Duy Thai Nguyen

Implantable Cardioverter Defibrillator Therapy in Patients with Cardiac Sarcoidosis

ICD Shocks in Cardiac Sarcoidosis. Background: An implantable cardioverter defibrillator (ICD) is indicated for some patients with cardiac sarcoidosis (CS) for prevention of sudden death. However, there are little data regarding the event rates of ICD therapies in these patients. We sought to identify the incidence and characteristics of ICD therapies in this patient population.

Pirfenidone mitigates left ventricular fibrosis and dysfunction after myocardial infarction and reduces arrhythmias

BACKGROUND Post-myocardial infarction (MI) complications include ventricular tachycardia (VT). Excessive non-MI fibrosis, involving the infarct border zone (IBZ) and beyond, is an important substrate for VT vulnerability. OBJECTIVE This study assessed whether the antifibrotic agent pirfenidone can mitigate fibrosis in remodeling and determined its effects on myocardial function and VT susceptibility in a rodent MI model. METHODS We studied 2 groups of rats undergoing MI 1 week prior to treatment: a control group (n = 15) treated with placebo and a pirfenidone group (n = 15). We performed serial echocardiograms, and after 4 weeks of treatment, we conducted electrophysiological and optical mapping studies as well as histology. RESULTS There was less decline in left ventricular (LV) ejection fraction for pirfenidone-treated rats, 8.6% versus 24.3% in controls (P <0.01). Pirfenidone rats also had lower rates of VT inducibility, 28.6% versus 73.3% in control rats (P <0.05). Furthermore, pirfenidone-treated rats had faster conduction velocities in their IBZs compared with controls, at all pacing cycle lengths (P <0.05). Rats treated with pirfenidone also had smaller infarct dense scar (8.9% of LV myocardium vs. 15.7% in controls, P <0.014), less total LV fibrosis (15% vs. 30% in controls, P <0.003), and less nonscar fibrosis (6.6% vs. 12.6% in controls, P <0.006). CONCLUSION Pirfenidone decreased total and nonscar fibrosis in a rat MI model, which correlated with decreased infarct scar, improved LV function, and decreased VT susceptibility. Directly targeting post-MI fibrotic substrates may have a role in limiting infarct-dense scar, improving LV function, and reducing VT vulnerability.

Utility of Cardiac Magnetic Resonance Imaging to Differentiate Cardiac Sarcoidosis from Arrhythmogenic Right Ventricular Cardiomyopathy

Some patients diagnosed with arrhythmogenic right ventricular cardiomyopathy (ARVC) are eventually found to have cardiac sarcoidosis (CS). Accurate differentiation between these 2 conditions has implications for immunosuppressive therapy and familial screening. We sought to determine whether cardiac magnetic resonance imaging (MRI) could be used to identify the characteristic findings to accurately differentiate between CS and ARVC. Consecutive patients with a diagnostic MRI scan indicating CS and/or ARVC constituted the cohort. All patients diagnosed with CS had histologic confirmation of sarcoidosis, and all patients with ARVC met the diagnostic task force criteria. The cardiac MRI data were retrospectively analyzed to identify possible differentiating characteristics. Of the patients, 40 had CS and 21 had ARVC. Those with CS were older and had more left ventricular scar. The presence of mediastinal lymphadenopathy or left ventricular septal involvement was seen exclusively in the patients with CS (p <0.001). A family history of sudden cardiac death was seen only in the ARVC group (p = 0.012). The right ventricular ejection fraction and ventricular volumes were also significantly different between the 2 groups. In conclusion, patients with CS have significantly different cardiac MRI characteristics than patients with ARVC. The cardiac volume, in addition to the degree and location of cardiac involvement, can be used to distinguish between these 2 disease entities. The presence of mediastinal lymphadenopathy and left ventricular septal scar favors a diagnosis of CS and not ARVC. Consideration of CS should be given if these MRI findings are observed during the evaluation for possible ARVC.

Effect of radiofrequency energy delivery in proximity to metallic medical device components

BACKGROUND Radiofrequency (RF) ablation of cardiac arrhythmias is often performed in the presence of metallic materials in the heart. OBJECTIVES We hypothesize that metal objects in proximity to an RF ablation source can lead to ohmic heating of surrounding tissue. Furthermore, we hypothesize that insulation of the metal can mitigate this RF effect. METHODS A model consisting of viable bovine myocardium or thermochromic liquid crystal medium, a circulating saline bath at 37°C, and a load cell was used. A 4-mm RF ablation catheter was positioned with 10 g of force over bovine myocardium and placed in proximity to a copper wire, a defibrillator lead, and a circular mapping catheter. RF was applied at 30 W, and tissue temperatures were measured. Ablation near insulated and noninsulated esophageal temperature probes was also performed. RESULTS Ablation in proximity to metal resulted in higher temperatures. Average maximum distances for observed thermal changes to >45°C for the ± lead were 5.2 ± 0.3 mm and 5.7 ± 0.4 mm when metal was interposed between the catheter and the ground electrode. Presence of an esophageal temperature probe increased temperatures in tissues adjacent to the probe and caused lesions remote to the ablation site. Esophageal probe insulation prevented these tissue temperature increases and injury to nontargeted tissues. CONCLUSION Effects of RF ablation are potentiated near metallic components of medical devices, leading to significant tissue heating. Further research is needed to assess the safety impact of RF in the myocardium near metallic objects, particularly esophageal temperature probes.

High-Resolution Optical Mapping of Ventricular Tachycardia in Rats with Chronic Myocardial Infarction

Background: Ventricular tachycardia (VT) is a common cause of mortality in post‐myocardial infarction (MI) patients, even in the current era of coronary revascularization treatment. We report a reproducible VT model in rats with chronic MI induced by ischemia‐reperfusion and describe its electrophysiological characteristics using high‐resolution optical mapping.

Effects of radiofrequency energy delivered through partially insulated metallic catheter tips on myocardial tissue heating and ablation lesion characteristics

BACKGROUND Cardiac radiofrequency (RF) ablation is typically achieved using symmetric catheter tips, which may result in unintended heating adjacent to targeted tissue. Partial insulation may alter lesion geometry and prevent collateral heating. OBJECTIVE The purpose of this study was to assess partially insulated focused ablation (PIFA). METHODS Partial insulation using thermally conductive materials was applied to a 4-mm or 8-mm nonirrigated catheter and a 3.5-mm open-irrigated catheter. These PIFA tips, or their noninsulated counterparts, were applied to ex vivo viable bovine myocardium. Ablations were delivered at various powers and under temperature control. Potential clinical applicability was evaluated in vivo by targeting porcine epicardium with irrigated PIFA and assessing its protective effects on the pericardium. RESULTS PIFA catheters exhibited different properties and produced asymmetric lesions compared with corresponding standard ablation catheters. Temperatures at 3- and 5-mm depths were higher for PIFA catheters, with a temperature increase measured at the catheter tip-tissue interface; however, in temperature control ablation, tip-tissue temperature increases did not limit power delivery. Furthermore, temperatures were lower on the insulated surface and were significantly higher on the noninsulated PIFA side. Impedance changes were significantly larger; more steam pops were observed with PIFA but were mitigated by external irrigation, a larger tip electrode, and use of more thermally conductive insulation. In contrast to standard ablation, open-irrigated PIFA created larger asymmetric lesions in vivo over porcine epicardium, without evidence of pericardial injury. CONCLUSION PIFA ablation has different characteristics compared with symmetrically conductive ablation. Further research is needed to assess the clinical implications of insulated catheter ablation.

Clinical and biophysical evaluation of variable bipolar configurations during radiofrequency ablation for treatment of ventricular arrhythmias

BACKGROUND Bipolar radiofrequency ablation (bRFA) has been used to create larger ablation lesions and to treat refractory arrhythmias. However, little is known about optimal bRFA settings. OBJECTIVE The purpose of this study was to evaluate various bRFA settings, including active and ground catheter tip orientation and use of variable active and ground catheters during bRFA. METHODS Two ablation catheters, 1 active and 1 ground, were oriented across from each other, with viable bovine myocardium in between. The catheter tips were placed in various combinations perpendicular or parallel to the myocardium. The active catheter was either a 3.5-mm externally irrigated or 8-mm tip, and the ground catheter was either a 4-mm, 3.5-mm irrigated, or 8-mm tip. Retrospective analysis was undertaken for all bRFA performed at University of Colorado. RESULTS The largest and deepest lesions were produced using irrigated active and ground tips, oriented perpendicularly. In 14 cases (10 patients) of bRFA for ventricular tachycardia and premature ventricular complexes, acute success was achieved in 13 of 14 procedures. Long-term success was achieved in 7 of 10 patients, but 3 patients required multiple bRFA ablations. CONCLUSION Active and ground catheter tip orientation and type are important determinants of lesion sizes during bRFA. The largest and deepest lesions, without a higher incidence of steam pops, were achieved using 2 irrigated catheters. As the largest published series to date, bRFA ablation can be performed safely and effectively in humans. Larger studies are necessary to better evaluate bRFA efficacy and safety.

Inappropriate Shocks due to Subcutaneous Air in a Patient With a Subcutaneous Cardiac Defibrillator

A 56-year-old man with a history of ischemic cardiomyopathy and a transvenous implanted cardiac defibrillator (ICD) for secondary prevention presented with device endocarditis requiring ICD removal and lead extraction. After extended therapy with intravenous antibiotics and resolution of systemic infection, a subcutaneous implantable cardiac defibrillator (S-ICD; Cameron Health/Boston Scientific, San Clemente, CA) was electively implanted with standard technique.1 Specifically, 3 subcutaneous pockets were created, a subaxillary pocket for the generator and 2 parasternal pockets, to which the defibrillator coil was tunneled. After the coil and generator were positioned and sutured and after the fascial layer was closed, sustained ventricular fibrillation was induced. Detection was successful in the primary vector, which involves the pulse generator and proximal parasternal sensing electrode (Figure 1). Sinus rhythm was effectively restored with a submaximal 65-J polarity shock with time to therapy of 13 seconds and impedance of 55 Ω. Device interrogation the next day was unremarkable; the device, per its automatic programming, chose the secondary vector for detection (which involves the pulse generator and distal parasternal sensing electrode; Figure 1). The postoperative course was otherwise uneventful, and the patient was discharged the following day. Figure 1. Anteroposterior chest film after device implantation, with notations illustrating possible sensing vectors that can be programmed with the subcutaneous implantable …

Percutaneous transhepatic access for catheter ablation of cardiac arrhythmias

AIMS Femoral venous access may be limited in certain patients undergoing electrophysiology (EP) study and ablation. The purpose of this study is to review a series of patients undergoing percutaneous transhepatic access to allow for ablation of cardiac arrhythmias. METHODS AND RESULTS Six patients with a variety of cardiac arrhythmias and venous abnormalities underwent percutaneous transhepatic access. Under fluoroscopic and ultrasound guidance, a percutaneous needle was advanced into a hepatic vein and exchanged for a vascular sheath over a wire. Electrophysiology study and radiofrequency ablation was then performed. All tachycardias, including atrial tachycardia, atrial flutter, atrioventricular nodal tachycardia, and atrial fibrillation, were ablated. Procedural times ranged from 227 to 418 min. Fluoroscopy times ranged from 32 to 95 min. There were no complications. All six patients have been arrhythmia-free in follow-up (5-49 months, mean 23.1 months). CONCLUSION Percutaneous transhepatic access is safe and feasible in patients with limited venous access who are undergoing EP study and ablation for a range of cardiac arrhythmias.

Enhanced Radiofrequency Ablation With Magnetically Directed Metallic Nanoparticles

Background—Remote heating of metal located near a radiofrequency ablation source has been previously demonstrated. Therefore, ablation of cardiac tissue treated with metallic nanoparticles may improve local radiofrequency heating and lead to larger ablation lesions. We sought to evaluate the effect of magnetic nanoparticles on tissue sensitivity to radiofrequency energy. Methods and Results—Ablation was performed using an ablation catheter positioned with 10 g of force over prepared ex vivo specimens. Tissue temperatures were measured and lesion volumes were acquired. An in vivo porcine thigh model was used to study systemically delivered magnetically guided iron oxide (FeO) nanoparticles during radiofrequency application. Magnetic resonance imaging and histological staining of ablated tissue were subsequently performed as a part of ablation lesion analysis. Ablation of ex vivo myocardial tissue treated with metallic nanoparticles resulted in significantly larger lesions with greater impedance changes and evidence of increased thermal conductivity within the tissue. Magnet-guided localization of FeO nanoparticles within porcine thigh preps was demonstrated by magnetic resonance imaging and iron staining. Irrigated ablation in the regions with greater FeO, after FeO infusion and magnetic guidance, created larger lesions without a greater incidence of steam pops. Conclusions—Metal nanoparticle infiltration resulted in significantly larger ablation lesions with altered electric and thermal conductivity. In vivo magnetic guidance of FeO nanoparticles allowed for facilitated radiofrequency ablation without direct infiltration into the targeted tissue. Further research is needed to assess the clinical applicability of this ablation strategy using metallic nanoparticles for the treatment of cardiac arrhythmias.