Safety of pulsed-field ablation in patients with cardiac implantable electronic devices. A single-center pilot study

Funding Acknowledgements

Type of funding sources: None.

Introduction

Pulsed-field ablation (PFA) is a novel energy source to perform pulmonary vein isolation (PVI) in patients with atrial fibrillation or cavo-tricuspid isthmus ablation (CTI) in patients with atrial flutter. Whether strong electrical fields generated by PFA could change the function and integrity of cardiac implantable electronic devices (CIED) is not known.

Aim

To assess the function and integrity of implanted devices before and after pulsed-field ablation.

Methods

This study included consecutive patients with CIED undergoing PFA at a large single center. Real-time CIED electrograms were recorded during PFA applications. CIED were interrogated before and after PFA assessing function (threshold, sensing), integrity (impedance), and arrhythmia episodes.

Results

We performed PFA in six patients (age 69±12 years, 1/6 female, left atrial diameter was 44±3 mm, left-ventricular ejection fraction 40±14%) for PVI in five patients with atrial fibrillation and CTI ablation in one patient with atrial flutter. All patients had CIEDs (one cardiac resynchronization device, two implantable cardioverter-defibrillators, three two-chamber pacemakers). Each patient undergoing PVI received 32 PFA applications of 2.5 s. (4x basket configuration and 4x flower configuration at each pulmonary vein), amounting to a total ablation time of 80 s and resulting in complete PVI in all five patients. For CTI ablation we applied 8 PFA applications of 2.5 s (20 s total ablation time) resulting in CTI blockade. Real-time intracardiac electrograms (iEGM) during PFA applications revealed sensing of single PFA application impulses in three patients and blanking of the iEGM in three patients. Postinterventional device testing revealed no changes in impedance, stimulation threshold or sensing. No leads were dislocated or damaged. No other device malfunctions occurred during the procedure, as well as no other major periprocedural complications occurred.

Conclusion

The function and integrity of pacemakers and defibrillators is not affected by PFA in our patient sample. Larger series are needed to confirm the apparent safety of PFA in patients with CIED.

Immunity to polyoma virus infection and tumorigenesis

Because oncogenic DNA viruses establish persistent infections in humans, continuous immunosurveillance for neoplastic cells is required to prevent virus-induced tumors. Antigen-specific CD8+ T lymphocytes are critical in vivo effectors for eliminating virus-infected and virus-transformed cells. Investigation into the induction, regulation, and maintenance of CD8+ T cells specific for these viruses is hindered by the lack of tractable animal models that mimic natural infection. Resistance to tumors induced by polyoma virus, a persistent natural mouse DNA virus, is mediated by polyoma-specific CD8+ T cells. Mice susceptible to polyoma virus tumorigenesis mount a smaller, albeit still considerable, expansion of anti-polyoma CD8+ T cells; importantly, these antiviral CD8+ T cells lack cytotoxic activity while retaining the phenotype of cytotoxic T lymphocyte (CTL) effectors. In this review, we will discuss potential in vivo mechanisms that regulate the functional competence of anti-polyoma CD8+ T cells, particularly in the context of chronic antigenic stimulation provided by persistent viral infections and tumors.

CD8 binding to MHC class I molecules is influenced by T cell maturation and glycosylation

CD8 serves both as an adhesion molecule for class I MHC molecules and as a coreceptor with the TCR for T cell activation. Here we study the developmental regulation of CD8-mediated binding to noncognate peptide/MHC ligands (i.e., those not bound by the TCR). We show that CD8's ability to bind soluble class I MHC tetramers and to mediate T cell adhesion under shear flow conditions diminishes as double-positive thymocytes mature into CD8(+) T cells. Furthermore, we provide evidence that this decreased CD8 binding results from increased T cell sialylation upon T cell maturation. These data suggest that CD8's ability to interact with class I MHC is not fixed and is developmentally regulated through the T cell's glycosylation state.

DNA vaccines for influenza virus: differential effects of maternal antibody on immune responses to hemagglutinin and nucleoprotein

Maternal antibody is the major form of protection from disease in early life when the neonatal immune system is still immature; however, the presence of maternal antibody also interferes with active immunization, placing infants at risk for severe bacterial and viral infection. We tested the ability of intramuscular and gene gun immunization with DNA expressing influenza virus hemagglutinin (HA) and nucleoprotein (NP) to raise protective humoral and cellular responses in the presence or absence of maternal antibody. Neonatal mice born to influenza virus-immune mothers raised full antibody responses to NP but failed to generate antibody responses to HA. In contrast, the presence of maternal antibody did not affect the generation of long-lived CD8(+) T-cell responses to both HA and NP. Thus, maternal antibody did not affect cell-mediated responses but did affect humoral responses, with the ability to limit the antibody response correlating with whether the DNA-expressed immunogen was localized in the plasma membrane or within the cell.

Polyomavirus-infected dendritic cells induce antiviral CD8(+) T lymphocytes

CD8(+) T cells are critical for the clearance of acute polyomavirus infection and the prevention of polyomavirus-induced tumors, but the antigen-presenting cell(s) involved in generating polyomavirus-specific CD8(+) T cells have not been defined. We investigated whether dendritic cells and macrophages are permissive for polyomavirus infection and examined their potential for inducing antiviral CD8(+) T cells. Although dendritic cells and macrophages both supported productive polyomavirus infection, dendritic cells were markedly more efficient at presenting the immunodominant viral epitope to CD8(+) T cells. Additionally, infected dendritic cells, but not infected macrophages, primed anti-polyomavirus CD8(+) T cells in vivo. Treatment with Flt3 ligand, a hematopoietic growth factor that dramatically expands the number of dendritic cells, markedly enhanced the magnitude of virus-specific CD8(+) T-cell responses during acute infection and the pool of memory anti-polyomavirus CD8(+) T cells. These findings suggest that virus-infected dendritic cells induce polyomavirus-specific CD8(+) T cells in vivo and raise the potential for their use as cellular adjuvants to promote CD8(+) T cell surveillance against polyomavirus-induced tumors.

Visualization of polyoma virus-specific CD8+ T cells in vivo during infection and tumor rejection

T cells are critical for clearing infection and preventing tumors induced by polyoma virus, a natural murine papovavirus. We previously identified the immunodominant epitope for polyoma virus-specific CTL in tumor-resistant H-2k mice as the Dk-restricted peptide, MT389-397, derived from the polyoma middle T oncoprotein. In this study, we developed tetrameric Dk complexes containing the MT389-397 peptide to directly visualize and enumerate MT389-397-specific CTL during polyoma virus infection. We found that Dk/MT389 tetramer+CD8+ T cells undergo a massive expansion during primary infection such that by day 7 postinfection these Ag-specific CD8+ T cells constitute approximately 20% of the total and approximately 40% of the activated CD8+ T cells in the spleen. This expansion of Dk/MT389 tetramer+CD8+ T cells parallels the emergence of MT389-397-specific ex vivo cytolytic activity and clearance of polyoma virus. Notably, Dk/MT389 tetramer+CD8+ T cells are maintained in memory at very high levels. The frequencies of Dk/MT389 tetramer+CD8+ effector and memory T cells in vivo match those of CD8+ T cells producing intracellular IFN-gamma after 6-h in vitro stimulation by MT389-397 peptide. Consistent with preferential Vbeta6 expression by MT389-397-specific CD8+CTL lines and clones, Dk/MT389 tetramer+CD8+ T cells exhibit biased expression of this Vbeta gene segment. Finally, we show that Dk/MT389 tetramer+CD8+ T cells efficiently infiltrate a polyoma tumor challenge to virus-immune mice. Taken together, these findings strongly implicate virus-induced MT389-397-specific CD8+ T cells as essential effectors in eliminating polyoma-infected and polyoma-transformed cells in vivo.

Cross-recognition of two middle T protein epitopes by immunodominant polyoma virus-specific CTL

We recently identified the immunodominant epitope for polyoma virus-specific CTL as the Dk-associated peptide MT389-397 derived from the middle T (MT) viral oncoprotein. Another Dk-restricted peptide corresponding to residues 236-244 of MT was recognized by nearly all MT389-397-reactive CTL clones, but required concentrations at least 2 logs higher to sensitize syngeneic target cells for lysis. Except for identity at the three putative Dk-peptide anchor residues, MT236-244 shares no homology with MT389-397. Using a novel europium-based class I MHC-peptide binding immunoassay, we determined that MT236-244 bound Dk 2-3 logs less well than MT389-397. Infection with a mutant polyoma virus whose MT is truncated just before the MT389-397 epitope or immunization with MT389-397 or MT236-244 peptides elicited CTL that recognized both MT389-397 and MT236-244. Importantly, infection with a polyoma virus lacking MT389-397 and mutated in an MT236-244 Dk anchor position induced polyoma virus-specific CTL recognizing neither MT389-397 nor MT236-244 epitopes. Despite predominant usage of the Vbeta6 gene segment, MT389-397/MT236-244 cross-reactive CTL clones possess diverse complementarity-determining region 3beta domains; this is functionally reflected in their heterogeneous recognition patterns of alanine-monosubstituted MT389-397 peptides. Using Dk/MT389-397 tetramers, we directly visualized MT236-244 peptide-induced TCR down-modulation of virtually all MT389-397-specific CD8+ T cells freshly explanted from polyoma-infected mice, suggesting that a single TCR recognizes both Dk-restricted epitopes. The availability of immunodominant epitope-specific CTL capable of recognizing a second epitope in MT, a viral protein essential for tumorigenesis, may serve to amplify the CTL response to the immunodominant epitope and prevent the emergence of immunodominant epitope-loss viruses and virus-induced tumors.

Use of cocaine during the immediate prepartum period by childbearing women in Ohio

Despite widespread concern about exposure of infants in utero to cocaine, population-based data regarding the prevalence of such exposures are limited. An official task force in Ohio called for studies to generate such data for that state. During three weeks in late 1990, urine was obtained within 48 hours of birth from 1,819 infants born in 25 Ohio hospitals randomly selected from a pool of hospitals accounting for over 80% of Ohio births. Maternal age, race/ethnicity, and residence information were collected so that results could not be linked to individual mothers or infants. Urines were screened for benzoylecgonine (BZE), a cocaine metabolite, using a commercially available immunoassay. The crude prevalence of BZE positivity was 2.0%. When adjusted for unequal cluster sizes and race/ethnicity, the prevalence was 1.4%. The adjusted prevalence for infants born to black mothers was 7.2%, for infants born to white mothers, 0.3%. Ninety-seven percent of the mothers whose infants tested positive were residents of a city of 20,000 or more people. The use of hospital maternity units as a basis for anonymous sampling, as demonstrated in this study, may be a useful model for other jurisdictions seeking population-based data concerning perinatal drug exposures. Such methods may be especially useful for trend studies and program evaluation. In this study, we found widely distributed prepartal cocaine usage in Ohio. Black newborns were significantly more likely than white newborns to show evidence of recent cocaine exposure.