Mutations of SGO2 and CLDN14 collectively cause coincidental Perrault syndrome

Perrault syndrome (PS) is a genetically heterogeneous disorder characterized by primary ovarian insufficiency (POI) in females and sensorineural hearing loss in males and females. In many PS subjects, causative variants have not been found in the five reported PS genes. The objective of this study was to identify the genetic cause of PS in an extended consanguineous family with six deaf individuals. Whole exome sequencing (WES) was completed on four affected members of a large family, and variants and co-segregation was confirmed by Sanger sequencing. All hearing impaired individuals, including the proband, are homozygous for a pathogenic variant of CLDN14, but this only explains the deafness. The PS proband is also homozygous for a frameshift variant (c.1453_1454delGA, p.(Glu485Lysfs*5)) in exon 7 of SGO2 encoding shugoshin 2, which is the likely cause of her concurrent ovarian insufficiency. In mouse, Sgol2a encoding shugoshin-like 2a is necessary during meiosis in both sexes to maintain the integrity of the cohesin complex that tethers sister chromatids. Human SGO2 has not previously been implicated in any disorder, but in this case of POI and perhaps others, it is a candidate for unexplained infertility.

Molecular genetics of MARVELD2 and clinical phenotype in Pakistani and Slovak families segregating DFNB49 hearing loss

Pathogenic mutations of MARVELD2, encoding tricellulin, a tricelluar tight junction protein, cause autosomal recessive non-syndromic hearing loss (DFNB49) in families of Pakistan and Czech Roma origin. In fact, they are a significant cause of prelingual hearing loss in the Czech Roma, second only to GJB2 variants. Previously, we reported that mice homozygous for p.Arg497* variant of Marveld2 had a broad phenotypic spectrum, where defects were observed in the inner ear, heart, mandibular salivary gland, thyroid gland and olfactory epithelium. The current study describes the types and frequencies of MARVELD2 alleles and clinically reexamines members of DFNB49 families. We found that MARVELD2 variants are responsible for about 1.5 % (95 % CI 0.8-2.6) of non-syndromic hearing loss in our cohort of 800 Pakistani families. The c.1331+2T>C allele is recurrent. In addition, we identified a novel large deletion in a single family, which appears to have resulted from non-allelic homologous recombination between two similar Alu short interspersed elements. Finally, we observed no other clinical manifestations co-segregating with hearing loss in DFNB49 human families, and hypothesize that the additional abnormalities in the Marveld2 mutant mouse indicates a critical non-redundant function for tricellulin in other organ systems.

Mutations in TBC1D24, a gene associated with epilepsy, also cause nonsyndromic deafness DFNB86

Inherited deafness is clinically and genetically heterogeneous. We recently mapped DFNB86, a locus associated with nonsyndromic deafness, to chromosome 16p. In this study, whole-exome sequencing was performed with genomic DNA from affected individuals from three large consanguineous families in which markers linked to DFNB86 segregate with profound deafness. Analyses of these data revealed homozygous mutation c.208G>T (p.Asp70Tyr) or c.878G>C (p.Arg293Pro) in TBC1D24 as the underlying cause of deafness in the three families. Sanger sequence analysis of TBC1D24 in an additional large family in which deafness segregates with DFNB86 identified the c.208G>T (p.Asp70Tyr) substitution. These mutations affect TBC1D24 amino acid residues that are conserved in orthologs ranging from fruit fly to human. Neither variant was observed in databases of single-nucleotide variants or in 634 chromosomes from ethnically matched control subjects. TBC1D24 in the mouse inner ear was immunolocalized predominantly to spiral ganglion neurons, indicating that DFNB86 deafness might be an auditory neuropathy spectrum disorder. Previously, six recessive mutations in TBC1D24 were reported to cause seizures (hearing loss was not reported) ranging in severity from epilepsy with otherwise normal development to epileptic encephalopathy resulting in childhood death. Two of our four families in which deafness segregates with mutant alleles of TBC1D24 were available for neurological examination. Cosegregation of epilepsy and deafness was not observed in these two families. Although the causal relationship between genotype and phenotype is not presently understood, our findings, combined with published data, indicate that recessive alleles of TBC1D24 can cause either epilepsy or nonsyndromic deafness.

Molecular basis of DFNB73: mutations of BSND can cause nonsyndromic deafness or Bartter syndrome

BSND encodes barttin, an accessory subunit of renal and inner ear chloride channels. To date, all mutations of BSND have been shown to cause Bartter syndrome type IV, characterized by significant renal abnormalities and deafness. We identified a BSND mutation (p.I12T) in four kindreds segregating nonsyndromic deafness linked to a 4.04-cM interval on chromosome 1p32.3. The functional consequences of p.I12T differ from BSND mutations that cause renal failure and deafness in Bartter syndrome type IV. p.I12T leaves chloride channel function unaffected and only interferes with chaperone function of barttin in intracellular trafficking. This study provides functional data implicating a hypomorphic allele of BSND as a cause of apparent nonsyndromic deafness. We demonstrate that BSND mutations with different functional consequences are the basis for either syndromic or nonsyndromic deafness.

USH1H, a novel locus for type I Usher syndrome, maps to chromosome 15q22-23

Usher syndrome (USH) is a hereditary disorder associated with sensorineural hearing impairment, progressive loss of vision attributable to retinitis pigmentosa (RP) and variable vestibular function. Three clinical types have been described with type I (USH1) being the most severe. To date, six USH1 loci have been reported. We ascertained two large Pakistani consanguineous families segregating profound hearing loss, vestibular dysfunction, and RP, the defining features of USH1. In these families, we excluded linkage of USH to the 11 known USH loci and subsequently performed a genome-wide linkage screen. We found a novel USH1 locus designated USH1H that mapped to chromosome 15q22-23 in a 4.92-cM interval. This locus overlaps the non-syndromic deafness locus DFNB48 raising the possibility that the two disorders may be caused by allelic mutations.

Haplogroup analysis supports a pathogenic role for the 7510T>C mutation of mitochondrial tRNA(Ser(UCN)) in sensorineural hearing loss

We ascertained a large North American family, LMG309, with matrilineal transmission of non-syndromic, progressive sensorineural hearing loss (SNHL). There was no history of aminoglycoside exposure, and penetrance was complete. We sequenced the entire mitochondrial genome and identified the previously reported 7510T>C transition in the tRNA(Ser(UCN)) gene. The 7510T>C was homoplasmic in all affected members. The LMG309 mitochondrial sequence belongs to an unnamed subgroup of mitochondrial haplogroup H. We demonstrate that the previously reported Spanish family S258 carries 7510T>C on a different mitochondrial sub-haplogroup, H1. We did not detect 7510T>C among 79 Caucasian haplogroup H control samples, including 11 from sub-haplogroup H1 and one from the same sub-haplogroup as LMG309. Our results provide strong genetic evidence that 7510T>C is a pathogenic mutation that causes non-syndromic SNHL.

Tricellulin is a tight-junction protein necessary for hearing

The inner ear has fluid-filled compartments of different ionic compositions, including the endolymphatic and perilymphatic spaces of the organ of Corti; the separation from one another by epithelial barriers is required for normal hearing. TRIC encodes tricellulin, a recently discovered tight-junction (TJ) protein that contributes to the structure and function of tricellular contacts of neighboring cells in many epithelial tissues. We show that, in humans, four different recessive mutations of TRIC cause nonsyndromic deafness (DFNB49), a surprisingly limited phenotype, given the widespread tissue distribution of tricellulin in epithelial cells. In the inner ear, tricellulin is concentrated at the tricellular TJs in cochlear and vestibular epithelia, including the structurally complex and extensive junctions between supporting and hair cells. We also demonstrate that there are multiple alternatively spliced isoforms of TRIC in various tissues and that mutations of TRIC associated with hearing loss remove all or most of a conserved region in the cytosolic domain that binds to the cytosolic scaffolding protein ZO-1. A wild-type isoform of tricellulin, which lacks this conserved region, is unaffected by the mutant alleles and is hypothesized to be sufficient for structural and functional integrity of epithelial barriers outside the inner ear.

Mutations in TRIOBP, which encodes a putative cytoskeletal-organizing protein, are associated with nonsyndromic recessive deafness

In seven families, six different mutant alleles of TRIOBP on chromosome 22q13 cosegregate with autosomal recessive nonsyndromic deafness. These alleles include four nonsense (Q297X, R788X, R1068X, and R1117X) and two frameshift (D1069fsX1082 and R1078fsX1083) mutations, all located in exon 6 of TRIOBP. There are several alternative splice isoforms of this gene, the longest of which, TRIOBP-6, comprises 23 exons. The linkage interval for the deafness segregating in these families includes DFNB28. Genetic heterogeneity at this locus is suggested by three additional families that show significant evidence of linkage of deafness to markers on chromosome 22q13 but that apparently have no mutations in the TRIOBP gene.

Life-threatening ventricular arrhythmias due to transient or correctable causes: high risk for death in follow-up

OBJECTIVES

This study evaluated the prognosis of patients resuscitated from ventricular tachycardia (VT) or ventricular fibrillation (VF) with a transient or correctable cause suspected as the cause of the VT/VF.

BACKGROUND

Patients resuscitated from VT/VF in whom a transient or correctable cause has been identified are thought to be at low risk for recurrence and often receive no primary treatment for their arrhythmias.

METHODS

In the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial, patients with a potentially transient or correctable cause of VT/VF were not eligible for randomization. The mortality of these patients was compared with the mortality of patients with a known high risk of recurrence of VT/VF in the AVID registry.

RESULTS

Compared with patients having high risk VT/VF, those with a transient or correctable cause for their presenting VT/VF were younger and had a higher left ventricular ejection fraction. These patients were more often treated with revascularization as the primary therapy, more commonly received a beta-blocker, less often required therapy for congestive heart failure and less commonly received either an antiarrhythmic drug or an implantable cardioverter defibrillator. Nevertheless, subsequent mortality of patients with a transient or correctable cause of VT/VF was no different or perhaps even worse than that of the primary VT/VF population.

CONCLUSIONS

Patients identified with a transient or correctable cause for their VT/VF remain at high risk for death. Further research is needed to define truly reversible causes of VT/VF. Meanwhile, these patients may require more aggressive evaluation, treatment and follow-up than is currently practiced.

Multi atrial maco-re-entry circuits in adults with repaired congenital heart disease: entrainment mapping combined with three-dimensional electroanatomic mapping

OBJECTIVES

We sought to characterize re-entry circuits causing intra-atrial re-entrant tachycardias (IARTs) late after the repair of congenital heart disease (CHD) and to define an approach for mapping and ablation, combining anatomy, activation sequence data and entrainment mapping.

BACKGROUND

The development of IARTs after repair of CHD is difficult to manage and ablate due to complex anatomy, variable re-entry circuit locations and the frequent co-existence of multiple circuits.

METHODS

Forty-seven re-entry circuits were mapped in 20 patients with recurrent IARTs refractory to medical therapy. In the first group (n = 7), ablation was guided by entrainment mapping. In the second group (n = 13), entrainment mapping was combined with a three-dimensional electroanatomic mapping system to precisely localize the scar-related boundaries of re-entry circuits and to reconstruct the activation pattern.

RESULTS

Three types of right atrial macro-re-entrant circuits were identified: those related to a lateral right atriotomy scar (19 IARTs), the Eustachian isthmus (18 IARTs) or an atrial septal patch (8 IARTs). Two IARTs originated in the left atrium. Radiofrequency (RF) lesions were applied to transect critical isthmuses in the right atrium. In three patients, the combined mapping approach identified a narrow isthmuses in the lateral atrium, where the first RF lesion interrupted the circuit; the remaining circuits were interrupted by a series of RF lesions across a broader path. Overall, 38 (81%) of 47 IARTs were successfully ablated. During follow-up ranging from 3 to 46 months, 16 (80%) of 20 patients remained free of recurrence. Success was similar in the first 7 (group 1) and last 13 patients (group 2), but fluoroscopy time decreased from 60 +/- 30 to 24 +/- 9 min/procedure, probably related to the increasing experience and ability to monitor catheter position non-fluoroscopically.

CONCLUSIONS

Entrainment mapping combined with three-dimensional electroanatomic mapping allows delineation of complex re-entry circuits and critical isthmuses as targets for ablation. Radiofrequency catheter ablation is a reasonable option for treatment of IARTs related to repair of CHD.

Saline-cooled versus standard radiofrequency catheter ablation for infarct-related ventricular tachycardias

BACKGROUND

Saline cooling of the electrode during radiofrequency (RF) ablation increases lesion size in animal models. If cooled RF also increases lesion size in human infarcts, it should facilitate the termination of ventricular tachycardia (VT).

METHODS AND RESULTS

In 66 patients with VT due to prior infarction, 366 ablation sites, which were classified by entrainment and isolated potentials followed by ablation during VT with either standard RF energy (247 sites) or cooled RF (119 sites), were retrospectively reviewed to compare the efficacy for terminating VT. RF energy was applied at 259 isthmus sites, 62 bystander sites, 28 inner loop sites, and 17 outer loop sites. Compared with standard RF, cooled RF terminated VT more frequently at isthmus sites where an isolated potential was present (89% versus 54%, P=0.003), isthmus sites without an isolated potential (36% versus 21%, P=0.04), and at inner loop sites (60% versus 22%, P=0.04). Termination rates were similarly low for cooled and standard RF at bystander sites (14% versus 9%, P=0.56) and outer loop sites (13% versus 11%, P=0.93).

CONCLUSIONS

Greater efficacy of cooled RF for terminating VT is consistent with the production of a larger lesion in human infarctions, which should facilitate successful ablation.

The N + 1 difference: a new measure for entrainment mapping

OBJECTIVES

The purpose of this study was to develop and test a new entrainment mapping measurement, the N + 1 difference.

BACKGROUND

Entrainment mapping is useful for identifying re-entry circuit sites but is often limited by difficulty in assessing: 1) changes in QRS complexes or P-waves that indicate fusion, and 2) the postpacing interval (PPI) recorded directly from the stimulation site.

METHODS

In computer simulations of re-entry circuits, the interval from a stimulus that reset tachycardia to a timing reference during the second beat after the stimulus was compared with the timing of local activation at the site during tachycardia to define an interval designated the N + 1 difference. The N + 1 difference was compared with the PPI-tachycardia cycle length (TCL) difference in simulations and at 65 sites in 10 consecutive patients with ventricular tachycardia (VT) after myocardial infarction and at 45 sites in 10 consecutive patients with atrial flutter.

RESULTS

In simulations, the N + 1 difference was equal to the PPI-TCL difference. During mapping of VT and atrial flutter, the N + 1 difference correlated well with the PPI-TCL difference (r > or = 0.91, p < 0.0001), identifying re-entry circuit sites with sensitivity of > or = 86% and specificity of > or = 90%. Accuracy was similar using either the surface electrocardiogram or an intracardiac electrogram (Eg) as the timing reference.

CONCLUSIONS

The N + 1 difference allows entrainment mapping to be used to identify re-entry circuit sites when it is difficult to evaluate Egs at the mapping site or fusion in the surface electrocardiogram.

Single catheter determination of local electrogram prematurity using simultaneous unipolar and bipolar recordings to replace the surface ECG as a timing reference

Bipolar recordings eliminate much of the far-field signal, while minimally filtered unipolar recordings contain substantial far-field signal components. These properties may allow the onset of the unipolar recording to serve as a timing reference for the bipolar recording obtained from the same electrode catheter during mapping of focal atrial or ventricular tachycardias. Mapping and RF ablation were performed in 26 patients with focal ventricular tachycardia and 14 patients with focal atrial tachycardia. At 205 mapping sites, simultaneous recordings of (1) minimally filtered unipolar electrograms (0.5-500 Hz), (2) high pass filtered unipolar electrograms (100 Hz), and (3) filtered bipolar recordings (30-500 Hz) were analyzed. The interval between the onset of the minimally filtered unipolar electrogram and the first peak of the bipolar electrogram (UniOn-BiP) correlated closely with the timing of the local electrogram referenced to the surface ECG (r = 0.85, P < 0.001). Of 53 sites where RF ablation was performed, UniOn-BiP was shorter at successful compared to unsuccessful sites (3.8 +/- 3.5 vs 9.2 +/- 5.2 ms, P < 0.001) and was < 15 ms at all successful sites. In conclusion, the comparison of simultaneous unipolar and bipolar electrograms from a single catheter allows assessment of the prematurity of local electrograms from a focal source without the use of the P wave or QRS onset as a timing reference.

A comparison of biphasic and monophasic shocks for external defibrillation. Physio-Control Biphasic Investigators

BACKGROUND AND OBJECTIVE

The ability of a shock to defibrillate the heart depends on its waveform and energy. Past studies of biphasic truncated exponential (BTE) shocks for external defibrillation focused on low energy levels. This prospective, randomized, double-blind clinical trial compared the first-shock efficacies of 200-joule (J) BTE, 130-J BTE, and 200-J monophasic damped sine wave shocks.

METHODS

Ventricular fibrillation (VF) was induced in 115 patients during evaluation of implantable cardioverter-defibrillator function and 39 patients during electrophysiologic evaluation of ventricular arrhythmias. After 19 +/- 10 seconds of VF, a randomized transthoracic shock was administered. Mean first-shock success rates of the three groups were compared using a "Tukey-like" statistical test, adjusting for multiple comparisons. Blood pressures and arterial oxygen saturations were measured before VF induction and 30, 90, and 150 seconds after successful defibrillation.

RESULTS

First-shock success rates were 61/68 (90%) for 200-J monophasic, 39/39 (100%) for 200-J biphasic, and 39/47 (83%) for 130-J biphasic shocks. The 200-J biphasic shocks were simultaneously superior in first-shock efficacy to both 200-J monophasic and 130-J biphasic shocks (experimentwise error rate, alpha < 0.01). There was no significant difference between the efficacies of 200-J monophasic and 130-J biphasic shocks, nor was there any significant difference between the three groups in hemodynamic parameters after successful shocks.

CONCLUSIONS

Biphasic shocks of 200 J provide better first-shock defibrillation efficacy for short-duration VF than 200-J monophasic and 130-J biphasic shocks and thus may allow earlier termination of VF in cardiac arrest patients.

Identification of left atrial origin of ectopic tachycardia during right atrial mapping: analysis of double potentials at the posteromedial right atrium

INTRODUCTION

The high posteromedial right atrium is adjacent to the left atrium near the right superior pulmonary vein. We hypothesized that analysis of electrograms at this site could distinguish left from right atrial tachycardia.

METHODS AND RESULTS

Atrial mapping was performed in 16 patients with left atrial origin ectopic tachycardia (11 patients with right superior pulmonary vein origin and 5 patients with other left atrial tachycardias). During left atrial tachycardia, earliest right atrial activation was recorded at the high posterior right atrium in 14 of 16 patients. At all of these 14 early sites, double potentials were recorded during tachycardia. The first potential was a far-field signal from left atrium as indicated by the following: (1) during sinus beats, the timing of the two potentials reversed such that the left atrial one was late; (2) ablation at the right atrial site did not decrease the amplitude of the first potential, but did decrease the amplitude of the second potential; and (3) the timing of activation at the adjacent left atrium agreed with that of the first potential. In the 11 right superior pulmonary vein tachycardias, the first potential was markedly earlier than the p wave onset, but in left atrial tachycardias with other origins it was later. In a control group of six patients with pacing to simulate right atrial tachycardia, double potentials were recorded in the posterior right atrium, but the timing of components did not reverse during sinus rhythm.

CONCLUSION

For some left atrial ectopic tachycardias, particularly those originating from the right superior pulmonary vein, recognition of left versus right atrial origin can be accomplished during right atrial mapping by analysis of double potentials in the posteromedial right atrium.

Advantages and disadvantages of trial designs: a review of analysis methods for ICD studies. AVID Investigators

General modalities of analyses that have been used for ICD studies are reviewed. Published "typical" examples are briefly described. The historical cohort method is exemplified with previously unpublished data from the Seattle Cardiac Arrest Survivor database. The AVID Study database is used to compare the results obtained from nonrandomized methodologies with randomized methodologies. Particular issues related to the use of the ICD for example, mode of death, inability to blind, selection practice, and treatment decision times make this a natural pedagogic platform.

Catheter ablation for hemodynamically unstable monomorphic ventricular tachycardia

INTRODUCTION

Hemodynamic collapse precludes extensive catheter mapping to identify focal target regions in many patients with ventricular tachycardia (VT) associated with heart disease. This study tested the feasibility of catheter ablation of poorly tolerated VTs by targeting a region identified during sinus rhythm.

METHODS AND RESULTS

Ablation was attempted in five patients, ages 44 to 59 years, with left ventricular ejection fractions of 0.15 to 0.20 and poorly tolerated VT causing multiple implantable defibrillator therapies (6 to 30 episodes/month). VT was due to prior infarction in three patients and nonischemic cardiomyopathy in two. Target regions were sought that met the following criteria: (1) evidence of slow conduction from fractionated sinus rhythm electrograms and stimulus-QRS delays during pace mapping, and (2) evidence that the region contains the reentrant circuit exit from pace mapping. In 4 of 5 patients, a target region was identified and radiofrequency lesions applied. Ablation abolished all recurrences of VT in 3 of 4 patients during follow-up of 14 to 22 months. There were no complications.

CONCLUSION

Ablation of poorly tolerated VT is feasible in some patients by mapping during sinus rhythm and performing ablation over a region of identifiable scar that contains abnormal conduction and a presumptive VT exit.

Mapping and radiofrequency catheter ablation of the three types of sustained monomorphic ventricular tachycardia in nonischemic heart disease

INTRODUCTION

Sustained monomorphic ventricular tachycardia (VT) associated with nonischemic cardiomyopathy (CMP) is uncommon. Optimal approaches to catheter mapping and ablation are not well characterized, but they are likely to depend on the VT mechanism. The purpose of this study was to evaluate the mechanisms of sustained monomorphic VT encountered in nonischemic CMP and to assess the feasibility, safety, and efficacy of catheter radiofrequency ablation for treatment.

METHODS AND RESULTS

Twenty-six consecutive patients with nonischemic CMP referred for management of recurrent VT were studied. In 16 (62%) patients, VT was related to a region of abnormal electrograms consistent with scar and the response to pacing suggested a reentrant mechanism. In 5 (19%) patients, VT was due to bundle branch or interfascicular reentry. In 7 (27%) patients, the VT mechanism was focal automaticity, 4 of whom had evidence of tachycardia-induced CMP. After catheter ablation targeting parts of reentrant circuits, VT was not inducible in 8 (53%) of 15 patients with scar-related reentry, was modified in 5 (33%) patients, and still was inducible in 2 (13%) patients. Ablation was successful in 5 of 5 patients with bundle branch reentry and in 6 of 7 patients with a focal automaticity mechanism. Overall, catheter ablation abolished clinical recurrence of VT in 20 (77%) of 26 patients during a follow-up of 15 +/- 12 months.

CONCLUSION

Three different mechanisms of VT are encountered in patients with nonischemic CMP. The mapping and ablation approach varies with the type of VT. In this selected population, the overall efficacy was 77%.

DDD-pacing-induced cardiomyopathy following AV node ablation for persistent atrial tachycardia

Ventricular rate control by catheter ablation of the AV node and pacing in patients with persistent atrial tachycardia has been reported to improve left ventricular function. However, this approach requires careful selection of the pacing mode. We report a patient who underwent AV node ablation for persistent multiple atrial tachycardias, and who then had a non-mode-switching pacemaker implanted. Because of an inappropriately programmed relatively high upper rate limit, the patient developed left ventricular dysfunction after 6 years. This resolved after programming the pacemaker to VVI at 70 bpm.

Characteristics of electrograms recorded at reentry circuit sites and bystanders during ventricular tachycardia after myocardial infarction

OBJECTIVES

The purpose of this study was to determine the relation of isolated potentials (IPs) recorded during ventricular tachycardia (VT) to reentry circuit sites identified by entrainment.

BACKGROUND

Reentry circuits causing VT late after myocardial infarction are complex. Both IPs and entrainment have been useful for identifying successful ablation sites, but the relation of IPs to the location in the reentry circuit as determined by entrainment has not been completely defined.

METHODS

Data from catheter mapping of 70 monomorphic VTs in 36 patients with prior myocardial infarction were retrospectively analyzed. Entrainment followed by radiofrequency current (RF) ablation was performed at 384 sites. On the basis of entrainment, sites were classified as reentry circuit exit, central-proximal, inner or outer loop sites. Sites outside the circuit were divided into remote and adjacent bystanders.

RESULTS

Isolated potentials were recorded at 50% (51 of 101) of reentry circuit exit, central and proximal sites as compared with only 8% (11 of 146, p < 0.001) of inner loop and outer loop sites and only 1.8% (2 of 106) of remote bystander sites (p < 0.001). Isolated potentials were also present at 45% of adjacent bystander sites. At central and proximal sites the presence of an IP increased the incidence of tachycardia termination by RF to 47.5% from 24% (p = 0.05). At exit sites tachycardia termination occurred frequently regardless of the presence or absence of IPs (45% vs. 48%, p = NS). Isolated potentials at exit, central and proximal sites had a shorter duration at sites where ablation terminated VT than at sites without termination (20.9 +/- 9.6 ms vs. 35.7 +/- 15.3 ms, p < 0.001).

CONCLUSIONS

Isolated potentials are a useful guide to sites in the central-proximal region of the reentry circuit, but often fail to identify exit sites where ablation is successful. Entrainment and analysis of electrograms provide complementary information during mapping of VT.

Ablation of ventricular tachycardia with a saline-cooled radiofrequency catheter: anatomic and histologic characteristics of the lesions in humans

INTRODUCTION

In animal models, active cooling of the electrode during radiofrequency (RF) ablation allows creation of larger lesions, presumably by increasing the power that can be delivered without coagulum formation. These RF lesions have not been characterized in human myocardium in regions of infarction and scarring.

METHODS AND RESULTS

Cooled-tip RF catheter ablation of ventricular tachycardias (VTs) was performed in two patients who had severe congestive heart failure and subsequently underwent cardiac transplantation. The first patient had four different monomorphic VTs. RF applications along the inferoseptal margin of a scarred region abolished all inducible VTs. The second patient had sarcoidosis involving the myocardium and four different inducible VTs. RF current applied at an inferobasal VT exit and at the right and left septa failed to abolish the VTs. The explanted hearts were examined at the time of cardiac transplantation 18 and 21 days later, respectively. Lesions extended to depths up to 7 mm, reaching clusters of myocardial cells deep to regions of fibrosis. Microscopically, the ablation sites contained coagulation necrosis with hemorrhage, surrounded by a rim of granulation tissue.

CONCLUSION

Saline-irrigated RF catheter ablation produces relatively large lesions capable of penetrating deep into scarred myocardium.

Left ventricular pseudoaneurysm after epicardial patch electrode placement

There are many known complications of implantable cardioverter-defibrillator placement. We treated a patient in whom a left ventricular pseudoaneurysm developed secondary to epicardial patch electrode placement and cardioverter-defibrillator implantation. The presenting symptoms, diagnostic evaluation, and surgical repair are described.

Proarrhythmia

Proarrhythmia is defined as the provocation of a new arrhythmia or the aggravation of a pre-existing one during therapy with a drug at doses or plasma concentrations below those considered to be toxic. Suggested criteria for proarrhythmia include (1) the new appearance of a sustained ventricular tachyarrhythmia; (2) change from a nonsustained to a sustained tachyarrhythmia; (3) acceleration of tachycardia rate; or (4) the new appearance of a clinically significant bradyarrhythmia or conduction defect. Proarrhythmia can be the direct result of a drug's electrophysiologic effects on conduction velocity, refractoriness, and automaticity. However, it may also be the result of metabolic abnormalities, changes in autonomic state, or drug/drug interactions that amplify or alter the drug's electrophysiologic effects. Some forms of ventricular proarrhythmia, such as torsade de pointes, are difficult to forecast and occur in patients with structurally normal hearts as well as in those with serious heart disease. Other forms of ventricular proarrhythmia, such as monomorphic ventricular tachycardia, occur predominantly in patients with structural heart disease or pre-existing ventricular arrhythmia. Atrial flutter with 1 : 1 conduction and bradyarrhythmias can be manifestations of proarrhythmia, particularly during drug therapy for atrial fibrillation. In patients with pacemakers or implantable cardiac defibrillators, antiarrhythmic drugs can change pacing thresholds and can alter the ability of a device to recognize or terminate a sustained ventricular tachyarrhythmia.

Feasibility of cardiac cryoablation using a transvenous steerable electrode catheter

We investigated the feasibility of using cryogenic technology in an electrode catheter for percutaneous ablation of cardiac tissue. Despite its high success rate, radiofrequency catheter ablation has important limitations especially with regards to the treatment of ventricular arrhythmias associated with a chronic scar. Arrhythmia surgery experience has shown that freezing with a hand held probe can permanently ablate the arrhythmogenic substrate of ventricular tachycardia associated with an old scar. Moreover, cryosurgery also allows for reversible "ice mapping," in which the area likely responsible for the arrhythmia can be evaluated by suppressing its electrophysiologic properties prior to the creation of an irreversible state. A new steerable cryoablation catheter using Halocarbon 502 as a refrigerant was utilized in six dogs. Serial cryoapplications were performed in the right and left ventricles. In two dogs, we attempted reversible ice mapping of the AV node. Pathological evaluation of the lesions was done acutely in all the animals. Forty-two cryoapplications were delivered at a mean temperature of -45 +/- 9.8 degrees C. No lesion was found at pathological evaluation for 16 cryoapplications which did not achieve a temperature of less (colder) than -30 degrees C. The remaining applications resulted in 26 lesions which were hemorrhagic and sharply demarcated from normal myocardium. Histological evaluation revealed contraction band necrosis. Reversible ice mapping of the AV node was successfully achieved in two animals. Cryoablation is feasible using an electrode catheter with multiple electrodes. This technology has the potential to allow for reversible ice mapping to confirm a successful ablation target before definitive ablation.

Entrainment mapping and radiofrequency catheter ablation of ventricular tachycardia in right ventricular dysplasia

OBJECTIVES

The purpose of this study was to determine if entrainment mapping techniques and predictors of successful ablation sites previously tested in coronary artery disease can be applied to ventricular tachycardia (VT) in arrhythmogenic right ventricular dysplasia (ARVD).

BACKGROUND

VT in ARVD has not been well characterized. Reentry circuits in areas of abnormal myocardium are the likely cause, but these circuits have not been well defined.

METHODS

Mapping of 19 VTs in 5 patients with ARVD was performed. At 58 sites pacing entrained VT and radiofrequency current (RF) was applied to assess acute termination of VT.

RESULTS

Sites classified as exits, central/proximal, inner loop, outer loop, remote bystander and adjacent bystander were identified by entrainment criteria. The reentrant circuit sites were clustered predominantly around the tricuspid annulus and in the right ventricular outflow tract (RVOT). RF ablation acutely terminated VT at 13 sites or 22% of the applications. Of the 19 VTs, eight were rendered noninducible and three were modified to a longer cycle length. In 2 patients ablation at a single site abolished two VTs.

CONCLUSION

VT in ARVD shows many of the characteristics of VT due to myocardial infarction. Entrainment mapping techniques can be used to characterize reentry circuits in ARVD. The use of entrainment mapping to guide ablation is feasible.

Recipient-to-donor atrioatrial conduction after orthotopic heart transplantation: surface electrocardiographic features and estimated prevalence

Recipient-to-donor atrioatrial conduction across a suture line has been rarely reported after orthotopic heart transplantation. The relation of such conduction to symptomatic arrhythmias and its prevalence are not known. Recipient-to-donor atrioatrial conduction was demonstrated in a 28-year-old woman with paroxysmal supraventricular tachycardia 7 years after orthotopic heart transplantation. Atrial tachycardia in the recipient atria conducted 2:1 to the donor atria and was eliminated by radiofrequency catheter ablation of a left-sided atrioatrial electrical connection. The electrocardiogram at rest and during exercise, recorded before ablation of the recipient-to-donor connection, showed frequent atrial premature complexes, with variable coupling to the preceding sinus beats, and a change in P-wave morphology during exercise, which reverted to normal during the recovery period. These findings were eliminated by ablation of the recipient-to-donor connection. To determine the prevalence of recipient-to-donor atrioatrial conduction late after transplantation, we evaluated the exercise electrocardiograms of 50 subjects > 5 years after heart transplantation for these features of recipient-to-donor conduction. At least 1 feature was present in 5 subjects, and both were present in 1 subject. Electrical conduction can occur across surgical suture lines in the atria. Recipient-to-donor atrioatrial conduction may occur in < or = 10% of patients late after heart transplantation. It is a potential cause of arrhythmias that can be effectively treated with radiofrequency catheter ablation.

Radiofrequency catheter ablation of ventricular tachycardia after myocardial infarction

BACKGROUND

Patients with ventricular tachycardia (VT) after myocardial infarction often have multiple morphologies of inducible VT, which complicates mapping and is viewed by some as a relative contraindication to ablation. Attempting to identify and target a single "clinical" VT is often limited by inability to obtain 12-lead ECGs of VTs that are terminated emergently or by defibrillators. This study assesses the feasibility of ablation in patients selected without regard to the presence of multiple VTs by targeting all VTs that allow mapping.

METHODS AND RESULTS

Radiofrequency catheter ablation targeting all inducible monomorphic VTs that allowed mapping was performed in 52 patients with prior myocardial infarction. Antiarrhythmic drug therapy had failed in 41 (79%) patients including amiodarone in 36 (69%) patients. An average of 3.6+/-2 morphologies of VT were induced per patient. More than 1 ablation session was required in 16 (31%) patients. Complications occurred in 5 (10%) patients, including 1 (2%) death caused by acute myocardial infarction. During follow-up 59% of patients continued to receive amiodarone; 23 (45%) had implantable defibrillators. During a mean follow-up of 18+/-15 months (range 0 to 51 months) 1 patient died suddenly, 2 died from uncontrollable VT, and 5 died from heart failure. Three-year survival rate was 70+/-10%, and rate for risk of VT recurrence was 33+/-7%.

CONCLUSIONS

Radiofrequency catheter ablation controls VT that is sufficiently stable to allow mapping in 67% of patients despite failure of antiarrhythmic drug therapy and multiple inducible VTs. However, ablation was largely adjunctive to amiodarone and defibrillators in this referral population.

Identification and ablation of macroreentrant ventricular tachycardia with the CARTO electroanatomical mapping system

Monomorphic ventricular tachycardias associated with regions of scar are most commonly due to reentry. Catheter based techniques have recently been described for mapping of reentry circuits. Fluoroscopic methods have obvious limitations when attempting to map large ventricular reentry circuit and localize target-sites of radiofrequency ablation. Three-dimensional right ventricular endocardial mapping was performed in a 38-year-old patient with ventricular tachycardia 28 years after surgical correction of tetralogy of Fallot by using the CARTO electroanatomical system. The map of electrogram voltage showed low amplitude electrograms over the anterior wall of the right ventricle extending into the right ventricular outflow tract, consistent with the location of the ventriculotomy scar. Recording of local activation time was combined with entrainment mapping to define the macroreentrant circuit during ventricular tachycardia. Since the activation propagated through a broad path around the right ventriculotomy scar, ablation was performed by creating a line of block, which was facilitated by tagging of the lesion sites on the endocardial activation map. Large ventricular reentry circuits can be identified and interrupted by creation of a line of block to interrupt a broad path. A practical approach to mapping combining analysis of electrogram voltage, activation sequence, and entrainment is presented.

Mortality in the Survival With ORal D-sotalol (SWORD) trial: why did patients die?

The Survival With ORal D-sotalol (SWORD) trial tested the hypothesis that the prophylactic administration of oral d-sotalol would reduce total mortality in patients surviving myocardial infarction (MI) with a left ventricular ejection fraction (LVEF) of < or = 40%. Two index MI groups were included: recent (6 to 42 days) and remote (> 42 days) with clinical heart failure (n = 915 and 2,206, respectively). The trial was discontinued when the statistical boundary for harm was crossed (RR = 1.65; p = 0.006). All baseline variables known to be associated with mortality risk (e.g., LVEF, heart failure class, age) as well as variables related to torsades de pointes (e.g., time from beginning of therapy, QTc, gender, potassium, renal function, dose of d-sotalol) were assessed for interaction of each variable with treatment assignment, computing RR and 95% confidence interval (CI) from Cox regression models. The d-sotalol-associated mortality was greatest in the group with remote MI and LVEFs of 31% to 40% (RR = 7.9; 95% CI 2.4 to 26.2). Most variables known to be associated with torsades de pointes were not differentially predictive of d-sotalol-associated risk, except female gender (RR = 4.7; 95% CI 1.4 to 16.5). These findings suggest that (1) most of the d-sotalol-associated risk was in patients remote from MI with a LVEF of 31% to 40%; comparable placebo patients had a very low mortality (0.5%); and (2) very little objective data supports torsades de pointes or any specific proarrhythmic mechanism as an explanation for d-sotalol-associated mortality risk.

Pace-mapping conduction delay at reentry circuit sites of ventricular tachycardia after myocardial infarction

This study was carried out to determine the relationship of conduction delay during pace-mapping, as indicated by the stimulus to QRS interval to different reentry circuit sites and bystanders, as identified by entrainment criteria, in patients with ventricular tachycardia late after myocardial infarction. Catheter mapping and ablation were performed in 40 patients with ventricular tachycardia after myocardial infarction. Data were retrospectively analyzed from 122 endocardial sites which met the following the criteria: a 12-lead electrocardiogram was recorded during pace-mapping, ventricular tachycardia was then induced and entrained by pacing to classify the type of the site relative to the reentry circuit exit. By entrainment criteria 77 sites were in the reentry circuit (28 exit sites, 49 other circuit sites) and 45 sites were bystanders not in the reentry circuit. The average stimulus conduction delay at central/proximal sites was 103 +/- 43 ms, which was significantly longer than at exit (57 +/- 31 ms), outer loop sites (57 +/- 32 ms), and bystander sites (57 +/- 37 ms); P < 0.05. Pace-mapping revealed evidence of greater conduction delay at sites proximal to the reentry circuit exit, consistent with slow conduction between these regions and the border of the infarct. Exit sites and outer loop sites were more likely to be located along the border of the infarct, with less conduction delay evident during pace-mapping.

Radiofrequency catheter ablation of ventricular tachycardia late after myocardial infarction

Radiofrequency catheter ablation is a promising method for controlling ventricular tachycardia (VT) due to prior myocardial infarction. Limitations of mapping and ablation techniques have largely restricted its use to selected patients who have hemodynamically tolerated sustained monomorphic VT that allows catheter mapping. Multiple monomorphologies of VT, which are usually present, often complicate the ablation procedure and interpretation of ablation effects. Ablation is generally restricted to experienced centers and is usually reserved for patients who have failed other therapies. Despite these difficulties, successful ablation can be life-saving in patients with incessant VT and can markedly improve quality of life with frequent shocks from implantable defibrillators.

Ablation therapy for cardiac arrhythmias

Ablation has become an important and, in some cases, the first-line therapy for a number of tachyarrhythmias. The feasibility of treating arrhythmias with ablation was initially demonstrated with surgical ablation techniques. Recently, catheter ablation techniques have replaced the surgical approach in nearly all cases. Catheter ablation is highly effective for the Wolff-Parkinson-White syndrome, atrioventricular nodal reentry, and atrial ectopic tachycardia. It is effective for atrial flutter, although approximately one quarter of patients treated with catheter ablation continue to require therapy for concomitant atrial fibrillation. The surgical maze procedure has proved to be feasible for preventing atrial fibrillation. The risks and long-term efficacy of catheter ablation maze procedures for atrial fibrillation need to be defined. The efficacy of ablation for ventricular tachycardia varies with the type of tachycardia. Catheter ablation is very effective for the rare idiopathic ventricular tachycardias that occur in structurally normal hearts and for bundle-branch reentry ventricular tachycardia, which occurs most frequently in patients with dilated cardiomyopathy. When performed at an experienced center, surgical ablation is an excellent option for selected patients with ventricular tachycardia due to prior myocardial infarction who have a discrete aneurysm but otherwise well-preserved ventricular function. Catheter ablation shows promise for this arrhythmia, but it can be offered only to those patients who have relatively slow tachycardias that allow catheter mapping. Substantial advances in mapping and ablation technology will continue to occur, allowing nonpharmacologic control of cardiac arrhythmias to be achieved in an ever greater number of patients.

Ablation of ventricular tachycardia due to a postinfarct ventricular septal defect: identification and transection of a broad reentry loop

INTRODUCTION

Ventricular tachycardia (VT) after postinfarct ventricular septal defect (VSD) repair has not been well characterized.

METHODS AND RESULTS

A 55-year-old man developed refractory VT after inferior wall infarction and VSD repair. Entrainment demonstrated a broad reentry circuit path (outer loop) between the tricuspid annulus and VSD patch. A series of radiofrequency (RF) lesions transected this path, abolishing VT and producing conduction block between the inferior and superior aspects of the basal right ventricular septum.

CONCLUSION

Some VTs have broad reentry loops requiring ablation by a series of RF lesions across the path to create a line of block. This approach is analogous to that for atrial flutter.

Catheter ablation of ventricular tachycardia after myocardial infarction: relation of endocardial sinus rhythm late potentials to the reentry circuit

OBJECTIVES

We sought to determine whether endocardial late potentials during sinus rhythm are associated with reentry circuit sites during ventricular tachycardia (VT).

BACKGROUND

During sinus rhythm, slow conduction through an old infarct region may depolarize tissue after the end of the QRS complex. Such slow conduction regions can cause reentry.

METHODS

Endocardial catheter mapping and radiofrequency ablation were performed in 24 patients with VT late after myocardial infarction. We selected for analysis a total of 103 sites where the electrogram was recorded during sinus rhythm and, without moving the catheter, VT was initiated and radiofrequency current applied in an attempt to terminate VT.

RESULTS

Late potentials were present at 34 sites (33%). During pace mapping, the stimulus-QRS complex was longer at late potential sites, consistent with slow conduction, than at sites without late potentials (p < 0.0001). Late potentials were present at 15 (71%) of 21 sites classified as central or proximal in the reentry circuit based on entrainment, but also occurred frequently at bystander sites (13 [33%] of 39) and were often absent at the reentry circuit exit (3 [23%] of 13). Late potentials were present at 20 (54%) of 37 sites where ablation terminated VT, compared with 14 (21%) of 66 sites where ablation did not terminate VT (p = 0.004). Ablation decreased the amplitude of the late potentials present at sites where ablation terminated VT.

CONCLUSIONS

Although sites with sinus rhythm late potentials often participate in VT reentry circuits, many reentry circuit sites do not have late potentials. Late potentials can also arise from bystander regions. Late potentials may help identify abnormal regions in sinus rhythm but cannot replace mapping during induced VT to guide ablation.

Risk of initiating antiarrhythmic drug therapy for atrial fibrillation in patients admitted to a university hospital

BACKGROUND

The risks of antiarrhythmic therapy are increasingly recognized, but the risks associated with the initiation of antiarrhythmic therapy in patients hospitalized for atrial fibrillation are poorly defined.

OBJECTIVE

To determine the incidence, time course, and predictors of adverse cardiac events that require intervention during initiation of antiarrhythmic drug therapy for atrial fibrillation.

DESIGN

Retrospective chart review.

SETTING

University hospital.

PARTICIPANTS

417 consecutive patients who underwent a total of 597 drug trials during a total of 550 hospitalizations for atrial fibrillation.

INTERVENTION

Initiation of therapy with antiarrhythmic drugs: procainamide (189 trials), quinidine (179 trials), disopyramide (20 trials), propafenone (110 trials), flecainide (2 trials), sotalol (72 trials), and amiodarone (25 trials). Electrical conversion was performed during 247 trials.

MEASUREMENTS

Incidence of adverse events and daily hazard rate were measured. Logistic regression was done to identify risk factors.

RESULTS

During the 597 drug trials, 80 (13.4%) cardiac adverse events occurred in 73 patients. The risk was greatest during the first 24 hours of therapy. Bradyarrhythmias were the most common adverse event, occurring in 47 trials (7.9%); prolongation of the QT interval warranting discontinuation of drug therapy (9 trials; 1.5%) and ventricular arrhythmias (8 trials; 1.3%) were less frequent. In multivariate analysis, previous myocardial infarction was associated with increased risk (odds ratio, 1.90 [95% CI, 1.05 to 3.43]) and the association between older age and increased risk (odds ratio, 1.29 per decade [CI, 0.97 to 1.72]) was of borderline statistical significance.

CONCLUSIONS

A significant risk for cardiac adverse events exists during initiation of antiarrhythmic therapy in patients hospitalized for atrial fibrillation. Observation with electrocardiographic monitoring seems advisable for 24 to 48 hours during initiation of antiarrhythmic therapy, particularly for elderly patients and patients who have previously had myocardial infarction.

Exploring postinfarction reentrant ventricular tachycardia with entrainment mapping

Ventricular tachycardia late after myocardial infarction is usually due to reentry in the infarct region. These reentry circuits can be large, complex and difficult to define, impeding study in the electrophysiology laboratory and making catheter ablation difficult. Pacing through the electrodes of the mapping catheter provides a new approach to mapping. When pacing stimuli capture the effects on the tachycardia depend on the location of the pacing site relative to the reentry circuit. The effects observed allow identification of various portions of the reentry circuit, without the need for locating the entire circuit. Isthmuses where relatively small lesions produced by radiofrequency catheter ablation can interrupt reentry can often be identified. A classification that divides reentry circuits into one or more functional components helps to conceptualize the reentry circuit and predicts the likelihood that heating with radiofrequency current will terminate tachycardia. These methods are helping to define human reentry circuits.

Preferential locations for critical reentry circuit sites causing ventricular tachycardia after inferior wall myocardial infarction

INTRODUCTION

For relatively slow monomorphic ventricular tachycardia (VT) after myocardial infarction, entrainment can be used to identify reentry circuit "isthmus sites" (exit sites and sites proximal to the exit) where radiofrequency (RF) catheter ablation has the greatest likelihood of interrupting reentry. Similarities in coronary and ventricular anatomy may cause such sites to form in preferential locations. The objective of this study is to determine if there are preferential locations for reentry circuit isthmus regions in chronic inferior wall infarctions causing VT.

METHODS AND RESULTS

Catheter mapping and RF catheter ablation was performed in 21 patients with an old inferior wall myocardial infarction and VT. The inferior wall was divided into 9 anatomic regions: 3 apical, 3 mid, and 3 basal segments. Of 46 different VTs, an endocardial isthmus site was identified in one or more zones in 28 (61%), with 10 VTs having isthmus sites in two or more adjacent regions. Isthmus zones were found in a basal region of the left ventricle in 24 (86%) of 28 VTs, in a mid segment in 9 (32%) VTs, and in an apical segment in 1 (4%) (P = 0.002). Of 30 RF current applications that terminated VT, 21 (70%) were at basal isthmus sites.

CONCLUSION

The high prevalence of endocardial isthmus zones near the base of the left ventricle suggests that the mitral annulus often plays a role in defining the margins of reentry circuits that cause relatively slow VTs after inferior wall myocardial infarction.

Effect of recording site on postpacing interval measurement during catheter mapping and entrainment of postinfarction ventricular tachycardia

INTRODUCTION

During entrainment of reentrant ventricular tachycardia (VT), the difference between the postpacing interval (PPI) and the VT cycle length (VTCL) measured at the pacing site is an indication of the conduction time from the pacing site to the reentry circuit. The difference is usually < or = 30 msec at successful ablation sites. However, electrical noise during pacing sometimes obscures the electrograms recorded directly from the pacing site. The objective of this study is to determine if the PPI-VTCL difference measured at the mapping catheter electrodes proximal to the stimulating electrode accurately predicts the PPI-VTCL difference at the stimulating electrode.

METHODS AND RESULTS

Endocardial catheter mapping was performed in 26 patients with infarct-related VT. At 191 sites during 56 VTs, unipolar pacing from the distal electrode entrained VT and electrograms recorded from the mapping catheter were discernable following pacing in both the bipolar recordings from the distal electrode pair (BI 1-2) and the electrode pair 6 mm proximal to the distal electrode (BI 3-4). The PPI-VTCL difference at BI 1-2 correlated well with that measured at BI 3-4 (r = 0.88, P = 0.001). A PPI-VTCL difference at BI 3-4 < or = 30 msec predicted a PPI-VTCL difference at BI 1-2 < or = 30 msec with a sensitivity of 95%, specificity of 87 %, and predictive accuracy of 91%.

CONCLUSIONS

Measurement of the PPI from electrodes proximal to the stimulating electrode is a reasonable alternative when the PPI cannot be assessed from the pacing electrode.