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PubMed1986

Presynaptic regulation of cardiac sympathetic function in guinea pigs.

Cold stress (4 degrees C) induces a pressor response and variable increases in an index of sympathetic neural function, the rate constant of norepinephrine turnover, kNE. In heart, presynaptic cholinergic muscarinic and alpha-2 adrenergic influences may contribute to regional variation in responses of kNE to cold stress. Animals were pretreated with vehicle, a muscarinic cholinergic antagonist, quinuclidinyl benzilate (QNB), an alpha-2 adrenergic antagonist, yohimbine (YOH) or combined QNB + YOH. An increase in kNE was determined from incorporation of radiolabeled tyrosine into norepinephrine in a control period at 24 degrees C and again at 4 degrees C. The increment in kNE factored by the increment in blood pressure indicated the extent of increased sympathetic function in each cardiac region. In sino-atrial node, sympathetic function was increased significantly (P less than .05) by QNB + YOH compared to other treatments, suggesting that both cholinergic and alpha-2 adrenergic presynaptic influences were important. In contrast, in right and left ventricles, YOH or QNB + YOH, but not QNB alone, increased sympathetic function significantly, suggesting that only alpha-2 adrenergic influences were important. These data support the concept that presynaptic regulation of cardiac sympathetic function differs in sino-atrial node and ventricles of guinea pigs during activation with cold stress.

Animals↗
PubMed1985

Changes in the conductivity and in the functional refractory period of the atrioventricular node during hypoxia.

The experiments were carried out on preparations from rabbit right atrium, containing the sinoatrial node, the interatrial barrier, the atrioventricular node and the His-bundle. Surface electrodes were used to record the atrial and His-electrograms. The conduction time (AH-interval) was measured and the functional refractory period of the node was determined during normoxia (95% O2, 5% CO2) and hypoxia (30% O2, 65% N2 and 5% CO2) for 45 min. Hypoxia causes a considerable delay in conduction. This delay is greater for the shorter coupling-intervals and at the higher frequencies of the imposed rhythm. The shifting of the conduction times towards the higher values during hypoxia is not parallel compared with hypoxia. In the case of hypoxia the refractory curve of the A-V node is situated higher than the curve during normoxia, owing to the greater duration of the H1H2 intervals. The functional refractory period is increased and shifted toward the longer coupling-intervals. The results obtained show that during hypoxia the functional refractory properties of the atrioventricular node are impaired, which, combined with the delayed conduction through it, creates conditions for serious disturbances in the function of the atrioventricular conduction system.

Animals↗
PubMed1985

[Direct atriopulmonary anastomosis (modified Fontan) for single ventricle and its equivalents].

The modified Fontan procedure is being used in an increasing number of complex cyanotic cardiac lesions with pulmonary stenosis. Seven patients aged 11 to 24 years (average 17.5 years) underwent surgery by a technique derived from the Fontan procedure: direct atriopulmonary anastomosis without a tube or valve. The tricuspid valve when patent was closed with a patch. The diagnoses were: single ventricule (4 cases), Taussig-Bing anomaly (2 cases) and tricuspid atresia (1 case). All patients had associated pulmonary stenosis with low pulmonary vascular resistances. The great vessels were in L-malposition in 3 cases. The hospital mortality was nil. Transient atrial fibrillation was observed in 2 cases and was well tolerated clinically. The follow-up period ranges from 2 months to 4 years (average 2.3 years). All patients are acyanotic with no signs of right-sided failure and in sinus rhythm. Control cardiac catheterisation and angiography were performed in 6 cases and showed good function of the anastomosis and a mean atrial pressure of 14 mmHg. Direct atriopulmonary anastomosis offers a very acceptable surgical solution to certain forms of single ventricle or equivalent with low pulmonary pressures. The short and medium term results seem to be better than those of intraventricular repair.

Adolescent↗
PubMedDate not supplied

Biventricular long axis function after repair of tetralogy of Fallot.

Right ventricular restrictive physiology is common after repair of tetralogy of Fallot and relates to exercise performance and symptomatic arrhythmias. In this study, we examined biventricular long axis function in an attempt to clarify further the mechanical substrate of this phenomenon. We studied prospectively 95 patients with tetralogy of Fallot (age range 1-44.3 years) at a median of 4.3 years after repair with Doppler and M-mode echocardiography. Pulmonary arterial, tricuspid, and mitral Doppler spectrals and 2-D guided M-mode recordings of ventricular minor and long axes were obtained with simultaneous phonocardiogram and respirometer recordings. Right ventricular restriction was defined by the presence of antegrade pulmonary arterial flow during atrial systole throughout the respiratory cycle. Restrictive right ventricular physiology was demonstrated in 36 (39%) [group 1] of the 92 patients in whom the data were analyzed. Left ventricular function (FS, isovolumic relaxation time and transmitral E wave deceleration time) was not different in the two groups (p < 0.1, p < 0.6, and p < 0.8, respectively). The presence of antegrade diastolic flow shortened the pulmonary regurgitation in the restrictive group (PR duration/square root of RR 10.7 +/- 2.1 vs 12.1 +/- 2.1, p < 0.01). There was delayed onset of shortening (97.4 +/- 24 vs 88.8 +/- 24 ms, p = 0.01), and the amplitude of right atrioventricular ring excursion, corrected for body surface area, was significantly lower during atrial systole in the restrictive group (0.43 +/- 0.15 vs 0.54 +/- 0.2 cm/m2, p < 0.01). There was also a tendency toward a smaller ratio of right to left total atrioventricular ring excursion in the same group (1.14 +/- 0.19 vs 1.22 +/- 0.23, p = 0.1). Impaired long axis function in patients with restrictive right ventricular physiology following repair of tetralogy of Fallot is associated with abnormal diastolic filling and may contribute to the long-term cardioprotective effect of restrictive physiology by limiting the degree of right ventricular dilatation.

Adolescent↗
PubMed1993

Magnesium enhances function of postischaemic human myocardial tissue.

OBJECTIVES: The effect of Mg2+ on the developed force and concentrations of high energy phosphate metabolites in isolated human atrial trabeculae has been investigated. METHODS: Human atrial trabeculae, obtained from right atrial appendages of patients undergoing cardiac surgery requiring cardiopulmonary bypass, were dissected at room temperature in modified Krebs-Henseleit buffer containing 1.2 or 16 mM Mg2+, mounted on muscle stands, and rewarmed to 34 degrees C in the same buffer. After 30 minutes, their mechanical function was assessed. At the end of the protocol, trabeculae were fast frozen for measurement of concentrations of metabolites of high energy phosphates. RESULTS: Trabeculae collected and rewarmed in 16 mM Mg2+ Krebs-Henseleit buffer showed significantly higher mean developed force (0.59(SEM 0.10) g, p < 0.01) than those rewarmed in 1.2 mM Mg2+ Krebs-Henseleit buffer (0.32(0.03) g). Trabeculae that had a developed force > or = 0.8 g, a resting force < or = 0.7 g, and a cross sectional area < or = 1 mm2 ("functional" trabeculae) were selected for further comparison. New reverse phase high performance liquid chromatography techniques developed for the analysis of small samples (0.5-5 mg dry weight) were used to measure nucleotide, nucleoside, and creatine compounds. Total adenylate (ATP+ADP+AMP) concentrations in trabeculae revived in the presence of 16 mM Mg2+ (15.4(1.1) mumol.g-1 dry weight) were significantly higher (p < 0.01) than in those revived with 1.2 mM Mg2+ (11.8(1.0) mumol.g-1), but lower (p < 0.01) than in trabeculae fast frozen immediately after removal from the patient (22.6(1.0) mumol.g-1). There were no significant differences in NAD and total creatine (phosphocreatine+creatine) concentrations between the three groups. CONCLUSIONS: The presence of high Mg2+ during the rewarming of human atrial trabecular preparations maintains a significantly higher developed force and a significantly higher total adenylate pool than does collection and rewarming with normal concentrations of Mg2+.

Aged↗
PubMed2003

Global right atrial mapping delineates double posterior lines of block in patients with typical atrial flutter: a study using a three dimensional noncontact mapping system.

UNLABELLED: Double Posterior Lines of Block in Typical Atrial Flutter. INTRODUCTION: The crista terminalis (CT) has been shown to be a barrier to transverse conduction during typical atrial flutter (AFL). However, some studies have demonstrated the presence of functional block in the sinus venosa region but not at the CT. The aim of this study was to define these regions of block in the right atrium using a three-dimensional noncontact mapping system. METHODS AND RESULTS: In 39 AFL patients (33 men and six women, mean age 56 +/- 13 years), a noncontact multielectrode array was used to reconstruct electrograms in the right atrium. Isochronal and isopotential propagation mapping was performed during AFL and during pacing from the coronary sinus ostium and the low lateral wall (cycle length from 600 to 240 msec) in sinus rhythm after creation of isthmus block. A single line of block along the CT area was found in 18 patients (46%). Two lines of block were found in 21 patients (54%), with the first line located along the CT area. The second was located in the sinus venosa region in 20 patients (51%) and in the lateral wall in 1 patient (3%). In all patients, the block in the lower part of the CT was observed during AFL (60%) and during pacing at all cycle lengths (48%-62%). The length and proportion of block were inversely proportional to pacing cycle length. CONCLUSION: Double lines of block were frequently observed in patients with AFL, and both lines may form the posterior boundaries of the AFL circuit. Block was fixed in the lower part of the CT and was functional in the upper part of the CT.

Atrial Flutter↗
PubMed1976

Bipolar catheter electrograms for study of retrograde atrial activation pattern in patients without pre-excitation syndromes.

The sequence of retrograde atrial activation of premature ventricular beats was studied in 12 patients without pre-excitation syndrome. Forward and retrograde AV nodal conduction times were within normal limits. The septal low right atrial (LRA2) deflection was inscribed 25 to 55 ms (ave: 37.9 ms) before the low left atrial (LLA2) electrogram and 35 to 75 ms (ave: 53.7 ms) ahead of the high right atrial (HRA2) deflection. LLA2 preceded HRA2 in 8 patients, more or less coincided with HRA2 in 3 cases, and was inscribed 10 ms ahead in 1 patient. In all cases a decrease in the coupling (St1-St2) interval resulted in a proportional increase of the septal LRA1-LRA2, LLA1-LLA2, and HRA1-HRA2 intervals. Atrial echoes occurring in 3 cases had a sequence of arrival of excitation at the recording sites which was similar to the ones shown by the same patients during ventricular pacing. This is in keeping with the existence of an upper common pathway located above the area where functional longitudinal dissociation occurred. Thus, it is concluded that impulses emerging from the AV node in a retrograde direction reach the septal low right atrium before they activate the explored low left atrial sites, regardless as to whether they arise in the ventricles or in the atria.

Arrhythmias, Cardiac↗
PubMed1990

Atrial enlargement as a consequence of atrial fibrillation. A prospective echocardiographic study.

To test the hypothesis that atrial enlargement can develop as a consequence of atrial fibrillation, left and right atrial dimensions were measured echocardiographically at two different time points in patients with atrial fibrillation. Patients were selected who initially had normal atrial sizes and who had no evidence of significant structural or functional cardiac abnormalities other than atrial fibrillation either by history or two-dimensional and Doppler echocardiography. Fifteen patients were studied (12 men and three women; mean age, 67.3 years). Average time between studies was 20.6 months. Three orthogonal left atrial dimensions and two right atrial dimensions were measured, and all were found to increase significantly between studies. Also, highly significant increases in calculated left atrial volume (from 45.2 to 64.1 cm3, p less than 0.001) and right atrial volume (from 49.2 to 66.2 cm3, p less than 0.001) were observed. The relative extents of left and right atrial volume increase did not differ, and left ventricular size did not change significantly between studies. These results indicate that atrial enlargement can occur as a consequence of atrial fibrillation. The maintenance of sinus rhythm, therefore, may prevent atrial enlargement and its adverse clinical effects.

Aged↗
PubMed2003

Beta-adrenoceptor activation plays a role in the reverse rate-dependency of effective refractory period lengthening by dofetilide in the guinea-pig atrium, in vitro.

1. Blockers of the rapid component of the delayed rectifier potassium current (I(Kr)) prolong cardiac action potential duration (APD) and effective refractory period (ERP) in a reverse rate-dependent manner. Since activation of beta-adrenoceptors attenuates prolongation of APD evoked by I(Kr) blockers, rate-dependent neuronal noradrenaline liberation in the myocardium may contribute to the reverse rate-dependent nature of the effects of I(Kr) blockers. In order to test this hypothesis, we studied the effects of dofetilide, a pure I(Kr) blocker, on ERP after activation or blockade of beta-adrenoceptors and after catecholamine depletion in guinea-pig left atrial myocardium paced at 3, 2 and 1 Hz, in vitro. 2. Dofetilide (100 nM) lengthened ERP in a reverse rate-dependent manner in the left atrial myocardium of guinea-pigs. Strong activation of beta-adrenoceptors using 10 nM isoproterenol abolished the dofetilide-induced lengthening of ERP at all pacing rates. 3. Blockade of the beta-adrenoceptors with metoprolol (1 micro M), atenolol (3 micro M) or propranolol (300 nM) increased the dofetilide-evoked prolongation of ERP at 3 and 2 Hz, but not at 1 Hz. As a consequence, metoprolol attenuated while propranolol and atenolol fully eliminated the reverse rate-dependent nature of the dofetilide-induced ERP lengthening. In catecholamine-depleted atrial preparations of the guinea-pig (24 h pretreatment with 5 mg kg(-1) reserpine i.p.), the effect of dofetilide on ERP was not frequency dependent, and propranolol did not alter the effects of dofetilide. 4. In contrast to results obtained in guinea-pig atrial preparations, propranolol failed to change the reverse rate-dependent effect of dofetilide on ERP in the right ventricular papillary muscles of rabbits and guinea-pigs. 5. As an indication of the functional consequences of rate-dependent noradrenaline liberation, propranolol decreased twitch tension at 3 and 2 Hz but not at 1 Hz in the atrial myocardium of control guinea-pigs, whereas no such effect was detected in catecholamine-depleted atrial preparations. Propranolol failed to change contractility of ventricular myocardium in guinea-pigs and rabbits. 6. It is concluded that rate-dependent noradrenaline release and the ensuing beta-adrenoceptor activation contributed to the reverse rate-dependent nature of ERP prolongation caused by I(Kr) blockers in isolated guinea-pig atrial myocardium.

Adrenergic beta-Antagonists↗
PubMed2000

Congestive heart failure treated by the upgrade from VVI to DDD pacing.

The case is presented of an elderly woman with normal left ventricular (LV) systolic function and VVI pacing complicated by severe congestive heart failure. The symptoms and findings of congestive heart failure became refractory to medical treatment and resolved with the upgrade of the VVI to a DDD system. Right heart catheterization during VVI pacing showed increased mean pulmonary capillary wedge and right atrial pressures both being normalized under DDD pacing. This case report illustrates the need to consider permanent physiological pacing in elderly patients, even in presence of normal LV systolic function, to ensure AV synchrony when the atrium can be paced, since diastolic LV dysfunction is quite common in these subjects.

Aged↗
PubMed1985

Effect of site of pacing on dispersion of refractoriness.

The variation in dispersion of ventricular refractoriness with different sites of pacing was measured in 11 patients not taking antiarrhythmic drugs. Dispersion of refractoriness between 3 right ventricular sites was determined at constant paced cycle lengths (S1S1). Refractoriness to ventricular extrastimulation (S2) using atrial pacing vs "clinical" pacing (drive or S1 at the right ventricular apex) vs the conventional measurement of dispersion (S1 at the site of S2) was compared. Effective and functional refractory periods (ERP and FRP) were measured from electrograms at the site of application of S2. Dispersion of ERP was always wider using clinical pacing (65.4 +/- 26 ms [+/- standard deviation]) than atrial pacing or traditional drive (20.4 +/- 14 and 19.1 +/- 10 ms, p less than 0.0001). Similarly, dispersion of FRP was greater with clinical pacing (45.0 +/- 35 vs 21.8 +/- 14 and 17.3 +/- 13, p less than 0.011). In 2 patients with left bundle branch block these differences were most striking. Clinical pacing foreshortened FRP relative to ERP (FRP shorter than ERP by an average 12.5 ms at nonapical sites) but this did not induce tachycardias, perhaps because FRP was still longer than the shortest V1V2 achieved conventionally (FRP was longer at nonapical sites than at the apex using clinical pacing, p less than 0.05). With atrial pacing there is less dispersion of refractoriness than with clinical ventricular pacing, although this difference is not appreciated when dispersion is measured in the conventional manner.

Arrhythmias, Cardiac↗
PubMed1991

[Quantitative analysis of systolic function of the right ventricule by Doppler echocardiography].

The recording of the velocity of tricuspid valve regurgitation by continuous wave Doppler enables the calculation of the instantaneous systolic pressure gradient between the right ventricle and right atrium. As right atrial pressure is relatively constant, the rate of acceleration of the regurgitant jet reflects the quality of the rise in pressure in the right ventricle in early diastole, and therefore right ventricular contractility. The authors studied 3 Doppler parameters of the rate of velocity increase of the tricuspid regurgitation; the maximum rate of acceleration (dV/dt max), the maximum derivative of the pressure (dP/dt max) and the mean rate of increase in pressure (T). The interobserver variability of these indices is low (r greater than 0.96); reproducibility is good in patients with sinus rhythm but mediocre in atrial fibrillation. The comparison of the Doppler indices with the right ventricular isotopic fraction in 26 patients with tricuspid regurgitation showed a good correlation (dV/dt max, r = 0.79, p less than 0.0001; dP/dt max, r = 0.69, p less than 0.0001; T, r = 0.60, p = 0.0012). These results show that right ventricular systolic function can be evaluated by continuous wave cardiac Doppler by recording the spectral envelope of tricuspid regurgitation.

Aged↗
PubMed2000

Hemodynamic effects of iodixanol and iohexol during ventriculography in patients with compromised left ventricular function.

A crossover study was performed to compare the hemodynamic effects of the iso-osmolar contrast agent iodixanol (Visipaque) 320 mg I/ml to those of the low-osmolar iohexol (Omnipaque) 350 mg I/ml. The main hypothesis was that iodixanol and iohexol would affect left ventricular end-diastolic pressure (LVEDP) to different degrees. In 48 patients with reduced cardiac function (mean ejection fraction 33. 4%), one ventricular injection was performed with each contrast medium. Ventricular, aortic and right atrial pressures and heart rate were measured continuously. Cardiac output (using Fick's principle) and systemic vascular resistance were calculated. LVEDP increased with both agents, but significantly less after iodixanol than after iohexol (P < 0.01), also in subgroups of patients in whom baseline LVEDP was severely increased and in whom 3-vessel disease was present. Immediate changes in variables reflecting vasodilatation were similar with both agents. In conclusion, both contrast agents influenced hemodynamics during ventriculography, but iodixanol had significantly less influence on LVEDP than did iohexol.

Adult↗
PubMed1992

A 5-HT4-like receptor in human left atrium.

The effects of 5-hydroxytryptamine (5-HT) on left atrial preparations obtained from 5 patients with terminal heart failure who were undergoing heart transplant surgery were investigated. The preparations were paced under isometric conditions. In the presence of (-)-pindolol 1 mumol/l (to block beta-adrenoceptors) and cocaine 6 mumol/l (to block tissue uptake of 5-HT) 5-HT increased contractile force with a pEC50 of 7.0. The maximum effect of 5-HT amounted to 24.5% of that caused by a maximally effective concentration of (-)-isoprenaline (200 mumol/l) and 25% of that caused by 6.75 mmol/l CaCl2. The effects of 5-HT were competitively antagonised by 3 alpha-tropanyl-1H-indole-3-carboxylate (ICS 205-930) with a pKB of 6.8. The effects of 5-HT on cyclic AMP levels and cyclic AMP-dependent protein kinase activity were also studied using left atrial tissues from one of the patients; 5-HT increased the cyclic AMP content and stimulated the kinase. The results are consistent with the existence of a human left atrial 5-HT receptor which is similar to the recently identified human right atrial 5-HT receptor that resembles the 5-HT4 receptor. The left atrial 5-HT4-like receptor is functional in tissues obtained from patients with terminal heart failure.

Adult↗
PubMed2005

Transposition of the great arteries: long-term outcome and current management.

There is a large group of young adults who survived atrial baffle repair of transposition of the great arteries. Most survivors are asymptomatic, although nearly all have decreased exercise capacity. Loss of sinus rhythm and atrial arrhythmias are common and increase with age. There is concern about the ability of the right ventricle to function long term as a systemic pump, and recent publications have highlighted right ventricular dysfunction in this patient population. Sudden death and congestive heart failure are the main causes of death, and outcomes beyond 30 years are unknown. Pulmonary artery banding, late arterial switch, and cardiac transplantation are employed when intractable arrhythmias or right ventricular failure threaten survival or quality of life.

Adult↗
PubMed1988

Increased circulating atrial natriuretic factor (ANF) release during induced ventricular tachycardia.

During sustained ventricular tachycardia (VT), there is usually a rise in mean atrial pressure. Atrial natriuretic factor (ANF) is a peptide released by the atria in response to increased atrial pressure or distension. ANF causes arterial vasodilation and natriuresis in man, and may contribute to the polyuria noted during tachycardia. We hypothesized that induction of sustained VT would cause elevation of right atrial pressure and lead to increased release of ANF. We measured mean arterial pressure, right atrial pressure, VT cycle length, atrial cycle length, plasma norepinephrine, and central ANF in 11 patients during 20 episodes of VT. The mean cycle length of induced tachycardia was 335 +/- 15 msec, with a mean atrial cycle length of 547 +/- 43 msec. Baseline plasma ANF was 70 +/- 11 femtomoles per milliliter and increased to 133 +/- 22 fmol/ml (p less than 0.001) after 4 minutes of VT. There was a decrease in mean arterial pressure from 87 +/- 3 to 66 +/- 3 mm Hg, and a rise in mean right atrial pressure from 4.0 +/- 0.8 to 11 +/- 1 mm Hg (p less than 0.001). The change in plasma ANF was quite variable among individual patients and was correlated with changes in mean right atrial pressure but poorly correlated with changes in mean arterial pressure, plasma norepinephrine, and atrial cycle length. Our data demonstrate that significant increased in ANF levels occur during sustained VT and are associated with increased right atrial pressure.

Atrial Function↗