Pulmonary vein narrowing after pulsed field versus thermal ablation.

AIMS: When it occurs, pulmonary vein (PV) stenosis after atrial fibrillation (AF) ablation is associated with significant morbidity. Even mild-to-moderate PV narrowing may have long-term implications. Unlike thermal ablation energies, such as radiofrequency (RF) or cryothermy, pulsed field ablation (PFA) is a non-thermal modality associated with less fibrotic proliferation. Herein, we compared the effects of PFA vs. thermal ablation on PV narrowing after AF ablation. METHODS AND RESULTS: ADVENT was a multi-centre, randomized, single-blind study comparing PFA (pentaspline catheter) with thermal ablation-force-sensing RF or cryoballoon (CB)-to treat drug-refractory paroxysmal AF. Pulmonary vein diameter and aggregate cross-sectional area were obtained by baseline and 3-month imaging. The pre-specified, formally tested, secondary safety endpoint compared a measure of PV narrowing between PFA vs. thermal groups, with superiority defined by posterior probability > 0.975. Among subjects randomized to PFA (n = 305) or thermal ablation (n = 302), 259 PFA and 255 thermal ablation (137 RF and 118 CB) subjects had complete baseline and 3-month PV imaging. No subject had significant (≥70%) PV stenosis. Change in aggregate PV cross-sectional area was less with PFA (-0.9%) than thermal ablation (-12%, posterior probability > 0.999)-primarily driven by the RF sub-cohort (-19.5%) vs. CB sub-cohort (-3.3%). Almost half of all PFA PV diameters did not decrease, but the majority (80%) of RF PVs decreased, regardless of PV anatomic location. CONCLUSION: In this first randomized comparison of PFA vs. thermal ablation, PFA resulted in less PV narrowing-thereby underscoring the qualitatively differential and favourable impact of PFA on PV tissue.

Pulsed Field or Conventional Thermal Ablation for Paroxysmal Atrial Fibrillation.

BACKGROUND: Catheter-based pulmonary vein isolation is an effective treatment for paroxysmal atrial fibrillation. Pulsed field ablation, which delivers microsecond high-voltage electrical fields, may limit damage to tissues outside the myocardium. The efficacy and safety of pulsed field ablation as compared with conventional thermal ablation are not known. METHODS: In this randomized, single-blind, noninferiority trial, we assigned patients with drug-refractory paroxysmal atrial fibrillation in a 1:1 ratio to undergo pulsed field ablation or conventional radiofrequency or cryoballoon ablation. The primary efficacy end point was freedom from a composite of initial procedural failure, documented atrial tachyarrhythmia after a 3-month blanking period, antiarrhythmic drug use, cardioversion, or repeat ablation. The primary safety end point included acute and chronic device- and procedure-related serious adverse events. RESULTS: A total of 305 patients were assigned to undergo pulsed field ablation, and 302 were assigned to undergo thermal ablation. At 1 year, the primary efficacy end point was met (i.e., no events occurred) in 204 patients (estimated probability, 73.3%) who underwent pulsed field ablation and 194 patients (estimated probability, 71.3%) who underwent thermal ablation (between-group difference, 2.0 percentage points; 95% Bayesian credible interval, -5.2 to 9.2; posterior probability of noninferiority, >0.999). Primary safety end-point events occurred in 6 patients (estimated incidence, 2.1%) who underwent pulsed field ablation and 4 patients (estimated incidence, 1.5%) who underwent thermal ablation (between-group difference, 0.6 percentage points; 95% Bayesian credible interval, -1.5 to 2.8; posterior probability of noninferiority, >0.999). CONCLUSIONS: Among patients with paroxysmal atrial fibrillation receiving a catheter-based therapy, pulsed field ablation was noninferior to conventional thermal ablation with respect to freedom from a composite of initial procedural failure, documented atrial tachyarrhythmia after a 3-month blanking period, antiarrhythmic drug use, cardioversion, or repeat ablation and with respect to device- and procedure-related serious adverse events at 1 year. (Funded by Farapulse-Boston Scientific; ADVENT ClinicalTrials.gov number, NCT04612244.).

A randomized controlled trial of pulsed field ablation versus standard-of-care ablation for paroxysmal atrial fibrillation: The ADVENT trial rationale and design.

Background: Pulmonary vein isolation (PVI) is an effective treatment for paroxysmal atrial fibrillation (PAF). However, potential complications can occur due to the propagation of thermal energy into nontarget tissues adjacent to the targeted myocardium. Pulsed field ablation (PFA) is a novel ablation modality with the potential for preferential myocardial tissue ablation to minimize damage to collateral cardiac structures. A multielectrode pentaspline catheter has demonstrated safety and efficacy in treating PAF in single-arm, first-in-human studies. Objective: The study sought to perform a randomized clinical trial to directly compare this PFA catheter with conventional ablation-either radiofrequency or cryoballoon ablation. Methods: The ADVENT (Randomized Controlled Trial for Pulsed Field Ablation versus Standard of Care Ablation for Paroxysmal Atrial Fibrillation) trial is a multicenter, prospective, single-blind, randomized controlled trial to compare PVI using PFA vs conventional thermal ablation for drug-resistant PAF-with each site employing either (but not both) cryoballoon or radiofrequency ablation as a control condition. The sample size is adaptively determined based on Bayesian statistical methods. All patients will undergo PVI, and be followed for 12 months. Results: The primary effectiveness endpoint is a composite of acute procedural success and freedom from any documented atrial arrhythmia recurrence, repeat ablation, or use of antiarrhythmic drugs after a 3-month postablation blanking period. The primary safety endpoint is a composite of defined acute and chronic device- and procedure-related serious adverse events. Both primary endpoints will be evaluated for noninferiority of the novel PFA system compared with standard-of-care thermal ablation. Conclusions: By providing objective, comparative data, this study aims to scientifically determine whether the pentaspline PFA catheter is safe and effective for PVI ablation to treat drug-resistant PAF.

Transcatheter Arterialization of Deep Veins in Chronic Limb-Threatening Ischemia.

BACKGROUND: Approximately 20% of patients with chronic limb-threatening ischemia have no revascularization options, leading to above-ankle amputation. Transcatheter arterialization of the deep veins is a percutaneous approach that creates an artery-to-vein connection for delivery of oxygenated blood by means of the venous system to the ischemic foot to prevent amputation. METHODS: We conducted a prospective, single-group, multicenter study to evaluate the effect of transcatheter arterialization of the deep veins in patients with nonhealing ulcers and no surgical or endovascular revascularization treatment options. The composite primary end point was amputation-free survival (defined as freedom from above-ankle amputation or death from any cause) at 6 months, as compared with a performance goal of 54%. Secondary end points included limb salvage, wound healing, and technical success of the procedure. RESULTS: We enrolled 105 patients who had chronic limb-threatening ischemia and were of a median age of 70 years (interquartile range, 38 to 89). Of the patients enrolled, 33 (31.4%) were women and 45 (42.8%) were Black, Hispanic, or Latino. Transcatheter arterialization of the deep veins was performed successfully in 104 patients (99.0%). At 6 months, 66.1% of the patients had amputation-free survival. According to Bayesian analysis, the posterior probability that amputation-free survival at 6 months exceeded a performance goal of 54% was 0.993, which exceeded the prespecified threshold of 0.977. Limb salvage (avoidance of above-ankle amputation) was attained in 67 patients (76.0% by Kaplan-Meier analysis). Wounds were completely healed in 16 of 63 patients (25%) and were in the process of healing in 32 of 63 patients (51%). No unanticipated device-related adverse events were reported. CONCLUSIONS: We found that transcatheter arterialization of the deep veins was safe and could be performed successfully in patients with chronic limb-threatening ischemia and no conventional surgical or endovascular revascularization treatment options. (Funded by LimFlow; PROMISE II study ClinicalTrials.gov number, NCT03970538.).

Complete 2-Year Results Confirm Bayesian Analysis of the SURTAVI Trial.

OBJECTIVES: The aim of this study was to report the 2-year results of the SURTAVI (Surgical Replacement and Transcatheter Aortic Valve Implantation) trial and confirm the interim Bayesian analysis. BACKGROUND: Transcatheter aortic valve replacement (TAVR) with a self-expanding valve was noninferior to surgery in patients with severe aortic stenosis and intermediate operative risk using Bayesian statistical methods. Novel Bayesian designs have been used to shorten the time to primary endpoint analysis in randomized clinical trials, although the predictive value of Bayesian analysis compared with frequentist approaches remains debated. METHODS: The SURTAVI trial randomized 1,660 patients. An interim analysis was performed 1 year after the 1,400th patient was treated to estimate the primary 2-year endpoint of all-cause mortality or disabling strokes for all patients. RESULTS: The Kaplan-Meier rate for the complete 2-year primary endpoint was 12.7% in the TAVR group and 12.6% in the surgery group (0.0% difference; 95% confidence interval: -3.4% to 3.5%), compared with 12.6% with TAVR and 14.0% with surgery (-1.4% difference; Bayesian credible interval: -5.2% to 2.3%) in the interim Bayesian analysis. A comparison of individual clinical, hemodynamic, and quality-of-life endpoints using Bayesian and frequentist methods found no significant differences. CONCLUSIONS: The complete analysis of all patients with aortic stenosis at intermediate risk for surgery in the SURTAVI trial confirmed the noninferiority, with respect to the frequency of all-cause mortality or disabling stroke, of TAVR to surgery, as determined in the interim Bayesian analysis. Follow-up will extend out to 10 years.

Transcatheter Aortic-Valve Replacement with a Self-Expanding Valve in Low-Risk Patients.

BACKGROUND: Transcatheter aortic-valve replacement (TAVR) is an alternative to surgery in patients with severe aortic stenosis who are at increased risk for death from surgery; less is known about TAVR in low-risk patients. METHODS: We performed a randomized noninferiority trial in which TAVR with a self-expanding supraannular bioprosthesis was compared with surgical aortic-valve replacement in patients who had severe aortic stenosis and were at low surgical risk. When 850 patients had reached 12-month follow-up, we analyzed data regarding the primary end point, a composite of death or disabling stroke at 24 months, using Bayesian methods. RESULTS: Of the 1468 patients who underwent randomization, an attempted TAVR or surgical procedure was performed in 1403. The patients' mean age was 74 years. The 24-month estimated incidence of the primary end point was 5.3% in the TAVR group and 6.7% in the surgery group (difference, -1.4 percentage points; 95% Bayesian credible interval for difference, -4.9 to 2.1; posterior probability of noninferiority >0.999). At 30 days, patients who had undergone TAVR, as compared with surgery, had a lower incidence of disabling stroke (0.5% vs. 1.7%), bleeding complications (2.4% vs. 7.5%), acute kidney injury (0.9% vs. 2.8%), and atrial fibrillation (7.7% vs. 35.4%) and a higher incidence of moderate or severe aortic regurgitation (3.5% vs. 0.5%) and pacemaker implantation (17.4% vs. 6.1%). At 12 months, patients in the TAVR group had lower aortic-valve gradients than those in the surgery group (8.6 mm Hg vs. 11.2 mm Hg) and larger effective orifice areas (2.3 cm2 vs. 2.0 cm2). CONCLUSIONS: In patients with severe aortic stenosis who were at low surgical risk, TAVR with a self-expanding supraannular bioprosthesis was noninferior to surgery with respect to the composite end point of death or disabling stroke at 24 months. (Funded by Medtronic; ClinicalTrials.gov number, NCT02701283.).

Surgical or Transcatheter Aortic-Valve Replacement in Intermediate-Risk Patients.

BACKGROUND: Although transcatheter aortic-valve replacement (TAVR) is an accepted alternative to surgery in patients with severe aortic stenosis who are at high surgical risk, less is known about comparative outcomes among patients with aortic stenosis who are at intermediate surgical risk. METHODS: We evaluated the clinical outcomes in intermediate-risk patients with severe, symptomatic aortic stenosis in a randomized trial comparing TAVR (performed with the use of a self-expanding prosthesis) with surgical aortic-valve replacement. The primary end point was a composite of death from any cause or disabling stroke at 24 months in patients undergoing attempted aortic-valve replacement. We used Bayesian analytical methods (with a margin of 0.07) to evaluate the noninferiority of TAVR as compared with surgical valve replacement. RESULTS: A total of 1746 patients underwent randomization at 87 centers. Of these patients, 1660 underwent an attempted TAVR or surgical procedure. The mean (±SD) age of the patients was 79.8±6.2 years, and all were at intermediate risk for surgery (Society of Thoracic Surgeons Predicted Risk of Mortality, 4.5±1.6%). At 24 months, the estimated incidence of the primary end point was 12.6% in the TAVR group and 14.0% in the surgery group (95% credible interval [Bayesian analysis] for difference, -5.2 to 2.3%; posterior probability of noninferiority, >0.999). Surgery was associated with higher rates of acute kidney injury, atrial fibrillation, and transfusion requirements, whereas TAVR had higher rates of residual aortic regurgitation and need for pacemaker implantation. TAVR resulted in lower mean gradients and larger aortic-valve areas than surgery. Structural valve deterioration at 24 months did not occur in either group. CONCLUSIONS: TAVR was a noninferior alternative to surgery in patients with severe aortic stenosis at intermediate surgical risk, with a different pattern of adverse events associated with each procedure. (Funded by Medtronic; SURTAVI ClinicalTrials.gov number, NCT01586910 .).

Peripheral artery disease is an independent predictor of mortality after implantable cardioverter-defibrillator implantation in patients with severe left ventricular dysfunction.

The impact of peripheral artery disease (PAD) on survival in implantable cardioverter defibrillator (ICD) patients is poorly understood. Thus, we assessed the risk of PAD in our adult ICD patients with left ventricular dysfunction (ejection fraction [EF] ≤35%). Survival was estimated with Kaplan-Meier method and compared by the log-rank test; a Cox proportional hazards model assessed the effects of clinical variables on survival. Average age and EF of 1399 patients were 67.0 ± 12.1 years and 23.8% ± 7.2%, respectively. The ICD patients with PAD had significantly worse survival than those without (unadjusted P < .0001). The multivariate predictors of survival at implant were (hazard ratio, HR [95% confidence interval]) age (HR 1.05 [1.04-1.07] P < .0001), PAD (HR 2.07 [1.53-2.80] P < .0001), class III/IV heart failure (HR 1.36 [1.06-1.76] P = .016), creatinine 1.4-2.0 mg/dL (HR 1.36 [1.05-1.76] P = .019), and creatinine ≥2.0 mg/dL (HR 2.01 [1.42-2.85] P < .0001). The PAD is an independent predictor of mortality and should be considered in the preimplant risk assessment.

Independent multicenter study of Riata and Riata ST implantable cardioverter-defibrillator leads.

BACKGROUND: Riata and Riata ST leads (St Jude Medical, Sylmar, CA) are prone to failure. There are no independent multicenter reports regarding Riata or Riata ST lead performance. OBJECTIVE: To conduct a retrospective multicenter study of Riata and Riata ST leads that were implanted and followed at 7 centers. METHODS: The study included adults who received St Jude Medical Riata or Riata ST leads. Data for Quattro Secure leads were obtained from an earlier study. RESULTS: From 2002 to 2010, 1081 patients received a Riata (n = 774) or Riata ST (n = 307) lead. Follow-up was longer for Riata than Riata ST leads (4.2 ± 2.4 years vs 3.3 ± 1.7 years; P<.0001). During the study, 67 leads failed (6.2%), including 62 of 774 Riata (8.0%) and 5 of 307 Riata ST (1.6%) leads. Forty-seven of 67 lead failures (70.1%) were caused by electrical malfunction, and 20 lead failures (29.9%) were due to externalized conductors (ECs) that were electrically intact. Of 110 leads examined fluoroscopically, ECs were found in 26 of 81 Riata (32%) and 1 of 29 Riata ST (3.4%) leads. Of 26 Riata leads with ECs, 7 (27%) were malfunctioning. Riata leads had lower overall and malfunction free survival compared to Quattro leads (P<.0001), while Riata ST lead survival was not different (P = .422). CONCLUSIONS: The survival of Riata (but not Riata ST) leads was lower than Quattro leads; however, Riata ST leads had significantly shorter follow-up than Riata leads. ECs were common in Riata leads, and more than a quarter of Riata leads that had ECs were malfunctioning. Our observations suggest that systematic fluoroscopic examination of patients with Riata leads is appropriate.

Effect of steroid-releasing sinus implants on postoperative medical and surgical interventions: an efficacy meta-analysis.

BACKGROUND: Endoscopic sinus surgery (ESS) for chronic rhinosinusitis (CRS) can be compromised by postoperative inflammation, polyposis, and adhesions, often requiring subsequent interventions. A bioabsorbable, steroid-releasing sinus implant has been studied in 2 prospective, randomized clinical trials for its ability to preserve sinus patency and reduce medical and surgical interventions after ESS in patients with CRS. The objective of this study was to perform a meta-analysis of the efficacy results from the 2 trials. METHODS: The 2 prospective, randomized, double-blinded, multicenter trials enrolled a total of 143 patients utilizing an intrapatient control design. Postoperative day 30 videos were obtained for each patient, randomly ordered, and presented to an independent panel of 3 otolaryngologists for grading of efficacy endpoints. The need for postoperative interventions, formation of polyposis, and adhesions were assessed. Results from the 2 studies were then pooled. RESULTS: Implants were successfully placed in all 286 ethmoid sinuses. According to the grading done by the panel, drug-releasing implants reduced postoperative interventions by 35% (p = 0.0008), lysis of adhesions by 51% (p = 0.0016), and oral steroid need by 40% (p = 0.0023), compared to controls. The relative reduction in frank polyposis was 46% (p < 0.0001). CONCLUSION: Early postoperative healing is a predictor of longer-term success after sinus surgery. Evaluation of postoperative outcomes by a blinded independent panel demonstrates that steroid-releasing implants that provide a sustained release of corticosteroid improve surgical outcomes by reducing frank polyp formation, sinus adhesions, and middle turbinate lateralization. Steroid-releasing implants reduce the need for surgical intervention, and the need for oral steroid treatment.

Early detection of an underperforming implantable cardiovascular device using an automated safety surveillance tool.

BACKGROUND: Postmarket medical device surveillance in the United States depends largely on voluntary reporting of adverse events. Consequently, early safety signals may be missed, exposing patients to potentially hazardous products. The aim of this study was to assess the feasibility of using an automated safety surveillance tool to detect early signals that a marketed implantable cardiac device was underperforming. METHODS AND RESULTS: For this purpose, we performed simulated prospective monthly full-cohort and propensity-matched comparative survival analyses on our 3-center database of Sprint Fidelis and Quattro Secure implantable cardioverter-defibrillator leads, using a commercially available automated surveillance tool that was preset to trigger an alert if the log rank probability value was <0.05. During the study, 84 of 1035 Fidelis (8.1%) and 23 of 1675 Quattro (1.4%) leads failed. The simulated full-cohort analysis triggered a sustained alert for Fidelis leads beginning 13 months after the first implant and 2 years before Fidelis leads were removed from the market. Of the 1035 patients who had Fidelis leads, up to 969 (93.6%) were successfully matched to Quattro patients. In the propensity-matched analysis, the alert triggered 22 months after the first Fidelis implant and more than 1 year before the lead was recalled. CONCLUSIONS: An active automated safety surveillance system could have identified this implantable cardiovascular device problem substantially sooner than was achieved through existing postmarket surveillance methods. Such a tool, when applied to clinical registries and remote monitoring databases, may limit the exposure of large populations to underperforming and potentially hazardous cardiovascular devices.

Advance II: a prospective, randomized study assessing safety and efficacy of bioabsorbable steroid-releasing sinus implants.

OBJECTIVE: Endoscopic sinus surgery (ESS) for chronic rhinosinusitis (CRS) may be compromised by postoperative inflammation, polyposis, and adhesions, often requiring subsequent intervention. To address this issue, the authors investigated the safety and effectiveness of controlled delivery of mometasone furoate to the sinus mucosa via bioabsorbable implants deployed at the time of ESS. STUDY DESIGN: Prospective, multicenter, randomized, controlled, double-blind trial using an intrapatient control design. SETTING: Otolaryngology-head and neck surgery centers; both academic and private practices. SUBJECTS AND METHODS: The study enrolled 105 patients with CRS undergoing bilateral ethmoidectomy to compare the effect of drug-releasing to non-drug-releasing implants using an intrapatient control design. Postoperative interventions, polyposis, and adhesions were assessed postoperatively. Efficacy was determined through independent analysis of randomized video-endoscopies by 3 blinded sinus surgeons. Safety assessments included ocular examinations. RESULTS: Implants were successfully deployed in all 210 ethmoid sinuses. Compared with control sinuses with non-drug-releasing implants, the drug-releasing implant provided a 29.0% relative reduction in postoperative interventions (P = .028) and a 52% (P = .005) decrease in lysis of adhesions. The relative reduction in frank polyposis was 44.9% (P = .002). Similar reductions were observed in real-time grading performed by the clinical investigators. No clinically significant changes from baseline in intraocular pressure or cataracts were observed. CONCLUSION: This study provides a high level of evidence that use of steroid-releasing implants that apply a sustained release of corticosteroid improves surgical outcomes by reducing synechiae formation, polyposis, and the need for postoperative interventions, with no observable ocular safety risk.

Longevity of Sprint Fidelis implantable cardioverter-defibrillator leads and risk factors for failure: implications for patient management.

BACKGROUND: Sprint Fidelis (Fidelis) implantable cardioverter-defibrillator leads are prone to fractures that have caused adverse events, primarily inappropriate shocks, and a few reported deaths. More than 100 000 patients have Fidelis leads. No independent multicenter long-term performance information exists for this lead, and single-center studies suggest that certain patients are at increased risk for Fidelis failure. Our aim was to assess the longevity of Fidelis leads and to evaluate clinical variables and adverse events associated with Fidelis failure. The results were compared with like data for Quattro Secure (Quattro) implantable cardioverter-defibrillator leads implanted at our centers. METHODS AND RESULTS: This 3-center study included adults ≥18 years of age who received Fidelis or Quattro leads for the prevention of sudden cardiac death. From November 2001 to January 2009,1023 Fidelis and 1668 Quattro leads were implanted and followed up. The failure rate for Fidelis leads was 2.81%/y compared with 0.43%/y for Quattro leads (P<0.0001). No deaths or injuries occurred as a result of lead failure, but 42% of fractures caused inappropriate shocks. The survival of Fidelis leads at 4 years was 87.0% (95% confidence interval, 83.6 to 90.1) compared with 98.7% (95% confidence interval, 97.9 to 99.4) for Quattro leads (P<0.0001). Multivariate predictors of Fidelis failure were younger age (hazard ratio, 0.98; 95% confidence interval, 0.96 to 0.99), female gender (hazard ratio, 0.61; 95% confidence interval, 0.40 to 1.00), and cardiac disease (P=0.041). CONCLUSIONS: Compared with Quattro leads, the survival of Fidelis leads continues to decline, and Fidelis failure is notably higher in younger patients, women, individuals with hypertrophic cardiomyopathy, and patients with arrhythmogenic right ventricular dysplasia or channelopathies. These findings have significant implications for the management of patients who have Fidelis leads, and they demonstrate the importance of weighing clinical variables in assessments of implantable cardioverter-defibrillator lead performance.

Safety and efficacy of a novel bioabsorbable, steroid-eluting sinus stent.

BACKGROUND: Inflammation/polyp recurrence, adhesions, and middle turbinate lateralization are causes of suboptimal outcomes following sinus surgery and lead to increased rates of revision. A bioabsorbable, drug-eluting stent was evaluated for its ability to preserve sinus patency by providing controlled steroid delivery to the sinus mucosa. The study objective was to assess safety and efficacy of a steroid-eluting sinus stent when used following functional endoscopic sinus surgery (FESS) in patients with chronic rhinosinusitis (CRS). METHODS: Prospective, multicenter, randomized, double-blind clinical trial, enrolling 43 patients in 2 groups. One group (n = 38) used an intrapatient control design comparing drug-eluting to non-drug-eluting stents. The other group (n = 5) received bilateral drug-eluting stents to assess systemic safety. Endoscopic follow-up was performed for 60 days. Efficacy endpoints included assessment of inflammation, polyp formation, adhesions, and middle turbinate position. RESULTS: Stents were successfully deployed in all 86 sinuses. Compared to the control stent, the drug-eluting stent provided statistically significant reduction in inflammation at days 21 to 45 (p < 0.003), frequency of polyp formation (p = 0.0391), and frequency of significant adhesion (p = 0.0313). Reduced frequency of middle turbinate lateralization was also apparent though not statistically significant. No device-related adverse events occurred. Eluted steroid was unquantifiable systemically and there was no evidence of adrenal cortical suppression. CONCLUSION: This study demonstrates the safety and efficacy of a novel bioabsorbable, steroid-eluting stent for use in CRS patients. The steroid-eluting stent is effective in improving wound healing by preserving sinus patency, reducing inflammation, and minimizing adhesions via controlled local steroid delivery without measurable systemic exposure.

Hierarchical statistical modelling of influenza epidemic dynamics in space and time.

An infectious disease typically spreads via contact between infected and susceptible individuals. Since the small-scale movements and contacts between people are generally not recorded, available data regarding infectious disease are often aggregations in space and time, yielding small-area counts of the number infected during successive, regular time intervals. In this paper, we develop a spatially descriptive, temporally dynamic hierarchical model to be fitted to such data. Disease counts are viewed as a realization from an underlying multivariate autoregressive process, where the relative risk of infection incorporates the space-time dynamic. We take a Bayesian approach, using Markov chain Monte Carlo to compute posterior estimates of all parameters of interest. We apply the methodology to an influenza epidemic in Scotland during the years 1989-1990.