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PubMed2001

Properties and substrate of slow pathway exposed with a compact node targeted fast pathway ablation in rabbit atrioventricular node.

INTRODUCTION: The properties and substrates of slow and fast AV nodal pathway remain unclear. This applies particularly to the slow pathway (SP), which is largely concealed by fast pathway (FP) conduction. We designed a new FP ablation approach that exposes the SP over the entire cycle length range and allows for its independent characterization and ablation. METHODS AND RESULTS: Premature stimulation was performed before and after FP ablation with 5.4 +/- 1.9 lesions (300-microm diameter each; overall lesion size 1.4 +/- 0.5 mm) targeting the junction between perinodal and compact node tissues in seven rabbit heart preparations. The resulting SP recovery curve and control curve had the same maximum nodal conduction time (165 +/- 22 msec vs 164 +/- 24 msec; P = NS) and effective refractory period (101 +/- 10 msec vs 100 +/- 9 msec; P = NS). The two curves covered the same cycle length range. However, the SP curve was shifted up with respect to control one at intermediate and long cycle lengths and thus showed a longer minimum nodal conduction time (81 +/- 15 msec vs 66 +/- 10 msec; P < 0.01) and functional refractory period (180 +/- 11 msec vs 170 +/- 12 msec; P < 0.05). The SP curve was continuous and closely fitted by a single exponential function. Small local lesions (2 +/- 1) applied to the posterior nodal extension resulted in third-degree nodal block in all preparations. CONCLUSION: The posterior nodal extension can sustain effective atrial-His conduction at all cycle lengths and account for both the manifest and concealed portion of SP. Slow and FP conduction primarily arise from the posterior extension and compact node, respectively.

Animals↗
PubMed1987

Atrioventricular nodal activation during periodic premature stimulation of the atrium.

To study the intranodal origin of the functional properties of the atrioventricular node, progressive changes in nodal cell activation time and cycle length occurring during complete sequences of periodic premature stimulation of the atrium were determined for 419 nodal cells recorded in 11 isolated rabbit heart preparations. The conduction time in proximal nodal cells including the N cells increased only at very short coupling intervals. Conduction time in the distal node (NH and H cells) first increased and then decreased with increasing prematurity. The major fraction of the basic and premature delays developed between N and NH cell activation, a period devoid of upstrokes. The effective and functional refractory periods were related to the minimum intervals between successive upstrokes at the node entrance and outlet, respectively. These results suggest that the cycle-length dependency of nodal conduction is the result of complex changes in propagation time occurring at three levels in the node, whereas the effective and functional refractory periods reflect reactivation limits of cells located at the node entrance and outlet, respectively.

Action Potentials↗
PubMed2006

Radiofrequency ablation of swallowing-induced atrial tachycardia: case report and review of literature.

We report the case of a 47-year-old white man who presented with 1-year history of palpitations while swallowing. Event monitor confirmed the episodes were atrial tachycardia. Medical management with a calcium channel blocker did not alleviate the patient's symptoms. Gastrointestinal endoscopy did not reveal any abnormality. Electrophysiologic study was performed to identify and map the tachycardia. Swallowing during the procedure was used to repeatedly induce the tachycardia. A focal right atrial tachycardia that was mapped to the lower posterior right atrium was successfully ablated. Follow-up at 6 months and 1 year showed complete resolution of symptoms. An in-depth review of the literature and all published case reports of swallowing-induced atrial tachycardia is presented, and possible mechanisms of this rare form of tachycardia are discussed.

Atrial Function↗
PubMed1991

Differentiation of arrhythmias by measurement of intracardiac pressures in man.

Antitachycardia devices currently use sustained high rate, abrupt changes in cycle length, and probability density function to determine the onset of ventricular tachycardia. Hemodynamic changes occur with the onset of tachycardia and may provide a method of discriminating supraventricular from ventricular tachycardia. In this study, patients had atrial and ventricular pressures measured during rapid atrial and ventricular pacing. Right atrial pressure increased significantly with ventricular pacing but not with atrial pacing. Right ventricular pressures did not significantly differ with atrial or ventricular pacing. The change in atrial pressure compared to baseline was greater, with ventricular pacing compared to atrial pacing. Right ventricular pressure increased compared to baseline with atrial or ventricular pacing, but there was no significant difference between pacing modalities. Measurement of right atrial pressure might prove useful in discriminating supraventricular from ventricular tachycardia.

Atrial Function, Right↗
PubMed1993

Adenosine induced intraatrial block.

Adenosine, an endogenous nucleoside with potent negative chronotropic and dromotropic effects on the sinus and AV nodes, is thought to have little if any antiarrhythmic effect on normal atrial tissue. However, there may be an electrophysiological basis for an adenosine effect on atrial tissue with atypical conduction properties. We examined the electrophysiological effects of adenosine in a patient with decremental atrial conduction properties. During incremental pacing from the high right atrium there was gradual prolongation of the intraatrial interval between the high right atrium and the low septal atrium, from 180 to 280 msec, until 2:1 intraatrial block occurred at a pacing cycle length of 280 msec. Adenosine (6 mg IV) resulted in transient intraatrial block followed by prolonged intraatrial conduction during high right atrial pacing at a cycle length of 400 msec. Thus, similar to its effects on the AV node and decremental AV accessory pathways, adenosine may also slow and abolish conduction in decremental atrial issue, an effect that is likely attributed to adenosine induced hyperpolarizing K+ current in partially depolarized atrial tissue.

Adenosine↗
PubMed2002

Anisotropic conduction properties in canine atria analyzed by high-resolution optical mapping: preferential direction of conduction block changes from longitudinal to transverse with increasing age.

BACKGROUND: Anisotropic conduction properties may provide a substrate for reentrant arrhythmias. We investigated the age-dependent changes of structural and functional anisotropy in isolated right atria from infant (1 to 2 months), young (6 to 12 months), and old (6 to 10 years) dogs. METHODS AND RESULTS: The histology of the mapped atrial tissues (a small subepicardial area, 2.8x4.2 mm) was characterized by an age-dependent increase of myofiber width and fat cell infiltration between myofibers. Cx43 was distributed homogeneously over the entire cell surface in infant dogs, whereas it progressively polarized to the cell termini with increasing age. The activation sequences were analyzed by high-resolution optical mapping using a voltage-sensitive dye. Activation fronts from the pacing site proceeded more rapidly along fiber orientation (longitudinal) than across it (transverse). Infant dogs showed "elliptical" isochrones with a smooth transition between longitudinal and transverse propagation, whereas old dogs had a "square" pattern with a sharp transition. Conduction block occurred predominantly during longitudinal propagation in infant dogs but during transverse propagation in old dogs. The shape of the wave front and the degree of lateral uncoupling seemed to decide the preferential direction of block. A zigzag activation causing an extremely slow transverse conduction was observed only in old dogs. CONCLUSIONS: Along with the age-dependent structural anisotropy, the preferential direction of block changed from longitudinal to transverse in association with a change in the wave front configuration. A zigzag propagation based on lateral uncoupling would predispose the elderly to multiple reentry and a higher incidence of atrial fibrillation.

Action Potentials↗
PubMed1995

Selection of patients for transesophageal echocardiography after stroke and systemic embolic events. Role of transthoracic echocardiography.

BACKGROUND AND PURPOSE: This study examined whether patients suffering from stroke and other systemic embolic events may be selected for transesophageal echocardiography on the basis of clinical and transthoracic echocardiographic findings. METHODS: We performed transthoracic and transesophageal echocardiography on 824 patients after stroke and other suspected embolic events. Patients were classified into group A if they were in sinus rhythm and had a normal transthoracic echocardiogram. Group B consisted of all other patients. Transesophageal echocardiographic findings of left atrial spontaneous contrast, left atrial thrombus, complex aortic atheroma, and interatrial septal anomalies were correlated with clinical and transthoracic echocardiographic results. RESULTS: Transesophageal echocardiography detected at least one potential source of embolism in 399 patients (49%): spontaneous contrast in 214 patients (26%), left atrial thrombus in 54 (7%), complex atheroma in 111 (13%), and interatrial septal anomalies in 126 (15%). In group A (n = 236), only 3 (1%) had spontaneous contrast, 11 (4.6%) had complex atheroma, and none had left atrial thrombus. In group B (n = 588), 211 patients (36%, P < .001) had spontaneous contrast, 54 (9.2%, P < .001) had atrial thrombus, and 100 (17%, P < .001) had complex atheroma. Interatrial septal anomalies were detected in similar proportions of patients (18% in group A versus 14% in group B). Left atrial spontaneous echo contrast, thrombus, and complex atheroma were significantly more prevalent in older patients, but interatrial septal anomalies were more prevalent in younger patients irrespective of transthoracic echocardiographic findings. Multivariate analysis identified both an abnormal transthoracic echocardiogram and patient age to be independent predictors of transesophageal echocardiographic findings of left atrial spontaneous echo contrast, left atrial thrombus, or complex atheroma. CONCLUSIONS: Transesophageal echocardiography has a low yield for left atrial spontaneous contrast, left atrial thrombus, or complex aortic atheroma in patients with normal transthoracic echocardiogram and sinus rhythm and in younger patients. Interatrial septal anomalies are more prevalent in younger patients. Transthoracic echocardiogram should be performed in patients after stroke or systemic embolic events as a noninvasive screening tool. We recommend transesophageal echocardiogram for patients with abnormal transthoracic echocardiogram and in younger patients when the finding of a patent foramen ovale may contribute to patient management.

Age Factors↗
PubMed1987

Graphic analysis of serotonin effects in dog heart-lung preparation.

Graphical analysis of the effects of serotonin on cardiac function and pulmonary circulation was performed, using the dog heart-lung preparation. The equilibrium points, at which the cardiac output (CO)-curve and venous return (VR)-curve cross in the right atrial pressure (RAP) or left atrial pressure (LAP)-CO relations, were directly recorded on two X-Y recorders. CO- and VR-curves were directly depicted by changing the blood level in the reservoir, and by inducing ventricular fibrillation and simultaneously occluding pulmonary arterial trunk, respectively. Single injections of serotonin, 300 micrograms, into the right or left atrium, induced a negative inotropic response. Low rate (less than 30 micrograms/min) of infusion of serotonin had no effect on the CO-curve or on the slope-gradient of VR-curve in the LAP-CO relation. At a rate of 60 or 120 micrograms/min, however, the CO-curve was moved downwards to the right, indicating a negative inotropic effect. Pulmonary mean filling pressure increased and the slope-gradient of pulmonary VR-curve decreased, indicating an increased resistance to venous return from the pulmonary circulation. Pulmonary arterial pressure was markedly elevated. In order to obtain the capacitance ratio between the extracorporeal circuit and the pulmonary circulation, a shift of blood volume to the pulmonary circulation was induced by elevating the aortic pressure, which also decreased the slope-gradient. The calculated capacitance ratio became greater during the infusion of serotonin, indicating that the capacitance in the pulmonary circulation was lowered. It is likely that serotonin has contractile effects on the pulmonary arterial and venous vascular beds, elevating the pulmonary filling pressure and resistance to venous return.

Animals↗
PubMed1976

Hemodynamic evaluation of Fontan operation in tricuspid atresia.

Six patients underwent hemodynamic studies at 2 to 34 months (mean 15 months) following a modified Fontan operation. Only one patient had a valve at the inferior vena cava (IVC)-right atrium (RA) junction. Average age at surgery was 12 years (range 5-26 years). Three patients were catheterized twice. Postoperative studies showed four patients to be in sinus rhythm and two in junctional rhythm. Two patients had a RA-left pulmonary artery (LPA) gradient across the conduit of 1.5-10 mm Hg. The RA pressure was elevated an average of 17 mm Hg (10-34). All patients showed good atrial transport function regardless of their rhythm. The average arterial saturation was 92% (87%-97%), which was an improvement of 13% over preoperative values. Residual hypoxemia was due to pulmonary vein desaturation and to atrial right-to-left shunting early after surgery and to atrial right-to-left shunt alone, later. Death followed re-operation for removal of the porcine valves in the patient with two valves inserted. Macroscopically, both valves were found to have fibrous tissue ingrowth that had fixed them in a semi-open position.

Adult↗
PubMed1995

Role of age on transmitral flow velocity patterns in assessing left ventricular diastolic function in normal infants and children.

This study demonstrated that both peak E and flow velocity integral of early diastole increased to reach the older children's values by 36 months of age and leveled off thereafter, whereas both peak A and flow velocity integral of atrial contraction had little change. These results suggest that age-related changes in E wave reflect the maturational or developmental alterations in LV diastolic properties, especially in the relaxation process.

Adolescent↗
PubMed2000

Plasma renin activities, angiotensin II concentrations, atrial natriuretic peptide concentrations and cardiopulmonary function values in dogs with severe heartworm disease.

Relationships among plasma renin activities (PRA), plasma angiotensin II (ATII) concentrations, atrial natriuretic peptide (ANP) concentrations and cardiopulmonary function values were examined in dogs with ascitic pulmonary heartworm disease and acute- and chronic-vena caval syndrome (CS). PRA, plasma ATII concentration and plasma ANP concentration tended to be higher or were significantly higher in dogs with ascites, acute- and chronic-CS. PRA correlated significantly with plasma ATII concentration, WBC count, ALP activity, plasma concentrations of urea nitrogen, creatinine, sodium, potassium, and chloride, right ventricular endodiastolic pressure and right atrial pressure. Plasma ATII concentration correlated significantly with WBC count, plasma concentrations of urea nitrogen, sodium, and potassium, right ventricular endodiastolic pressure and right atrial pressure. Plasma ANP concentration did not correlate with PRA or ATII concentration, but correlated significantly only with pulmonary arterial pressure.

Angiotensin II↗
PubMed1992

Epicardial sites for vagal mediation of sinoatrial function.

The posterior atrial fat pad (PAFP) has been described as the probable anatomic location of parasympathetic ganglia mediating sinoatrial (SAN) and atrioventricular nodal function in the mammalian heart. This contrasts with recent localizations of such control elements in the pulmonary vein fat pad (PVFP) and in fatty tissues overlying the junction of inferior vena cava-inferior left atrium (IVC-ILA), respectively. Short bursts (5-8 pulses/burst, 3 bursts/train) of electrical current (1-16 Hz, 400 ms, 1-5 mA) applied directly to the ventral right atrial epicardium via a concentric bipolar electrode (separation 0.3-0.6 mm) during the atrial muscle refractory period, activated subepicardial postganglionic pathways from PVFP and entering the SAN; identical stimulation of dorsal right atrial epicardium between PAFP and SAN excited few or no fiber pathways controlling SAN discharge rate or patterns. In a second series of experiments, injection of a neuronal marker (Fast Blue) into and around SAN, with time (5-10 days) allowed for retrograde transport, resulted in staining of many soma in PVFP but none in IVC-ILA or PAFP. These data strongly affirm the primary, and perhaps exclusive, localization of ganglia that mediate parasympathetic regulation of SAN function in PVFP of the dog's heart, with little or no such participation by ganglia within PAFP or IVC-ILA.

Adipose Tissue↗
PubMed1990

Central effects of atrial natriuretic peptide on plasma catecholamines, vasopressin, renin and beta-endorphin and on renal excretory functions in the dog.

Atrial natriuretic peptide (ANP) has been identified in the central nervous system and its participation in regulation of various regulatory brain functions has been postulated. To elucidate whether central ANP influences endocrine systems related to blood pressure regulation and renal excretory functions, effects of infusion of ANP at a rate of 120 ng.min-1 into the third cerebral ventricle on plasma level of epinephrine (E), norepinephrine (NE), renin, vasopressin and beta-endorphin as well as on excretion of urine, sodium, potassium (UKV) solutes and free water (CH2O) were investigated in conscious dogs. Significant decrease of plasma E from 77.6 +/- 7.0 to 62.1 +/- 4.8 pg.ml-1 and of NE from 345.5 +/- 20.7 to 286.4 +/- 15.0 pg.ml-1 was found at the end of 30 min lasting ANP infusion. Significant elevation of PRA and UKV and a decrease in CH2O were found 60 min after ANP infusion. No significant changes in other variables were found. In time control experiments plasma hormones concentration and renal excretory functions were not significantly influenced. The results suggest that central ANP may affect the sympatho-adrenal outflow.

Animals↗