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P R Roberts

Publications and source records attributed to P R Roberts.

At least 19 recordsLinked to original sources
PubMed2004

Evaluation of body weight as a predictive factor for transvenous ventricular defibrillation characteristics.

AIMS: To investigate the correlation between body weight and defibrillation threshold (DFT) for transvenous lead systems using a porcine model. METHODS AND RESULTS: Twenty-eight pigs were anaesthetised and DFTs assessed in single and dual coil configurations using a four-reversal binary search method. DFT was correlated with body weight in the RV --> Can and RV --> SVC + Can configurations. A Pearson correlation coefficient and a two-sided p-value were calculated. A positive correlation exists between body weight and DFT in RV --> Can (r=0.66, p<0.000) and RV --> SVC + Can (r=0.44, p=0.018). CONCLUSION: There is a significant correlation between body weight and DFT in swine. This tends to be greater in the two-electrode than in the three-electrode configuration. With these and previous human observations, one may predict a higher DFT in heavy individuals and make appropriate procedural adjustments.

Animals↗
PubMed2004

Radiation peak skin dose to risk stratify electrophysiological procedures for deterministic skin damage.

UNLABELLED: Ionising radiation is has the potential to cause harm both by increasing the probability future malignancy (stochastic mechanisms) and by direct physical injury (deterministic mechanisms). Several measures have been developed to quantify radiation exposure during a procedure and cardiologists usually refer to fluoroscopic screening time (FST). FST, however, has limitations for predicting deterministic injury which is directly dependant on peak skin dose (PSD). We compared FST to PSD for a range of interventional cardiac electrophysiology procedures. METHODS: All patients undergoing electrophysiology procedures during a 2-month period in our institution were studied. Demographic details, nature of procedure, FST and PSD were measured. The FST to PSD ratio was calculated and compared between patient and procedural factors. RESULTS: 67 procedures on patients (23 female) with body mass index (BMI) of 28 (SD 5) Kg/m2 were studied. Screening times ranged from 0.2 to 96.6 min (median 11.2). PSD ranged from <0.1 to 1108 mGy (median 141). There was a positive correlation between PSD to FST ratio and BMI (r = 0.59, p < 0.001). The PSD to FST ratio was higher in cardiac resynchronization therapy (CRT) devices than single or dual chamber ICDs (p = 0.002). CONCLUSION: FST is not a reliable predictor of deterministic skin injury and in high-risk procedures such as CRT devices and those on individuals of high BMI PSD should be measured.

Body Mass Index↗
PubMed2003

Comparison of coronary venous defibrillation with conventional transvenous internal defibrillation in man.

OBJECTIVE: Animal studies have shown that defibrillation in coronary veins is more effective than in the right ventricle. We aimed to assess the feasibility of placing defibrillation electrodes in the middle cardiac vein (MCV) in man and its impact on defibrillation requirements. METHODS: A prospective randomised study conducted in a tertiary referral centre. 10 patients (9 male) undergoing ICD implantation (65 (12) yrs) for NASPE/BPEG indications were studied. Defibrillation thresholds (DFT) were measured, using a binary search and an external defibrillator after 10 seconds of ventricular fibrillation, for the following configurations in each patient (order of testing randomised): RV + MCV --> Can and RV --> SVC + Can. INTERVENTIONS: A dual coil defibrillation electrode was placed transvenously in the right ventricle (RV) in the conventional manner. Using a guiding catheter a 3.2 Fr (67.5 mm length) electrode was placed transvenously in MCV. A test-can was placed subcutaneously in the left pectoral region. RESULTS: Lead placement was possible in 8/10 pts. Time to perform a middle cardiac venogram and place the electrode was 21 (23) mins. No adverse events were observed. Defibrillation current was less (6.7 (2.7) A) with RV + MCV --> Can compared to the conventional RV --> SVC + Can configuration (8.9 (3.4) A, p = 0.03). There was no significant difference in defibrillation voltage or energy. However, shock impedance was higher in the former configuration (57 (10) v. 43 (6) Omega, p = 0.001). CONCLUSIONS: In the majority of cases placement of a defibrillation lead in MCV is feasible. Defibrillation current requirements are 25% less when the shock is delivered using a MCV electrode.

Aged↗
PubMed2002

Use of implantable cardioverter defibrillator and anti-arrhythmic agents in a parturient.

We describe a case of a 36-yr-old patient who presented at 14 weeks gestation with multifocal dysrrhythmic episodes. Despite treatment with anti-arrythmic agents and an implantable cardioverter defibrillator (ICD) in situ, she continued to experience persistent dysrrhythmic episodes. She was delivered by Caesarean section at 34 weeks under general anaesthesia. We discuss some of the anaesthetic challenges of parturients with ICD devices.

Adult↗
PubMed2001

Single capacitive discharge utilizing an auxiliary shock in the coronary venous system reduces the defibrillation threshold.

UNLABELLED: Auxiliary shocks (AS) from electrodes sutured to the left ventricle (LV) prior to primary biphasic shocks (PS) have been shown to reduce defibrillation thresholds (DFT). Two capacitors are required to generate these waveforms. We investigate delivery of AS from one capacitor using a novel waveform. The epicardial surface of the LV is accessed transvenously via the middle cardiac vein (MCV) avoiding a thoracotomy. METHODS: A defibrillation electrode was placed in the right ventricle (RV) and superior vena cava (SVC) in 12 pigs (37+/-2 kg). A 50x1.8 mm electrode was inserted in the MCV through a guide catheter. A can was placed in the left pectoral region. A monophasic AS (100 microF, 1.5 J) was delivered along one pathway before switching to deliver a biphasic waveform (40% tilt, 2 ms phase 2) along another. DFTs (PS+AS) were assessed using a binary search. Two configurations not incorporating AS acted as controls. DFTs were compared using repeated measures analysis of variance. RESULTS: DFTs of the four novel configurations (AS/PS) were: RV-->Can/MCV-->Can=14.9+/-3.7 J, MCV-->Can/RV-->Can=17.2+/-5.7 J, RV-->SVC+Can/MCV-->SVC+Can=13.4+/-4.6 J, MCV-->SVC+Can/RV-->SVC+Can=17.1+/-5.9 J. Delivering AS in the RV followed by PS in the MCV reduced the DFT (RV-->Can (19.9+/-7.3 J, P<0.01) and RV-->SVC+Can (19.2+/-6.0 J, P<0.05)). CONCLUSIONS: Delivering AS prior to PS in the MCV reduces the DFT by up to a third compared to conventional configurations of RV-->Can and RV-->SVC+Can. This is possible using only a single capacitor and an entirely transvenous approach to the LV.

Animals↗
PubMed2001

Inappropriate shock therapy in a heart failure defibrillator.

A 63-year-old male with dilated cardiomyopathy underwent implantation of a "heart failure" defibrillator capable of biventricular pacing. He received an inappropriate shock 5 hours after the procedure. Stored electrograms revealed that during each sinus beat the ventricular channel recorded up to three separate events. These resulted from far-field atrial sensing by the coronary venous lead, appropriate right ventricular sensing, then delayed left ventricular sensing (the result of left bundle branch block). As a consequence of far-field left atrial sensing the two subsequent ventricular electrograms fell within the VF zone. Following an atrial premature beat, VF detection criteria were satisfied and shock therapy delivered. Although coronary venous lead repositioning eliminated far-field atrial sensing, double counting of the widely split right and left ventricular electrograms still occurred during sinus rhythm. Shortening the programmed AV delay resulted in constant biventricular pacing with a single electrogram.

Algorithms↗
PubMed2001

Feasibility of a left atrial electrical disconnection procedure for atrial fibrillation using transcatheter radiofrequency ablation.

INTRODUCTION: An effective, catheter-based treatment for persistent atrial fibrillation (AF) remains elusive. This study assessed the feasibility of transcatheter left atrial (LA) electrical disconnection and its effect on AF inducibility. METHOD AND RESULTS: Thirteen anesthetized swine underwent noncontact mapping of the right atrium (RA) during coronary sinus (CS) pacing. Sites of earliest RA activation were identified using isopotential maps. An ablation catheter was navigated to these sites and a cluster of radiofrequency (RF) lesions applied until earliest activation shifted to a new site. The procedure was repeated until the atria were electrically disconnected. AF induction was attempted before and after ablation. Earliest RA activation was the CS os during proximal CS pacing and Bachmann's bundle during distal CS pacing. These two sites were successfully ablated in all 13 animals. Earliest activation then shifted to the fossa ovalis. RF energy was applied at a median of 2.5 sites (range 1 to 5) around the fossa, then at sites in the triangle of Koch, septum, cavotricuspid isthmus, and posterior wall. Atrial electrical disconnection was achieved in 10 of 13 animals (5 LA electrical disconnection, 3 RA electrical disconnection, 2 biatrial electrical disconnection with complete heart block). After atrial electrical disconnection, the LA became electrically silent. Before ablation, AF was inducible in every animal. After atrial electrical disconnection, AF was inducible in 3 of 10 animals. CONCLUSION: Atrial electrical disconnection is feasible using noncontact mapping and RF ablation. Successful electrical disconnection of the atria reduces AF inducibility. This approach is worthy of further evaluation as a management strategy for persistent AF, combined with device therapies.

Animals↗
PubMed2001

Nutritional support in acute pancreatitis: an update on management issues.

About 20% of acute pancreatitis cases develop necrosis and have a high risk of inflammatory and infectious complications and a high mortality rate. Acute pancreatitis has a variety of causes and despite years of research its pathogenesis remains complex and obscure. Both local and systemic inflammatory responses play key roles in the pathophysiology of this disorder. Treatment plans continue to rely on supportive care without proven specific therapies. Pancreatic rest and use of total parenteral nutrition (TPN) were the gold standard for nutritional support of these challenging patients. Because numerous studies in other critically ill patients demonstrated benefits of enteral nutrition, recent investigations compared TPN to enteral nutrition in acute pancreatitis. These studies indicated that enteral nutrition delivered into the jejunum was tolerated well, even in patients with severe acute pancreatitis. "Mild'' cases of pancreatitis should improve and tolerate oral nutrition within a few days. In contrast, "severe'' cases of pancreatitis or those with a protracted clinical course require nutritional support to aid in preventing adverse effects of starvation and nutrient deficiencies. Current recommendations are to attempt enteral nutrition in patients with acute pancreatitis prior to instituting TPN. Further studies to determine optimal nutrient composition are warranted and should investigate the possibility of modulating the inflammatory response induced by pancreatitis to improve outcomes.

Journal Article↗
PubMed2000

Electrophysiological mapping and ablation of intra-atrial reentry tachycardia after Fontan surgery with the use of a noncontact mapping system.

BACKGROUND: Atrial tachyarrhythmias are a complication of Fontan surgery. Conventional electrophysiological mapping and ablation techniques are limited by the complex anatomic and surgical substrate and a high arrhythmia recurrence rate. This study investigates the use of noncontact mapping to identify arrhythmia circuits and guide ablation in Fontan patients. METHODS AND RESULTS: Eleven arrhythmias were recorded in 6 patients. Noncontact mapping improved recognition of the anatomic and surgical substrate and identified exit sites from zones of slow conduction in all clinical arrhythmias. Radiofrequency linear lesions were targeted across these critical zones in 5 patients. One patient underwent surgical cryotherapy. Although immediate success was achieved in 3 of 5 patients with radiofrequency ablation, 2 patients had a recurrence after a mean of 6.4 months of follow-up. The patient who underwent cryoablation remains free of arrhythmias. CONCLUSIONS: Noncontact mapping can identify arrhythmia circuits in the Fontan atrium and guide placement of ablation lesions. Arrhythmia recurrence is high, possibly because of inadequate lesion creation rather than inaccurate mapping and lesion targeting.

Adolescent↗
PubMed2000

Future directions in health for the new Government: our health and the public health.

The 'no model' model awaited the invisible hand. However, 'more government' demands more hands-on direction of the health system. To whom will the government turn for advice? The health professionals were excluded from the market experiment because of the concern that they would 'capture the process'. With the change in the political will, some of the most simplistic, fallacious perceptions of New Zealand's society should have less influence on health policy. The new government has the opportunity to re-engage New Zealanders in advancing the health of the nation. Public health specialists have a wealth of information to guide decision-making which deserves wider dissemination and more executive consideration. In personal health care, health professionals have the will to continue innovation but need a system in which their values are respected. One caveat: there is a tendency, whether the approach is 'more market' or 'more government', to try to measure everything and tick every box. When dealing with complex systems which need highly skilled professionals, however, there simply needs to be a high level of trust As when getting on a plane, central planners, like the rest of us, need to understand that sometimes the pilots must 'capture the process' in order to get back on course.

Government↗
PubMed2000

Vasodilatory actions of the dietary peptide carnosine.

The objective of this study was to test the hypothesis that the dietary dipeptide carnosine (beta-alanine-L-histidine) causes direct decreases in arterial tone. Isolated descending thoracic aortic rings from male Sprague-Dawley rats were used for all studies. Preconstriction of vessels was accomplished with phenylephrine. Carnosine (0.625-20 mM) produced dose-dependent vascular relaxation (P < 0.05) that was independent of endothelium. The constituent amino acid L-histidine did not produce any significant relaxation over the same dose range, whereas beta-alanine actually produced dose-dependent vasoconstriction (P < 0.05). The soluble guanylate cyclase inhibitor methylene blue (10(-5) M) significantly decreased the relaxation produced by carnosine (P < 0.05). Measurement of cyclic GMP in the presence and absence of methylene blue after carnosine and phenylephrine exposure was also done. Methylene blue 10(-5) M resulted in a decrease in cyclic GMP levels from 65.3 +/- 15.6 fmol/mg protein to 8.6 +/- 0.9 fmol/mg of protein (P = 0.001). We conclude that carnosine produces relaxation of isolated rat aorta independent of endothelium. The effect of carnosine is at least in part mediated via cyclic GMP production and is not reproduced by its constituent amino acids, L-histidine and beta-alanine.

Animals↗
PubMed2000

Increased defibrillation threshold with right-sided active pectoral can.

UNLABELLED: The aim of this study was to identify the optimal position on the chest wall to place an implant able cardioverter defibrillator in a two-electrode system, consisting of a right ventricular electrode and active can. METHODS AND RESULTS: Defibrillation thresholds (DFT) were measured in 10 anaesthetised pigs (weight 33-45 kg). An Angeflextrade mark lead was introduced transvenously to the right ventricular apex. The test-can (43 cc) was implanted submuscularly in each of four locations: left pectoral (LP), right pectoral (RP), left lateral (LL) and apex (A). The sequence in which the four locations were tested was randomized. Ventricular fibrillation (VF) was induced using 60 Hz alternating current. Rectangular biphasic shocks were delivered 10 seconds after VF induction. The DFT was measured using a modified four-reversal binary search. The results of the four configurations were: LP, 14.6+/- 4.0 J; RP, 18.8+/- 4.2 J; LL, 14.7+/- 4.1 J; A, 14.9+/- 3.1 J. Repeated measures analysis of variance showed that the DFT of RP was significantly higher than LP, LL and A (p < 0.05). CONCLUSIONS: Implanting an active can in the RP position increases the DFT by 29% compared to LP, LL and A sites. The can position on the left thorax does not appear to have a significant influence on DFT.

Animals↗
PubMed2000

Autonomic dysfunction secondary to intracerebral hemorrhage.

IMPLICATIONS: We report a case of autonomic dysfunction secondary to intracranial hemorrhage. The patient had periodical episodes of hypertension, tachycardia, tachypnea, and diaphoresis that responded dramatically to Thorazine, but not to conventional measures.

Adult↗
PubMed2000

Inhibition of nitric oxide synthase enhances the myocardial toxicity of phenylpropanolamine.

OBJECTIVE: To investigate the direct and indirect effects of the anorexic agent phenylpropanolamine (PPA) on the heart and to determine whether nitric oxide deficiency exacerbates the myocardial toxicity of PPA. DESIGN: Dose response effects using sequential drug administration. SETTING: Animal research laboratory of a large tertiary academic medical center. SUBJECTS: Isolated hearts (n = 8) from male Sprague-Dawley rats weighing 300-400 g. INTERVENTIONS: Measurement of heart rate, maximal change in pressure over time (dP/dtmax), -dP/dtmax, and coronary blood flow in isolated hearts perfused on a Langendorff apparatus. PPA was infused through the aortic cannula at 0.05, 0.125, 0.25, 0.5, and 1.25 mmol/L before and after inhibition of nitric oxide synthesis with N-nitro-L-arginine methyl ester (L-NAME). RESULTS: PPA had little effect on myocardial contractility of normal hearts until the highest dose of PPA (1.25 mmol/L). However, after L-NAME, PPA significantly depressed contractility at a dose of 0.25 mmol/L. PPA had no significant effects on coronary blood flow. PPA failed to induce arrhythmias in normal hearts. However, after L-NAME, PPA induced ventricular fibrillation in 50% of the hearts. CONCLUSION: PPA causes myocardial contractile depression without altering global coronary artery blood flow. Inhibition of nitric oxide synthesis sensitizes the heart to the myocardial depressant effects of PPA and increases the risk for ventricular fibrillation.

Animals↗