The Significance of Shocks in Implantable Cardioverter Defibrillator Recipients.

Large-scale implantable cardioverter defibrillator (ICD) trials have unequivocally shown a reduction in mortality in appropriately selected patients with heart failure and depressed left ventricular function. However, there is a strong association between shocks and increased mortality in ICD recipients. It is unclear if shocks are merely a marker of a more severe cardiovascular disease or directly contribute to the increase in mortality. The aim of this review is to examine the relationship between ICD shocks and mortality, and explore possible mechanisms. Data examining the effect of shocks in the absence of spontaneous arrhythmias as well as studies of non-shock therapy and strategies to reduce shocks are analysed to try and disentangle the shocks versus substrate debate.

Ventricular fibrillation treated by cryotherapy to the right ventricular outflow tract: a case report.

BACKGROUND: Arrhythmias originating from the right ventricular outflow tract are generally considered benign but cases of cardiac arrest have been described, usually associated with polymorphic ventricular tachycardia or extrasystoles with short coupling intervals. CASE PRESENTATION: We report the case of a 54-year-old Caucasian woman with symptomatic right ventricular outflow tract arrhythmias without structural heart disease who suffered a ventricular fibrillation arrest without prior malignant clinical features. Cryoablation was performed and an implantable cardioverter defibrillator was implanted. She has since been free of arrhythmia for 7 years and has asked that the implantable cardioverter defibrillator not be replaced when the battery becomes depleted. CONCLUSIONS: Although usually benign, right ventricular outflow tract tachycardia can be life-threatening. Even the most malignant cases can be cured by ablation.

Femoral implantation and pull through as an adjunct to traditional methods in cardiac resynchronization therapy.

BACKGROUND: We have described the use of femoral access followed by pull through of the lead to a pectoral position to circumvent difficulty in implanting a left ventricular (LV) lead by standard methods. OBJECTIVE: The purpose of this study was to establish the effect of femoral implantation and pull through on the overall rate of success in percutaneous implantation of LV leads. METHODS: We collected data prospectively in all attempts at LV lead implantation from the time that we envisioned the femoral pull-through approach. RESULTS: In the 6 years to September 30, 2014, our group attempted to implant a new LV lead in 736 patients, including 16 who previously had failed attempts by other groups. A standard superior approach was successful in 726 of 731 patients (99.3%) in whom it was attempted. In 5 patients (0.7%), we failed to deliver a lead from a superior approach; in 5 of 16 patients, with previous failed attemtps (31%), we judged that those attempts had been exhaustive. In all 10 cases, LV lead placement was achieved from a femoral approach, with the procedure time being 186 ± 65 minutes. In the first case attempted, the pull through failed; the lead was tunneled to the pectoral generator. In 1 case, the coronary sinus was found to be occluded at the ostium: a transseptal approach was used with the subsequent pull through. No complication occurred. At 22.3 ± 18.5 months after the implantation, all systems implanted by a femoral approach continued to function. CONCLUSION: Used as an adjunct to standard methods, the femoral access and pull through method allows percutaneous LV lead placement in virtually all cases.

Architectural correlates of myocardial conduction: changes to the topography of cellular coupling, intracellular conductance, and action potential propagation with hypertrophy in Guinea-pig ventricular myocardium.

BACKGROUND: We tested the hypothesis that alterations to action potential conduction velocity (CV) and conduction anisotropy in left ventricular hypertrophy are associated with topographical changes to gap-junction coupling and intracellular conductance by measuring these variables in the same preparations. METHODS AND RESULTS: Left ventricular papillary muscles were excised from aortic-banded or sham-operated guinea-pig hearts. With intracellular stimulating and recording microelectrodes, CV was measured in 3 dimensions with simultaneous conductance mapping with subthreshold stimuli and correlated with quantitative histomorphometry of myocardial architecture and connexin 43 distribution. In hypertrophied myocardium, CV in the longitudinal axis was smaller and transverse velocity was greater compared with control; associated with similar differences of intracellular conductance, consistent with more cell contacts per cell (5.7 ± 0.2 versus 8.1 ± 0.5; control versus hypertrophy), and more intercalated disks mediating side-to-side coupling (8.2 ± 0.2 versus 10.2 ± 0.4 per cell). Intercalated disk morphology and connexin 43 immunolabelling were not different in hypertrophy. Hypertrophied preparations showed local submillimeter (≈250 µm) regions with slow conduction and low intracellular conductance, which, although not affecting CV on the millimeter scale, were consistent with discontinuities from increased microscopical connective tissue content. CONCLUSIONS: With myocardial hypertrophy, altered longitudinal and transverse CV, and greater nonuniformity of CV anisotropy correspond to changes of intracellular conductance. These are associated with alteration of myocardial architecture, specifically the topography of cell-cell coupling and gap-junction connectivity.

Relationship between connexin expression and gap-junction resistivity in human atrial myocardium.

BACKGROUND: The relative roles of the gap-junctional proteins connexin40 (Cx40) and connexin43 (Cx43) in determining human atrial myocardial resistivity is unknown. In addressing the hypothesis that changing relative expression of Cx40 and Cx43 underlies an increase in human atrial myocardial resistivity with age, this relationship was investigated by direct ex vivo measurement of gap-junctional resistivity and quantitative connexin immunoblotting and immunohistochemistry. METHODS AND RESULTS: Oil-gap impedance measurements were performed to determine resistivity of the intracellular pathway (Ri), which correlated with total Cx40 quantification by Western blotting (rs=0.64, P<0.01, n=20). Specific gap-junctional resistivity (Rj) correlated not only with Western immunoquantification of Cx40 (rs=0.63, P=0.01, n=20), but also more specifically, with the Cx40 fraction localized to the intercalated disks on immunohistochemical quantification (rs=0.66, P=0.02, n=12). Although Cx43 expression showed no correlation with resistivity values, the proportional expression of the 2 connexins, (Cx40/[Cx40+Cx43]) correlated with Ri and Rj (rs=0.58, P<0.01 for Ri and rs=0.51, P=0.02 for Rj). Advancing age was associated with a rise in Ri (rs=0.77, P<0.0001), Rj (rs=0.65, P<0.001, n=23), Cx40 quantity (rs=0.54, P=0.01, n=20), and Cx40 gap-junction protein per unit area of en face disk (rs=0.61, P=0.02, n=12). CONCLUSIONS: Cx40 is associated with human right atrial gap-junctional resistivity such that increased total, gap-junctional, and proportional Cx40 expression increases gap-junctional resistivity. Accordingly, advancing age is associated with an increase in Cx40 expression and a corresponding increase in gap-junctional resistivity. These findings are the first to demonstrate this relationship and a mechanistic explanation for changing atrial conduction and age-related arrhythmic tendency.

Feasibility and efficacy of simultaneous pulmonary vein isolation and cavotricuspid isthmus ablation using cryotherapy.

INTRODUCTION: Pulmonary vein isolation (PVI) and cavotricuspid isthmus (CTI) ablation are often performed as part of the same procedure. In many cases, PVI is performed by cryotherapy and then CTI ablation by radiofrequency (RF) energy. We sought to determine whether it is more efficient to perform CTI ablation simultaneously with PVI using separate cryogenerators. METHODS AND RESULTS: We performed cryoablation of the CTI during PVI with the Arctic Front cryoballoon in 25 consecutive patients with clinical indications for both (PVI/CTI-cryo group). Procedural data were compared to those of 25 matched patients who underwent PVI only by the same operator (PVI-only group), and 25 patients who underwent PVI by cryotherapy and CTI ablation using RF energy sequentially during the same procedure (PVI/CTI-mixed group). No complication occurred. All veins were isolated; bidirectional CTI block was demonstrated in all cases where it was attempted, except for 1 patient in the PVI/CTI-mixed group. Procedure and fluoroscopy duration were significantly shorter in the PVI/CTI-cryo group (162 ± 34 and 24 ± 5 minutes) than in the PVI/CTI-mixed group (209 ± 46 minutes, P < 0.001 and 59 ± 28 minutes, P < 0.001). Procedure and fluoroscopy duration in the PVI-only group (155 ± 32 and 22 ± 8 minutes) were similar to those in the PVI/CTI-cryo group (P = NS) but significantly shorter than in the PVI/CTI-mixed group (P < 0.001 for both). Clinical outcomes were similar in all groups. CONCLUSION: When CTI ablation is performed with RF energy after PVI by cryoballoon, it adds significantly to the procedure and fluoroscopy durations; when performed contemporaneously using cryotherapy at both sites, the procedure and fluoroscopy durations are not prolonged.

The biophysics of renal sympathetic denervation using radiofrequency energy.

Renal sympathetic denervation is currently performed in the treatment of resistant hypertension by interventionists who otherwise do not typically use radiofrequency (RF) energy ablation in their clinical practice. Adequate RF lesion formation is dependent upon good electrode-tissue contact, power delivery, electrode-tissue interface temperature, target-tissue impedance and the size of the catheter's active electrode. There is significant interplay between these variables and hence an appreciation of the biophysical determinants of RF lesion formation is required to provide effective and safe clinical care to our patients. In this review article, we summarize the biophysics of RF ablation and explain why and how complications of renal sympathetic denervation may occur and discuss methods to minimise them.

Relationship between gap-junctional conductance and conduction velocity in mammalian myocardium.

BACKGROUND: Gap junction resistivity, R(j), has been proposed as a key determinant of conduction velocity (CV). However, studies in connexin-gene knockout mice demonstrated significant CV slowing only with near-complete connexin deletion, and these findings led to the concept of a significant redundancy of myocardial gap junctions. We challenged this prevailing concept and addressed the hypothesis that there is a continuous relationship between R(j) and CV, each independently measured in human and guinea-pig myocardium. METHODS AND RESULTS: R(j) and CV were directly measured by oil-gap impedance and microelectrode techniques in human left ventricular myocardium from patients with hypertrophic cardiomyopathy and in guinea-pig atrial and ventricular myocardium before and during pharmacological uncoupling with 20-µmol/L carbenoxolone. There was a continuous relationship between R(j) and CV in human and guinea-pig myocardium, pre- and post-carbenoxolone (r(2)=0.946; P<0.01). In guinea-pig left ventricle, left atrium, and right atrium, carbenoxolone increased R(j) by 28±9%, 26±16%, and 25±14% and slowed CV by 17±3%, 23±8%, and 11±4% respectively (all P<0.05 versus control). As a clinically accessible measure of local microscopic myocardial conduction slowing in vivo in the intact human heart, carbenoxolone prolonged electrogram duration in the right atrium (39.7±4.2 to 42.3±4.3 ms; P=0.01) and right ventricle (48.1±2.5 to 53.3±5.3 ms; P<0.01). CONCLUSIONS: There is a continuous relationship between R(j) and CV that is consistent between cardiac chambers and across species, indicating that naturally occurring variations in cellular coupling can account for variations in CV, and that the concept that there is massive redundancy of coupling is not tenable.

Skin burns associated with radiofrequency catheter ablation of cardiac arrhythmias.

Skin burns are a rare complication associated with radiofrequency catheter ablation of cardiac arrhythmias. Burns related to the indifferent electrode patch may be severe and result in significant comorbidity. We describe our experience of skin burns and discuss potential predisposing and possible causative factors.

Why we Should Not Delay Ablation in New Onset Recurrent Atrial Fibrillation.

Recurrent episodes of atrial fibrillation are associated with progressive left atrial substrate remodelling over time. We present an argument for early ablation in the treatment of recurrent paroxysmal atrial fibrillation prior to such deleterious changes in "left atrial electrical health".

Functional Pulmonary Vein Isolation During Atrial Fibrillation Ablation.

We report a case of apparent isolation of the right inferior pulmonary vein during atrial fibrillation ablation coincident with the onset of an atrial tachycardia. This report highlights the importance of assessing pulmonary vein conduction during sinus or paced rhythm at relatively long cycle length, rather than in atrial fibrillation or atrial tachycardia.

Intra-isthmus reentry associated with uncorrected double inlet left ventricle and transposition of the great arteries.

A 62-year-old man with uncorrected cyanotic congenital heart disease involving double inlet left ventricle with visceral and atrial situs solitus, L-looped ventricles, L-transposed great vessels, and pulmonary stenosis, presented with recurrent atrial tachycardia. Entrainment mapping revealed the arrhythmia mechanism to be an uncommon micro-reentrant cavotricuspid isthmus-dependent circuit (intra-isthmus reentry), which was amenable to radiofrequency ablation. This uncommon right atrial arrhythmia is yet to be reported in patients with complex congenital heart disease and was amenable to radiofrequency ablation.

Cryoballoon ablation for iatrogenic left atrial tachycardia.

Percutaneous and surgical left atrial ablation has been widely used to treat paroxysmal and persistent atrial fibrillation. However, left atrial ablation may result in left atrial tachycardia due to an iatrogenic substrate created by the ablation lesion sets. Ablation of these iatrogenic arrhythmias can be technically challenging, requiring prolonged procedures and the use of three-dimensional electroanatomical mapping systems. In some cases, the atrial tachycardia may terminate during mapping, or may degenerate into atrial fibrillation during the procedure before adequate mapping. Some patients also have several arrhythmia circuits, each requiring separate mapping, which may be time consuming. The present article reports the cases of three patients in whom a large cryoballoon was used to empirically ablate the pulmonary vein antral region, which is important for the initiation and maintenance of these arrhythmias.

Safety and feasibility of cephalic venous access for cardiac resynchronization device implantation.

BACKGROUND: Cardiac resynchronization therapy (CRT) devices are usually implanted using subclavian vein access, which is associated with the risk of pneumothorax. We examined whether cephalic venous access is an effective alternative to subclavian access by the Seldinger technique for CRT delivery. METHODS: We retrospectively analyzed all CRT procedures performed over a 1-year period at our center with respect to the access methods, primary success rate, safety, and efficiency. RESULTS: We retrospectively analyzed 103 consecutive primary implantation procedures. The procedure was accomplished using cephalic access alone for 54 of 61 (89%) CRT implants attempted by this route. The overall success rate was 100% (61/61) with additional use of subclavian access. CRT implantation via subclavian vein access was successful in 37 of 42 (88%) (P < 0.05 vs cephalic group). The procedure duration was shorter for the cephalic group (118 ± 39 vs 147 ± 36 minutes, P < 0.0005) as were the screening times and radiation exposure (15 ± 9 vs 27 ± 18 minutes and 4.7 ± 5.8 vs 9.3 ± 9.1 Gcm(2) , both P < 0.01). In the cephalic group, procedure duration and radiation exposure diminished significantly with increasing experience of the technique. Complications occurred in two of 61 (3.3%) cases in the cephalic group and three of 42 (7.1%) in the subclavian group (P = NS). CONCLUSION: CRT devices can be implanted using cephalic access alone in a large majority of cases. This approach is safe and efficient.

Femoral vein implantation with subclavian vein pullthrough for left ventricular lead placement.

Variations of coronary sinus anatomy can make a superior approach difficult or even impossible for left ventricular (LV) lead delivery. We describe a new technique in which the LV lead was placed in a cardiac vein via the right femoral vein and then pulled up through the venous circulation to the subclavian vein and a conventionally sited generator.