% and 81% and 84% inhibition of TxB2 and 6-keto-PGF1 alpha, respectively, as compared with controls. We therefore conclude that rapid activation of both platelet prostaglandin metabolism and vascular PGI2 biosynthesis occurs at the site of platelet-vessel wall interaction, and low-dose aspirin results in a significant inhibition of both platelet and vascular cyclooxygenase activity. Thus, our data fail to confirm the concept of a differential effect of low-dose aspirin on platelet and vascular prostaglandin synthesis in man in vivo.
Catheter ablation of ventricular tachycardia with intracardiac shocks: results in 33 patients.
Authors: Morady F , Scheinman M M , Di Carlo L A , Davis J C , Herre J M , Griffin J C , Winston S A , de Buitleir M , Hantler C B , Wahr J A
Published: June 2011

Catheter electrical ablation of ventricular tachycardia (VT) was attempted in 33 patients who had recurrent unimorphic VT refractory to 3.7 +/- 1.2 (mean +/- SD) antiarrhythmic drugs. Their mean age was 56 +/- 14 years. Twenty-two patients had coronary artery disease, six had other types of heart disease, and five had no structural heart disease. The mean left ventricular ejection fraction was 0.34 +/- 0.17. Thirty patients had only one documented morphologic type of spontaneous VT, whereas three patients had more than one. One to four shocks of 100 to 300 J each were delivered to the endocardial exit site of VT, as identified by endocardial activation mapping and pace-mapping. In each patient endocardial activation at the exit site of VT preceded the onset of the QRS complex (mean activation time -50 +/- 30 msec). Pace-mapping was possible in 26 patients, and in all but two patients the QRS complexes during VT and during pacing at the exit site of VT were very similar in at least 10 of 12 electrocardiographic leads. In 29 patients, shocks were delivered between an endocardial electrode (cathode) and a patch electrode on the chest wall (anode). Seven patients (including three who first received shocks using an external anode) whose VT originated in the septum received transseptal shocks between two electrodes positioned on either side of the septum. The procedure was successful in 15 patients (45%), who had no recurrence of VT either on no antiarrhythmic therapy or on the same regimen that was ineffective before ablation, over a follow-up period of 15.5 +/- 10 months (range 5 to 35). The ablation attempt was unsuccessful in 18 patients (55%). There were no significant differences in clinical and electrophysiologic variables between patients with and without a successful outcome. Seven nonfatal complications occurred in six patients: sustained nonclinical VT immediately after the shock, ventricular fibrillation on days 5 and 6 after ablation, neurologic deficits (n = 2), atrioventricular block (n = 2), and brachial artery thrombosis. In conclusion, catheter electrical ablation of VT has modest efficacy and is relatively safe in a selected group of patients who have predominantly one configuration of unimorphic VT.
Neutrophil accumulation in experimental myocardial infarcts: relation with extent of injury and effect of reperfusion.
Authors: Chatelain P , Latour J G , Tran D , de Lorgeril M , Dupras G , Bourassa M
Published: June 2011

The effects of reperfusion on the myocardial accumulation of neutrophils and their role in the extent of injury were investigated in a canine preparation with a 3 hr coronary occlusion followed by 21 hr of reperfusion. The left anterior descending coronary artery (LAD) was permanently occluded in group 1 and reperfused after 3 hr in four others (groups 2 to 5). All but group 5 received lidocaine (1 mg/min over 8 hr). A critical stenosis was produced and left in place at reperfusion only in group 2. In groups 1 and 2, 111In-labeled autologous neutrophils were injected at the time of coronary occlusion. Group 4 animals were rendered leukopenic 2 hr before the coronary ligature and throughout the experiment by injection of an antineutrophil rabbit serum. Quantification of the radioactivity by digitized scintigraphy of the heart slices revealed an 80% (p less than .05) increase in neutrophil accumulation in the infarct region after reperfusion (group 2) as compared with permanent occlusion (group 1). Gamma counting of myocardial tissue samples showed that the neutrophil accumulation ratio in the subendocardial central zone of the infarct was increased five times (p less than .05) by reperfusion, whereas no difference was evident in the subepicardium. Infarct size and myocardial area at risk were not statistically different among the five groups. However LAD flow in the leukopenic group (group 4) was significantly higher (p less than .05) 30 min after reperfusion (40.0 +/- 5 ml/min) when compared with the preocclusion value (21.7 +/- 4 ml/min). In contrast, in a parallel experiment without leukopenia (group 3), LAD flow after reperfusion did not differ from the preocclusion value.(ABSTRACT TRUNCATED AT 250 WORDS)
Catheter balloon valvuloplasty of aortic and mitral stenosis in adults: 1987.
Authors: Rahimtoola S H
Published: June 2011

CBV for adults with aortic and mitral stenosis is investigational at the present time and should usually be performed within the guidelines of clinical investigation. The technology is an evolving one with regard to types of catheters and balloons, methods of catheter insertion and placement, and patients and valves that are suitable for and will respond well to CBV. The initial results range from disappointing to excellent and must be kept in perspective. The procedure is clearly a palliative one; ideal results are not being achieved at present. Some of the complications are very serious. Nevertheless, CBV is a most promising catheter interventional technique for patients with valvular heart disease. Proper selection of patients and complete reporting of results is important.
Flow dynamics in the main pulmonary artery after the Fontan procedure in patients with tricuspid atresia or single ventricle.
Authors: Nakazawa M , Nojima K , Okuda H , Imai Y , Nakanishi T , Kurosawa H , Takao A
Published: June 2011

We analyzed the flow velocity pattern in the main pulmonary artery after Fontan operation in patients with tricuspid atresia (n = 10) or with single ventricle (n = 10) by means of a catheter-mounted velocity probe. The area underneath the velocity signal of the forward flow was integrated, and ratios of the portions during atrial systole and during the diastolic phase to the total area (Fa and Fd) were calculated. The Fa was 0.54 +/- 0.09 in patients with tricuspid atresia and 0.45 +/- 0.05 in those with single ventricle (p less than .01). Cardiac output, obtained by the thermodilution method, was 2.45 +/- 0.48 liters/min/m2 in patients with tricuspid atresia and 2.75 +/- 0.72 liters/min/m2 in those with single ventricle. The forward flow during atrial contraction, calculated by multiplying Fa by cardiac output, was 1.32 +/- 0.35 liters/min/m2 in patients with tricuspid atresia and 1.23 +/- 0.33 liters/min/m2 in those with single ventricle. The diastolic forward flow, calculated from Fd and cardiac output, was 0.99 +/- 0.25 liter/min/m2 in patients with tricuspid atresia and 1.52 +/- 0.45 liters/min/m2 in those with single ventricle (p less than 0.005). The sum of cross-sectional areas of the right and left pulmonary arteries normalized by body surface area (PA index) was 282 +/- 85 cm2/m2 in patients with tricuspid atresia and 462 +/- 65 cm2/m2 in those with single ventricle (p less than .005). The Fa was inversely correlated with the PA index in the whole group (r = -.69) and also in the tricuspid atresia group alone (r = -.87).(ABSTRACT TRUNCATED AT 250 WORDS)
Nonsustained ventricular tachycardia in patients with coronary artery disease: role of electrophysiologic study.
Authors: Buxton A E , Marchlinski F E , Flores B T , Miller J M , Doherty J U , Josephson M E
Published: June 2011

Sixty-two consecutive patients with chronic coronary artery disease referred for evaluation of nonsustained ventricular tachycardia (VT) underwent electrophysiologic studies. Sustained VT was induced by one to three ventricular extrastimuli in 28 patients (45%). Therapy was guided by the results of electrophysiologic testing in 44 patients: 19 patients without inducible sustained VT received no antiarrhythmic therapy, and 25 patients with inducible sustained or symptomatic nonsustained VT received therapy guided by the results of electrophysiologic studies. The results of electrophysiologic studies were ignored by physicians for a second group of 18 patients: four had inducible sustained VT but received no antiarrhythmic therapy, and 14 had inducible sustained or nonsustained VT and received antiarrhythmic therapy not guided by results of electrophysiologic testing. After a mean follow-up period of 28 months, 11 patients had died suddenly. Seven of the 11 patients who died suddenly had inducible sustained VT. Three of 44 patients in the group receiving therapy guided by electrophysiologic studies died suddenly versus eight of 18 in the group receiving therapy not guided by electrophysiologic studies (p = .001). Only one of 19 patients without inducible sustained VT who were not treated experienced sudden death. Two of four patients with inducible sustained VT who did not receive antiarrhythmic therapy died suddenly. Multivariate analysis of the relationship of induced arrhythmias, left ventricular ejection fraction, site of myocardial infarction, history of syncope, or type of antiarrhythmic therapy to outcome revealed a greater than twofold increased risk for sudden cardiac death in patients whose therapy was not guided by results of electrophysiologic study.(ABSTRACT TRUNCATED AT 250 WORDS)
Comparative circulatory effects of isoproterenol, dopamine, and dobutamine in conscious lambs with and without aortopulmonary left-to-right shunts.
Authors: Toorop G P , Hardjowijono R , Dalinghaus M , Koers J H , Wildevuur C R , Zijlstra W G , Kuipers J R
Published: June 2011

We studied the effect on the circulation of the catecholamines isoproterenol, dopamine, and dobutamine in chronically instrumented lambs with aortopulmonary left-to-right shunts (ages 11 to 87 days) and without shunts (ages 8 to 97 days). Infusion of 0.1 microgram/kg/min isoproterenol or 10 micrograms/kg/min dobutamine markedly increased heart rate and systemic and pulmonary blood flows, while stroke volume and the left-to-right shunt flow did not change. Since pulmonary blood flow increased and the left-to-right shunt flow did not change, the left-to-right shunt fraction decreased with the infusions of isoproterenol and dobutamine. The hemodynamic changes during the infusion of isoproterenol and dobutamine occurred immediately after the start of infusion and stabilized within a few minutes. The pattern of hemodynamic changes was not influenced by the presence of an aortopulmonary left-to-right shunt or by age. Infusion of 10 micrograms/kg/min dopamine caused only small hemodynamic changes. This study shows that heart rate and systemic blood flow in the lamb are closely related. Furthermore, it demonstrates that despite an increased systemic blood flow, left-to-right shunt flow does not change after infusion of isoproterenol and dobutamine. Any decision as to which positive inotropic agent might be preferred at an early age should await experimental work concerning the effect of these agents on the myocardial oxygen demand and on the distribution of the systemic blood flow.
Nonuniformity of pericardial surface pressure in dogs.
Authors: Smiseth O A , Scott-Douglas N W , Thompson C R , Smith E R , Tyberg J V
Published: June 2011

Previously, we have shown that pericardial constraint cannot be measured by true (hydrostatic) pressure except when an excess of pericardial fluid is present and that a device such as a balloon (which reflects radial contact stress as well as hydrostatic pressure) must be used. Since radial contact stress is the major component of the constraint exerted by the pericardium when little pericardial liquid is present, it follows that the pressure measured by the balloon might be different over different parts of the heart. In an attempt to test this hypothesis, in 11 anesthetized dogs we placed pericardial balloons over the right and left ventricular free walls, instrumented the animals to measure ventricular dimensions (sonomicrometry) and pressure, mounted pneumatic constrictors on the aortic and pulmonary artery, reapproximated the pericardium, and closed the chest under suction. We studied the transient effects of constrictions of the ascending aorta and pulmonary artery and of angiotensin infusion before and after intravenous saline infusion. Aortic constriction and, to a lesser degree, angiotensin increased pericardial pressure over the left ventricle more than over the right ventricle. Pulmonary artery occlusion increased pericardial pressure over the right ventricle but significantly decreased pericardial pressure over the left ventricle. We conclude that there are significant local differences in pericardial pressure (recorded by balloon) over the lateral ventricular surfaces during acute changes in afterload. These observations may be explained in part by decreased venous return to the contralateral ventricle, the tendency of the heart to resist lateral displacement, and the limited mobility of the pericardium.
Intramuscular administration of human tissue-type plasminogen activator in rabbits and dogs and its implications for coronary thrombolysis.
Authors: Sobel B E , Saffitz J E , Fields L E , Myears D W , Sarnoff S J , Robison A K , Owensby D A , Fox K A
Published: June 2011

To determine whether sustained plasma concentration of human tissue-type plasminogen activator (t-PA) can be induced promptly after intramuscular injection with enhancers of absorption devoid of deleterious local and systemic effects, we studied 250 rabbits and 13 dogs. In rabbits with t-PA injected directly into exposed muscle followed by local electrical stimulation at the site, early absorption was increased markedly by addition of 0.63M methylamine plus 0.079M hydroxylamine to the excipient. Elevations peaked within 5 min and increased with dose of t-PA, concentration of methylamine, and volume of injection medium. The enhancers were effective with percutaneous injections in the absence of local electrical stimulation as well. They did not elicit any obviously deleterious local or systemic effects. In separate experiments in rats, intramuscular injections of 0.63M methylamine plus 0.079M hydroxylamine induced local egress of intravascular radiolabeled albumin within the injection site and endothelial gaps in venules detected with colloidal carbon--changes consistent with direct effects on vascular permeability. In dogs, percutaneous intramuscular injection of t-PA in excipient without enhancers did not lead to early elevations of human t-PA in plasma, although late elevations were seen. When the enhancers were used, early elevations occurred as well, with functional activity documented by fibrin plate assays of serially obtained plasma samples and by sequential coronary angiography delineating thrombolysis after experimentally induced coronary thrombosis. The results indicate that intramuscular administration of t-PA with selected enhancers of absorption is a feasible approach for rapid induction of fibrinolysis.
Influences of localized aortic valve damage on coronary artery blood flow in acute aortic regurgitation: an experimental study.
Authors: Nakao S , Nagatomo T , Kiyonaga K , Kashima T , Tanaka H
Published: June 2011

We examined the influences of localized aortic valve damage on coronary artery blood flow and the prognosis in acute aortic regurgitation. Aortic regurgitation was produced in 18 open-chest dogs by extensively cutting one of the three aortic cusps with a nerve knife introduced via the cardiac apex. The dogs were separated into three groups of six dogs each. In each group the noncoronary cusp (NCC), the right coronary cusp (RCC), or the left coronary cusp (LCC) was cut. Aortic and left ventricular pressures; the phasic aortic, left anterior descending (LAD), and right coronary artery (RCA) blood flows; and electrocardiograms were simultaneously recorded before and after production of acute AR. All dogs in the NCC and RCC groups survived for at least 30 to 60 min, but all dogs in the LCC group died after 5 to 9 min of production of acute AR due to left ventricular failure. After 2 min of aortic regurgitation, the total, systolic, and diastolic LAD flows were 39 +/- 14, 19 +/- 9, and 20 +/- 8 ml/min (mean +/- SD) in the NCC group, 41 +/- 15, 31 +/- 9, and 10 +/- 6 ml/min in the RCC group, and 9 +/- 5, 19 +/- 5, and -10 +/- 2 ml/min in the LCC group, respectively. The corresponding RCA flows were 19 +/- 9, 15 +/- 6, and 4 +/- 3 ml/min in the NCC group, 13 +/- 8, 21 +/- 12, and -8 +/- 4 ml/min in the RCC group, and 14 +/- 4, 19 +/- 4, and -5 +/- 1 ml/min in the LCC group, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Differential electrophysiologic properties of decremental retrograde pathways in long RP' tachycardia.
Authors: Lerman B B , Greenberg M , Overholt E D , Swerdlow C D , Smith R T , Sellers T D , DiMarco J P
Published: June 2011

Long RP' supraventricular tachycardias (SVT) often demonstrate both slow and decremental conduction properties in the retrograde pathway of the reentrant circuit. The electrophysiologic properties of these pathways are poorly understood. We studied 10 patients with long RP' SVT (RP'/RR, 0.52 to 0.71); five had the unusual form of atrioventricular nodal reentry (fast-slow) and five patients had accessory AV pathways with slow, decremental retrograde conduction properties. During SVT, the effects of intravenous adenosine (37.5 to 150 micrograms/kg), which increases potassium current (iK) in supraventricular tissue and hyperpolarizes membrane potential toward Ek (-90 mV), and the response to slow-inward channel blockade with verapamil (0.10 to 0.20 mg/kg iv) were evaluated. Adenosine and verapamil has similar effects in the presence of fast-slow AV nodal reentry since both agents terminated SVT by producing block in the retrograde slow AV nodal pathway. In contrast, adenosine and verapamil had differential effects on retrograde conduction in decremental accessory pathways. Adenosine terminated all episodes of SVT in the retrograde decremental pathway, whereas verapamil had a direct effect on this tissue in only two of five patients. Decremental retrograde accessory pathways can therefore demonstrate at least two types of electrophysiologic responses. Pathways that respond only to adenosine-induced hyperpolarizing K+ current likely comprise depressed fast-Na+ channel tissue, i.e., partially depolarized (greater than -60 to -70 mV) atrial tissue. In contrast, decremental accessory pathways that respond to both modulation of the slow-inward calcium current and K+ conductance have pharmacologic properties similar to those of the AV node and may represent more completely depolarized atrial fibers with resting membrane potentials of -60 mV or less.
The cellular electrophysiologic changes induced by ablation: comparison between argon laser photoablation and high-energy electrical ablation.
Authors: Levine J H , Merillat J C , Stern M , Weisman H F , Kadish A H , Moore E N , Spear J F , Fonger J , Guarnieri T
Published: June 2011

The cellular electrophysiologic effects of myocardial ablation performed in vitro with argon laser energy were compared with those of high-energy electrical shocks. A border zone of injured but nonnecrotic tissue surrounding the site of energy delivery was present after tissue ablation by both energy modalities. A decrease in resting membrane potential, action potential amplitude, and maximum rate of upstroke velocity was noted in each tissue sample, was greatest nearest the site of energy delivery, and was of graded severity at increasing distances from the crater edge. The extent of injury, as indexed by changes in action potential variables and necrosis, histologically determined, was greater for tissues exposed to high-energy shocks. The relatively focal injury after argon laser photoablation may explain the lower incidence of arrhythmias and hemodynamic dysfunction noted with the use of this method of ablation in vivo.
The relationship of various measures of end-systole to left ventricular maximum time-varying elastance in man.
Authors: Starling M R , Walsh R A , Dell'Italia L J , Mancini G B , Lasher J C , Lancaster J L
Published: June 2011

This investigation was designed to calculate left ventricular maximum time-varying elastance (Emax), to define the relationship between Emax and pressure-volume (P-V) relations at other, more easily defined measured of end-systole, and to determine whether these measures of left ventricular contractile function can be normalized in man. Accordingly, we studied 10 subjects with simultaneous high-fidelity micromanometer left ventricular and ascending aortic pressure recordings and biplane contrast cineangiograms at control conditions and during infusion of methoxamine and nitroprusside. Emax was defined as the maximum slope of the linear relation of isochronal, instantaneous P-V data points obtained from each of the three loading conditions. Left ventricular end-systole was also defined for each loading condition as: the time of the maximum P-V ratio (maxPV), minimum ventricular volume (minPV), (-)dP/dtmin [(-)dP/dtPV], and zero systolic flow approximated by the central aortic dicrotic notch (AodiPV). The mean heart rates and LV (+)dP/dtmax were insignificantly altered during the three loading conditions. Isochronal Emax ranged from 3.38 to 6.73 mm Hg/ml (mean 5.48 +/- 1.23 [SD] mm Hg/ml) and the volume-axis intercepts at zero pressure ranged from -2 to 51 ml (mean 18 +/- 16 ml). The isochronal slope calculations were reproducible (r = .97 to .99). The end-systolic P-V slope values for the maxPV, minPV, (-)dP/dtPV, and AodiPV relations correlated with isochronal Emax (r = .90, .88, .69, and .74, respectively). The average slope values for these end-systolic P-V relations, however, underestimated the mean Emax (p less than .01 to p less than .001). The mean extrapolated volume-axis intercepts for these end-systolic P-V relations also underestimated that for Emax. Finally, the isochronal Emax and other end-systolic P-V relation slope values demonstrated inverse linear relationships with left ventricular mass (r = -.68 to -.91, p less than .05 to p less than .001). Only the Emax volume-axis intercepts showed a linear relationship with left ventricular end-diastolic volume (r = .75). Thus we conclude that the time-varying elastic properties of the left ventricle can be calculated in man, that commonly used end-systolic P-V relations significantly underestimate isochronal Emax, and that normalization of isochronal Emax and other end-systolic P-V relation slope values might be performed in man with left ventricular mass; no obvious relationship between volume-axis intercepts and measures of left ventricular or body size was apparent.
Spatial distribution and prognostic significance of ST segment potential determined by body surface mapping in patients with acute inferior myocardial infarction.
Authors: Walker S J , Bell A J , Loughhead M G , Lavercombe P S , Kilpatrick D
Published: June 2011

We investigated the mechanism and significance of ST segment changes in inferior infarction by studying 100 patients with acute inferior infarction in whom body surface maps were recorded on admission. The magnitude of the maximum ST segment elevation (denoted Vmax) and magnitude of the maximum ST segment depression (denoted Vmin), as well as the ST depression on the standard 12-lead electrocardiogram were analyzed against morbidity and mortality (at a median follow-up time of 14 months). A value obtained by subtracting Vmax from Vmin correlated (p less than .0002) with outcome. Correlations were also found between Vmin and complications, Vmin and mortality, and between increasing levels of ST depression on the 12-lead electrocardiogram and mortality. The maps were also studied by grouping the 100 ST segment map patterns into five groups by cluster analysis techniques. One group showed marked anterior negativity and had 37% mortality compared with an overall 5% mortality for the remaining groups. The limited arteriographic and autopsy data available indicated that the findings of a diseased artery or arteries corresponded with the results of mapping. The mean map patterns of the five groups showed that, in most patients with inferior infarction, the standard chest leads V1 to V6 are over a region of steep voltage gradient. Small changes in the position of the standard chest lead can cause large changes in the displayed potentials. This study indicates that patients at high risk after acute inferior infarction can be identified by surface mapping on admission to the coronary care unit.
Comparison of single and multiple doses of prophylactic antibiotics in experimental streptococcal endocarditis.
Authors: Malinverni R , Francioli P B , Glauser M P
Published: June 2011

Single-doses or short-term administration of beta-lactam antibiotics alone or combined with aminoglucoside antibiotics have failed to consistently prevent experimental streptococcal endocarditis induced by high inocula of bacteria poorly susceptible to killing by these antibiotics. The optimal duration of administration of antibiotics for successful prophylaxis under these circumstances has not been established. We therefore tested, in rats with catheter-induced sterile aortic vegetations, the duration of administration of antibiotic necessary to prevent endocarditis induced by bacterial inocula 100 to 10,000 times the 90% infective dose of two tolerant viridans-group streptococci and two Streptococcus faecalis strains. Multiple-dose regimens of amoxicillin alone or of amoxicillin combined with gentamicin were studied. Against the two viridans group streptococci, successful prophylaxis was achieved with multiple doses of amoxicillin alone given over 24 to 48 hr and by the combination of amoxicillin and gentamicin given for 6 to 24 hr. Against the two S. faecalis strains, multiple-dose regimens with amoxicillin alone failed, but the combination of amoxicillin and gentamicin was successful when administered for 48 to 72 hr. Thus, after challenge with high bacterial inocula, repeated doses of a beta-lactam antibiotic alone were sufficient to prevent viridans streptococcal endocarditis, but multiple doses of a bactericidal combination (beta-lactam plus aminoglucoside), as necessary for the treatment of established endocarditis, were a prerequisite for successful prophylaxis of S. faecalis endocarditis.
Low-energy transvenous ablation of the canine atrioventricular conduction system with a suction electrode catheter.
Authors: Saksena S , Tarjan P P , Bharati S , Boveja B , Cohen D , Joubert T , Lev M
Published: June 2011

A single suction electrode catheter was used for His bundle electrogram recording. His bundle pacing, and low-energy (20 or 30 J) His bundle ablation in seven dogs. The suction electrode catheter was actively fixed to the atrial endocardium at the His bundle level. Electrophysiologic studies were performed in the control state, immediately after, and late (greater than 40 days) after His bundle ablation and results were correlated with histologic findings in the conduction system. Unipolar His bundle recording and pacing were successfully performed in all dogs with the suction electrode catheter before and after ablation. Complete heart block developed after a single 20 J shock delivered via the suction electrode catheter in all dogs immediately, but reverted to 1:1 atrioventricular conduction with first-degree atrioventricular block in two dogs in which one or two additional shocks (20 or 30 J) produced complete heart block. Mean ablation energy per shock was 22 +/- 4 J. The mean total delivered energy per dog was 31 +/- 20 J. Late electrophysiologic study in all dogs showed persistent complete heart block in five dogs and paroxysmal second-degree or third-degree atrioventricular block in two dogs. Gross examination of the ablation site showed a white plaque above the medial tricuspid leaflet (1.4 to 2.0 cm long and 0.4 to 0.6 cm wide). Microscopically, fibrosis of the penetrating and branching His bundle was seen in all dogs, with minimal atrioventricular node and atrial involvement. Significant proximal right bundle branch fibrosis was observed in the two dogs receiving one or two additional shocks. We conclude that the suction electrode catheter permits repeated His bundle recording, pacing, and ablation with a single catheter. Permanent and safe low-energy ablation of the canine His bundle is feasible. Focal injury localized to the target area in the conduction system can be obtained.
Electrophysiologic mechanisms underlying arrhythmias due to reperfusion of ischemic myocardium.
Authors: Pogwizd S M , Corr P B
Published: June 2011

The mechanisms responsible for malignant ventricular arrhythmias associated with reperfusion of ischemic myocardium were delineated with a computerized, three-dimensional mapping system, with simultaneous eight-level transmural recordings from 232 bipolar sites. In six chloralose-anesthetized cats, regional ischemia was induced for 10 min by occlusion of the left anterior descending coronary artery, followed by reperfusion. At 10 min after ischemia, just before reperfusion, total ventricular activation time during sinus rhythm was significantly delayed (63 +/- 8 vs 25 +/- 2 msec before ischemia, p less than .001). Ventricular tachycardia (VT) occurred within 15 sec after reperfusion and in three animals culminated in ventricular fibrillation. In 75% of cases of nonsustained VT, initiation occurred in the subendocardium, at the border of the reperfused zone via a mechanism not involving reentry, as determined by the fact that continuous activation was not apparent and the time from the end of the sinus beat to the beginning of VT (142 +/- 14 msec) was not associated with any intervening depolarizations. In the remaining 25% of cases of nonsustained VT, initiation of the VT resulted from intramural reentry in the subendocardium adjacent to the site of delayed midmyocardial activation from the preceding sinus beat (total activation time = 151 +/- 9 msec, p less than .001 vs just before reperfusion). This reentrant mechanism was similar to that responsible for the majority of cases of VT during ischemia without reperfusion. Maintenance of VT during reperfusion occurred by nonreentrant mechanisms as well as by intramural reentry, with most cases of VT involving both mechanisms. Ventricular tachycardia leading to ventricular fibrillation was initiated in the subendocardium at the border of the reperfused zone by a nonreentrant mechanism and was maintained by both nonreentrant and reentrant mechanisms, at times in combination in the same beat. The coupling interval of the first ectopic beat of VT leading to ventricular fibrillation was not significantly different from that of nonsustained VT (199 +/- 16 vs 189 +/- 9 msec, p = NS). However, during the transition from VT to ventricular fibrillation, nonreentrant mechanisms arising both in the subendocardium and subepicardium led to very rapid acceleration of the tachycardia to the coupling interval of 92 +/- 2 msec, resulting in enhanced functional block and further conduction delay, with the total activation time of the transition beats exceeding the coupling interval of the tachycardia.(ABSTRACT TRUNCATED AT 400 WORDS)