Ventricular rate control during atrial fibrillation by cardiac parasympathetic nerve stimulation: a transvenous approach. (9/450)

OBJECTIVES: To identify intravascular sites for continuous, stable parasympathetic stimulation (PS) in order to control the ventricular rate during atrial fibrillation (AF). BACKGROUND: Ventricular rate control during AF in patients with congestive heart failure is a significant clinical problem because many drugs that slow the ventricular rate may depress ventricular function and cause hypotension. Parasympathetic stimulation can exert negative dromotropic effects without significantly affecting the ventricles. METHODS: In 22 dogs, PS was performed using rectangular stimuli (0.05 ms duration, 20 Hz) delivered through a catheter with an expandable electrode-basket at its end. The catheter was positioned either in the superior vena cava (SVC, n = 6), coronary sinus (CS, n = 10) or right pulmonary artery (RPA, n = 6). The basket was then expanded to obtain long-term catheter stability. Atrial fibrillation was induced and maintained by rapid atrial pacing. RESULTS: Nonfluoroscopic (SVC) and fluoroscopic (CS/RPA) identification of effective intravascular PS sites was achieved within 3 to 10 min. The ventricular rate slowing effect during AF started and ceased immediately after on-offset of PS, respectively, and could be maintained over 20 h. In the SVC, at least a 50% increase of ventricular rate (R-R) intervals occurred at 22 +/- 11 V (331 +/- 139 ms to 653 +/- 286 ms, p < 0.001), in the CS at 16 +/- 10 V (312 +/- 102 ms vs. 561 +/- 172 ms, p < 0.001) and in the RPA at 18 +/- 7 V (307 +/- 62 ms to 681 +/- 151 ms, p < 0.001). Parasympathetic stimulation did not change ventricular refractory periods. CONCLUSIONS: Intravascular PS results in a significant ventricular rate slowing during AF in dogs. This may be beneficial in patients with AF and rapid ventricular response since many drugs that decrease atrioventricular conduction have negative inotropic effects which could worsen concomitant congestive heart failure.  (+info)

Pulmonary vein morphology in patients with paroxysmal atrial fibrillation initiated by ectopic beats originating from the pulmonary veins: implications for catheter ablation. (10/450)

BACKGROUND: Successful ablation of ectopic beats originating from the pulmonary veins (PV) could eliminate paroxysmal atrial fibrillation (PAF). However, information about the structure of the PV in patients with PAF that is initiated by PV ectopic beats has not been reported. METHODS AND RESULTS: We studied the morphology of the PVs and measured their diameters in 3 groups of patients. Group I included 52 patients (aged 66+/-14 years; 44 men) with focal atrial fibrillation (AF) from the PVs. Group II included 8 patients (aged 50+/-10 years; 3 men) with focal AF from the superior vena cava or cristal terminalis. Group III included 23 control patients (aged 55+/-16 years; 17 men). Of the control patients, 11 had AV node and 12 had AV reentrant tachycardia. After an atrial transseptal procedure, selective PV angiography using a biplane system with a right anterior oblique view of 30 degrees, a left anterior oblique view of 60 degrees, and a cranial angle of 20 degrees was performed. The ostial and proximal portions of the right and left superior PVs (RSPV and LSPV) were significantly dilated in group I patients compared with those in groups II and III. Furthermore, the ostia of the RSPV and LSPV were significantly dilated in group II compared with group III patients. However, the mean diameters of the inferior PVs were similar between the 3 groups. Comparisons of the individual PV diameters among the 3 subgroups of group I (which was divided according to where the ectopic focus was located) showed nonselective dilatation of the PV. CONCLUSIONS: Nonspecific dilatation of the ostia and proximal portion of superior PVs were found in patients with PAF initiated by ectopic beats from the superior PVs.  (+info)

Electrogram characteristics indicative of a recurrent conduction site after ablation of the inferior vena cava-tricuspid annulus isthmus: a study in the canine blood-perfused atrioventricular preparation. (11/450)

Analysis of the electrograms recorded along the ablation line can identify a recurrent conduction site after ablation of the isthmus between the inferior vena cava (IVC) and tricuspid annulus (TA) for atrial flutter. The present study examined the relationship between the activation sequence and electrogram characteristics using a model of recurrent conduction in the isthmus. The canine heart was isolated (n=8) and cross-circulated with the arterial blood of a support dog. A plaque electrode was placed at the isthmus, and 42 bipolar electrograms (filtered and unfiltered) were recorded during pacing at 120beats/min from the lateral right atrium before and after creating a narrow gap by 2 discontinuous incisions from the TA to the IVC. All bipolar electrodes, with the cathode in the TA side and the anode in the IVC side, were placed perpendicular to the TA. Before creating the incisions, the wavefront (WF) from the pacing impulse traveled uniformly in the isthmus and almost in parallel to the TA, and the filtered electrogram at each site showed a single potential. After creating the incisions, the WF propagated through the gap and spread radially to the area distal to the incisions. In close proximity to the incision lines opposite to the pacing site, the WF advanced from the gap towards the TA and IVC perpendicularly to the TA. Filtered electrograms on the incision lines showed double or split potentials, whereas those on the gap showed a single or fractionated potential. In unfiltered electrograms recorded from the TA to the IVC in close proximity to the incision lines opposite the pacing site, reversal of electrogram polarity was noted at the gap. A single or fractionated potential between double potentials indicates a gap between lines of conduction block. Electrogram polarity reversal along the ablation line indicates the presence of 2 opposing WF arising from the gap.  (+info)

Superior vena cava flow in newborn infants: a novel marker of systemic blood flow. (12/450)

BACKGROUND: Ventricular outputs cannot be used to assess systemic blood flow in preterm infants because they are confounded by shunts through the ductus arteriosus and atrial septum. However, flow measurements in the superior vena cava (SVC) can assess blood returning from the upper body and brain. OBJECTIVES: To describe a Doppler echocardiographic technique that measures blood flow in the SVC, to test its reproducibility, and to establish normal ranges. DESIGN: SVC flow was assessed together with right ventricular output and atrial or ductal shunting. Normal range was established in 14 infants born after 36 weeks' gestation (2 measurements taken in the first 48 hours) and 25 uncomplicated infants born before 30 weeks (4 measurements taken in the first 48 hours). Intra-observer and interobserver variability were tested in 20 preterm infants. RESULTS: In 14 infants born after 36 weeks, median SVC flow rose from 76 ml/kg/min on day 1 to 93 ml/kg/min on day 2; in 25 uncomplicated very preterm infants, it rose from 62 ml/kg/min at 5 hours to 86 ml/kg/min at 48 hours. The lowest SVC flow for the preterm babies rose from 30 ml/kg/min at 5 hours to 46 ml/kg/min by 48 hours. Median intra-observer and interobserver variability were 8. 1% and 14%, respectively. In preterm babies with a closed duct, SVC flow was a mean of 37% of left ventricular output and the two measures correlated significantly. CONCLUSIONS: This technique can assess blood flow from the upper body, including the brain, in the crucial early postnatal period, and might allow more accurate assessment of the status of systemic blood flow and response to treatment.  (+info)

Low superior vena cava flow and intraventricular haemorrhage in preterm infants. (13/450)

OBJECTIVES: To document the incidence, timing, degree, and associations of systemic hypoperfusion in the preterm infant and to explore the temporal relation between low systemic blood flow and the development of intraventricular haemorrhage (IVH). STUDY DESIGN: 126 babies born before 30 weeks' gestation (mean 27 weeks, mean body weight 991 g) were studied with Doppler echocardiography and cerebral ultrasound at 5, 12, 24, and 48 hours of age. Superior vena cava (SVC) flow was assessed by Doppler echocardiography as the primary measure of systemic blood flow returning from the upper body and brain. Other measures included colour Doppler diameters of ductal and atrial shunts, as well as Doppler assessment of shunt direction and velocity, and right and left ventricular outputs. Upper body vascular resistance was calculated from mean blood pressure and SVC flow. RESULTS: SVC flow below the range recorded in well preterm babies was common in the first 24 hours (48 (38%) babies), becoming significantly less common by 48 hours (6 (5%) babies). These low flows were significantly associated with lower gestation, higher upper body vascular resistance, larger diameter ductal shunts, and higher mean airway pressure. Babies whose mothers had received antihypertensives had significantly higher SVC flow during the first 24 hours. Early IVH was already present in 9 babies at 5 hours of age. Normal SVC flows were seen in these babies except in 3 with IVH, which later extended, who all had SVC flow below the normal range at 5 and/or 12 hours. Eight of these 9 babies were delivered vaginally. Late IVH developed in 18 babies. 13 of 14 babies with grade 2 to 4 IVH had SVC flow below the normal range before development of an IVH. Two of 4 babies with grade 1 IVH also had SVC flow below the normal range before developing IVH, and the other 2 had SVC flow in the low normal range. In all, IVH was first seen after the SVC flow had improved, and the grade of IVH related significantly to the severity and duration of low SVC flow. The 9 babies who had SVC flow below the normal range and did not develop IVH or periventricular leucomalacia were considerably more mature (median gestation 28 v 25 weeks). CONCLUSIONS: Low SVC flow may result from an immature myocardium struggling to adapt to increased extrauterine vascular resistances. Critically low flow occurs when this is compounded by high mean airway pressure and large ductal shunts out of the systemic circulation. Late IVH is strongly associated with these low flow states and occurs as perfusion improves.  (+info)

Tracking dynamic conduction recovery across the cavotricuspid isthmus. (14/450)

OBJECTIVES: We sought to assess the dynamic temporal course of conduction recovery during and after radiofrequency (RF) catheter ablation of the cavotricuspid isthmus. BACKGROUND: Although cavotricuspid isthmus block is accepted as the best end point of ablation for typical flutter, conduction recovery is thought to underlie many eventual recurrences. Its time course and frequency have not been determined. METHODS: In a prospective group of 30 patients (26 men and 4 women, age 64 +/- 12 years) undergoing ablation of typical flutter in the cavotricuspid isthmus, the morphology of the P wave during pacing from the low lateral right atrium after achievement of complete isthmus block was identified as a reference. Regression of this morphologic P wave change was confirmed to be associated with intracardiac evidence of the recovery of cavotricuspid isthmus conduction and was observed throughout the procedure both during ablation in sinus rhythm (n = 15, group B) and just after flutter termination (n = 15, group A). RESULTS: Stable complete isthmus block was achieved in all patients; 29 had a terminal positivity of the paced P wave. Flutter termination resulted in stable block and terminal P wave positivity in three patients, transient terminal P wave positivity and transient block despite continuing RF at the same site in five patients and no block in the remaining seven patients. Conduction recovery identified by recovery of P wave changes was nearly as common (48%) during ablation in sinus rhythm. Multiple recoveries were noted in some patients, and 72% of all recoveries occurred within 1 min. Conduction recovery was only rarely associated with coagulum, impedance elevation or pops. CONCLUSIONS: Conduction recovery in the cavotricuspid isthmus is common during and after ablation and can be accurately, dynamically and continuously observed by monitoring the recovery of the low lateral right atrial paced P wave change.  (+info)

Oxytocin and its receptors are synthesized in the rat vasculature. (15/450)

Produced and released by the heart, oxytocin (OT) acts on its cardiac receptors to decrease the cardiac rate and force of contraction. We hypothesized that it might also be produced in the vasculature and regulate vascular tone. Consequently, we prepared acid extracts of the pulmonary artery and vena cava of female rats. OT concentrations in dog and sheep aortae were equivalent to those of rat aorta (2745 +/- 180 pg/mg protein), indicating that it is present in the vasculature of several mammalian species. Reverse-phase HPLC of aorta and vena cava extracts revealed a single peak corresponding to the amidated OT nonapeptide. Reverse-transcribed PCR confirmed OT synthesis in these tissues. Using the selective OT receptor ligand compound VI, we detected a high number of OT-binding sites in the rat vena cava and aorta. Furthermore, OT receptor (OTR) mRNA was found in the vena cava, pulmonary vein, and pulmonary artery with lower levels in the aorta, suggesting vessel-specific OTR distribution. The abundance of OTR mRNA in the vena cava and pulmonary vein was associated with high atrial natriuretic peptide mRNA. In addition, we have demonstrated that diethylstilbestrol treatment of immature female rats increased OT significantly in the vena cava but not in the aorta and augmented OTR mRNA in both the aorta (4-fold) and vena cava (2-fold), implying regulation by estrogen. Altogether, these data suggest that the vasculature contains an intrinsic OT system, which may be involved in the regulation of vascular tone as well as vascular regrowth and remodeling.  (+info)

Reconstruction of the superior vena cava with the aid of an extraluminal venovenous jugulo-atrial shunt. (16/450)

A 57-year-old woman had chronic benign superior vena cava syndrome related to the long-term use of multiple central venous catheters for chemotherapy. Treatment included resection of the obstructed segment and repair of the superior vena cava with an autologous pericardial patch. Intraoperatively, return venous flow was maintained with an extraluminal venovenous jugulo-atrial shunt. The shunt relieved upper-body hypertension and congestion, resulting in early extubation and a short, smooth postoperative course.  (+info)