Hemodynamic benefits of right ventricular outflow tract pacing: comparison with right ventricular apex pacing

To assess optimal hemodynamics in relation to stimulation site during right ventricular pacing, 17 consecutive patients who underwent cardiac catheterization were studied. In all patients, right ventricular apex and right ventricular outflow tract stimulation was performed at 85, 100, and 120 beats/min. Cardiac index at both pacing sites was compared using the left ventricular outflow tract continuous wave Doppler technique. Comparison of the two stimulation sites demonstrated that right ventricular outflow tract pacing resulted in a higher cardiac index at 85 beats/min (2.42 +/- 1.2 vs 2.04 +/- 1.0 L/min per m2, P < 0.002) at 100 beats/min (2.78 +/- 1.4 vs 2.35 +/- 1.1 L/min per m2, P < 0.001) and 120 beats/min (3.00 +/- 1.5 vs 2.61 +/- 0.9 L/min per m2, P < 0.001). From a total of 51 paired observations, 45 showed an increase in cardiac index during outflow tract pacing as compared to apex pacing. Right ventricular outflow tract pacing at 120 beats/min resulted in a lower cardiac index than right ventricular apex pacing in patients with significant coronary artery disease and/or impaired left ventricular function (ejection fraction < or = 50%), whereas right ventricular outflow tract pacing produced higher cardiac indices in the absence of these abnormalities. Right ventricular outflow tract pacing resulted in higher cardiac indices as compared to apex pacing in all other subgroups at all other pacing sites tested. It is concluded that stimulation of the right ventricular outflow tract offers a significant hemodynamic benefit during single chamber pacing as compared to conventional apex pacing, particularly in the absence of significant coronary artery disease and/or left ventricular dysfunction.     

Nonthoracotomy implantation of cardioverter defibrillators: preliminary experience with a defibrillation lead placed at the right ventricular outflow tract

Although morbidity and mortality associated with defibrillator implantation using a nonthoracotomy approach have decreased as compared with a thoracotomy approach, defibrillation thresholds have been higher and fewer patients satisfied implant criteria. It may be possible to improve on the success of nonthoracotomy defibrillator implantation by the placement of a right ventricular (RV) outflow defibrillation lead. Implantable cardioverter defibrillator implantation data of 30 consecutive patients with clinical VT or VF were reviewed. Three defibrillation leads were routinely used. When either pacing threshold at the RV apex was inadequate (n = 2) or 18-J shocks were not successful in terminating VF in 3 of 4 trials (n = 8), the RV apex lead was positioned to the RV outflow tract attaching to the septum. Defibrillation testing was first performed with the RV apex lead in combination with CS, SVC, and/or subcutaneous leads. Twenty patients satisfied implant criteria with a defibrillation threshold of 13.5 +/- 3.6 J. In 7 of the 10 patients, whose RV lead was repositioned to the RV outflow tract, this lead in combination with SVC, CS, or subcutaneous leads produced successful defibrillation at < or = 18 J or in 3 of 4 trials. This approach improved the overall success of nonthoracotomy implantation of defibrillators from 69% to 90%. After a follow-up of 27 +/- 6 months, there was no dislodgment of the RV outflow tract defibrillation leads. CONCLUSIONS: This article reports the preliminary observation that placement of defibrillation leads to the RV outflow tract in humans was possible and without dislodgment. RV outflow tract offers an alternative for placement of defibrillation leads, which may improve on the success of nonthoracotomy defibrillator implantation.     

Catheter ablation for ventricular tachycardia from a diverticulum at the right ventricular outflow tract

A case is presented of a 73-year-old man with drug resistant ventricular tachycardia that originated from the right ventricular outflow tract. A right ventriculogram showed a diverticulum in the interventricular septum at the right ventricular outflow tract. Low energy radiofrequency catheter ablation within the diverticulum was performed successfully and safely.     

Radiofrequency catheter ablation of right ventricular outflow tract tachycardia in a preschooler

A 3-year-old girl presented with a febrile illness complicated by right ventricular outflow tract tachycardia, which persisted after resolution of the presumed viral infection. The tachycardia was intermittent, but was significantly exacerbated by exercise. Radiofrequency ablation (RFA) of the ectopic focus was successfully performed and the child remains free of tachycardia 12 months later. A review of the literature suggests that RFA in children is increasingly seen as a safe and convenient option for the treatment of supraventricular tachycardia, whereas the management of ectopic ventricular tachycardia in pediatric practice has not been well defined.     

Pulmonary valve atresia with ventricular septum defect: interventional recanalization of the right ventricular outflow tract]

A case of pulmonary atresia with ventricular septal defect is reported where continuity between the right ventricle and the hypoplastic pulmonary artery was established interventionally. The atretic valve was perforated using a special "perforation needle" with a sharp and stiff distal and a flexible proximal part. Perforation of the bifurcation was well tolerated without later sequelae. After perforation of the atresia, dilation was successfully performed using 2, 4, and 7.2 mm balloons with a pressure of 10 atm; the arterial oxygen saturation increased from 72% to 84%. Four weeks later repeated "valvuloplasty" was performed (balloon diameters 8 mm, 9.5 mm, and 12 mm) and the "valve" ring was dilated to a diameter of 10.5 mm. Although no general conclusions can be drawn from this single application, mechanical perforation of the atresia could become an attractive interventional approach for the treatment of pulmonary atresia.     

Monocusp valve and transannular patch reconstruction of the right ventricular outflow tract: an experimental study

Repair of congenital right ventricular outflow tract obstruction often requires reconstruction with a transannular patch to alleviate pulmonary stenosis. Post repair pulmonary insufficiency with right ventricular dilatation and volume overload may result and lead to acute or progressive right heart failure. The use of a monocusp valve has been proposed as a means to prevent this problem. Fresh pericardium is well known to fail clinically, leading to pulmonary insufficiency limiting mid- and long-term results. In a chronic dog model (147 +/- 34 days), three valve types were evaluated: 1) polytetrafluoroethylene (PTFE; n = 9), 2) fresh pericardium (PERI; n = 6), and glutaraldehyde fixed pericardium (GLU; n = 6). Hemodynamics, angiography, and echocardiography were performed at implantation and sacrifice. Gross and microscopic pathology were evaluated. No significant differences were found among the three groups with regard to stenosis as evaluated by echocardiography, measured right ventricular wall thickness, and hemodynamic pressure gradients across the valve. By echocardiography, both PTFE (1 of 9) and GLU (0 of 6) showed less regurgitation than PERI (5 of 6) (p < 0.05). This was confirmed by angiography. PTFE showed less neo-intimal hyperplasia, less thrombus formation, and less calcification than GLU or PERI (p = NS). The PTFE monocusp developed no prohibitive gradients, no early pathologic deterioration, and maintained competence compared with the GLU and PERI groups. Although continued investigation of long-term durability and competence of the PTFE monocusp valve is warranted, both PTFE and GLU values seem to demonstrate less regurgitation than the PERI monocusp valve in an adult dog model of right ventricular outflow tract reconstruction.     

Influence of right ventricular stimulation site on left ventricular function in atrial synchronous ventricular pacing

Septic shock is a dangerous condition with high mortality rates. In sepsis, the inducible form of nitric oxide (NO) synthase is induced, releasing high amounts of NO. Glucocorticoids have potent anti-inflammatory properties and are very effective in inhibiting the induction of this enzyme if administered before the shock onset. It is known that glucocorticoid receptor (GR) has critical cysteine residues for steroid binding in its hormone-binding and DNA-binding domains. It has also been reported that NO reacts with ---SH groups, forming S-nitrosothiols. Therefore, we examined the potential effect of NO on the ligand-binding ability of GR. NO donors (S-nitroso-acetyl-DL-penicillamine, S-nitroso-DL-penicillamine, or S-nitroso-glutathione) decreased, in a time- and dose-dependent manner, the binding of [3H]triamcinolone to immunoprecipitated GR from mouse L929 fibroblasts. The nonnitrosylated parent molecules, N-acetyl-DL-penicillamine, and reduced gluthatione were without effect. Scatchard plots revealed that the number of ligand binding sites and Kd were reduced (50%) by NO donors. Western blot analysis ruled out the possibility that dissociation of GR/heat shock protein 90 heterocomplex or decrease in GR protein would account for the inhibitory effect of NO. Decreased ligand binding to GR was found when NO donors were incubated with intact fibroblasts. Incubation with NO donors also decreased the steroid-induced reduction in [3H]uridine incorporation into RNA. All of these NO effects were inhibited by the thiol-protecting agent dithiothreitol. Therefore, S-nitrosylation of critical ---SH groups in GR by NO with consequent decreases in binding and affinity may be the mechanisms which explain the failure of glucocorticoids to exert their anti-inflammatory effects in septic shock.     

Significance of morphological abnormalities detected by MRI in patients undergoing successful ablation of right ventricular outflow tract tachycardia

BACKGROUND: MRI can demonstrate subtle morphological changes of the right ventricle in patients with idiopathic right ventricular outflow tract tachycardia (RVOT). The present study examines the incidence and significance of right ventricular (RV) abnormalities detected by MRI with respect to the site of successful radiofrequency catheter ablation of the clinical tachycardia. METHODS AND RESULTS: The study population comprised 20 patients (mean age, 40+/-12 years) undergoing elimination of recurrent RVOT by radiofrequency catheter ablation. MRI studies were performed before ablation to assess RV volumes and function, as well as structural abnormalities of the RV myocardium. Ten healthy age- and sex-matched subjects served as control subjects. The successful ablation sites, as documented by radiographs of the catheter position, were compared with MRI findings. Patients with RVOT showed no difference in respect to RV volumes and ejection fractions compared with control subjects. Whereas RV abnormalities were limited to prominent fatty deposits of the right atrioventricular groove extending into the inlet portion of the RV wall in 2 of 10 control subjects, MRI studies demonstrated morphological changes of the RV free wall in 13 (65%) of 20 patients with RVOT, including presence of fatty tissue (n=5), wall thinning (n=9), and dyskinetic wall segments (n=4). Eight of these patients had additional fat deposits, thinning, or a saccular aneurysm in the RV outflow tract, corresponding with the ablation site in 6 patients. CONCLUSIONS: In RVOT, structural abnormalities of the right ventricle can be detected in a substantial number of patients despite normal RV volumes and global function. MRI abnormalities within the RV outflow tract are significantly associated with the origin of tachycardia.     

Early results of AV sequential pacing on left ventricular outflow obstruction after Senning procedure

Dual chamber pacing was shown to decrease left ventricular outflow tract (LVOT) obstruction in patients with hypertrophic cardiomyopathy 30 years ago. We report early results of AV sequential pacing from the LV apex in a patient with transposition of the great arteries who is post-Senning procedure. LVOT obstruction resulted from septal deviation and systolic anterior motion of the mitral valve. Pacing was indicated for sinus node dysfunction. AV sequential pacing with a short optimal AV interval of 60 ms demonstrated a 45% reduction in the degree of LVOT obstruction. This article suggests that LVOT obstruction after the Senning procedure can be palliated by asynchronous septal contraction induced by AV sequential pacing, even if the activation is from LV apex, and avoid or postpone surgery in selected situations.     

Why not simple ventricular pacing? The hemodynamics of cardiac pacing for noncardiologists

For many years, cardiac pacing consisted primarily of implanting and following fixed-rate ventricular systems. While this mode of pacing restored a more acceptable rate and in fact reduced mortality, prevented syncope, and brought clinical improvement in patients with acquired complete heart block, that it often failed to restore the degree of wellness provided by the normal electrical conduction sequence became increasingly apparent. This paper contrasts normal cardiac mechanics to those of simple ventricular pacing, making clear why clinical outcome with the latter is often disappointing. An approach to selecting pacing modes for specific abnormalities is outlined. The legitimate role of simple ventricular pacing continues to diminish as physicians turn to more hemodynamically efficient atrial and dual chamber pacing with sensor-mediated rate modulation where appropriate.     

Permanent cardiac pacing after a cardiac operation: predicting the use of permanent pacemakers

BACKGROUND: The need for permanent cardiac pacing after cardiac operations is infrequent but associated with increased morbidity and resource utilization. We identified patient risk factors for pacemaker insertion to enable development of a predictive model. METHODS: Data were collected prospectively for 10,421 consecutive patients who had cardiac operations between January 1990 and December 1995. Two hundred fifty-five patients (2.4%) were identified as having received a permanent pacemaker during the same hospitalization. Logistic regression analysis was performed to determine the independent, multivariate predictors of permanent pacing. The predictive accuracy and precision of the logistic regression model was evaluated in the 1996 database of 2,236 consecutive patients by the calculation of Brier scores. RESULTS: Eight independent predictors of permanent pacemaker requirement were identified. The factor-adjusted odds ratios (OR) with 95% confidence interval (CI) associated with each predictor are as follows: (1) valve replacement surgery (aortic: OR 5.8, CI 3.9-8.7; mitral: OR 4.9, CI 3.1-7.8; tricuspid: OR 8.0, CI 5.5-11.9; double: OR 8.9, CI 5.5-14.6; and triple: OR 7.5, CI 2.9-19.3); (2) repeat operation: OR 2.4, CI 1.8-3.3; (3) age 75 years or older: OR 3.0, CI 2.0-4.4; (4) ablative arrhythmia operation: OR 4.2, CI 1.9-9.5; (5) mitral valve annular reconstruction: OR 2.4, CI 1.4-4.2; (6) use of cold blood cardioplegia: OR 2.0, CI 1.2-3.6; (7) preoperative renal failure: OR 1.6, CI 1.0-2.6; and (8) active endocarditis: OR 1.7, CI 0.9-3.0. A model for postoperative permanent pacemaker requirement using the eight predictors was formulated and tested (Brier score = 0.017+/-0.003; Z = 0.18). CONCLUSIONS: The proposed predictive model correlated highly with actual pacemaker use, which suggests that the requirement for pacing results from either operative trauma or increased ischemic burden. Preoperative identification of patients at increased risk of conduction disturbances may allow for earlier detection and improved treatment. Patients requiring postoperative pacing had increased morbidity and length of stay.     

Indications, effectiveness, and long-term dependency in permanent pacing after cardiac surgery

The purposes of this study were to define predictors of long-term pacemaker dependency in patients having permanent pacemakers implanted shortly after cardiac surgery, and to evaluate short- and long-term results and survival in this population. Data from 120 adult patients with implantation since 1980 were retrospectively analyzed. Acute and chronic complication rates (4.2% and 16.6%, respectively) were not higher than those expected in the general paced population. In addition, continuous rhythm was evaluated by use of pacemaker inhibition in a subgroup of 20 patients to verify the validity of clinical criteria for pacemaker dependency. Of the patients evaluated for dependency, 41% eventually became nondependent. Prolonged monitoring with an inhibited pacemaker confirmed the accuracy of our method of clinical evaluation of pacemaker dependency. Significant predictors of long-term pacemaker dependency were complete atrioventricular block as the indication and bypass time of > 120 minutes (by multivariate and univariate analyses, respectively). Postoperative complete atrioventricular block is the most important predictor of pacemaker dependency, enabling an earlier decision on permanent pacemaker implantation (no later than the sixth and the ninth postoperative days for wide-complex and narrow-complex escape, respectively). Further prospective studies are needed to define optimal implantation times for indications other than complete atrioventricular block.     

Changes in cardiac repolarization following short periods of ventricular pacing

1. (5R)-3-[2-((1S)-3-cyano-1-hydroxypropyl)benzothiazol-6-yl]-5-metho xymethyl-2-oxazolidinone (E2011) has two chiral centers in its structure. In vivo optical inversion of the hydroxy group at one of the chiral centers converts E2011 to a diastereoisomer (ER-20593). Pharmacokinetic parameters of E2011 and ER-20593 were determined after administration of E2011 to rat at 10 mg/kg, and the plasma concentration ratios of E2011 to ER-20593 were almost constant after Tmax of the plasma concentrations. 2. E2011 and ER-20593 were separately administered orally to six species in addition to rat, and the species differences in both directions of epimerization (i.e. from E2011 to ER-20593 and from ER-20593 to E2011) were studied by measuring the plasma concentrations of both compounds. In mouse, guinea pig, dog, and squirrel monkey, the epimerization of E2011 to ER-20593 did not occur, but the epimerization of ER-20593 to E2011 did. In rat, pig and rhesus monkey, the inversion of E2011 to ER-20593 occurred, but the ratios of this inversion were smaller than those for the inversion in the opposite direction. E2011 underwent about 15% inversion to ER-20593 in rat, which was the largest inversion in the seven species examined. 3. To study the mechanism of the epimerization, deuterium-labelled E2011 and ER-20593 (created by substituting the proton at the chiral center of the parent compounds for deuterium) were orally administered (separately) to rat and dog, and the concentration ratios and molecular weights of E2011 and ER-20593 in the plasma were determined by hplc and FAB(+)-mass spectrometry respectively. The results indicated that the major mechanism of the epimerization was oxidation to the carbonyl form followed by reduction to the original epimer and/or the other epimer. 4. The carbonyl form of E2011 (CO-E2011) was reduced to E2011 and ER-20593 (alcohol forms) by liver cytosol and microsomes from rat and dog in vitro with NADH or NADPH. The resultant epimeric ratios (E2011:ER-20593) were consistent with the in vivo results in rat and dog. 5. In conclusion, species differences in the epimerization of E2011 would result from product stereoselectivity of the reductase activity with the carbonyl intermediate.     

Efficacy and safety of permanent cardiac DDD pacing with contemporaneous double spinal cord stimulation

A case of simultaneous bilateral tubal pregnancy resulting from in-vitro fertilization and embryo transfer is presented. Repeated transvaginal ultrasound examinations confirmed an intrauterine sac but no fetus. A diagnosis of early missed abortion was incorrectly made and a curettage was performed. The pathological examination showed the presence of decidua and Arias-Stella phenomenon but no chorionic villi. Diagnostic laparoscopy and laparotomy performed 40 days after embryo transfer (eighth week of gestation), revealed bilateral tubal pregnancy. Bilateral salpingectomy was performed.     

Ventricular tachycardia originating at the right ventricular outflow tract--surgical treatment of extrasystole

A boy with Down syndrome who developed acute nonlymphocytic leukemia (ANLL/M2) at the age of 40 months is presented. Chromosomal analysis of cultured peripheral blood cells without mitogen revealed a constitutional abnormality, trisomy 21, associated with the acquired chromosome change t(8;21)(q22;q22).     

Effects of right ventricular pacing on ventriculoatrial conduction and systemic venous responses in sick sinus patients

This study was designed to assess the ventriculoatrial (VA) conduction and systemic venous responses to right ventricular pacing at different pacing rates and the feasibility of identifying patients prone to pacemaker syndrome by means of a Doppler and two-dimensional echocardiographic technique. Twenty-two sick sinus patients who received ventricular-demand permanent pacemakers constituted the study group. The proximal inferior vena cava (IVC) diameters were measured by two-dimensional echocardiography. Fourteen patients had VA conduction by preimplant electrophysiologic study or paced electrocardiogram (Group II), while the other 8 patients presented no VA conduction (Group I). Abnormal systolic retrograde flow in the hepatic vein following each paced beat could be demonstrated in those patients with VA conduction in the basal state. In the 8 patients without VA conduction, the IVC diameters were significantly increased during rapid right ventricular pacing in those with left ventricular dysfunction (n = 4) as compared with those with normal left ventricular function (n = 4) (% increment at 120 beats per minute.     

Cardiac neural crest cells provide new insight into septation of the cardiac outflow tract: aortic sac to ventricular septal closure

Time series of daily administrative cardio-respiratory health and environmental information have been extensively used to assess the potential public health impact of ambient air pollution. Both series are subject to strong but unrelated temporal cycles. These cycles must be removed from the time series prior to examining the role air pollution plays in exacerbating cardio-respiratory disease. In this paper, we examine a number of methods of temporal filtering that have been proposed to eliminate such temporal effects. The techniques are illustrated by linking the number of daily admissions to hospital for respiratory diseases in Toronto, Canada for the 11 year period 1981 to 1991 with daily concentrations of ambient ozone. The ozone-hospitalization relationship was found to be highly sensitive to the length of temporal cycle removed from the admission time series, and to day of the week effects, ranging from a relative risk of 0.874 if long wave cycles were not removed at all to 1.020 for models which removed at least cycles greater than or equal to one month based on the interquartile pollutant range. The specific statistical method of adjustment was not a critical factor. The association was not as sensitive to removal of cycles less than one month, except that negative autocorrelation increased for series in which cycles of one week or less were removed. We recommend three criteria in selecting the degree of smoothing in the outcome: removal of temporal cycles, minimizing autocorrelation and optimizing goodness of fit. The association between ambient ozone levels and hospital admissions for respiratory diseases was also sensitive to the season of examination, with weaker associations observed outside the summer months.