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Biomedical subjects

R Lazzara

Publications and source records attributed to R Lazzara.

At least 19 recordsLinked to original sources
PubMed2001

Reversing the direction of paced ventricular and atrial wavefronts reveals an oblique course in accessory AV pathways and improves localization for catheter ablation.

BACKGROUND: The purpose of this study was to determine how often accessory atrioventricular (AV) pathways (AP) cross the AV groove obliquely. With an oblique course, the local ventriculoatrial (VA) interval at the site of earliest atrial activation (local-VA) and the local-AV interval at the site of earliest ventricular activation (local-AV) should vary by reversing the direction of the paced ventricular and atrial wavefronts, respectively. METHODS AND RESULTS: One hundred fourteen patients with a single AP were studied. Two ventricular and two atrial pacing sites on opposite sides of the AP were selected to reverse the direction of the ventricular and atrial wavefronts along the annulus. Reversing the ventricular wavefront increased local-VA by >/=15 ms in 91 of 106 (91%) patients. With the shorter local-VA, the ventricular potential overlapped the atrial potential along a 17.2+/-8.5-mm length of the annulus. No overlap occurred with the opposite wavefront. Reversing the atrial wavefront increased local-AV by >/=15 ms in 32 of 44 (73%) patients. With the shorter local-AV, the atrial potential overlapped the ventricular potential along an 11.9+/-8.9-mm length of the annulus. No overlap occurred with the opposite wavefront. Mapping during longer local-VA or local-AV identified an AP potential in 102 of 114 (89%) patients. Catheter ablation eliminated AP conduction in all 111 patients attempted (median, 1 radiofrequency application in 99 patients with an AP potential versus 4.5 applications without an AP potential). CONCLUSIONS: Reversing the direction of the paced ventricular or atrial wavefront reveals an oblique course in most APs and facilitates localization of the AP potential for catheter ablation.

Adolescent↗
PubMed2001

Characterization of reentrant circuit in macroreentrant right atrial tachycardia after surgical repair of congenital heart disease: isolated channels between scars allow "focal" ablation.

BACKGROUND: The purpose of this study was to characterize the circuit of macroreentrant right atrial tachycardia (MacroAT) in patients after surgical repair of congenital heart disease (SR-CHD). METHODS AND RESULTS: Sixteen patients with atrial tachycardia (AT) after SR-CHD were studied (atrial septal defect in 6, tetralogy of Fallot in 4, and Fontan procedure in 6). Electroanatomic right atrial maps were obtained during 15 MacroATs in 13 patients, focal AT in 1 patient, and atrial pacing in 2 patients without stable AT. A large area of low bipolar voltage (</=0.5 mV) involved most of the free wall in all patients and contained 2 to 7 dense scars or lines of double potentials, forming 29 narrow channels (width </=2.7 cm) between scars in all but 1 patient, who had a single scar and only focal AT. All 15 MacroATs were propagated through narrow channels. Ablation within the channel eliminated all 15 MacroATs with 1 to 3 (median 1) radiofrequency applications. Ablation was performed in 9 other channels identified during MacroAT (5 patients) and in 5 channels identified during atrial pacing (2 patients). Conduction block was obtained across 28 of 29 channels. After ablation, reproducible sustained right AT was not induced in any patient. During follow-up (median 13.5 months), new MacroATs, atrial fibrillation, or palpitations occurred in 3 of 16 patients. CONCLUSIONS: MacroAT after SR-CHD requires a large area of low voltage containing >/=2 scars forming narrow channels. Ablation within the channels eliminates MacroAT.

Adult↗
PubMed2001

Transseptal left heart catheterization for cardiac ablation procedures.

UNLABELLED: Transseptal left heart catheterization has been performed as an alternative to the retrograde approach since 1958. However, this procedure can result in life-threatening complications, some of which may occur because of insufficient anatomical landmarks. Accordingly, we sought to assess the safety and efficacy of a new transseptal left heart catheterization technique designed for ablation procedures. Specifically, we examined whether electrode catheters could be used as anatomical landmarks, permitting identification of the aortic root and other critical structures. RESULTS: One hundred and eight consecutive patients underwent transseptal left heart catheterization under biplane fluoroscopy during catheter ablation. Electrode catheters positioned in the right atrial appendage, His bundle region, and coronary sinus were used as anatomical landmarks to guide the transseptal unit to the fossa ovalis. The angles of the right anterior and left anterior oblique projections were selected in each patient based on the orientation of the His bundle and coronary sinus catheters. Transseptal left heart catheterization was successfully performed in all patients without complications. In contrast to previous reports, the direction of the needle at the successful puncture site in the last 96 patients varied substantially: 2 o'clock in 13 patients (13 %); 3 o'clock in 43 patients (45 %); and 4 o'clock in 40 patients (42 %). CONCLUSION: The use of electrode catheters as anatomical landmarks and biplane fluoroscopy facilitates transseptal catheterization. This approach can be used safely during catheter ablation procedures.

Adolescent↗
PubMed2001

Optimal implant stabilization in low density bone.

Initial stability of the implant is one of the fundamental criteria for obtaining osseointegration. An adequate primary anchorage is often difficult to achieve in low density bone (type IV). Various surgical suggestions were advanced in the 1980s which were aimed at achieving optimal osseous integration in poor quality bone. They offered satisfactory short-term results. Recently, as a result of surgical and technological innovations, new therapeutic proposals have shown very interesting results in their initial studies.

Bone Density↗
PubMed2001

Focal atrial fibrillation: experimental evidence for a pathophysiologic role of the autonomic nervous system.

INTRODUCTION: Focal paroxysmal atrial fibrillation (AF) was shown recently to originate in the pulmonary veins (PVs) and superior vena cava (SVC). In the present study, we describe an animal model in which local high-frequency electrical stimulation produces focal atrial activation and AF/AT (atrial tachycardia) with electrogram characteristics consistent with clinical reports. METHODS AND RESULTS: In 21 mongrel dogs, local high-frequency electrical stimulation was performed by delivering trains of electrical stimuli (200 Hz, impulse duration 0.1 msec) to the PVs/SVC during atrial refractoriness. Atrial premature depolarizations (APDs), AT, and AF occurred with increasing high-frequency electrical stimulation voltage. APD/AT/AF originated adjacent to the site of high-frequency electrical stimulation and were inducible in 12 of 12 dogs in the SVC and in 8 of 9 dogs in the left superior PV (left inferior PV: 7/8, right superior PV: 6/8; right inferior PV: 4/8). In the PVs, APDs occurred at 13+/-8 V and AT/AF at 15+/-9 V (P < 0.01; n = 25). In the SVC, APDs were elicited at 19+/-6 V and AT/AF at 26+/-6 V (P < 0.01; n = 12). High-frequency electrical stimulation led to local refractory period shortening in the PVs. The response to high-frequency electrical stimulation was blunted or prevented after beta-receptor blockade and abolished by atropine. In vitro, high-frequency electrical stimulation induced a heterogeneous response, with shortening of the action potential in some cells (from 89+/-35 msec to 60+/-22 msec; P < 0.001; n = 7) but lengthening of the action potential and development of early afterdepolar-izations that triggered APD/AT in other cells. Action potential shortening was abolished by atropine. CONCLUSION: High-frequency electrical stimulation evokes rapid ectopic beats from the PV/SVC, which show variable degrees of conduction block to the atria and induce AF, resembling findings in patients with focal idiopathic paroxysmal AF. The occurrence of the arrhythmia in this animal model was likely due to alterations in local autonomic tone by high-frequency electrical stimulation. Further research is needed to prove absolutely that the observed effects of high-frequency electrical stimulation were caused by autonomic nerve stimulation.

Animals↗
PubMed2001

The modified osteotome technique.

Patients who have been partially edentulous in the posterior segments for many years frequently present with reduced alveolar bone and/or enlarged sinuses. The choice of treatment for these patients will depend on the volume of residual bone, morphology of the alveolar crest, and amount of space available for the prosthesis. A new, minimally invasive surgical procedure using Summers osteotomes is described for the treatment of the edentulous posterior maxilla in which the bone thickness below the sinus is limited (> or = 5 mm). This suggested modified treatment is based on the use of a combination of osteotomes, drills, and screw-type implants with a rough surface texture.

Bone Transplantation↗
PubMed2000

Catheter ablation of cardiac autonomic nerves for prevention of vagal atrial fibrillation.

BACKGROUND: Vagal stimulation shortens the atrial effective refractory period (AERP) and maintains atrial fibrillation (AF). This study investigated whether the parasympathetic pathways that innervate the atria can be identified and ablated by use of transvenous catheter stimulation and radiofrequency current catheter ablation (RFCA) techniques. METHODS AND RESULTS: In 11 dogs, AERPs were determined at 7 atrial sites during bilateral cervical vagal nerve stimulation (VNS) and electrical stimulation of the third fat pad (20 Hz) in the right pulmonary artery (RPA). VNS shortened the AERP at all sites (from 123+/-4 to 39+/-4 ms, P<0.001) and increased the covariance of AERP (COV-AERP) (from 9+/-3% to 27+/-13%, P<0.001). RPA stimulation shortened the AERP at all sites from 123+/-4 to 66+/-13 ms (P<0.001) and increased the COV-AERP from 9+/-3% to 30+/-12% (P<0.001). In 7 dogs, transvascular RFCA of the parasympathetic pathways along the RPA was performed, and in 3 dogs, additional RFCA of parasympathetic fibers along the inferior (n=2) or superior (n=1) vena cava was performed. RFCA blunted the AERP shortening at all sites during VNS (114+/-4 ms after RFCA), abolished the increase of COV-AERP during VNS (12+/-7% after RFCA), and led to an increase of the baseline AERP (123+/-4 ms before versus 127+/-3 ms after RFCA, P=0.002). Before RFCA, AF could be induced and maintained as long as VNS was continued, whereas after RFCA, AF was no longer inducible during VNS. CONCLUSIONS: -Transvascular atrial parasympathetic nerve system modification by RFCA abolishes vagally mediated AF. This antifibrillatory procedure may provide a foundation for investigating the usefulness of neural ablation in chronic animal models of AF and eventually in patients with AF and high vagal tone.

Animals↗
PubMed2000

Effect of GLG-V-13, a class III antiarrhythmic agent, on potassium currents in rabbit ventricular myocytes.

The effects of a new Class III antiarrhythmic drug, GLG-V-13, on the 4-aminopyridine sensitive transient outward current, on the inward rectifier potassium current, on the ATP sensitive potassium current and on the rapid and slow components of the delayed rectifier potassium current were studied in single rabbit ventricular myocytes using the whole-cell voltage-clamp technique. GLG-V-13 blocked the rapid component of the delayed rectifier potassium current in a dose-dependent manner, with an estimated EC50 value of 0.36 microM. At high concentration, the slow component of the delayed rectifier potassium current was also depressed by the drug (40% effect at 10 microM concentration). The transient outward current, the inward rectifier potassium current and the ATP sensitive potassium current were not influenced by GLG-V-13, even at 10 microM concentration. Thus, GLG-V-13 blocks predominantly the rapid component of the delayed rectifier potassium current which may play a significant role in the prolongation of repolarization by the drug in ventricular tissue.

4-Aminopyridine↗
PubMed2000

The acute and subchronic toxicity of BRB-I-28, a novel class Ib antiarrhythmic agent, in CD-1 mice.

The acute and subchronic toxic effects of BRB-I-28 (7-benzyl-3-thia-7-azabicyclo[3.3.1]nonane HCl), a novel class Ib antiarrhythmic agent, were investigated in male and female mice. The estimated oral LD(50) for BRB-I-28 was 128 mg/kg (male mice) and 131 mg/kg (female mice). In subchronic oral studies, four groups of mice (15/sex/group/dose) were fed daily with diets containing BRB-I-28 for 90 consecutive days. The equivalent daily doses were approximately 0, 16, 32, 76 (male) and 0, 18, 37, 89 mg/kg (female). All mice survived. Food consumption per day was decreased, but water consumption per day was increased (in a non-dose-dependent manner). However, both mean body weight and mean body weight gain were not significantly changed as were true for hematological and clinical chemistry profiles, except for serum Na(+) concentration (male) and serum K(+) concentration in male and female mice (high dose levels). Hepatocellular necrosis occurred in male and female mice (in a dose-dependent fashion). Renal cortical vacuoles and myocardial necrosis with low numbers of lymphocytic infiltrations were present in female mice (middle and high doses). Lesions in the liver, kidney and heart were mild with (very small) changes in serum biochemical values. These data suggest that BRB-I-28 has limited toxic potential, and coupled with low proarrhythmic and other desirable cardiovascular effects, makes BRB-I-28 worthy of further development.

Animals↗
PubMed2000

Endovascular neural stimulation via a novel basket electrode catheter: comparison of electrode configurations.

We previously showed that parasympathetic stimulation by a basket electrode catheter (BEC) positioned in the superior vena cava (SVC) can slow sinus rate (SR) or ventricular response (VR) during atrial fibrillation (AF). In 11 dogs, anesthetized with Na-pentobarbital, standard ECG leads II and aVR, blood pressure and right atrial electrograms were continuously monitored. Two different BEC configurations (B1, B2) were tested in the SVC. B1 consisted of five metal splines, each 3 cm in length. Stimulation was applied between adjacent splines. B2 consisted of 2 electrodes at opposite ends of each of 5 splines and a larger electrode at the middle of each spline. Stimulation was delivered between the two end electrodes and the middle electrode on the same arm. Stimulation consisted of square wave stimuli, each 0.1 msec duration, frequency 20 Hz at voltages from 1-40 V. Six dogs were studied with B1 and five were studied with the B2 configuration. The average voltage required to produce a 50% decrease in heart rate was 22+/- 12 V when stimulating between adjacent splines (B1) compared to 10+/- 5 V when stimulating along a single spline (B2), a 55% decrease (p</=0.05). During AF, the voltage required to reduce the average ventricular rate to 100 beats/min was 19+/- 13 V for B1 and 8+/- 5 V for B2, a 58% reduction (p</=0.05). Thus, the significant difference between B1 and B2 and in slowing SR or VR during AF was probably due to a greater current density delivered with B2 to the endovascular wall and adjacent neural elements.

Animals↗
PubMed2000

Is there longitudinal dissociation in the undamaged his bundle? In vitro studies in the normal canine heart.

We investigated the concept of longitudinal dissociation in the His-Purkinje system in vitro. Hearts were excised from the eleven anesthetized dogs and a septal preparation containing the exposed His bundle and the entire right bundle branch and left bundle branch were displayed in a two-dimensional arrangement pinned to the bottom of a superfusion chamber. Tyrodes solution, gassed with 95% O2 and 5% CO2, at 37 degrees C was continuously passed over the preparation. Pacing was performed over a wide range of heart rates (30 to 180/min) from the proximal His bundle and by moving bipolar electrodes we monitored activation at various sites along the right and left bundle branch. The earliest site of muscle activation (27+/-2 msec) on the left septum was a relatively large area in the midposterior septal region; whereas, on the right septum the earliest site of activation (27+/-3 msec) was a relatively small zone at the base of the anterior papillary muscle, (p, N.S). The larger area of early activation on the left compared to the right is consonant with a left to right septal vector accounting for the Q wave in the standard bipolar leads in the normal heart and the loss of Q waves in left bundle branch block. We conclude that His-Purkinje and ventricular muscle activation is remarkably synchronous on both sides of the heart and accounts for optimal contractile function during His bundle or biventricular pacing compared to standard site ventricular pacing, particularly in patients with left ventricular dysfunction.

Animals↗
PubMed2000

Preliminary acute and subchronic toxicity studies of GLG-V-13, a novel class III antiarrhythmic agent, in mice.

The acute and subchronic toxic effects of GLG-V-13 (3-[4-(1H-imidazol-1-yl)benzoyl]-7-isopropyl-3,7-diazabicyclo[3.3.1]nona ne dihydroperchlorate, CAS 155029-33-7), a novel class III with some class Ib antiarrhythmic activity, were investigated in mice. The estimated LD50 for GLG-V-13 given orally were 419 mg/kg for male mice and 383 mg/kg for female mice, respectively. The acute toxic signs appeared to be of the central nervous system in origin. Four groups of mice (15 per sex, group and dose) were fed daily with diets containing GLG-V-13 for 90 consecutive days. The equivalent daily doses were 0, 22, 50 and 121 mg/kg/day and 0, 27, 60 and 136 mg/kg/day for male and female mice, respectively. All of the mice survived. Food consumption was decreased. However, mean body weight and body weight gain were not significantly changed. Gross pathological changes, especially in the lungs and liver, were found in the middle and high dose groups. Consistent increased mean corpuscular hemoglobin concentration and decreased mean corpuscular hemoglobin were observed in all dose groups. Hepatocellular necrosis was found in both male and female mice treated with the drug and was dose-dependent. Marked vacuolation of the X zone in the adrenal gland with mild to moderate deposition of ceroid pigments (brown degeneration) was observed in female mice. Lesions in the kidneys and adrenal glands may be a possible reason for changes in serum sodium and potassium ions concentrations leading to an increase in water intake. A significant reduction in cholesterol in the high dose group may be a favorable pharmacological effect of GLG-V-13. The data from the 90-day subchronic toxicity studies indicate that GLG-V-13 appears to have limited systemic toxicity potential.

Animals↗
PubMed2000

Transvenous parasympathetic nerve stimulation in the inferior vena cava and atrioventricular conduction.

INTRODUCTION: In previous reports, we demonstrated a technique for parasympathetic nerve stimulation (PNS) within the superior vena cava, pulmonary artery, and coronary sinus to control rapid ventricular rates during atrial fibrillation (AF). In this report, we describe another vascular site, the inferior vena cava (IVC), at which negative dromotropic effects during AF could consistently be obtained. Moreover, stimulation at this site also induced dual AV nodal electrophysiology. METHODS AND RESULTS: PNS was performed in ten dogs using rectangular stimuli (0.1 msec/20 Hz) delivered through a catheter with an expandable electrode basket at its tip. Within 3 minutes and without using fluoroscopy, the catheter was positioned at an effective PNS site in the IVC at the junction of the right atrium. AF was induced and maintained by rapid atrial pacing. During stepwise increase of the PNS voltage from 2 to 34 V, a graded response of ventricular rate slowing during AF was observed (266 +/- 79 msec without PNS vs 1,539 +/- 2,460 msec with PNS at 34 V; P = 0.005 by analysis of variance), which was abolished by atropine and blunted by hexamethonium. In three animals, PNS was performed during sinus rhythm. Dual AV nodal electrophysiology was present in 1 of 3 dogs in control, whereas with PNS, dual AV nodal electrophysiology was observed in all three dogs. PNS did not significantly change sinus rate or arterial blood pressure during ventricular pacing. CONCLUSION: Stable and consistent transvenous electrical stimulation of parasympathetic nerves innervating the AV node can be achieved in the IVC, a transvenous site that is rapidly and readily accessible. The proposed catheter approach for PNS can be used to control ventricular rate during AF in this animal model.

Animals↗
PubMed2000

Small-diameter implants: indications and contraindications.

The choice of implant diameter depends on the type of edentulousness, the volume of the residual bone, the amount of space available for the prosthetic reconstruction, the emergence profile, and the type of occlusion. Small-diameter implants are indicated in specific clinical situations, for example, where there is reduced interradicular bone or a thin alveolar crest, and for the replacement of teeth with small cervical diameter. Before using a small-diameter implant, the biomechanical risk factors must be carefully analyzed. Preliminary reports of this type of implant show good short- and medium-term results.

Alveolar Bone Loss↗