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At least 415 records · Page 23Linked to original sources
PubMed2003

Radiofrequency catheter ablation of various kinds of arrhythmias guided by virtual electrograms using a noncontact, computerized mapping system.

Three-dimensional visualization of cardiac activation has become important for providing further insights into the pathophysiological mechanisms of arrhythmias and to increase the efficacy of catheter ablation. The noncontact mapping system enables a single-beat analysis of the reconstructed geometry of the cardiac chamber. In 8 patients with various kinds of arrhythmias (3 with atrial flutter, 2 with right ventricular outflow tract ventricular tachycardia, 1 with idiopathic left ventricular tachycardia, 1 with atrioventricular nodal reentrant tachycardia and 1 with concealed Wolff-Perkinson-White syndrome), non-contact mapping using an EnSite 3000 system was performed for the guidance of catheter ablation. The optimal sites for successful ablation were detected and all of these arrhythmias were successfully eliminated with the radiofrequency energy applications without any adverse effects. The computerized EnSite 3000 mapping system described here computes accurate isopotential maps that are a useful guide for catheter ablation.

Adult↗
PubMed1992

Effects of the class III antiarrhythmic drug dofetilide on ventricular monophasic action potential duration and QT interval dispersion in stable angina pectoris.

The effects of intravenous dofetilide on ventricular monophasic action potential duration and effective refractory period at the right ventricular apex and outflow tract were studied in 18 patients (aged 37 to 70 years) with ischemic heart disease. Six patients received low-dose dofetilide as a 3 micrograms/kg loading dose over 15 minutes and a 1.5 micrograms/kg maintenance dose over 45 minutes; 6 received high-dose dofetilide 6 + 3 micrograms/kg and 6 placebo. During atrial pacing at a cycle length of 800 ms high-dose dofetilide prolonged right ventricular apex monophasic action potential duration by 45 ms (16%) and the effective refractory period by 40 ms (16%). At the right ventricular outflow tract, monophasic action potential duration was prolonged by 45 ms (15%) and effective refractory period by 55 ms (21%). During atrial pacing at a cycle length of 500 ms high-dose dofetilide prolonged the right ventricular apex monophasic action potential duration by 40 ms (18%) and the effective refractory period by 43 ms (21%). The right ventricular outflow tract monophasic action potential duration was prolonged by 33 ms (14%) and effective refractory period by 45 ms (21%). Dofetilide produced no increase in the dispersion of repolarization between the 2 sites. During the maintenance infusion QTc prolongation by high-dose dofetilide averaged 43 ms (10%) with no increase of interlead QT dispersion. The effects of dofetilide on QT interval and effective refractory period are shown to be due to a direct effect on action potential duration with no effect on dispersion. No rate dependence of monophasic action potential prolongation was detected at these cycle lengths.

Action Potentials↗
PubMed1993

Doppler analysis of portal vein flow in tricuspid regurgitation.

Portal and hepatic vein flow-velocity profiles were examined by pulsed Doppler in 66 patients with tricuspid regurgitation (color Doppler grading: severe: 37, moderate: 18; mild: 11) and 20 normal subjects to determine if portal vein flow analysis is useful in the evaluation of tricuspid regurgitation. Portal vein flow was defined as one of the following categories: subcontinuous (dependent on respiration), pulsatile systolic (not inverted), inverted after systole, and continuous (not dependent on respiration). An index of portal vein flow pulsatility was also calculated. Standard classification of hepatic vein flow pattern was performed. Portal vein flow was pulsatile in 20% of normals subjects, and in 27.3% 44.5% and 51.3% of patients with respectively mild, moderate and severe tricuspid regurgitation; portal vein flow was inverted after systole in further 32.4% of patients with severe tricuspid regurgitation. Portal vein pulsatility index correlated with color Doppler grading of tricuspid regurgitation (r:0.63; p < 0.001) and right ventricle-atrium pressure gradient (r:0.39; p < 0.01). However, when compared with hepatic vein flow, both sensitivity and specificity of quantitative portal vein flow analysis was less reliable in diagnosing and grading tricuspid regurgitation. In particular, in patients with severe tricuspid regurgitation, the portal vein flow pattern was quite variable (pulsatile in 19 patients, inverted after systole in 12, and continuous in six). Liver biopsy was performed in nine patients, four of them with severe tricuspid regurgitation and continuous portal vein flow. Histology showed severe liver fibrosis in all four.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1996

Transvalvular impedance (TVI) recording under electrical and pharmocological cardiac stimulation.

The cardiac electric impedance was recorded between right atrium and ventricle, throughout the cardiac cycle, by means of a tripolar single pass lead for VDD pacing. The transvalvular impedance signal (TVI) is a sharp periodic wave, with high signal-to-noise ratio, that is detected exclusively in the presence of cardiac mechanical activity. The minimum TVI value is attained during the atrial systole, the maximum at the end of ventricular systole. Different parameters of TVI waveform are affected by changes in the inotropic state, and could therefore be proposed as potential signals for new rate responsive algorithms based on the correlation between inotropic and chronotropic regulation. The signal might be used, moreover, for pacing and sensing validation in autoregulating pacemakers and for fibrillation recognition in ICDs.

Adrenergic Agonists↗
PubMed2000

Pregnancy alters cardiac receptor afferent discharge in rats.

Reflex effects of cardiac receptor (CR) stimulation are attenuated in pregnant rats. We tested whether CR afferent discharge is reduced during pregnancy by measuring single fiber activity in response to increases in right atrial pressure (RAP) in anesthetized pregnant and virgin rats with sinoaortic denervation. Single fiber activity was isolated from fine filaments of the right cervical vagus nerve. Changes in CR discharge, RAP, and arterial pressure were recorded in response to atrial saline injections (25-300 microl). Resting RAP was similar between groups, and spontaneous CR discharge was similar in pregnant rats (1.95+/-0.21 Hz) and in low-frequency (LF) receptors in virgin rats (1.30+/-0.2 Hz). In virgin, but not pregnant rats, a subset (24%) of CR had higher-frequency (HF) spontaneous discharge (9.91+/-1.19 Hz). During stimulation, the level of RAP above which CR firing increased was significantly higher in pregnant rats, but CR activity was clustered into an LF discharge range. Thus gestation appears to reduce the activity of CR afferents, possibly by increasing stimulus threshold or by selective inactivation of a subset of HF discharging receptors.

Animals↗
PubMed2005

[Experimental study on early escharectomy after major burns in minipigs].

OBJECTIVE: To investigate optimal time for early escharectomy after severe scald in minipigs. METHODS: Minipigs inflicted with 35% TBSA full thickness burn were employed in the study, and they were randomly divided into A (n = 7, with escharectomy at 6PSH), and B (n = 7, with escharectomy at 24 PSH) groups. The hemodynamics indices, hemorrheology, and the serum levels of cytokines in the two groups were determined before burns and at 6, 8, 16, 24 and 72PSH. RESULTS: The hemodynamics indices in A group obviously improved compared with those in B group. The cardiac output (CO, 2.28 +/- 0.03 L/min) and right arterial pressure (RAP, 4.54 +/- 0.04 mmHg) in A group recovered to the pre-injury levels at 48 PSH. There was no difference of the hemorrheology indices between the two groups (P > 0.05). The serum contents of cytokines in A group declined to the pre-injury level on 1 PBW, while those in B group were significantly higher than those before injury and those in A group (P < 0.05 or P > 0.01). CONCLUSION: Escharectomy during 6 PBH might be safe and feasible, thus preventing long-term complications effectively.

Acute-Phase Reaction↗
PubMed1997

Elevated right atrial pressure does not reduce collateral blood flow to ischemic myocardium.

Right atrial pressure (RAP) may become substantially elevated during heart failure and has been reported to reduce collateral flow to the ischemic myocardium of isolated hearts. The effect of elevated RAP on blood flow to collateral-dependent and normal myocardium of in situ hearts was studied in 20 open-chest anesthetized dogs with acute occlusion of the left anterior descending coronary artery. Regional myocardial blood flow was measured with radioactive microspheres while RAP was elevated by restricting right ventricular (RV) outflow with constant aortic pressure. Increasing RAP from 3.8 +/- 0.5 to 21.5 +/- 0.8 and then to 34.3 +/- 0.9 mmHg did not reduce blood flow to any transmural region of LV normal or collateral-dependent myocardium. Further elevation of RAP to 49.3 +/- 1.1 mmHg reduced subepicardial but not subendocardial collateral flow. Blood flow to normal RV increased. Retrograde flow and peripheral coronary pressure increased as RAP was elevated. Previously injected 11-micron microspheres were present in the retrograde flow when RAP was elevated; thus retrograde capillary flow contributed to the retrograde flow. The results explain discrepancies among previous reports, and they are consistent with a waterfall phenomenon in the coronary collateral circulation.

Animals↗
PubMed1996

Impact of medical therapy on pulmonary hypertension in patients with congestive heart failure awaiting cardiac transplantation.

Pulmonary artery (PA) hypertension in transplant recipients increases mortality from right heart failure following heart transplantation. We examined the impact of long-term medical therapy on the severity of PA hypertension in patients with end-stage congestive heart failure on a transplant waiting list. The initial and final, quarterly right heart catheterization data on 60 patients (50 men, aged 50 +/- 9 years, New York Heart Association class III to IV) awaiting heart transplantation were analyzed and the patients divided into 2 groups: group A, those with persistent elevated systolic PA pressures throughout the 10-month follow-up (n = 31 of 60), and group B, those who had any decrease in systolic PA pressure during that period (n = 29 of 60). Group A had no change in hemodynamics. Group B had a significant decrease( +/- SD) in right atrial (11 +/- 7 to 5 +/- 4 mm Hg), PA (57 +/- 11 to 37 +/- 11 mm Hg), and PA wedge (25 +/- 9 to 14 +/- 7 mm Hg) pressures, with increases in cardiac output (3.8 +/- 0.9 to 4.7 +/- 1.1 L/min) and ejection fraction (18 +/- 6% to 27 +/- 11%) (p < 0.05). The combined end point of transplant or death occurred in 28 of 31 patients (90%) in group A versus 14 of 29 (50%) in group B (p = 0.0004). Ischemic etiology was present in 71 % of patients in group A versus 68% with idiopathic dilated cardiomyopathy in group B (p = 0.003). The reversibility of PA hypertension rather than its initial severity is predictive of patient clinical outcome. Idiopathic, as opposed to ischemic, cardiomyopathy responds better to medical therapy.

Antihypertensive Agents↗
PubMed2002

A critical analysis of the view that right atrial pressure determines venous return.

A. C. Guyton pioneered major advances in understanding cardiovascular equilibrium. He superimposed venous return curves on cardiac output curves to reveal their intersection at the one level of right atrial pressure (Pra) and flow simultaneously consistent with independent properties of the heart and vasculature. He showed how this point would change with altered properties of the heart (e.g., contractility, sensitivity to preload) and/or of the vasculature (e.g., resistance, total volume). In such graphical representations of negative feedback between two subdivisions of a system, one input/output relationship is necessarily plotted backward, i.e., with the input variable on the y-axis (here, the venous return curve). Unfortunately, this format encourages mistaken ideas about the role of Pra as a "back pressure," such as the assertion that elevating Pra to the level of mean systemic pressure would stop venous return. These concepts are reexamined through review of the original experiments on venous return, presentation of a hypothetical alternative way for obtaining the same data, and analysis of a simple model.

Algorithms↗
PubMed2002

A computational model-based validation of Guyton's analysis of cardiac output and venous return curves.

Guyton developed a popular approach for understanding the factors responsible for cardiac output (CO) regulation in which 1) the heart-lung unit and systemic circulation are independently characterized via CO and venous return (VR) curves, and 2) average CO and right atrial pressure (RAP) of the intact circulation are predicted by graphically intersecting the curves. However, this approach is virtually impossible to verify experimentally. We theoretically evaluated the approach with respect to a nonlinear, computational model of the pulsatile heart and circulation. We developed two sets of open circulation models to generate CO and VR curves, differing by the manner in which average RAP was varied. One set applied constant RAPs, while the other set applied pulsatile RAPs. Accurate prediction of intact, average CO and RAP was achieved only by intersecting the CO and VR curves generated with pulsatile RAPs because of the pulsatility and nonlinearity (e.g., systemic venous collapse) of the intact model. The CO and VR curves generated with pulsatile RAPs were also practically independent. This theoretical study therefore supports the validity of Guyton's graphical analysis.

Atrial Function, Right↗
PubMed1997

Hemodynamic, hormonal, and renal effects of adrenomedullin in conscious sheep.

Adrenomedullin is a recently discovered peptide that has been shown to reduce arterial pressure and induce natriuresis. However, few studies have examined the biological actions of adrenomedullin in conscious animals in an integrative manner. Accordingly, we have examined the hemodynamic, renal, and endocrine actions of adrenomedullin infused intravenously at 10 and 100 ng.kg-1.min-1 (each 90 min) in a vehicle-controlled study in eight normal conscious sheep. Adrenomedullin reduced right atrial pressure (P < 0.05) and diastolic (15 mmHg, P < 0.01) and mean arterial pressure (10 mmHg, P < 0.05) and increased cardiac output (3 l/min, P < 0.001). Total peripheral resistance was reduced 40% (P < 0.001). Urinary sodium was reduced to 35% of control during the 90-min clearance period immediately postinfusion (P < 0.05). Adrenomedullin increased plasma adenosine 3',5'-cyclic monophosphate levels (P < 0.001). Plasma renin activity was elevated during adrenomedullin (P < 0.001) coincident with the peak hypotensive effect, whereas plasma aldosterone was not affected and plasma norepinephrine levels fell (P < 0.05). In conclusion, adrenomedullin had clear blood pressure-lowering effects with increased cardiac output and stimulation of renin but suppressed sympathetic activation in conscious sheep. The physiological implications of these findings require further study.

Adrenomedullin↗
PubMed1996

Reduction of right atrial peak systolic velocity in growth-restricted discordant twins.

OBJECTIVE: The objective of this study was to measure blood flow velocity changes through the tricuspid valve in intrauterine growth-restricted twins. STUDY DESIGN: Discordant twins were evaluated by measurement of tricuspid valve flow velocities. Twin pairs with one intrauterine growth-restricted fetus caused by uteroplacental insufficiency and one appropriately grown fetus were included in the analysis. Fetuses with chromosomal or structural abnormalities and confirmed twin-twin transfusion syndrome were excluded. Eighteen pairs met these criteria. Student's t test was used for comparison of flow velocities. RESULTS: Peak ventricular diastolic flow velocities through the tricuspid valve in the twin with intrauterine growth restriction and the appropriately grown twin were 35.8 +/- 4.43 cm/sec and 34.0 +/- 6.7 cm/sec, respectively (p = 0.35). The atrial peak systolic flow velocity values were 42.1 +/- 1.2 and 50.3 +/- 1.2, respectively (p = 0.049). CONCLUSIONS: The velocity of blood flow through the tricuspid valve during atrial systole is lower in growth-restricted twins than in appropriately grown cotwins when growth restriction is caused by uteroplacental insufficiency. Its potential in differentiating discordancy from the other causes remains to be explored.

Atrial Function, Right↗
PubMed1991

[Comparison of negative chronotropic action of nitrendipine, nifedipine and verapamil on the isolated right atrium of normotensive and renovascular hypertensive rats].

PURPOSE: To study the negative chronotropic effects of nitrendipine, nifedipine and verapamil in isolated right atria from normotensive and renovascular hypertensive rats. MATERIAL AND METHODS: Hypertension (medium arterial pressure, MAP = 154 +/- 4 mmHg) was induced by applying a silver clip to the left renal artery and right nephrectomy. Control rats (MAP = 109 +/- 2 mmHg) were submitted to right nephrectomy only. The animals were studied 2 weeks after surgery. Different preparations were used to obtain cumulative dose-response curves (0.01 microM to 100 microM) with each drug. RESULTS: No difference in "in vitro" initial sinusal rate of control (243 +/- 7 bpm) and hypertensive (245 +/- 5 bpm) rats was observed. The negative chronotropic response produced by calcium channel blockers was similar in normotensive and hypertensive groups. 2 microM verapamil, 4 microM nitrendipine or 20 microM nifedipine was necessary to produce a 50% decrease of the initial sinusal rate. CONCLUSION: Sensitivity of the sinusal pacemaker to calcium antagonists does not change in this model of hypertension. Moreover, the negative chronotropic effect of nitrendipine is stronger than nifedipine and weaker than verapamil.

Animals↗
PubMed1991

Study on the genesis of the double potential recorded in the high right atrium in atrial flutter and its role in the reentry circuit of atrial flutter.

To investigate the genesis of the double potential (DP), which is two separate waves, and its role in the reentry circuit of atrial flutter (AF), we performed overdrive pacing (ODP) from the high right atrium (HRA) in six cases of spontaneous AF in which the DP was recorded in the HRA. In four of the six cases, when the DP was arbitrarily designated D1 and D2, D1 and D2 showed progressive fusion during ODP. In addition, the D1 return cycle, immediately after the termination of ODP, corresponded to the AF cycle, and the D2 return cycle corresponded to the pacing cycle. This may indicate that the DP is caused by the collision of two directional waves. Furthermore, it is suggested that the HRA plays an important role in preventing a possible shortcutting of reentry waves and in stabilizing the reentry circuit of AF.

Action Potentials↗
PubMed1999

Regional differences in the recovery course of tachycardia-induced changes of atrial electrophysiological properties.

BACKGROUND: Regional differences in recovery of tachycardia-induced changes of atrial electrophysiological properties have not been well studied. METHODS AND RESULTS: In the control group (5 dogs), atrial effective refractory period (AERP) and inducibility of atrial fibrillation (AF) were assessed before and every 4 hours for 48 hours after complete atrioventricular junction (AVJ) ablation with 8-week VVI pacing. In experimental group 1 (15 dogs), AERP and inducibility of AF were assessed before and after complete AVJ ablation with 8-week rapid right atrial (RA) pacing (780 bpm) and VVI pacing. In experimental group 2 (7 dogs), AERP and inducibility of AF were assessed before and after 8-week rapid left atrial (LA) pacing and VVI pacing. AERP and inducibility and duration of AF were obtained from 7 epicardial sites. In the control group, atrial electrophysiological properties obtained immediately and during 48-hour measurements after pacing did not show any change. In the 2 experimental groups, recovery of atrial electrophysiological properties included a progressive recovery of AERP shortening, recovery of AERP maladaptation, and decrease of duration and episodes of reinduced AF. However, recovery of shortening and maladaptation of AERP and inducibility of AF was slower at the LA than at the RA and Bachmann's bundle. CONCLUSIONS: The LA had a slower recovery of tachycardia-induced changes of atrial electrophysiological properties, and this might play a critical role in initiation of AF.

Animals↗
PubMed2003

A model for in vivo validation of linear lesions in the right atrium.

UNLABELLED: Linear lesions have been proposed for treatment of complex atrial arrhythmias including atrial macroreentry tachycardia and compartmentalization in atrial fibrillation. AIM: To judge the effectiveness of a given lesion design, definite endpoints are necessary to ascertain the completeness of the line of block produced. METHODS AND RESULTS: We report validation criteria for long linear lesions in the right atrium in 42 pts, that combine both conventional and 3D mapping information (CARTO). Transferring from the validation of bi-directional block of the cavotricuspid isthmus line for atrial flutter, we validated 2 additional long linear lesions in the right atrium (anterior line and intercaval line). In addition to a complete isthmus line in all 42 pts, in 28 pts a complete anterior line was achieved and validated by both conventional and CARTO criteria. A complete intercaval line was deployed in 11 pts with complete anterior and isthmus lines (with a characteristic shift for the intercaval line) and in 5 pts without a complete anterior line (without characteristic shift). CONCLUSIONS: Conventional catheters placed at strategic locations on opposite sides of the intended ablation line, can depict a sudden characteristic change in the activation sequence. Using a combination of both techniques, deployment and validation of long linear lesion can be facilitated.

Action Potentials↗
PubMed1992

Alfentanil sedation for cardiac catheterization of children with Fontan shunts.

After Fontan operation, prolonged invasive cardiac assessment is often needed. This study is a clinical evaluation of the effectiveness of flunitrazepam premedication, EMLA cream, and alfentanil continuous infusion for management of children undergoing such catheterization. Fourteen consecutive subjects aged 5-20 yr with Fontan shunts (right atrium to pulmonary artery) undergoing elective haemodynamic and electrophysiological catheterization were sedated with an individually titrated alfentanil infusion. After oral premedication with flunitrazepam 2 mg, the mean induction dose and mean maintenance requirement of alfentanil were 4.4 +/- 2.7 micrograms.kg-1 and 10.3 +/- 8.6 micrograms.kg-1 x hr-1, respectively. Mean oxygen consumption during haemodynamic catheterization was 4.1 +/- 0.4 ml.kg-1 x min-1 with an average individual variation of 10%. For every patient, tranquil and stable conditions during catheterization could be produced. It is concluded that alfentanil infusion is a method of sedation of children and adolescents with Fontan shunts during haemodynamic and electrophysiologic catheterization. However, continuous monitoring of ventilation and an understanding of the slow circulation time after Fontan operation are essential with such sedation in these patients.

Adolescent↗
PubMed2000

Differences in organization between acute and chronic atrial fibrillation in dogs.

OBJECTIVES: The purpose of this study was to determine differences in acute and chronic atrial fibrillation (AF) "organization" in canine models. BACKGROUND: Electrophysiologic changes occur during atrial remodeling, but little is known about how remodeling affects AF organization. We hypothesized that atrial remodeling induced by long-term rapid atrial rates heterogeneously decreases AF organization. METHODS: In seven dogs, acute AF was induced by atrial burst pacing, and in eight dogs chronic AF was created by six weeks of continuous rapid atrial pacing. Atrial fibrillation was epicardially mapped from the right atria (RA) and left atria (LA). Atrial cycle length (CL), spatial organization and activation maps were compared. Spatial organization was quantified by an objective signal processing measure between multiple electrograms. RESULTS In acute AF, mean CL was slightly shorter in the LA (124 +/- 16 ms) than it was in the RA (131 +/- 14 ms) (p < 0.0001). In chronic AF, LA CL (96 +/- 14 ms) averaged 24 ms shorter than RA CL (121 +/- 18 ms) (p < 0.0001). Right atria and LA in acute AF had similar levels of organization. In chronic AF, the LA became approximately 25% more disorganized (p < 0.0001) while the RA did not change. In acute AF, a single broad wave front originating from the posterior and medial atrium dominated LA activation. In chronic AF, LA activation was more complex, sustaining multiple reentrant wavelets in the free wall and lateral appendage. CONCLUSIONS: Acute and chronic AF exhibit heterogeneous differences in CL, organization and activation patterns. The LA in chronic AF is faster and more disorganized than it is in acute AF. Differences in the models may be due to heterogeneous electrophysiologic remodeling and anatomic constraints. The design of future AF therapies may benefit by addressing the patient specific degree of atrial remodeling.

Acute Disease↗