Insights Into the Spatiotemporal Patterns of Complexity of Ventricular Fibrillation by Multilead Analysis of Body Surface Potential Maps.

BACKGROUND: Ventricular fibrillation (VF) is the main cause of sudden cardiac death, but its mechanisms are still unclear. We propose a noninvasive approach to describe the progression of VF complexity from body surface potential maps (BSPMs). METHODS: We mapped 252 VF episodes (16 ± 10 s) with a 252-electrode vest in 110 patients (89 male, 47 ± 18 years): 50 terminated spontaneously, otherwise by electrical cardioversion (DCC). Changes in complexity were assessed between the onset ("VF start") and the end ("VF end") of VF by the nondipolar component index (N D I B S P M ), measuring the fraction of energy nonpreserved by an equivalent 3D dipole from BSPMs. Higher NDI reflected lower VF organization. We also examined other standard body surface markers of VF dynamics, including fibrillatory wave amplitude (A BSPM ), surface cycle length (BsCL BSPM ) and Shannon entropy (S h E n B S P M ). Differences between patients with and without structural heart diseases (SHD, 32 vs. NSHD, 78) were also tested at those stages. Electrocardiographic features were validated with simultaneous endocardium cycle length (CL) in a subset of 30 patients. RESULTS: All BSPM markers measure an increase in electrical complexity during VF (p < 0.0001), and more significantly in NSHD patients. Complexity is significantly higher at the end of sustained VF episodes requiring DCC. Intraepisode intracardiac CL shortening (VF start 197 ± 24 vs. VF end 169 ± 20 ms; p < 0.0001) correlates with an increase in NDI, and decline in surface CL, f-wave amplitude, and entropy (p < 0.0001). In SHD patients VF is initially more complex than in NSHD patients (N D I B S P M , p = 0.0007; S h E n B S P M , p < 0.0001), with moderately slower (BsCL BSPM , p = 0.06), low-amplitude f-waves (A BSPM , p < 0.0001). In this population, lower NDI (p = 0.004) and slower surface CL (p = 0.008) at early stage of VF predict self-termination. In the NSHD group, a more abrupt increase in VF complexity is quantified by all BSPM parameters during sustained VF (p < 0.0001), whereas arrhythmia evolution is stable during self-terminating episodes, hinting at additional mechanisms driving VF dynamics. CONCLUSION: Multilead BSPM analysis underlines distinct degrees of VF complexity based on substrate characteristics.

Post-Myocardial Infarction Scar With Fat Deposition Shows Specific Electrophysiological Properties and Worse Outcome After Ventricular Tachycardia Ablation.

Background Fat deposition (FD) is part of the healing process after myocardial infarction. The characteristics of FD and its impact on the outcome in patients undergoing ventricular tachycardia (VT) ablation have not been thoroughly studied. Methods and Results We studied consecutive patients undergoing post-myocardial infarction VT ablation with pre-procedural cardiac computed tomography. FD was defined as intra-myocardial attenuation ≤ -30 HU on computed tomography. Clinical, anatomical, and post-procedural outcome was assessed in the overall population. Electrophysiological characteristics were assessed is a subgroup of patients with high-density electro-anatomical maps. Sixty-nine patients were included (66±12 years). FD was detected in 44 (64%) patients. The presence of FD related to scar age (odds ratio [OR]: 1.14 per year; P=0.001) and scar extent (OR: 1.27 per segment; P=0.02). On electro-anatomical maps, FD was characterized by lower bipolar amplitude (P<0.001) and prolonged electrogram duration (P<0.001). Although the proportion of local abnormal ventricular activation was similar (P=0.22), local abnormal ventricular activation showed lower amplitude (P<0.001) and were more delayed (P<0.001) in scars with FD. After a mean follow-up of 26 months, patients with FD experienced a worse outcome including all-cause mortality and VT recurrence (70% versus 28%, P log rank=0.009). On multivariate analysis, FD (hazard ratio=2.69; 95% CI, 1.12-6.46; P=0.027) and left ventricular systolic dysfunction (hazard ratio=2.57; 95% CI, 1.13-5.85; P=0.024) were independent predictors of adverse outcomes. Conclusions FD in patients with post-myocardial infarction VT undergoing catheter ablation relates to scar age and size and may be a marker of adverse outcomes including all-cause mortality and VT recurrence.

Noninvasive Mapping and Electrocardiographic Imaging in Atrial and Ventricular Arrhythmias (CardioInsight).

Electrocardiographic imaging is a mapping technique aiming to noninvasively characterize cardiac electrical activity using signals collected from the torso to reconstruct epicardial potentials. Its efficacy has been demonstrated clinically, from mapping premature ventricular complexes and accessory pathways to of complex arrhythmias. Electrocardiographic imaging uses a standardized workflow. Signals should be checked manually to avoid automatic processing errors. Reentry is confirmed in the presence of local activation covering the arrhythmia cycle length. Focal breakthroughs demonstrate a QS pattern associated with centrifugal activation. Electrocardiographic imaging offers a unique opportunity to better understand the mechanism of cardiac arrhythmias and guide ablation.

Cardiac Propagation Pattern Mapping With Vector Field for Helping Tachyarrhythmias Diagnosis With Clinical Tridimensional Electro-Anatomical Mapping Tools.

Ventricular (VT) and atrial (AT) tachycardias are some of the most common clinical cardiac arrhythmias. For ablation of tachycardia substrates, two clinical diagnosis methods are used: invasive electroanatomical mapping for an accurate diagnosis using electrograms (EGMs) acquired with intracardiac catheters, and localized on the surface mesh of the studied cavities; and noninvasive electrocardiographic imaging (ECGi) for a global view of the arrhythmia, with EGMs mathematically reconstructed from body surface electrocardiograms using 3-D cardio-thoracic surface meshes obtained from CT-scans. In clinics, VT and AT are diagnosed by studying activation time maps that depict the propagation of the activation wavefront on the cardiac mesh. Nevertheless, slow conduction areas-a well-known proarrhythmic feature for tachycardias-and tachycardia specific propagation patterns are not easily identifiable with these maps. Therefore, local characterization of the activation wavefront propagation can be helpful for improving VT and AT diagnoses. The purpose of this study is to develop a method to locally characterize the activation wavefront propagation for clinical data. For this, a conduction velocity vector field is estimated and analyzed using divergence and curl mathematical operators. The workflow was first validated on a simulated database from computer models, and then applied to a clinical database obtained from ECGi to improve AT diagnosis. The results show the relevancy and the efficacy of the proposed method to guide ablation of tachyarrhythmias.

Atrial Fibrillation Mechanisms and Implications for Catheter Ablation.

AF is a heterogeneous rhythm disorder that is related to a wide spectrum of etiologies and has broad clinical presentations. Mechanisms underlying AF are complex and remain incompletely understood despite extensive research. They associate interactions between triggers, substrate and modulators including ionic and anatomic remodeling, genetic predisposition and neuro-humoral contributors. The pulmonary veins play a key role in the pathogenesis of AF and their isolation is associated to high rates of AF freedom in patients with paroxysmal AF. However, ablation of persistent AF remains less effective, mainly limited by the difficulty to identify the sources sustaining AF. Many theories were advanced to explain the perpetuation of this form of AF, ranging from a single localized focal and reentrant source to diffuse bi-atrial multiple wavelets. Translating these mechanisms to the clinical practice remains challenging and limited by the spatio-temporal resolution of the mapping techniques. AF is driven by focal or reentrant activities that are initially clustered in a relatively limited atrial surface then disseminate everywhere in both atria. Evidence for structural remodeling, mainly represented by atrial fibrosis suggests that reentrant activities using anatomical substrate are the key mechanism sustaining AF. These reentries can be endocardial, epicardial, and intramural which makes them less accessible for mapping and for ablation. Subsequently, early interventions before irreversible remodeling are of major importance. Circumferential pulmonary vein isolation remains the cornerstone of the treatment of AF, regardless of the AF form and of the AF duration. No ablation strategy consistently demonstrated superiority to pulmonary vein isolation in preventing long term recurrences of atrial arrhythmias. Further research that allows accurate identification of the mechanisms underlying AF and efficient ablation should improve the results of PsAF ablation.

Mapping and Ablation of Idiopathic Ventricular Fibrillation.

Idiopathic ventricular fibrillation (IVF) is the main cause of unexplained sudden cardiac death, particularly in young patients under the age of 35. IVF is a diagnosis of exclusion in patients who have survived a VF episode without any identifiable structural or metabolic causes despite extensive diagnostic testing. Genetic testing allows identification of a likely causative mutation in up to 27% of unexplained sudden deaths in children and young adults. In the majority of cases, VF is triggered by PVCs that originate from the Purkinje network. Ablation of VF triggers in this setting is associated with high rates of acute success and long-term freedom from VF recurrence. Recent studies demonstrate that a significant subset of IVF defined by negative comprehensive investigations, demonstrate in fact subclinical structural alterations. These localized myocardial alterations are identified by high density electrogram mapping, are of small size and are mainly located in the epicardium. As reentrant VF drivers are often colocated with regions of abnormal electrograms, this localized substrate can be shown to be mechanistically linked with VF. Such areas may represent an important target for ablation.

Noninvasive Assessment of Atrial Fibrillation Complexity in Relation to Ablation Characteristics and Outcome.

Background: The use of surface recordings to assess atrial fibrillation (AF) complexity is still limited in clinical practice. We propose a noninvasive tool to quantify AF complexity from body surface potential maps (BSPMs) that could be used to choose patients who are eligible for AF ablation and assess therapy impact. Methods: BSPMs (mean duration: 7 ± 4 s) were recorded with a 252-lead vest in 97 persistent AF patients (80 male, 64 ± 11 years, duration 9.6 ± 10.4 months) before undergoing catheter ablation. Baseline cycle length (CL) was measured in the left atrial appendage. The procedural endpoint was AF termination. The ablation strategy impact was defined in terms of number of regions ablated, radiofrequency delivery time to achieve AF termination, and acute outcome. The atrial fibrillatory wave signal extracted from BSPMs was divided in 0.5-s consecutive segments, each projected on a 3D subspace determined through principal component analysis (PCA) in the current frame. We introduced the nondipolar component index (NDI) that quantifies the fraction of energy retained after subtracting an equivalent PCA dipolar approximation of heart electrical activity. AF complexity was assessed by the NDI averaged over the entire recording and compared to ablation strategy. Results: AF terminated in 77 patients (79%), whose baseline AF CL was 177 ± 40 ms, whereas it was 157 ± 26 ms in patients with unsuccessful ablation outcome (p = 0.0586). Mean radiofrequency emission duration was 35 ± 21 min; 4 ± 2 regions were targeted. Long-lasting AF patients (≥12 months) exhibited higher complexity, with higher NDI values (≥12 months: 0.12 ± 0.04 vs. <12 months: 0.09 ± 0.03, p < 0.01) and short CLs (<160 ms: 0.12 ± 0.03 vs. between 160 and 180 ms: 0.10 ± 0.03 vs. >180 ms: 0.09 ± 0.03, p < 0.01). More organized AF as measured by lower NDI was associated with successful ablation outcome (termination: 0.10 ± 0.03 vs. no termination: 0.12 ± 0.04, p < 0.01), shorter procedures (<30 min: 0.09 ± 0.04 vs. ≥30 min: 0.11 ± 0.03, p < 0.001) and fewer ablation targets (<4: 0.09 ± 0.03 vs. ≥4: 0.11 ± 0.04, p < 0.01). Conclusions: AF complexity can be noninvasively quantified by PCA in BSPMs and correlates with ablation outcome and AF pathophysiology.

Localized Structural Alterations Underlying a Subset of Unexplained Sudden Cardiac Death.

BACKGROUND: Sudden cardiac death because of ventricular fibrillation (VF) is commonly unexplained in younger victims. Detailed electrophysiological mapping in such patients has not been reported. METHODS: We evaluated 24 patients (29±13 years) who survived idiopathic VF. First, we used multielectrode body surface recordings to identify the drivers maintaining VF. Then, we analyzed electrograms in the driver regions using endocardial and epicardial catheter mapping during sinus rhythm. Established electrogram criteria were used to identify the presence of structural alterations. RESULTS: VF occurred spontaneously in 3 patients and was induced in 16, whereas VF was noninducible in 5. VF mapping demonstrated reentrant and focal activities (87% versus 13%, respectively) in all. The activities were dominant in one ventricle in 9 patients, whereas they had biventricular distribution in others. During sinus rhythm areas of abnormal electrograms were identified in 15/24 patients (62.5%) revealing localized structural alterations: in the right ventricle in 11, the left ventricle in 1, and both in 3. They covered a limited surface (13±6 cm2) representing 5±3% of the total surface and were recorded predominantly on the epicardium. Seventy-six percent of these areas were colocated with VF drivers (P<0.001). In the 9 patients without structural alteration, we observed a high incidence of Purkinje triggers (7/9 versus 4/15, P=0.033). Catheter ablation resulted in arrhythmia-free outcome in 15/18 patients at 17±11 months follow-up. CONCLUSIONS: This study shows that localized structural alterations underlie a significant subset of previously unexplained sudden cardiac death. In the other subset, Purkinje electrical pathology seems as a dominant mechanism.

Frontiers in non-invasive cardiac mapping: future implications for arrhythmia treatment.

Electrocardiographic mapping (ECM) is a noninvasive technique using body surface potentials and CT geometry to reconstruct epicardial maps. ECM is emerging as an important tool not only for diagnostic mapping, but also as a guide for trans-catheter ablation of complex arrhythmias such as atrial fibrillation. It provides the clinician with an immediate global view of the substrate, allowing easier pre-procedural planning, potentially improving clinical outcomes. Panoramic mapping of ventricular fibrillation (VF) is helping to develop a better understanding of its physiology, with future implications for the identification of therapeutic targets in patients with structural heart disease, as well as in idiopathic VF.

From old alkylating agents to new minor groove binders.

Alkylating agents represent the oldest class of anticancer agents with the approval of mechloretamine by the FDA in 1949. Even though their clinical use is far beyond the use of new targeted therapies, they still occupy a major place in the treatment of specific malignancies, sometimes representing the unique option for the treatment of refractory tumors. Here, we are reviewing the major classes of alkylating agents, with a particular focus on the latest generations of compounds that specifically target the minor groove of the DNA. These naturally occurring derivatives have a unique mechanism of action that explains the recent regain of interest in developing new classes of alkylating agents that could be used in combination with other anticancer drugs to enhance tumor response in the clinic.

Gene expression signature predicting high-grade prostate cancer responses to oxaliplatin.

Prostate cancer is one of the leading causes of cancer-related deaths among men. Several prognostic factors allow differentiation of low-grade tumors from high-grade tumors with high metastatic potential. High-grade tumors are currently treated with hormone therapy, to which taxanes are added when the tumors become resistant to castration. Clinical trials with other anticancer agents did not take into account the genetic backgrounds of the tumors, and most trials demonstrated low response rates. Here we used an in silico approach to screen for drug candidates that might be used as alternatives to taxanes, on the basis of a published expression signature involving 86 genes that could distinguish high-grade and low-grade tumors (Proc Natl Acad Sci USA 103:10991-10996, 2006). We explored the National Cancer Institute databases, which include data on the gene expression profiles of 60 human tumor cell lines and the in vitro sensitivities of the cell lines to anticancer drugs, and we identified several genes in the signature for which expression levels were correlated with chemosensitivity. As an example of the validation of this in silico approach, we identified a set of six genes for which expression levels could predict cell sensitivity to oxaliplatin but not cisplatin. This signature was validated in vitro through silencing of the genes in DU145, LNCaP, and C4-2B prostate cancer cells, which was accompanied by changes in oxaliplatin but not cisplatin cytotoxicity. These results demonstrate the relevance of our approach for the identification of both alternative treatments for high-grade prostate cancers and new biomarkers to predict clinical tumor responses.

The polyphenolic ellagitannin vescalagin acts as a preferential catalytic inhibitor of the α isoform of human DNA topoisomerase II.

Polyphenolic ellagitannins are natural compounds that are often associated with the therapeutic activity of plant extracts used in traditional medicine. They display cancer-preventing activity in animal models by a mechanism that remains unclear. Potential targets have been proposed, including DNA topoisomerases II (Top2). Top2α and Top2ß, the two isoforms of the human Top2, play a crucial role in the regulation of replication, transcription, and chromosome segregation. They are the target of anticancer agents used in the clinic such as anthracyclines (e.g., doxorubicin) or the epipodophyllotoxin etoposide. It was recently shown that the antitumor activity of etoposide was due primarily to the inhibition of Top2α, whereas inhibition of Top2ß was responsible for the development of secondary malignancies, pointing to the need for more selective Top2α inhibitors. Here, we show that the polyphenolic ellagitannin vescalagin preferentially inhibits the decatenation activity of Top2α in vitro, by a redox-independent mechanism. In CEM cells, we also show that transient small interfering RNA-mediated down-regulation of Top2α but not of Top2ß conferred a resistance to vescalagin, indicating that the α isoform is a preferential target. We further confirmed that Top2α inhibition was due to a catalytic inhibition of the enzyme because it did not induce DNA double-strand breaks in CEM-treated cells but prevented the formation of Top2α- rather than Top2ß-DNA covalent complexes induced by etoposide. To our knowledge, vescalagin is the first example of a catalytic inhibitor for which cytotoxicity is due, at least in part, to the preferential inhibition of Top2α.

Impact of EGFR gene polymorphisms on anticancer drug cytotoxicity in vitro.

BACKGROUND AND OBJECTIVE: The epidermal growth factor receptor (EGFR) plays a major role in cell proliferation of epithelial tissues, and its alterations frequently contribute to oncogenesis. Several common polymorphisms of the EGFR gene have been described, at the level of both coding and regulatory sequences. Some of these polymorphisms are associated with alterations of EGFR expression and/or activity and may have an impact on the activity of anticancer agents. This study aims to analyze the relationships between specific EGFR functional polymorphisms and anticancer drug activity. METHOD: We investigated, in the panel of 60 human tumor cell lines established by the National Cancer Institute (NCI-60), whether the EGFR polymorphisms -216G>T, -191C>A, Arg521Lys (R521K), Val592Ala (V592A), and Cys624Phe (C624F), and the intron 1 (CA)n repeat were associated with EGFR gene expression and the in vitro cytotoxicity of anticancer agents using data extracted from the NCI database. We also looked for mutations of exons 18-21, known to enhance the activity of tyrosine kinase inhibitors, and the deletion of exons 2-7, associated to the oncogenesis of glioblastomas. RESULTS: In the NCI-60 cell lines, only two mutations were observed, both in exon 19, in a leukemia and melanoma cell line. These mutations have not been described previously in clinical samples and their functional role is uncertain. The allele frequencies of the -216G>T, -191C>A, and R521K single nucleotide polymorphisms (SNPs) in the NCI-60 panel were 33%, 8.5%, and 27%, respectively; the V592A and C624F SNPs were not found in any NCI-60 cell line. The intron 1 CA repeat was highly variable in the cell lines; 32 cell lines having a total number of repeats below 35, and 27 having a total number of repeats above 35. The heterozygous and variant homozygous cell lines for the -216G>T SNP presented a significantly higher expression of the EGFR gene than the homozygous wild-type lines. In contrast, there was no association between the -191C>A or R521K SNPs and EGFR gene expression. No association could be detected between the number of CA repeats in intron 1 and the expression of EGFR. The cell lines having at least one variant T allele at the -216G>T SNP were more sensitive to erlotinib and less sensitive to geldanamycin, topoisomerase I and II inhibitors, and alkylating agents than those without a variant allele. No relationship was detected between anticancer drug sensitivity and the -191C>A SNP. The R521K SNP was associated to lower sensitivity to alkylating agents. The number of CA repeats was associated with significant differences in anticancer drug activity: a high total number of CA repeats (>35 per diploid genome) was associated to increased sensitivity to alkylating agents and topoisomerase I and II inhibitors. DISCUSSION: We provide evidence in this work that EGFR polymorphisms are associated with significant differences in the in vitro cytotoxicity of several types of DNA-interfering agents. Studies attempting a clinical validation of these clues are warranted.