Multidetector computed tomography identification of previous ablation lines: insights for left atrial flutter ablation

Funding Acknowledgements

Type of funding sources: None.

Background

Left atrial flutter (LAFL) frequently occurs in patients with history of previous left atrial (LA) ablation. LAFL ablation is still considered a challenging and time-consuming procedure (1). Conduction gaps on ablation lines are frequently due to non-transmural or non-contiguous lesions. It was recently demonstrated that aiding AF ablation procedures with the integration of multidetector computed tomography (MDCT)-derived left atrial wall thickness (LAWT) maps into the navigation system allowed decreasing radiofrequency (RF) delivery, fluoroscopy, and procedure time while obtaining a high rate of first-pass isolation (2).

Purpose

We hypothesized that MDCT-derived 3D-LAWT map could be useful to aid LAFL ablation procedure in patients with previous LA ablation lines.

Methods

Consecutive patients with history of previous LA ablation who underwent LAFL ablation were prospectively enrolled from a single referral center. LAWT three-dimensional maps were obtained from MDCT and integrated into the navigation system. LAWT information was used to focus mapping in the areas of the probable crucial isthmus: the presence of previous ablation lines was searched at the level of linear segments with reduced parietal thickness at the LAWT-maps (LAWT <1mm), while the search for conduction gaps was started at the level of the thicker areas of these lines. Conduction gap was defined as the presence of peak-to-peak bipolar potentials > 0.5 mV at the level of the previous ablation line or as the presence during arrhythmia of a LAT delay <30 ms between contiguous points lying in the same axial plane at the two sides of the line. Ablation was performed transecting the crucial isthmus with the documentation of bidirectional block; ablation first-attempt was guided by color-coded maps by connecting the parts of identified previous ablation lines with reduced LAWT. Finally, RF delivery was adapted to the local LAWT.

Results

Five patients [4 (80%) male, age 62 years (57-73)] were included. LAWT-aided LAFL ablation procedures had a median procedure time of 78 minutes (75-114) and a RF time of 5.9 minutes (4.7-8.5); fluoroscopy time was 3.2 minutes (1.5-3.6) with a fluoroscopy dose of 6.1 Gy*cm2 (2.8-8.2). Mean wall thickness of the gap zone was significantly higher with respect to the thickness of the zones of previous ablation lines (1.8 ± 0.5 mm vs. 1.0 ± 0.4 mm, p=0.047). All patients presented sinus rhythm at the end of the procedure and no acute complication occurred. No patient reported arrhythmic recurrence at 1-year follow-up (Figure 2).

Conclusions

LAWT-aided approach for LAFL ablation can facilitate identifying the wall thinning produced by the previous RF ablation line and the gap (seen as relative wall thickening) acting as the isthmus for the reentry circuit. This, in turn might help analysis of reentry circuits and increase procedure efficacy and efficiency. Further data are needed to reproduce these findings in a larger study cohort.

Personalized persistent atrial fibrillation ablation guided by left atrial wall thickness: a multicenter study

Funding Acknowledgements

Type of funding sources: None.

Background

Pulmonary vein isolation (PVI) has been proven to be effective in treating persistent atrial fibrillation (PeAF), although long-term ablation outcomes have been significantly less satisfactory than in paroxysmal AF (1). A recent personalized PVI approach, aiming for contiguous lesions with ablation index (AI) titration according to the local left atrial wall thickness (LAWT) as per multidetector cardiac tomography (MDCT), has demonstrated to achieve an arrhythmia-free survival > 95% at 12 months in patients with paroxysmal AF (2).

Purpose

We sought to investigate the safety and clinical outcomes of this personalized PVI approach guided by LAWT in patients with PeAF.

Methods

Consecutive patients referred for PeAF first ablation were prospectively enrolled from three referral centers. PeAF was defined in the presence of at least one AF episode sustained beyond 7 days. LAWT three-dimensional maps were obtained from MDCT and integrated into the navigation system. LAWT was categorized into 1 mm layers and AI was titrated to the LAWT. The ablation line was personalized to avoid thicker regions (Figure 1) while encircling PV antrum. Follow-up was scheduled at 1, 3, 6, and every 12-months thereafter.

Results

One hundred twenty-seven patients [89 (70.6%) male, age 64 ± 10 years] were included. 68 (60.7%) patients were hypertensive, 10 (18%) patients suffered of type 2 diabetes, and mean CHA2DS2-VASc score was 2.3 ± 2.1. Mean procedure time was 61 ± 20 minutes and mean fluoroscopy time was 1.3 ± 2.2 minutes. Radiofrequency (RF) time was 9.0 ± 2.3 minutes for the right pulmonary veins with a first-pass isolation in 109 (85.8%) patients and 7.6 ± 1.9 minutes for the left pulmonary veins with first-pass in 110 (86.6%). No major complication occurred. The rate of survival free from AF recurrences at a mean follow-up of 12 ± 6 months was 82% (Figure 2).

Conclusions

Personalized Persistent AF ablation by wide circle PV isolation guided by LAWT, proved to be safe and highly efficient, requiring a low amount of RF delivery, procedure time, and fluoroscopy use, while obtaining a high rate of first-pass isolation and of freedom from AF recurrences.

A novel weighted hybrid clinical and electrocardiographic score to predict the origin of outflow tract ventricular arrhythmias: a multicenter study

Funding Acknowledgements

Type of funding sources: None.

Background

To correctly predict the outflow tract ventricular arrhythmia (OTVA) site of origin (SOO) before the ablation is still a procedural major step, having important implications for correct patient counseling, ablation planning, and periprocedural complication evaluation. Although multiple ECG criteria have been proposed for predicting OTVA SOO, their accuracy and usefulness are still limited as recently (1).

Purpose

The present study sought to prospectively evaluate the accuracy of a previously published Hybrid Score (HS) for prediction of OTVAs with LVOT origin. Besides, multiple ECG measurements of patients with V3 precordial transition (V3PT) OTVA were analyzed to identify potential variables useful to improve the accuracy of the HS (2).

Methods

Consecutive patients (n=105) referred for OTVA ablation were prospectively enrolled from three referral centers. Vascular access and first-mapped ventricle were decided based on the previously published HS, which includes ECG (R/S precordial transition) and clinical information (age, hypertension, and gender). Surface ECGs during the OTVA were analyzed by two independent electrophysiologists to compare the discriminative performance of HS and previous published ECG-alone criteria, to assess their inter-observer variability and to identify potential variables useful to improve the proposed model.

Results

Of the 105 VAs, 70.5% had an RVOT origin and 29.5% an LVOT origin. HS achieved a correct prediction in 90% patients. This rate dropped to 75% in the subgroup of patients with V3PT OTVA. The correct prediction rate of the other ECG-alone criteria in the whole population ranged from 74 to 82% and from 41 to 76% in V3PT patients, and their Cohen’s Kappa coefficient for inter-observer variability assessment ranged from 0.63 to 0.81. R-wave amplitude in V3 was the best ECG parameter for discriminating LVOT origin in V3PT patients. When this parameter was incorporated in the novel Weighted Hybrid Score (WHS) (Figure 1), it correctly classified 99 (94.2%) patients (90% sensitivity, 96% specificity, AUC: 0.97). The WHS discriminatory capacity was maintained in V3PT subgroup, (87% sensitivity, 91% specificity AUC: 0.95). WHS showed a Cohen’s kappa coefficient of 0,82. Finally, WHS was validated in an additional population of 97 patients with OTVAs referred for catheter ablation from three additional external centers; in this testing sample the WHS correctly predicted the SOO in 90% patients and proved to have 89% sensitivity and 90% specificity (AUC: 0.94) for a score ≥2 to predict a LVOT origin.

Conclusions

The novel simple-to-use WHS proved to accurately anticipate the PVC’s SOO and can be introduced in clinical practice for choosing the first chamber to map.

Prospective evaluation of a hybrid clinical and electrocardiographic algorithm to predict the origin of outflow tract PVCs. A prospective multicenter study

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): Beca de la Asociación del Ritmo Cardiaco para Formación en Investigación Post-Residencia en centros españoles.

Background

To predict the premature ventricular complex (PVC) site of origin (SOO) before the ablation procedure has important implications. 12 lead ECG information as well clinical characteristics are related with the PVC-SOO, but there is no prospective data validation.

Purpose

This prospective multicenter study sought to analyze the applicability and accuracy of a simple hybrid algorithm that includes electrocardiographic and clinical information in a consecutive patient population with outflow tract (OT) PVCs undergoing catheter ablation.

Methods

Consecutive patients with frequent OT-PVCs and indication for catheter ablation were prospectively included in 4 centers. The vascular access (femoral vein vs femoral artery) and the first outflow tract to be mapped were decided based on a two-steps hybrid algorithm (see Figure 1) including ECG information [R/S PVC precordial transition (PT): early PT if it occurs before V3; late PT if beyond V3) and clinical information [the following variables compute 1 point in a clinical score: age (>59 y.o); presence of hypertension; and gender (man)].

Results

115 consecutive patients [42 (37%) man, 52 + 15 y.o] were included. Mean PVC burden at baseline was 20 ± 13% and mean LVEF was 59 ± 8%. Mean procedure time was 55 ± 26 min. Complete acute abolition of the PVC was achieved in 110 (96%) patients. 84 (73%) patients had the PVC’s SOO in the right ventricle OT (RVOT) whereas 31 (27%) in the left ventricular OT (LVOT). Compared with patients with a RVOT-SOO, those with a LVOT-SOO were more frequently man [18 (58%) vs 24 (29%), p = 0.004], more frequently suffered from hypertension [18 (58%) vs 15 (18%), p < 0.001) and had an early R/S PVC transition [17 (55%) early PT, 3 (10%) late PT) in the case of LVOT-SOO vs 4 (5%) early PT, 55 (65%) late PT in the case of RVOT-SOO, p < 0.001]. The hybrid algorithm accurately anticipated the PVC’s SOO in 101 (88%) patients. A reduction of at least 80% of PVC burden was achieved by 90% of patients at 6 months.

Conclusions

The hybrid algorithm, prospectively evaluated in an international multicenter study, has proved to permit to accurately anticipate the PVC’s SOO (right vs left) in a consultive population of patients with OT PVCs. Abstract Figure 1

Personalized atrial fibrillation ablation by tailoring ablation index to the left atrial wall thickness. the ablate by-law single center study

Funding Acknowledgements

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Dr Teres is funded by the research fellowship grant from the Swiss Heart Rhythm Foundation, Dr Carreno was funded was funded by a Scholarship from Sociedad Española de Cardiología (SEC).

Introduction

Left atrial wall thickness (LAWT) is a determinant of transmural lesion formation during atrial fibrillation (AF) ablation. The utility of ablation index (AI) to dose radiofrequency (RF) delivery for the reduction of AF recurrences has already been proven with a target AI ≥ 400 at the posterior wall and ≥550 at the anterior wall.

Objective

To determine if adapting AI to atrial wall thickness (AWT) is feasible, effective and safe during AF ablation.

Methods

Consecutive patients referred for a first PAF ablation. LAWT 3D-maps were obtained from multidetector computed tomography (MDCT) and integrated into the CARTO navigation system. LAWT maps were semi-automatically computed from the MDCT as the local distance between the LA endo and epicardium and categorized into 1mm-layers and AI was titrated to the LAWT, as follows: Thickness < 1 mm (red): 300; 1-2 mm (yellow): 350; 2-3 mm (green): 400; 3-4 mm (blue): 450; > 4 mm (purple): 450 (Figure). The ablation line was designed in a personalized fashion to avoid thicker regions. All ablation procedures were performed under general anesthesia with a high frequency low-volume ventilation. Primary endpoints were acute efficacy and safety, and freedom from AF recurrences. Follow-up (FU) was scheduled at 1, 3, 6, and every 6 months thereafter.

Results

90 patients [60 (67 %) male, age 58 ± 13 years] were included. Mean LAWT was 1.25 ± 0.62 mm. Mean AI was 366 ± 26 on the right pulmonary veins (RPVs) with a first-pass isolation in 84 (93%) patients and 380 ± 42 on the left pulmonary veins (LPVs) with first-pass in 87 (97%). Procedure time was 59 min [49-66]; RF time 14 min [12,5-16]; fluoroscopy time 0.7 min [0.5-1.4]. No major complication occurred. Eighty-six out of 90 (95.5%) patients were free of recurrence after a mean FU of 11 ± 4 months.

Conclusions

 Personalized AF ablation, adapting the AI to LAWT allowed decreasing RF delivery, fluoroscopy and procedure time while obtaining a high rate of first-pass isolation. Lesion durability as estimated by freedom from AF recurrences was as high as in more demanding ablation protocols. Abstract Figure. Personalized protocol and results

Cardiovascular magnetic resonance determinants of ventricular arrhythmic events after myocardial infarction

Funding Acknowledgements

Type of funding sources: None.

Background

 Late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) permits to identify the arrhythmogenic substrate in chronic post-myocardial infarction (MI) patients. It is unknown why a minority of chronic post-MI patients develop sustained ventricular tachycardias (VT) over follow-up, regardless of their left ventricular ejection fraction (LVEF).

Objectives

 To noninvasively characterize scar differences and potential predictors of VT occurrence in chronic post-MI patients.

Methods

 A case-control study was designed through retrospective LGE-CMR data analysis of chronic post-MI patients i) consecutively referred for VT substrate ablation after a first VT episode (n = 66), and ii) from a control group (n = 84) with no arrhythmia evidence. The myocardium was characterized differentiating core, border zone (BZ) and BZ channels (BZC) using the ADAS 3D post-processing imaging platform. Clinical and scar characteristics, including a novel parameter, the BZC mass, were compared between both groups.

Results

 150 post-MI patients were included for analysis. Four multivariate Cox proportional hazards regression models were created for total scar mass (model 1), BZ mass (model 2), core mass (model 3), and BZC mass (model 4, see table). All of them were adjusted by age, sex, and LVEF. In the corresponding models, only total scar mass, BZ mass, core mass, and BZC mass were independent variables associated with the development of VT. BZC mass showed the best performance: a cut-off of 5.15 g identified the cases with 92.4% sensitivity and 86.9% specificity  [AUC 0.93 (0.89–0.97); p < 0.001], with a significant increase in the AUC compared to the other scar parameters (p < 0.001 for all pairwise comparisons using the De Long’s test). By using BZC mass as a risk stratification parameter together with LVEF, the net reclassification improvement (NRI) was 33.3% for the cases, and 39.3% for the controls. The net proportion of patients reclassified correctly was 36.7%

Conclusions

 The mass of BZC, automatically obtained with a commercially available CMR post-processing software, is the strongest independent variable associated with the occurrence of clinical SMVT in post-MI patients after covariate adjustment for age, sex, and LVEF. The measurement of BZC mass could permit a more accurate arrhythmia risk stratification than LVEF in chronic post-MI patients (NRI 36.7%). Scar characteristics analyzed from LGE-CMR imaging should be taken into consideration to better stratify ventricular arrhythmia risk in chronic post-MI patients. Abstract Figure. ROC curves for predicting VT occurrence

Esophagus-to-posterior Atrial wall relationship: pre- and Intra-procedural three-dimensional multimodality imaging for esophageal position

Funding Acknowledgements

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Dr Teres was funded by the research fellowship grant of the Swiss Heart Rhythm Foundation. Dr Carreno-Lineros was funded by a Scholarship from Sociedad Española de Cardiología (SEC).

Introduction

  pulmonary vein isolation (PVI) approach implies unavoidable ablation  on the posterior atrial wall which is closely related to the esophagus. PVI may result in several complications.

Objective

the present study aims to analyze the stability of the esophageal position inside the mediastinum at the level of the posterior atrial wall from one procedure to another (Redo group) and during a single procedure (multi-image group).

Methods

the esophageal position was compared in two groups. First, pre-procedural multidetector computerized tomography (MDCTs) of the first PVI and the redo intervention (Redo group) were segmented with ADAS 3D™ software to compare the esophageal position and the atrio-esophageal distance prints (Figure A). Second, three imaging modalities were compared for the same procedure (multi-image group): i) preprocedural MDCT; ii) intraprocedural fluoroscopy obtained with the TEE probe in place in three projections with CARTOUNIVU™ (Biosense Webster); and iii) esophageal fast-anatomical map (FAM) obtained at the end of the procedure (Figure D). Ablation procedures were performed under general anesthesia. Exclusion criteria were unavailability or contraindication to obtain any of the techniques. The 3D correlation of the esophageal position acquired with different techniques, was computed in Matlab using semiautomatic segmentation analysis.

Results

35 patients were analyzed for the Redo group. Mean age 61 ± 10 years, 17 (65%) male, mean LVEF 57 ± 7%, mean LA diameter 43 ± 5 mm, median time since previous ablation (and therefore between MDCT acquisitions) was 6 months (IQR 3-9). Mean atrio-esophageal distance for both MDCTs was 1.2 ± 0.6 mm . The esophageal trajectory as related to the atrial posterior wall was left for 20 (57%) patients, central for 6 (18%) patients, and right for 3 (9%) patients, left-central for 4 (11%) patients, and right-central for 2 (5%) patients. There was a 91 ± 5% correlation on the esophageal position between the first procedure and the redo procedure MDCT. In 3 cases the position was clearly different with a correlation of only 40 ± 22%. The multi-imaging group was composed of 100 patients, mean age 61 ± 10 years, 17 (65%) male, mean LVEF 56 ± 7%, mean LA diameter 39 ± 6 mm. The esophageal trajectory as related to the atrial posterior wall was left for 55 (55%) patients, central for 23 (23%) patients, and right for 9 (9%) patients, left-central for 8 (8%) patients, and right-central for 5 (5%) patients. The correlation between MDCT and CARTOUNIVU™ was 82 ± 10% (Figure B); between MDCT and ESOFAM 80 ± 12% (Figure B); and between ESOFAM and CARTOUNIVU™ 83 ± 15% (Figure C).

Conclusions

There is a high stability of the esophageal position between procedures and from the beginning to the end of procedure. This observation needs to be tested for its clinical utility by designing studies that take into account the esophagus distance print to modulate RF delivery Abstract Figure. Multimodal Esophageal imaging

A Left sided site of origin is associated with adverse cardiovascular outcomes in patients with LV dysfunction undergoing PVC ablation

Funding Acknowledgements

Type of funding sources: None.

Background

Epidemiological studies suggested that premature ventricular complexes (PVCs) are associated with cardiac mortality. But data are still inconclusive.

Aim

This study sought to analyze predictors of adverse outcomes in a population of patients with left ventricular (LV) systolic dysfunction who underwent PVC ablation.

Methods

135 consecutive patients [100 (74%) men, 59 +12 y.o.] with LV systolic dysfunction [LV ejection fraction (LVEF) <50%] and frequent PVCs who underwent PVC ablation were included in a multicenter prospective international register. Patients were followed-up at 6 and 12 months and annually thereafter. The last evaluation performed was considered the long-term follow-up (LTFUP) evaluation. Cardiac mortality and/or cardiac transplantation and/or admission for heart failure was considered the primary endpoint.

Results

82 (61%) patients had a left-sided PVC’s site of origin (LS-SOO), 51 (38%) had a right-sided SOO (RS-SOO) whereas SOO could not be determined in 2 (1%) patients. LS-SOO patients were older (61 ± 11 vs 52 ± 10, p < 0.001) more frequently men [71 (87%) vs 27 (53%), p < 0.001] with previous history of atrial fibrillation (AF) [14 (15%) vs 0, p = 0.001] and with a previously diagnosed structural heart disease (SHD) [43 (52%) vs 6 (11%), p < 0.001].

After a mean follow-up of 39 ± 21 months (range 24-94 months) there was a significant reduction in the PVC burden from 24 ± 13% at baseline to 4 ± 6% at LTFUP, p < 0.001; LVEF improved from 33 ± 8% at baseline to 41 ± 13% at LTFUP (p < 0.001) and NYHA class from 2.1 ± 0.6% to 1.4 ± 0.6% (p < 0.001); BNP levels decreased from 237 ± 231 pg/mL to 137 ± 185 pg/mL (p = 0.001). The primary end-point was reached in 10% patients (7 cardiac deaths, 1 cardiac transplantation and 5 heart failure admisions), 14,8% in LS-SOO and 1,9% in RS-SOO patients, log rank = 0.05 (Figure 1).

Conclusions

Among patients with LV dysfunction who underwent PVC ablation, those with LS-SOO were older and more frequently had AF and SHD. LS-SOO was associated with adverse cardiovascular outcomes. These findings suggest that PVCs with LS and RS-SOO should be considered as two different clinicals entities, with different prognostic values. Abstract Figure 1

Usefulness of late gadolinium enhancement cardiac magnetic resonance to predict appropriate therapies in implantable cardioverter defibrillator patients in primary prevention

Background

The scar and the amount of border zone measured by late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) has been proposed as an independent predictor of ventricular arrhythmias in patients with ischemic and non-ischemic cardiomyopathy. However, at the present time, the guidelines are based only on the ejection fraction to recommend an implantable cardioverter defibrillator (ICD) in primary prevention, and only a minority of these patients receive appropriate therapies. So, prevention needs to be improved.

Purpose

To identify predictors of appropriate therapies in patients with a primary prevention ICD using cardiac magnetic resonance imaging and a dedicated software (ADAS-3D) to characterize the scar.

Methods

Patients who underwent a LGE-MR prior to ICD implantation in primary prevention were retrospectively included. Clinical and cardiac imaging characteristics were collected. The myocardium was segmented with ADAS-3D software in 10 layers (from endocardium to epicardium). The scar, border zone, core and conducting channels were automatically measured in grams by the software.

Results

Since 2008 to 2017, 206 patients were included. Mean age was 67±28 years, 80% men, mean ejection fraction 26%±9, 52% with ischemic cardiomyopathy and 48% non-ischemic. The primary endpoint was appropriate therapies and/or sudden cardiac death (SCD). Median follow-up was 46.33 months. 46 patients (22%) reached the primary endpoint. Greater scar mass (36.05 grams vs 21.5 grams; HR 1.04; 95% CI (1.03–1-05), p<0.001), core mass (9.8 grams vs 5.6 grams; HR 1.06; 95% CI (1.04–1-09), p<0.001), border zone mass (26.2 grams vs 15.9 grams; HR 1.05; 95% CI (1.04–1-09), p<0.001) and channel mass (3.0 grams vs 1.6 grams; HR 1.15 95% CI (1.06–1.25), p<0.001) were associated with appropriate therapies and SCD. A border zone mass >5.3 grams was independently associated with the primary endpoint (HR: 4.77; 95% CI (1.15–19.73), p=0.03).

Conclusions

The amount of border zone, core and channel mass measured by LGE-MR and ADAS software are independent predictors of appropriate therapies and SCD in patients with ICD in primary prevention.

Scar characterization

Funding Acknowledgement

Type of funding source: None

Enablers and barriers of maternal and neonatal immunization programs in Latin America

BACKGROUND

The Region of the Americas has a long history of implementing maternal and neonatal immunization (MNI) programs. Our study aimed to understand the state of MNI policies, strategies and implementation practices in Latin America (LA).

METHODS

Study conducted in 5 middle-income countries: Argentina, Brazil, Honduras, Mexico and Peru. The methods included a desk review, interviews with national stakeholders and health care providers, focus groups with pregnant women and observations in health facilities. Enablers and barriers were identified and categorized as individual, societal or related to the health system.

RESULTS

All 5 participating countries had similar MNI policies and high access to antenatal care. Key enablers were the high acceptability of vaccination during pregnancy, high-level of political will and a national legal framework ensuring free access to vaccines. At the health system level, implementation was facilitated by the existence of immunization advisory committees, a pooled vaccine procurement mechanism, complementary vaccine delivery strategies, conditional cash transfer to users and performance incentives to health facilities. The main programmatic barriers were the lack of adequate MNI information; limited coordination between antenatal and immunization services; inadequate supply, resources and infrastructure; high staff turnover; insufficient training for health care providers; and weak monitoring and reporting systems.

CONCLUSION

Middle-income countries in LA have successfully implemented MNI programs and several enablers were identified. To overcome remaining barriers, there is a need to focus on improving the "immunization journey" for pregnant women through providing more clear and timely information to users and providers; removing barriers to access; ensuring adequate supply, human resources and infrastructure; making the health service experience positive; and establishing integrated information systems that allow for monitoring the progress toward achieving MNI goals. Strengthening the MNI programs can also improve equitable access to health services and prepare for the introduction of future vaccines for pregnant women.

P1111Arrhythmogenic substrate detection in ischemic patients undergoing ventricular tachycardia ablation using multi-detector computed tomography: compared evaluation with cardiac magnetic resonance

Background

 Cardiac magnetic resonance (CMR) is capable of accurately identifying arrhythmogenic substrate (AS), leading to longer arrhythmia-free survival when used to guide ventricular tachycardia (VT) substrate ablation procedures. However, the use of CMR may be limited in certain centers or patient subsets. 

Purpose

 To evaluate the performance of multidetector cardiac computed tomography (MDCT) imaging in identifying heterogeneous tissue channels (HTCs) detected by CMR in ischemic patients undergoing VT substrate ablation.

Methods

 Thirty ischemic patients undergoing both CMR and MDCT before VT substrate ablation were included. Using a dedicated post-processing software, two blinded operators, assigned either to CMR or MDCT analysis, characterized the presence of CMR- and CT-channels, respectively. CMR-channels were classified as endocardial (layers <50%), epicardial (layers ≥50%) or transmural. CMR- vs. CT-channel concordance was considered when the orientation was the same and they were located in the same AHA segment.

Results

 Mean age was 69 ± 10 years; 90% were male. Mean left ventricular ejection fraction (LVEF) was 35 ± 10%. All patients had CMR-channels (n = 76), whereas only 26/30 (86.7%) had CT-channels (n = 91). Global sensitivity (Se) and positive predictive values (PPV) for detecting CMR-channels were 61.8% and 51.6%, respectively. MDCT performance improved in patients with epicardial CMR-channels (Se 80.5%), and transmural scars (Se 72.2%). In 4/11 (36%) patients with subendocardial MI, MDCT was unable to identify the AS.

Conclusion

 MDCT fails to detect the presence of AS in 36% of patients with subendocardial MI and shows a modest sensitivity identifying the presence of HTCs, although its performance improves in patients with transmural scar.

Abstract Figure. Multimodality imaging AS detection

1244Feasibility, safety and efficacy of tailoring ablation index to left atrial wall thickness (lawt) during atrial fibrillation ablation. The Ablate By-LAW Study

Funding Acknowledgements

Dr Teres was funded by Swiss Heartrhythm Foundation

Introduction

Circumferential pulmonary vein isolation (PVI) has become a mainstay in the treatment of atrial fibrillation (AF). The utility of ablation index (AI) to dose radiofrequency delivery for the reduction of AF recurrences has already been proven with a target AI ≥ 400 at the posterior wall and ≥550 at the anterior Wall. Nevertheless, the left atrial wall is a thin, heterogeneous structure with an important inter and intra-patient variability of LAWT.

Objective

To determine if adapting AI to atrial wall thickness (AWT) is feasible, effective and safe during AF ablation.

Methods

Single-Center study that included 80 consecutive patients referred for a first paroxysmal AF ablation that was performed with a single catheter approach with the intention to reduce vascular access complication rate. All patients had a MDCT prior to the ablation procedure. LAWT maps were semi-automatically computed from the MDCT as the local distance between the LA endo and epicardium. All procedures were performed under general anesthesia with a high-rate low-volume ventilation protocol for obtaining higher catheter stability. The transeptal puncture was TEE-guided. During the procedure, the WT map was fused with the LA anatomy using CARTO-merge. LAWT was categorized into 1mm-layers and the AI was titrated to the local atrial WT as follows: Thickness < 1 mm (red): 300; 1-2 mm (yellow): 350; 2-3 mm (green): 400; 3-4 mm (blue): 450; > 4 mm (purple): 450 (Figure). Maximal inter-lesion distance was set at 6 mm. VisiTag settings were: catheter position stability: minimum time 3 s, maximum range 4 mm; force over time: 25%, minimum force 3 g; lesion tag size: 3 mm. Respiration training was not possible due to the high catheter stability.  The circumferential ablation line was designed in a personalized fashion to avoid thicker regions.

Results

80 patients [41 (51,2 %) male, age 60± 11 years] were included. Mean LVEF was 59 ± 5 %, Mean LA diameter 39,1 ± 5,8 mm, Mean LAWT was 1.36 ± 0.63 mm. Mean AI was 352 ± 36 on the RPVs and 356 ± 36 on the LPVs. Procedure time was 60,0 min (IQR 51-70). Fluoroscopy time was 58,5 s (35-97,5). First pass isolation was obtained in 72 (90%) of the RPVs and 75 (93,8%) of the LPVs.

Conclusions

the present study, assessing a novel, personalized protocol for radiofrequency titration during atrial fibrillation ablation, shows a high rate of first pass isolation with a lower need for RF energy delivery and lower procedure requirements, as compared to previous PV ablation protocols. Further studies are needed to evaluate the long-term results of this approach.

Abstract Figure. LAWT-map Visitag points with tailored AI

659Left atrial wall thickness evaluation during atrial fibrillation redo procedures

Funding Acknowledgements

Dr Teres was funded by Swiss Heartrhythm Foundation

Introduction

pulmonary vein (PV) reconnections due to gaps on circumferential ablation lines are responsible for atrial fibrillation recurrences after catheter ablation. We sought to analyze the local left atrial wall thickness (LAWT) of PV line gaps at AF redo ablation during real-time catheter positioning. LAWT was measured on the MDCT 3D reconstruction and fused with the LA anatomy using CARTO-merge.

Objective

To analyze the relationship between local reconnection gaps and the LAWT during AF redo procedures.

Methods

Single-Center cohort study that included 41 consecutive patients referred for AF redo procedure. All patients had a MDCT prior to the ablation procedure. LAWT maps were semi-automatically computed from the MDCT as the local distance between the LA endo and epicardium. Each PV line was subdivided into 8 segments and mean LAWT was computed. During the procedure, the local gap was defined as the earliest activation site at the reconnected segment of the circumferential PV line (Figure 1A & 1B).

Results

41 patients [31 (75.6%) male, age 60 ± 10 years] were included. Mean LAWT was 1.36 ± 0.20 mm. Mean PV circumferential line WT was higher in left PVs than in the right PVs 1.68 ± 0.57 vs. 1.31 ± 0.39 mm p < 0.001 respectively. Mean WT of the reconnected points was 44% higher than the mean WT of the segment where the reconnection was located. Mean reconnection point WT was at the 87th percentile of the circumferential line in the LPVs and at the 76th percentile in the RPVs. The reconnected point WT was higher in the LPVs than RPVs 2.13 ± 1.14 vs. 1.47 ± 0.48 mm p < 0.001 respectively.  The most frequent location for reconnections was the left anterior carina (71%), with a mean WT of 2.24 ± 0.91mm; and the right anterior carina (56%) with a mean WT of 1.57 ± 0.62mm (Figure 2A & 2B).

Conclusions

Reconnection points were more frequently present in the thicker segments of the PV circumferential line. The most frequently reconnected segment was the anterior carina in both right and left PVs. Atrial wall thickness maps derived from MDCT are useful to guide AF redo procedures.

Abstract Figure. 1) Activation & WT map; 2) Segment WT

P1106Fundamental differences and predictors of scar arrhythmogenicity in ischemic patients using cardiac magnetic resonance: a propensity score-matching study

Introduction

 Late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) permits to identify the arrhythmogenic substrate (AS) in ischemic patients. However, it is unknown why the majority of them never develop ventricular tachycardias (VT), irrespectively of their left ventricular ejection fraction (LVEF). 

Purpose

 To characterize the fundamental differences and potential predictors of scar arrhythmogenicity in post-myocardial infarction (MI) patients with and without VT.

Methods

 36 consecutive ischemic patients with no arrhythmia evidence underwent a LGE-CMR study 4 years after the MI (controls). Scar data were compared with those obtained from 49 ischemic patients referred for VT substrate ablation (cases). Propensity score matching (PSM) was performed to adjust for age, LVEF, scar mass, and time from MI. The myocardium was segmented in 10 layers (endo- to epicardium), characterizing the core, border zone (BZ) and BZ channels (BZCs) using a dedicated post-processing software.

Results

 Compared to controls, cases were significantly older (67.3 ± 9.1 vs. 56.5 ± 11), had lower LVEF (33.1 ± 10.1 vs. 51 ± 9.4), greater scar mass (33.9 ± 17.2 vs. 14.2 ± 11.6 g), BZ mass (21.1 ± 9.9 vs. 9.6 ± 7.6 g), core mas (12.6 ± 8.8 vs. ± g), number of BZC (2.9 ± 1.4 vs. 1.1 ± 1.1) and BZC mass (10.5 ± 4.2 vs. 2.3 ± 2.4 g) (p < 0.001 in all cases). After PSM (2:1) adjustment[BJG1] , cases had more BZCs (2.9 ± 1.4 vs. 2.2 ± 0.6; p = 0.01) and a greater BZC mass (10.5 ± 4.2 vs. 4.6 ± 2.6 g; p < 0.001). In the multivariable logistic regression analysis, the BZC mass was the only independent predictor of being a case [OR 2.3 (1.5–3.4); p < 0.001]. Receiver operating characteristic curve analysis identified a cut-off point of BZC mass >4.28 g (AUC 0.98; p < 0.001), showing 100% sensitivity and 91% specificity for cases’ discrimination.

Conclusions

 Compared with the cases, an otherwise similar control group (PS-matched for age, LVEF, scar mass, and time from MI) showed fewer BZC and a reduced BZC mass. BZC mass was the only independent predictor of being a case. A BZC mass cut-off point of > 4.28 g showed a 100% sensitivity and 91% specificity for the identification of ischemic patients with documented VT.

Abstract Figure. Mean BZC mass and ROC curve analysis

125Manual vs. automatic local activation time annotation for guiding premature ventricular complex ablation procedures (MANIaC - PVC study)

Funding Acknowledgements

Financial support was provided in form of a research grant from Biosense Webster

Introduction

 The use of an algorithmic method (wavefront, WF) based on automatic annotation of the maximal negative slope of the unipolar electrogram (uni-EGM) within the window demarcated by the bipolar EGM (bi-EGM) may accurately identify the earliest activation site (EAS) during premature ventricular complex (PVC) ablation procedures.

Purpose

 To assess the potential benefits of a local activation time (LAT) automatic acquisition protocol using WF plus an automatic algorithm for ECG pattern matching recognition (AUT-arm) instead of a manual LAT annotation plus ECG visual inspection (MAN-arm) during premature ventricular complexes (PVCs) ablation procedures.

Methods

 Prospective, randomized, controlled and international multicenter study (NCT03340922). 69 consecutive patients with indication for PVC ablation were enrolled and randomized to AUT (n = 34) or MAN (n = 35) annotation protocols using the CARTO3 navigation system. The primary endpoint was mapping success, defined as complete PVC abolition after a maximum of 2 radiofrequency (RF) applications or up to 90 seconds at the identified EAS, considered the site of origin (SOO). Complete PVC abolition was considered as the procedure success, whereas clinical success was defined as the PVC-burden reduction of >80% in the 24-h Holter at least 1 month after the procedure. Concordance analysis of the maps obtained with both methods was performed.

Results

 Mean age was 69 ± 15, 58% men. The mean baseline PVC burden was 26 ± 13%, mean LVEF 55 ± 12%. Baseline characteristics were similar between groups. The most frequent PVC-SOO were RVOT (41%), LV (25%; being the summit the most frequent location), and LVOT (16%), with no MAN-AUT differences. Total mapping time, number of RF applications, RF time, and procedure time were similar for both groups. The AUT-arm had a higher number of mapping points acquired (164 vs. 61; p = 0.002). There was a delayed detection of LAT at the EAS in the AUT-arm (mean 23 ± 13 ms), being more significant in left-sided PVCs (30 ± 12 vs. 15 ± 9 ms, p < 0.001). The 10-ms isochronal area was significantly bigger in the MAN-arm (1.95 ± 2.7 vs. 1.0 ± 1.0; p = 0.05). The median (interquartile range) distance between AUT-EAS and MAN-EAS was 4 (0–6.8) mm. Mapping success was similar for AUT (65%) and MAN (63%) (p = 1.0). Procedure success was significantly better for the AUT-arm (100% AUT vs. 86% MAN; p = 0.04), but without differences in clinical success (87% AUT vs. 82% MAN; p = 0.7). There were no procedure-related complications.

Conclusions

 The use of a complete automatic protocol for LAT annotation (WF + ECG pattern matching) during PVC ablation procedures is feasible and safe, allowing to achieve equivalent procedural and clinical endpoints as compared to manual procedures carried out by expert operators.

3255Characterization of the arrhythmogenic substrate with multimodality imaging in ischemic patients undergoing VT ablation: relationship between cardiac computed tomography and magnetic resonance

Background

Cardiac magnetic resonance (CMR)-aided ventricular tachycardia (VT) substrate ablation has shown to improve VT recurrence-free survival, through a better identification of the arrhythmogenic substrate. However, the access to CMR may be limited in certain centers or sometimes Its use can be contraindicated in patients with cardiac implantable electronic device. Cardiac computed tomography (CT) has shown to improve the results of substrate ablation, correlating with low-voltage areas and local abnormal ventricular activity, and identifying ridges of myocardial tissue (CT-channels) that may be appropriate target sites for ablation.

Purpose

To evaluate the correlation between CT and CMR imaging in identifying anatomical heterogeneous tissue channels (CMR-channels) or CT-channels in ischemic patients undergoing VT substrate ablation.

Methods

The study included 30 post-myocardial infarction (MI) patients (mean age 69±10; 94% male, left ventricular ejection fraction 35±10%), who underwent both CMR and cardiac CT before VT substrate ablation. Using a dedicated post-processing software, the myocardium was segmented in 10 layers from endocardium to epicardium both for the CMR and CT, characterizing the presence of CMR-channels and CT-channels, respectively, by two blinded operators, assigned either to CMR or CT analysis. CMR-channels were classified as endocardial (CMR-channels in layer <50%), epicardial (CMR-channels in layers ≥50%) or transmural (in both endo and epicardial layers). Presence and location of CT and CMR-channels were compared.

Results

In 26/30 patients (86.7%) 91 CT-channels (mean 3.0±1.9 per patient) were identified while 30/30 (100%) showed CMR-channels (n=76; mean 2.4±1.2 per patient). We found 190 CT-channel entrances (mean 6.3±4.1 per patient), and 275 CMR-channel entrances (mean 8.9±4.9 per patient) on cardiac CT and CMR, respectively. There were 47/91 (51.6%) true positive CT-channels. On the contrary, 44/91 (48.4%) CT-channels were considered false positives [19/91 (20.9%) identified out of CMR scar], and 29/76 (38.2%) CMR-channels could not be identified on CT. Thirty-six out of 76 (47.4%) CMR-channels were considered as non-endocardial (epi- or transmural). Twenty-nine out of 36 (80.5%) non-endocardial CMR-channels were coincident with CT-channels.

CT and CMR Channels

Conclusion

CT shows a modest sensitivity in identifying CMR-channels and fails in ascertain their complexity, underestimating the number of entrances; however, channels location at CT fit well with CMR for those classified as transmural or epicardial.

Emerging and Reemerging Aedes-Transmitted Arbovirus Infections in the Region of the Americas: Implications for Health Policy

The increasing geographical spread and disease incidence of arboviral infections are among the greatest public health concerns in the Americas. The region has observed an increasing trend in dengue incidence in the last decades, evolving from low to hyperendemicity. Yellow fever incidence has also intensified in this period, expanding from sylvatic-restricted activity to urban outbreaks. Chikungunya started spreading pandemically in 2005 at an unprecedented pace, reaching the Americas in 2013. The following year, Zika also emerged in the region with an explosive outbreak, carrying devastating congenital abnormalities and neurologic disorders and becoming one of the greatest global health crises in years. The inadequate arbovirus surveillance in the region and the lack of serologic tests to differentiate among viruses poses substantial challenges. The evidence for vector control interventions remains weak. Clinical management remains the mainstay of arboviral disease control. Currently, only yellow fever and dengue vaccines are licensed in the Americas, with several candidate vaccines in clinical trials. The Global Arbovirus Group of Experts provides in this article an overview of progress, challenges, and recommendations on arboviral prevention and control for countries of the Americas.

Impact and effectiveness of meningococcal vaccines: a review

Objectives.

To summarize and critically evaluate the evidence on the impact and effectiveness of meningococcal vaccination programs around the world in order to inform decisionmaking in Latin America and the Caribbean.

Methods.

A review of the literature was conducted following several components of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. PubMed Central® was searched for papers published in any language from January 1999 – March 2017.

Results.

In all, 32 studies were included, most of which evaluated the meningococcal C conjugate vaccine. Fourteen studies measured effectiveness and 30 measured impact. The effectiveness of polysaccharide vaccines was 65% – 83.7% (different age groups), while the effectiveness of the conjugate vaccines was 66% – 100%. Incidence decline of laboratory-confirmed meningococcal disease for the conjugate vaccine ranged from 77% – 100% among different ages groups. The only study that evaluated the protein subunit vaccine reported a vaccine effectiveness of 82.9%.

Conclusions.

The studies reviewed show impact and effectiveness of both polysaccharide vaccines and conjugate vaccines on vaccine-serogroup meningococcal disease. The conjugate vaccines, however, show higher impact and effectiveness with longer-lasting protection over the polysaccharide vaccines. Given the variance in potential use of a meningococcal vaccine, epidemiological surveillance systems should be strengthened to inform national decisions.

The path towards polio eradication over 40 years of the Expanded Program on Immunization in the Americas

This article synthesizes the important lessons learned from polio eradication in the Region of the Americas, including initial and more recent challenges and best practices, as well as particular factors surrounding attainment of this ambitious goal. Using documents, interviews, and country surveys, the authors describe and analyze the strategies and lessons learned during the 40 years of the Expanded Program on Immunization (1977 – 2017). Some major milestones and chxallenges specifically covered are: the Vaccine-derived Poliovirus (VDPV) outbreak in the Dominican Republic; the regional “mop-up operation;” poliovirus containment in essential facilities; the unprecedented introduction of inactivated polio vaccine (IPV); the synchronized switch from trivalent to bivalent OPV; and the countries’ unfailing commitment to the cause.

Progress towards a comprehensive approach to maternal and neonatal immunization in the Americas

Maternal and neonatal immunization (MNI) is a core component of the new immunization model in the Americas, which transitioned from immunization of children to that of the entire family. Immunization during pregnancy protects the mother and the fetus by providing the neonate with maternal antibodies against disease. It has the potential to impact early childhood morbidity and mortality, and thus MNI has gained visibility and priority on the global health agenda.

The Region of the Americas is a leader in MNI, as seen by its elimination of congenital rubella syndrome in 2015 and the progress made toward neonatal tetanus elimination. In the Americas, 31 countries currently target pregnant women for influenza vaccination; and 21 countries—over 90% of the Region’s birth cohort—have nationwide newborn hepatitis B vaccination.

This paper describes the status of MNI in the Americas and identifies gaps in the evidence, obstacles to optimal implementation, and opportunities for future improvements. Catalysts for MNI in the Region have been political commitment, endorsement by scientific societies, an established “culture of vaccination,” widespread access to antenatal care, and context-specific communications; however, universal and equitable access for pregnant women and their newborns continues to be a formidable challenge, and additional vaccine safety and effectiveness evidence is needed. Continued efforts to integrate MNI with maternal and child health services will be critical to furthering the MNI platform as well.

Systematization of the Introduction of IPV and Switch from tOPV to bOPV in the Americas

The synchronized introduction of the inactivated polio vaccine (IPV) and the switch from trivalent oral polio vaccine (tOPV) to bivalent oral polio vaccine (bOPV) has constituted an effort without precedents, and with astonishing results. Within the established time frame, all countries in our region managed to carry out the decision, planning, and introduction of this vaccine and subsequent switch to their national immunization schedules.The purpose of this article is to systematize the process of IPV introduction and switch in Latin America and the Caribbean, which constitutes an important piece in the documentation of the polio legacy in the Americas. Regional level as well as country perspectives and viewpoints are described. Analyzing and summarizing the lessons learned from the introduction of IPV and the switch from tOPV to bOPV can be useful for the introduction of new vaccines in the Pan American Health Organization (PAHO) region and in other regions of the world, and to help our own region successfully carry out another synchronized vaccine introduction in the future, if necessary.

Evidence-based decision-making for vaccine introductions: Overview of the ProVac International Working Group's experience

INTRODUCTION

Pan American Health Organization's (PAHO) ProVac Initiative aims to strengthen countries' technical capacity to make evidence-based immunization policy. With financial support from the Bill and Melinda Gates Foundation, PAHO established the ProVac International Working Group (IWG), a platform created for two years to transfer the ProVac Initiative's tools and methods to support decisions in non-PAHO regions.

METHODS

In 2011, WHO Regional Offices and partner agencies established the IWG to transfer the ProVac framework for new vaccine decision support, including tools and trainings to other regions of the world. During the two year period, PAHO served as the coordinating secretariat and partner agencies played implementing or advisory roles.

RESULTS

Fifty nine national professionals from 17 countries received training on the use of economic evaluations to aid vaccine policy making through regional workshops. The IWG provided direct technical support to nine countries to develop cost-effectiveness analyses to inform decisions. All nine countries introduced the new vaccine evaluated or their NITAGs have made a recommendation to the Ministry of Health to introduce the new vaccine.

DISCUSSION

Developing countries around the world are increasingly interested in weighing the potential health impact due to new vaccine introduction against the investments required. During the two years, the ProVac approach proved valuable and timely to aid the national decision making processes, even despite the different challenges and idiosyncrasies encountered in each region. The results of this work suggest that: (1) there is great need and demand for technical support and for capacity building around economic evaluations; and (2) the ProVac method of supporting country-owned analyses is as effective in other regions as it has been in the PAHO region.

CONCLUSION

Decision support for new vaccine introduction in low- and middle-income countries is critical to guiding the efficient use of resources and prioritizing high impact vaccination programs.

ProVac Global Initiative: a vision shaped by ten years of supporting evidence-based policy decisions

INTRODUCTION

The Pan American Health Organization (PAHO) created the ProVac Initiative in 2004 with the goal of strengthening national technical capacity to make evidence-based decisions on new vaccine introduction, focusing on economic evaluations. In view of the 10th anniversary of the ProVac Initiative, this article describes its progress and reflects on lessons learned to guide the next phase.

METHODS

We quantified the output of the Initiative's capacity-building efforts and critically assess its progress toward achieving the milestones originally proposed in 2004. Additionally, we reviewed how country studies supported by ProVac have directly informed and strengthened the deliberations around new vaccine introduction.

RESULTS

Since 2004, ProVac has conducted four regional workshops and supported 24 health economic analyses in 15 Latin American and Caribbean countries. Five Regional Centers of Excellence were funded, resulting in six operational research projects and nine publications. Twenty four decisions on new vaccine introductions were supported with ProVac studies. Enduring products include the TRIVAC and CERVIVAC cost-effectiveness models, the COSTVAC program costing model, methodological guides, workshop training materials and the OLIVES on-line data repository. Ten NITAGs were strengthened through ProVac activities.

DISCUSSION

The evidence accumulated suggests that initiatives with emphasis on sustainable training and direct support for countries to generate evidence themselves, can help accelerate the introduction of the most valuable new vaccines. International and Regional Networks of Collaborators are necessary to provide technical support and tools to national teams conducting analyses. Timeliness, integration, quality and country ownership of the process are four necessary guiding principles for national economic evaluations to have an impact on policymaking. It would be an asset to have a model that offers different levels of complexity to choose from depending on the vaccine being evaluated, the availability of data, and the time frame of the decision.

CONCLUSION

Decision support for new vaccine introduction in low- and middle-income countries is critical to maximizing the efficiency and impact of vaccination programs. Global technical cooperation will be required. In the future, PAHO and WHO have an opportunity to expand the reach of the ProVac philosophy, models, and methods to additional regions and countries requiring real-time support. The ProVac Global Initiative is proposed as an effective mechanism to do so.

TRIVAC decision-support model for evaluating the cost-effectiveness of Haemophilus influenzae type b, pneumococcal and rotavirus vaccination

The TRIVAC decision support model has been used widely in Latin America and other regions to help national teams evaluate the cost-effectiveness of Haemophilus influenzae type b (Hib) vaccine, pneumococcal conjugate vaccine (PCV) and rotavirus vaccine (RV). We describe the structure and functioning of this model, and identify the parameters with the greatest influence on the results. The TRIVAC model is a spreadsheet software program that calculates incremental cost-effectiveness ratios (ICERs) and other indicators for three childhood vaccines (Hib, PCV and RV) utilising parameters such as demography, disease burden, vaccine costs, vaccine coverage, vaccine efficacy, health service utilisation and costs. There is a good deal of uncertainty about the local values of many of the parameters that have most influence on the cost-effectiveness of these new vaccines. Cost-effectiveness models can be used to explore the implications of different values of these parameters. However, for such models to be seen as relevant and helpful by decision-makers, they need to be transparent, flexible, easy to use, and embedded in a process which is owned and led by national teams. In this paper the key drivers of cost-effectiveness in the model are identified by one-way sensitivity analyses, run for each vaccine in 147 countries. The data used are mainly from standard international sources and the published literature. The primary indicator was the discounted cost per Disability Adjusted Life-Year (DALY) averted, from a government perspective, over a 20-year period (2013-2032). For all three vaccines, the ICER was most sensitive to changes in relative coverage (the coverage of the children who would have become diseased or, more importantly, died if the population had not been vaccinated, as a % of overall national coverage) and the herd effect multiplier. Other influential parameters for all three vaccines were: the incidence and case fatality of disease, the baseline trend in disease mortality in the absence of vaccination, vaccine efficacy, vaccine price and the % decline in vaccine price per year. Important vaccine-specific parameters included the cost of Hib meningitis sequelae, PCV serotype coverage and the rotavirus gastro-enteritis (RVGE) admission rate. While vaccine efficacy, herd effects, disease mortality and vaccine price are commonly cited as important drivers of cost-effectiveness, this analysis highlights the potentially important influence of relative coverage, a parameter rarely considered in models of vaccine impact and cost-effectiveness.

Indicators to assess National Immunization Technical Advisory Groups (NITAGs)

A National Immunization Technical Advisory Group (NITAG) is an expert advisory committee that provides evidence-based recommendations to the Ministry of Health (MoH) to guide immunization programs and policies. The World Health Organization (WHO), the Initiative for Supporting National Independent Immunization and Vaccine Advisory Committees (SIVAC) at Agence de Médecine Préventive (AMP) and the US Centers for Disease Control and Prevention (US CDC) engaged NITAG stakeholders and technical partners in the development of indicators to assess the effectiveness of NITAGs. A list of 17 process, output and outcome indicators was developed and tested in 14 countries to determine whether they were understandable, feasible to collect, and useful for the countries. Based on the findings, a revised version of the indicators is proposed for self-assessment in the countries, as well as for global monitoring of the NITAGs.

Challenges to building capacity for evidence-based new vaccine policy in developing countries

There are many challenges to ensuring that people in developing countries have equitable access to new vaccines. Two of the most important are having the capacity to make evidence-based new vaccine policy decisions in developing countries, and then when appropriate actually distributing those new vaccines to those who will most benefit from them. Based on our review of the Pan American Health Organization's ProVac Initiative in the Americas, we found that when national governments in developing countries develop the expertise to make the best technical decisions about immunization programs; take responsibility for helping to pay for and distribute vaccines; and are supported by strong partnerships with international organizations, they succeed in saving more lives more quickly.

Human papillomavirus vaccines: new tools for accelerating cervical cancer prevention in developing countries

Despite the available knowledge and tools to prevent cervical cancer, it remains the second most common cancer in women, with four-fifths of the cases occurring in developing countries. Projections are for a 90% increase in global cervical cancer cases by 2020 if no additional public-health interventions are implemented. Prophylactic human papillomavirus (HPV) vaccines, which have proven immunogenicity, safety and efficacy, are now commercially available; and coupled together with quality screening have the potential to dramatically accelerate reductions in cervical cancer mortality rates and save millions of women's lives. The current cost of the new HPV vaccines and new screening technologies, however, are a major barrier to their widespread implementation. There is an urgent need for HPV vaccines and new technologies for effective screening to become more available and affordable, especially to poor communities everywhere.

Strengthening the technical capacity at country-level to make informed policy decisions on new vaccine introduction: lessons learned by PAHO's ProVac Initiative

Rotavirus, pneumococcal conjugate and HPV vaccines have the potential to make substantial gains in health, specifically in reducing child mortality and improving women's health. Decisions regarding new vaccine introduction should be grounded in a broad evidence base that reflects national conditions. In this paper, we describe the Pan American Health Organization ProVac Initiative's experience in strengthening national decision making regarding new vaccine introduction through five sets of activities: (1) strengthening infrastructure for decision making; (2) developing tools for economic analyses and providing training to national multidisciplinary teams; (3) collecting data, conducting analysis, and gathering a framework of evidence; (4) advocating for evidence-based decisions; and (5) effectively planning for new vaccine introduction when evidence supports it. Key lessons learned regarding the role of multidisciplinary country teams, provision of direct technical support, development of tools, and provision of distance and in-person training are highlighted.

Descriptive analysis of immunization policy decision making in the Americas

OBJECTIVES

Reducing and eliminating vaccine-preventable diseases requires evidence-based and informed policy decision making. Critical to determining the functionality of the decision-making process for introduction of a new vaccine is understanding the role of the national immunization technical advisory group (ITAG) in each country. The aim of this study is to document the current situation of national level immunization policy decision making for use in the Pan American Health Organization (PAHO) ProVac Initiative.

METHODS

A structured 66-variable questionnaire developed by the World Health Organization (WHO) in collaboration with the University of Ottawa was distributed to all WHO regions; it was composed of dichotomous, multiple-choice, and open-ended questions. Questionnaires were e-mailed or faxed to the six WHO regional offices and the offices distributed them to all member states. This paper analyzes surveys from the Americas as part of PAHO's ProVac Initiative.

RESULTS

Twenty-nine countries of the Americas answered the survey. They conveyed that immunization policy making needed to be improved and further supported by organizations such as PAHO. Areas of improvement ranged from organization and technical support to strengthening capacity and infrastructure to improved coordination among stakeholders. This survey also highlighted a variety of ITAG processes that need further investigation.

CONCLUSION

This survey supports the efforts of PAHO's ProVac Initiative to disseminate knowledge and best practices for an immunization policy decision-making framework through the development of clear definitions and guidelines. By highlighting each problem noted in this study, ProVac will assist countries in Latin America and the Caribbean to build national capacity for making evidence-based decisions about introduction of new vaccines.

Rheology of hydroxyethylated starch aqueous systems. Analysis of gel formation

This paper reports dynamic viscoelastic and steady shear measurements of aqueous solutions of two commercial hydroxyethyl ethers of potato starch, allowing us to define three different viscoelastic regions, depending on the polymer concentrations. The fluid-like zone (I) corresponds to a homogeneous solution, free of associations between chains, where the linear viscoelastic model can be applied; the fluid-gel transition zone (II) is associated with the rheology of complex systems which possess intermolecular specific interactions; and the gel-like zone (III) involves a network formation giving rise to a gel. The reversibility of the hydrogels was studied by means of steady/dynamic transient experiments allowing breakdown of the gel network and analysis of rehealing. Comparing the elastic moduli of the starch derivative gels leads us to assume that the functionality depends on the capacity to form hydrogen-bonding associations between polymer chains.