Personalized pulmonary vein isolation with very high-power short-duration lesions guided by left atrial wall thickness: the QDOT-by-LAWT randomized trial

AIMS

Pulmonary vein isolation (PVI) for paroxysmal atrial fibrillation (PAF) using very high-power short-duration (vHPSD) radiofrequency (RF) ablation proved to be safe and effective. However, vHPSD applications result in shallower lesions that might not be always transmural. Multidetector computed tomography-derived left atrial wall thickness (LAWT) maps could enable a thickness-guided switching from vHPSD to the standard-power ablation mode. The aim of this randomized trial was to compare the safety, the efficacy, and the efficiency of a LAWT-guided vHPSD PVI approach with those of the CLOSE protocol for PAF ablation (NCT04298177).

METHODS AND RESULTS

Consecutive patients referred for first-time PAF ablation were randomized on a 1:1 basis. In the QDOT-by-LAWT arm, for LAWT ≤2.5 mm, vHPSD ablation was performed; for points with LAWT > 2.5 mm, standard-power RF ablation titrating ablation index (AI) according to the local LAWT was performed. In the CLOSE arm, LAWT information was not available to the operator; ablation was performed according to the CLOSE study settings: AI ≥400 at the posterior wall and ≥550 at the anterior wall. A total of 162 patients were included. In the QDOT-by-LAWT group, a significant reduction in procedure time (40 vs. 70 min; P < 0.001) and RF time (6.6 vs. 25.7 min; P < 0.001) was observed. No difference was observed between the groups regarding complication rate (P = 0.99) and first-pass isolation (P = 0.99). At 12-month follow-up, no significant differences occurred in atrial arrhythmia-free survival between groups (P = 0.88).

CONCLUSION

LAWT-guided PVI combining vHPSD and standard-power ablation is not inferior to the CLOSE protocol in terms of 1-year atrial arrhythmia-free survival and demonstrated a reduction in procedural and RF times.

Outcomes of cavotricuspid isthmus-dependent flutter ablation: randomized study comparing single vs. multiple catheter procedures-the SIMPLE study

BACKGROUND

Catheter ablation is recommended as first-line therapy for patients with symptomatic typical AFl. Although the conventional multi-catheter approach is the standard of care for cavotricuspid isthmus (CTI) ablation, a single-catheter approach was recently described as a feasible alternative. The present study sought to compare safety, efficacy, and efficiency of single vs. multi-catheter approach for atrial flutter (AFl) ablation.

METHODS

In this randomized multi-center study, consecutive patients referred for AFl ablation (n = 253) were enrolled and randomized to multiple vs. single-catheter approach for CTI ablation. In the single-catheter arm, PR interval (PRI) on the surface ECG was used to prove CTI block. Procedural and follow-up data were collected and compared between the two arms.

RESULTS

128 and 125 patients were assigned to the single-catheter and to the multi-catheter arms, respectively. In the single-catheter arm, procedure time was significantly shorter (37 ± 25 vs. 48 ± 27 minutes, p = 0.002) and required less fluoroscopy time (430 ± 461 vs. 712 ± 628 seconds, p < 0.001) and less radiofrequency time (428 ± 316 vs. 643 ± 519 seconds, p < 0.001), achieving a higher first-pass CTI block rate (55 (45%) vs. 37 (31%), p = 0.044), compared with the multi-catheter arm. After a median follow-up of 12 months, 11 (4%) patients experienced AFl recurrences (5 (4%) in the single-catheter arm and 6 (5%) in the multi-catheter arm, p = 0.99). No differences were found in arrhythmia-free survival between arms (log-rank = 0.71).

CONCLUSIONS

The single-catheter approach for typical AFl ablation is not inferior to the conventional multiple-catheter approach, reducing procedure, fluoroscopy, and radiofrequency time.

A hybrid clinical and electrocardiographic score to predict the origin of outflow tract ventricular arrhythmias

BACKGROUND

To predict the outflow tract ventricular arrhythmias (OTVA) site of origin (SOO) before the ablation procedure has important practical implications. The present study sought to prospectively evaluate the accuracy of a clinical and electrocardiographic hybrid algorithm (HA) for the prediction of OTVAs-SOO, and at the same time to develop and to prospectively validate a new score with improved discriminatory capacity.

METHODS

In this multicenter study, we prospectively enrolled consecutive patients referred for OTVA ablation (N = 202), and we divided them in a derivation sample and a validation cohort. Surface ECGs during OTVA were analyzed to compare previous published ECG-only criteria and to develop a new score.

RESULTS

In the derivation sample (N = 105), the correct prediction rate of HA and ECG-only criteria ranged from 74 to 89%. R-wave amplitude in V3 was the best ECG parameter for discriminating LVOT origin in V3 precordial transition (V3PT) patients, and was incorporated to the novel weighted hybrid score (WHS). WHS correctly classified 99 (94.2%) patients, presenting 90% sensitivity and 96% specificity (AUC 0.97) in the entire population; WHS mantained a 87% sensitivity and 91% specificity (AUC 0.95) in patients with V3PT subgroup. The high discriminatory capacity was confirmed in the validation sample (N = 97): the WHS exhibited an AUC (0.93), and a WHS ≥ 2 allowed a correct prediction of LVOT origin in 87 (90.0%) cases, yielding a sensitivity of 87% and specificity of 90%; moreover, the V3PT subgroup showed an AUC of 0.92, and a punctuation ≥ 2 predicted an LVOT origin with a sensitivity of 94% and specificity of 78%.

CONCLUSIONS

The novel hybrid score has proved to accurately anticipate the OTVA's origin, even in those with a V3 precordial transition. A Weighted hybrid score. B Typical examples of the use of the weighted hybrid score. C ROC analysis of WHS and previous ECG criteria for prediction of LVOT origin in the derivation cohort. D ROC analysis of WHS and previous ECG criteria for prediction of LVOT origin in the V3 precordial transition OTVA subgroup.

The critical isthmus of left atrial anterior wall flutter is mostly circumscribed into a small area immediately behind the aortic root. Implications for catheter ablation

Funding Acknowledgements

Type of funding sources: None.

Background

Left atrial flutters (LAFL) are typically observed in patients with previous ablation lines or surgery in the left atrium (LA). Less frequently, scar-related left atrial anterior wall (LAAW) flutters may occur. Although the presence of low-voltage areas (LVAs, a surrogate of scar) in the LA is considered an arrhythmogenic substrate and a marker of atrial cardiomyopathy, the pathophysiologic factors responsible for its formation remain unclear. We hypothesized that compression of the LAAW by the aortic root could be responsible of LVAs found in the LAAW, and therefore, be the substrate for the development of LAAW flutter.

Purpose

We aimed to describe: 1) the relationship between the aortic root and the presence of LVAs in the LAAW, which is the substrate for reentry; and 2) the clinical and electrophysiological characteristics of LAAW atrial flutter.

Methods

Consecutive patients referred for LAFL ablation between April 2019 and September 2022 in a single center were retrospectively collected. Among 55 patients with LAFL, 10 (18%) demonstrated a macroreentrant circuit with a critical isthmus identified in the LAAW, in the absence of previous ablation lines or surgery, and were included in the analysis. Previous pulmonary vein isolation (PVI) was not an exclusion criterion. All patients underwent a multidetector computerized tomography (MDCT) prior to the procedure and the images were analyzed using ADAS 3DTM imaging platform. Activation mapping was performed in all patients using a multielectrode mapping catheter and CARTO 3 navigation system.

Results

9 of 10 patients were male (mean age 74,3 ± 6,3 years). LA enlargement was present in all patients (48,3 ± 4,7 mm) and the mean aortic root diameter was 34,8 ± 3,4 mm. The mean LAAW flutter cycle length was 293,4 ± 68,3 ms. In 9 of the patients (90%), the LAAW flutter critical isthmus was just behind the aortic root, separated by &lt; 1 mm according to the LA-aortic root fingerprinted isodistance map (mean fingerprinted isodistance area was 5,8 ± 2,5 cm2). The remaining patient had the critical isthmus just below the aortic root, between the area in contact with the latter and the mitral annulus. Furthermore, in all cases, the critical isthmus was immersed in LVAs. All but 1 LAAW flutter terminated during radiofrequency (RF) energy applications and rendered it non-inducible. After a median follow-up of 13,6 months (IQ range 5,3-21,6), 7 patients (70%) remained without recurrences.

Conclusion

In patients with LAAW atrial flutter, the presence of LVAs and the critical isthmus of the tachycardia are mostly circumscribed into small areas immediately behind the aortic root. Knowledge of this close relationship and the use of the isodistance map could be useful when mapping and ablating LAAW flutter, helping to straightforward the ablation procedure.

Personalized pulmonary vein antrum isolation guided by left atrial wall thickness for persistent atrial fibrillation

AIMS

Pulmonary vein (PV) antrum isolation proved to be effective for treating persistent atrial fibrillation (PeAF). We sought to investigate the results of a personalized approach aimed at adapting the ablation index (AI) to the local left atrial wall thickness (LAWT) in a cohort of consecutive patients with PeAF.

METHODS AND RESULTS

Consecutive patients referred for PeAF first ablation were prospectively enrolled. The LAWT three-dimensional maps were obtained from pre-procedure multidetector computed tomography and integrated into the navigation system. Ablation index was titrated according to the local LAWT, and the ablation line was personalized to avoid the thickest regions while encircling the PV antrum. A total of 121 patients (69.4% male, age 64.5 ± 9.5 years) were included. Procedure time was 57 min (IQR 50-67), fluoroscopy time was 43 s (IQR 20-71), and radiofrequency (RF) time was 16.5 min (IQR 14.3-18.4). The median AI tailored to the local LAWT was 387 (IQR 360-410) for the anterior wall and 335 (IQR 300-375) for the posterior wall. First-pass PV antrum isolation was obtained in 103 (85%) of the right PVs and 103 (85%) of the left PVs. Median LAWT values were higher for PVs without first-pass isolation as compared to the whole cohort (P = 0.02 for left PVs and P = 0.03 for right PVs). Recurrence-free survival was 79% at 12 month follow-up.

CONCLUSION

In this prospective study, LAWT-guided PV antrum isolation for PeAF was effective and efficient, requiring low procedure, fluoroscopy, and RF time. A randomized trial comparing the LAWT-guided ablation with the standard of practice is in progress (ClinicalTrials.gov, NCT05396534).

Preventive substrate ablation in chronic post-myocardial infarction patients with high-risk scar characteristics for ventricular arrhythmias: rationale and design of PREVENT-VT study

BACKGROUND

Recent studies showed that an early strategy for ventricular tachycardia (VT) ablation resulted in reduction of VT episodes or mortality. Cardiac magnetic resonance (CMR)-derived border zone channel (BZC) mass has proved to be a strong non-invasive predictor of VT in post-myocardial infarction (MI). CMR-guided VT substrate ablation proved to be safe and effective for reducing sudden cardiac death (SCD) and VA occurrence.

METHODS

PREVENT-VT is a prospective, randomized, multicenter, and controlled trial designed to evaluate the safety and efficacy of prophylactic CMR-guided VT substrate ablation in chronic post-MI patients with CMR-derived arrhythmogenic scar characteristics. Chronic post-MI patients with late gadolinium enhancement (LGE) CMR will be evaluated. CMR images will be post-processed and the BZC mass measured: patients with a BZC mass > 5.15 g will be eligible. Consecutive patients will be enrolled at 3 centers and randomized on a 1:1 basis to undergo a VT substrate ablation (ABLATE arm) or optimal medical treatment (OMT arm). Primary prevention ICD will be implanted following guideline recommendations, while non-ICD candidates will be implanted with an implantable cardiac monitor (ICM). The primary endpoint is a composite outcome of sudden cardiac death (SCD) or sustained monomorphic VT, either treated by an ICD or documented with ICM. Secondary endpoints are procedural safety and efficiency outcomes of CMR-guided ablation.

DISCUSSION

In some patients, the first VA episode causes SCD or severe neurological damage. The aim of the PREVENT-VT is to evaluate whether primary preventive substrate ablation may be a safe and effective prophylactic therapy for reducing SCD and VA occurrence in patients with previous MI and high-risk scar characteristics based on CMR.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT04675073, registered on January 1, 2021.

Relationship between the posterior atrial wall and the esophagus: esophageal position and temperature measurement during atrial fibrillation ablation (AWESOME-AF). A randomized controlled trial

BACKGROUND

Pulmonary vein isolation (PVI) implies unavoidable ablation lesions to the left atrial posterior wall, which is closely related to the esophagus, leading to several potential complications. This study evaluates the usefulness of the esophageal fingerprint in avoiding temperature rises during paroxysmal atrial fibrillation (PAF) ablation.

METHODS

Isodistance maps of the atrio-esophageal relationship (esophageal fingerprint) were derived from the preprocedural computerized tomography. Patients were randomized (1:1) into two groups: (1) PRINT group, the PVI line was modified according to the esophageal fingerprint; (2) CONTROL group, standard PVI with operator blinded to the fingerprint. The primary endpoint was temperature rise detected by intraluminal esophageal temperature probe monitoring. Ablation settings were as specified on the Ablate BY-LAW study protocol.

RESULTS

Sixty consecutive patients referred for paroxysmal AF ablation were randomized (42 (70%) men, mean age 60 ± 11 years). Temperature rise (> 39.1 °C) occurred in 5 (16%) patients in the PRINT group vs. 17 (56%) in the CONTROL group (p < 0.01). Three AF recurrences were documented at a mean follow-up of 12 ± 3 months (one (3%) in the PRINT group and 2 (6.6%) in the CONTROL group, p = 0.4).

CONCLUSION

The esophageal fingerprint allows for a reliable identification of the esophageal position and its use for PVI line deployment results in less frequent esophageal temperature rises when compared to the standard approach. Further studies are needed to evaluate the impact of PVI line modification to avoid esophageal heating on long-term outcomes. The development of new imaging-derived tools could ultimately improve patient safety (NCT04394923).

V-042 MOVING THE CONCEPT ASSOCIATED TO LAPAROSCOPIC INTRACORPOREAL RECTUS APONEUROPLASTY (LIRA) TO LATERAL HERNIA

Aims

Lateral hernias(LH) are rare and there are difficulties associated to minimally invasive approach, LIRA-technique has been described as an alternative to simple closure of the defect. Despite this, the indications of the concept associated to this technique are beginning to expand to other complex locations. Aims of this video is to show the surgical steps for LH where the concept associated to LIRA is followed to repair this type of hernias.

Material & Methods

56-year-old female patient without previous surgical history. Clinical examination and CT-scan showed a LH(L2) 6.4 cm in width(W2) and a length of 6.6 cm.

Results

We started by opening the peritoneum and fascia, exposing the fibers of the internal oblique and the posterior rectus sheath near the border of the defect. Then, the peritoneum and the fascia transversalis, and medially the posterior aponeurosis of the rectus muscle, are opened. Also, it is important to create a lateral peritoneum flap, using a hybrid procedure that involves a partially extraperitoneal and transabdominal (TAPE), then loop-suture are used for closing the defect. Finally, the mesh is placed intraperitoneally and partially extraperitoneal.

Conclusions

Best surgical technique for LH is still not clear. The anatomical location of these hernias is challenging, recurrence and bulging are also frequent. Since the introduction of the concept of primary closure of the hernia defect, the surgical repair of hernias in different locations has changed, although the idea of expanding the indication of LIRA could be related to better results in term of recurrences, bulging and pain.

V-053 USE OF HYBRID LAPAROSCOPIC INTRACORPOREAL RECTUS APONEUROPLASTY (LIRA-TECHNIQUE) IN COMPLEX VENTRAL HERNIAS

Aim

The hybrid approach (HA) to ventral hernias (VH), combining the laparoscopic and open approaches, is not very common at present. The great contribution of this approach is that it combines the advantages of the minimally invasive approach with the advantages of the open approach, making it possible to correct aesthetic defects and major skin and subcutaneous problems.

Material & Methods

40-year-old-man with previous surgery for supraumbilical hernia, with placement of a supraaponeurotic mesh with hernia recurrence and chronic infection with a meshoma. Physical examination revealed VH of 5–8cm in transverse diameter and 10cm in vertical diameter. A CT-scan showed a 6.5cm transverse supraumbilical recurrent hernia with a fatty content.

Results

A laparoscopic approach was performed, revealing an 8×8cm supraumbilical defect in the abdominal cavity with no adhesions. A midline repair was performed according to the principles of the LIRA technique by performing a posterior fascial flap 2cm above the edges of the defect: the midline was reinforced with a loop-suture. An intra-abdominal mesh was placed and fixed with tackers and fibrin glue. In the open procedure, the chronic sinus, meshoma, excess skin and hernial sac were removed.

Conclusions

The treatment of complex abdominal hernias is a field in constant evolution. The HA aims to solve the skin problems associated with laparoscopic repairs alone. The use of intraperitoneal on-lay meshes combined with the use of open approach for excision of the sac and remaining skin tissue allows a complete and effective treatment of complex hernias.

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 &lt;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 &gt; 0.5 mV at the level of the previous ablation line or as the presence during arrhythmia of a LAT delay &lt;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 &gt; 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.

Rad52 function prevents chromosome loss and truncation in Candida albicans

RAD52 is required for almost all recombination events in Saccharomyces cerevisiae. We took advantage of the heterozygosity of HIS4 in the Candida albicans SC5314 lineage to study the role of Rad52 in the genomic stability of this important fungal pathogen. The rate of loss of heterozygosity (LOH) at HIS4 in rad52-ΔΔ strains was ∼10(-3) , at least 100-fold higher than in Rad52(+) strains. LOH of whole chromosome 4 or truncation of the homologue that carries the functional HIS4 allele was detected in all 80 rad52-ΔΔ His auxotrophs (GLH -GL lab His(-)) obtained from six independent experiments. Isolates that had undergone whole chromosome LOH, presumably due to loss of chromosome, carried two copies of the remaining homologue. Isolates with truncations carried centric fragments of broken chromosomes healed by de novo telomere addition. GLH strains exhibited variable degrees of LOH across the genome, including two strains that became homozygous for all the heterozygous markers tested. In addition, GLH strains exhibited increased chromosomal instability (CIN), which was abolished by reintroduction of RAD52. CIN of GLH isolates is reminiscent of genomic alterations leading to cancer in human cells, and support the mutator hypothesis in which a mutator mutation or CIN phenotype facilitate more mutations/aneuploidies.

Shell shape of the land snail Cornu aspersum in North Africa: unexpected evidence of a phylogeographical splitting

Anatomical and molecular characters used to differentiate populations of the land snail Cornu aspersum (Helix aspersa) exhibit, in the western Mediterranean, definite and concordant patterns of correlation with geography. Scenarios involving Pliocene geological changes and postglacial expansion during the Pleistocene were proposed in previous studies to account for the establishment of this geographical structure. In the present work, we have performed a spatial analysis of variation in shell morphometrics, after the partitioning of the overall variation into size and shape components by means of a principal component-based approach (Cadima and Jolliffe, 1996). In order to know if the same historical events have also structured shell variation, the analysis includes all the populations from North Africa which were investigated for anatomical and molecular surveys. Contrary to shell size, which shows a significant spatial heterogeneity essentially related to environmental pressures, variation in shell shape components splits the populations according to a geographical pattern reflective of hypotheses suggested for molecular markers and genital anatomy. This implies that the selective forces often invoked to explain spatial changes in shell shape are not the deciding factors in the present case. Moreover, within each of the two geographical clusters defined, Mantel correlograms show that the similarity between populations declines according to an isolation by distance model. Because of the different allometric relationships between shell size and genitalia measurements in Western and Eastern entities of North Africa, mechanical constraints, possibly leading to a precopulatory isolation in the contact zone, are involved.

Spatial structure of shell polychromatism in populations of Cepaea nemoralis: new techniques for an old debate

A conspicuous shell polychromatism is observed in colonies of Cepaea nemoralis from western France (Brittany). The present study is intended to search for a spatial structure of shell features at this scale and to infer evolutionary processes from the observed patterns. We used a database of morph frequencies (six composite phenotypes were retained) measured on 213 samples regularly distributed on the whole studied area. Data analysis was based on two distinct multivariate methods leading to the following steps: (i) to search for a structure without reference to environmental conditions with a method (global principal components analysis: GPCA) which takes into account the spatial information by means of a neighbouring relationship between sampling points (Delaunay triangulation); (ii) to test the structuring power of environmental conditions by means of two explanatory factors (distance from the sea, altitude) involved in a redundancy analysis (RDA); (iii) to search for a spatial structure using residuals of the previous analysis, ie, after removing effects of environmental conditions. Global covariance accounted for 26.4% of the total variance, leading to a highly significant autocorrelation for each phenotype (step 1). Geographical mapping of factorial scores resulting from global analysis showed a well structured littoral zone and a strong southern-northern inland differentiation. Sixteen percent of the total variance was expressed in RDA but all morphs were not equally concerned. After removing environmental effects, a significant spatial structure still remains but was essentially caused by random processes. We argue for the importance of these last phenomena.

Life cycle of the tick Ixodes uriae in penguin colonies: relationships with host breeding activity

A survey of the temporal pattern of population structure and feeding activity of the seabird tick Ixodes uriae was conducted for the first time in two host species colonies: King penguin (Aptenodytes patagonicus halli) and Macaroni penguin (Eudyptes chrysolophus chrysolophus). The life cycle of the tick was investigated over 3 years in a King penguin colony and 2 years in a Macaroni penguin colony at Possession Island (Crozet Archipelago). There was a marked seasonal feeding activity pattern of ticks in both host species, connected with the presence of birds during the breeding season. Although the King penguin colonies were occupied throughout the year by birds, the favourable period for engorgement was limited to 3.5-4.5 months, and almost all the ticks overwintered in the unengorged state. Consequently, I. uriae probably completed its life cycle over 3 years in King penguin colonies. In contrast, this life cycle could be shortened to 2 years in Macaroni penguin colonies, as a result of a different timetable of the presence of birds for breeding and moulting. The relationships between such plasticity and the host behaviour and subantarctic climatic conditions are discussed.

Spatial analysis of allozyme and microsatellite DNA polymorphisms in the land snail Helix aspersa (Gastropoda: Helicidae)

The genetic structure of the land snail Helix aspersa was investigated for 21 populations collected along a road located in the polders of the Bay of Mont-Saint-Michel (Brittany, France), following a sampling scheme the area of which did not exceed 900 m in length. A total of 369 individuals were genotyped for five enzymatic markers and seven microsatellite loci. We used sequential hierarchical F-statistics at different spatial scales and spatial autocorrelation statistics to explore recent historical patterns involved in the observed genetic distribution. Whatever the statistics used, congruent levels of spatial genetic substructuring across loci were demonstrated, excepted for one allozyme locus. Overall spatial genetic arrangement matched in a substantial fashion theoretical predictions based on the limited dispersal power of land snails. Positive autocorrelation over short-distance classes may result from the development of genetically distinct patches of individuals organized in family-structured colonies. Therefore, spatial signatures of average I correlograms can be viewed as the expression of a stepping-stone model of population structure, sometimes involving external migrational events. Overall, the revealed pattern of population subdivision on a microgeographical scale was suggestive of a neighbourhood structure. Finally, microsatellite loci are especially suitable for the detection of small genetic clustering, and combining different classes of markers offers the potential to gain further insight into the description of spatial genetic variability over short temporal and geographical scales.

Microspatial genetic structure in the land snail helix aspersa (Gastropoda: helicidae)

The microspatial genetic structure of allele frequencies at seven isozyme loci was examined for 15 populations of the land snail Helix aspersa sampled in a village from Brittany (north-western France). Spatial heterogeneity of allele frequencies was highly significant (P < 0.001). Fixation indices reflected nonrandom mating within neighbourhoods and a slight but consistent differentiation between colonies (FST=0.044; P < 0.01). Analyses of gene flow or genetic distances failed to reveal a significant relationship with geographical distance, probably because of the complexity of environmental heterogeneity. However, matrix comparisons between genetic distances and connectivity networks among adjacent colonies (Gabriel-connected graph) yielded a significant correlation in every case, indicating a 'step-by-step' relationship between neighbouring localities. Moreover, most of the allozymes were spatially structured and showed (i) a gradual isolation of colonies with increasing geographical distances, and (ii), for some correlogram profiles, a circular gradient illustrating a multidirectional colonization of the village. The probable existence of disperser individuals allowed us to suggest a metapopulation model which would explain the maintenance of such animals in fragmented habitats where anthropogenic disturbances and extinction/recolonization events are commonly observed.

Genetic distances and ordination: the land snail Helix aspersa in north Africa as a test case

We examined the efficiencies of ordination methods in the treatment of gene frequency data at intraspecific level, using metric and nonmetric distance measures (Nei's and Rogers' genetic distances, chi 2 distance). We assessed initial processes responsible for the geographical distribution of the Mediterranean land snail Helix aspersa. Seventeen enzyme loci from 30 North African snail populations were considered in the present analysis. Five combinations of distance/multivariate analysis were compared: correspondence analysis (CA), nonmetric multidimensional scaling (NMDS) on Nei's, Rogers', and chi 2 distances, and principal coordinates analysis on Rogers' distances. Configuration of the objects resulting from ordination was projected onto three-dimensional graphics with the minimum spanning tree or the relative neighborhood graph superimposed. Pre- and postordination or clustering distance matrices were compared by means of correlation methods. As expected, all combinations led to a clear west versus east pattern of variation. However, the intraregional relationships and degree of connectivity between pairs of operational taxonomic units were not necessarily constant from one method to another. Ordination methods when applied with Nei's and Rogers' distances provided the best fit, with original distances (r = 0.98) compared with UPGMA clustering (r approximately 0.75). The Nei/NMDS combination seems to be a good compromise (distortion index dt = 10%) between Rogers/NMDS, which produces a more confusing pattern of differentiation (dt = 24%), and chi 2/CA, which tends to distort large distances (dt = 31%). NMDS obviously provides a powerful method to summarize relationships between populations, when neither hierarchical structure nor phylogenetic inference are required. These findings led the discussion on the good performance of NMDS, the appropriate distances to be used, and the potential application of this method to other types of allelic data (such as microsatellite loci) or data on nucleotide sequences of genes.

Caractéristiques biodémographiques d'un acarien oribate (Carabodes willmanni) des pelouses xérophiles

An analysis of biodemographic characteristics was undertaken under experimental conditions in Carabodes willmanni, the first study of its kind in the superfamily Carabodoidea. The species dominates the microarthropod fauna of dry Cladonia cover. Immature stages have a very soft integument and live within the decomposing lichen layer. The population is characterized by the following: (i) low fecundity, strongly density dependent; (ii) relatively long postembryonic development for such a small species, lasting 117 days at 20 °C; (iii) extended premoulting stage (pupation), lasting 28% of postembryonic development; (iv) high but very variable longevity, with values varying from 200 to 600 days between egg laying and death of the adult; (v) strong influence of temperature on fecundity, adult survival, and duration of embryonic and postembryonic developments: development is inhibited at 10 °C. Based on previously acquired information on the phenology of the population, a model for the life cycle under natural conditions is proposed. Periods favorable to development being greatly shortened by environmental factors, the duration of the cycle is lengthened and probably takes as much as 1 year under the harshest conditions. The success of C. willmanni in such an environment can be explained by the capacity of the immature stages to take advantage of the lichen substrate both as a source of food and as a means of protection against desiccation.[Journal translation]