Circulation: Arrhythmia and Electrophysiology June 2020 Issue


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Paul J. Wang:

Welcome to the monthly podcast, On the Beat for Circulation: Arrhythmia and Electrophysiology. I'm Dr. Paul Wang, editor in chief, with some of the key highlights from this month's issue.

In our first paper, Vivek Reddy and associates studied a novel, 7.5, French lattice tip catheter with the compressible 9 mm nitinol tip that is able to deliver either focal radio frequency ablation [RFA] or pulsed field ablation [PFA], 2 to 5 second lesions. In a 3 center, single-arm, first in human trial, the catheter was used with a custom mapping system to treat paroxysmal or persistent atrial fibrillation. Toggling between energy sources, point by point, pulmonary vein [PV] encirclement was performed using biphasic pulsed field ablation, posteriorly, and either temperature controlled irrigated RFA or pulse field ablation, anteriorly (RF/PF or PF/PF) respectively. Linear lesions were created with either PFA or RFA. The 76 patient cohort included 55 paroxysmal and 21 persistent atrial fibrillation [AF] patients undergoing either RF/PF [pulse field ablation] 40 patients or PF/PF ablation in 36 patients, pulmonary vein isolation therapy duration was 22.6 minutes per patient with a mean of 50.1 RF/PF ablation lesions per patient. Linear lesions included 14 mitral, 34 left atrial roof and 44 cavo-tricuspid isthmus lines with therapy duration times of 5.1, 1.8 and 2.4 min/patient respectively. All lesion sets were acutely successful using 4.7 minutes of fluoroscopy. There were no device-related complications, including no strokes. Post-procedure esophagogastroduodenoscopy revealed minor mucosal thermal injury in two of the 36 RF/PF and zero of the 24 PF/PF patients. Post-procedure brain MRI revealed DWI positive flair, negative and DWI positive flare positive asymptomatic lesions in 5 and 3 of the 51 patients respectively.

In our next paper, Moussa Saleh and associates examined whether chloroquine, hydroxychloroquine plus or minus azithromycin lead to a prolongation of the QT interval, possibly increasing the risk of torsades de pointes and sudden death in a hospitalized population of patients with COVID-19. 201 patients were treated for COVID-19 with chloroquine/hydroxychloroquine. 10 patients or 5% received chloroquine, and 191 or 95% received hydroxychloroquine and 119 or 59% also received azithromycin. The primary outcome of Torsades de pointes was not observed in the entire population. Baseline QTC interval did not differ between patients treated with chloroquine or hydroxychloroquine monotherapy versus those treated with combination group chloroquine/hydroxychloroquine and azithromycin (440 ms versus 439.9 ms). The maximum QT during treatment was significantly longer in the combination versus the monotherapy group, 470 ms versus 453 ms (P = 0.004). Seven patients (3.5%) required discontinuation of these medications due to QTC prolongation. No arrhythmic deaths were reported.

In our next paper, Mikko Tulppo and associates examine whether the association between leisure time physical activity and the risk of sudden death and non-sudden cardiac death in coronary artery disease patients. 1,946 patients with angiographically verified coronary artery disease were classified into four groups: inactive, irregularly active, active exercise regularly two to three times per week, and highly active, exercise four times or more weekly. During follow-up, median 6.3 years, 52 sudden cardiac death and 49 non-sudden cardiac deaths occurred. Inactive patients had increased risk for sudden cardiac death compared to active patients, hazard ratio 2.45. Leisure time was not associated with sudden cardiac death in patients with Canadian cardiovascular class one, 18 events in 1,107 patients. Among patients with Canadian cardiovascular society, class two or higher, 34 events in 839 patients. An increased risk for sudden cardiac death encountered in highly active patients, hazard ratio 7.46 (P < 0.001). In inactive patients hazard ratio 3.64 as compared to active patients. A linear association was observed between leisure time, physical activity and non-sudden cardiac death. Those with high leisure time physical activity had the lowest risk for non sudden cardiac death.

In our next paper, Jacob Koruth and associates examined the preclinical feasibility and safety of a 9mm lattice tip catheter with focal biphasic pulse field [PF] based thoracic vein isolation and linear ablation combined focal biphasic pulse field and radio-frequency [RF] focal ablation and vocal biphasic pulse field delivered directly on top of the esophagus. They treated two cohorts of six swine with pulse fields at low dose and high dose followed for four weeks and two weeks, respectively to isolate 25 thoracic veins and to create five right atrial low dose PF, six mitral high dose PF, and six roof lines with combined RF and high dose PF. Baseline and follow-up voltage mapping, venus potentials, ostial diameters and phrenic nerve viability were assessed. High dose PF in RF lesions were delivered in 4 and 1 swine from the inferior vena cava onto a forcefully deviate esophagus. 100% of thoracic veins, 25 out of 25, were successfully isolated with 12.4 applications per vein with a mean pulse field times of less than 90 seconds per vein. Durable isolation improved from 61.5% in the low dose pulse field to 100% with a high dose pulse field (P = 0.04). And all linear lesions were successfully completed without incurring venous stenosis or phrenic injury. High dose pulse field sections had higher trans mortality rates than low dose pulse field (98.3% versus 88.1%, P = 0.03). Despite greater thickness, 2.5 versus 1.3 mm, pulse field lesions demonstrated homogeneous fibrosis without epicardial fat, nerve or vessel involvement. In comparison, combined RF plus high dose PF sections revealed similar transmurality, but expectedly more necrosis, inflammation and epicardial fat, nerve and vessel involvement. Significant ablation related esophageal and necrosis inflammation and fibrosis were seen in all RF sections as compared to no PF sections.

In our next paper, Hagai Yavin and associates investigated the effects of a novel, lattice tip catheter designed for focal radiofrequency ablation [RFA] or pulse field ablation in 25 swine. In 14 animals, they examined in step one (n = 14) the feasibility to create atrial line of block and described as acute effects on the phrenic nerve and esophagus. In step two (n = 7), they examined the subacute effects of pulse field ablation on block durability, phrenic nerve, and esophagus 2 or more weeks. In 4 animals in step three, they compare the effects of pulse field ablation and RFA on the esophagus using a mechanical deviation model, approximating the esophagus through the right atrium in 4 and direct ablation honest lumen in 4. The effects of endocardial PFA and RFA on the phrenic nerve were also compared (n = 10). Histological analysis were performed. Pulse field ablation produced acute block in 100% of lines achieved with 2.1 applications per centimeter line. Histological analysis following a mean of 35 days showed 100% transmurality (thickness range 0.4 to 3.4 mm) with a lesion width of 19.4 mm. Pulse field ablation selectively affected cardiomyocytes, but spared blood vessels and nervous tissue. Pulse field ablation applied from the posterior atrium to the approximated esophagus produced transmural lesions without esophageal injury. Pulse field ablation applied within the esophageal lumen produced mild edema compared to radiofrequency ablation (13 applications) which produced epithelial ulcerations. Pulse field ablation resulted in no or transient stunning of the phrenic nerve, less than 5 minutes without histological changes while radiofrequency ablation produced paralysis.

In our next paper, Elad Anter and associates investigated the optimal methods to identify arrhythmogenic substrate of scar related VT. They examine how often sites of activation slowing during sinus rhythm co localize with ventricular tachycardia VT circuit. In a multicenter study in patients with infarct-related VT, the left ventricle was mapped during activation from three directions, sinus rhythm, or atrial pacing, right ventricular and left ventricular LV pacing at 600 ms. Ablation was applied selectively to the cumulative area of slow activation defined as a sum of all regions with activation time of 40 ms or greater per 10 mm. Hemodynamically tolerated ventricular tachycardias or VT were mapped with activation or entrainment. The primary outcome was a composite of appropriate ICD therapies and cardiovascular death. In 85 patients, the left ventricle was mapped during activation from 2.4 directions. The direction of LV activation influenced the location and magnitude of activation slowing. The spacial overlap of activation slowing between sinus rhythm and right ventricular RV pacing was 84.2%, between sinus rhythm and LV pacing was 61.4%, and between right ventricular and left ventricular pacing, 71.3% (P < 0.05) between all comparisons. Mapping during sinus rhythm identified only 66.2% of the entire area of activation slowing and 58% of critical isthmus sites. Activation from other directions, right ventricular or left ventricular stimulation unmasked an additional 33% of slowly conducting zones and 25% critical isthmus sites. The area of maximal activation slowing often corresponded to the site where the wavefront first interacted with the infarct. During a follow-up period of 3.6 years, the primary end point incurred in 14 out of 85 or 16.5% of patients. The authors concluded that the spatial distribution of activation slowing is dependent on the direction of LV activation with the area of maximal slowing corresponding to the site where the wavefront first interacts with the infarct.

In our next paper, Georg Gussak and associates identified a novel form of abnormal calcium wave activity in normal and failing dog atrial myocytes, which occurs during the action potential and is absent during diastole. The goal of this study was to determine if triggered calcium waves affect cellular electrophysiological properties. The authors use simultaneous recordings of intracellular calcium, and action potentials for the measurement of maximum diastolic potential and action potential duration during triggered calcium waves in isolated dog atrial myocytes. Computer simulations then explored electrophysiological behavior arising from triggered calcium waves at the tissue scale. At 3.3 to five Hertz, triggered calcium waves occurred during the action potential and outlasted several action potential cycles. Maximum diastolic potential was reduced and actual potential duration was significant prolonged during trigger calcium waves. All electrophysiological responses that triggered calcium waves were abolished by using SCA 0400 and ORM 10103, indicating that sodium calcium exchange current caused depolarization. The time constant recovery from inactivation of calcium current was 40 to 70 ms in atrial myocytes, depending on the holding potential. This current could be responsible for action potential (AP) activation during repolarization induced by triggered waves. Modeling studies demonstrate the characteristic properties of triggered calcium waves are potentially arrhythmogenic by promoting both conduction block and reentry arising from the repolarization induced by triggered calcium waves. The authors concluded that triggered calcium waves activate inward sodium calcium exchange and dramatically reduce atrial maximum diastolic potential and prolonged action potential duration establishing the substrate for reentry that could contribute to initiation and maintenance of atrial arrhythmias.

In our next paper Faisal Merchant and Omid Sayadi and associates evaluate the ability of a real-time, closed loop system to record and analyze repolarization alternans from multiple intracardiac leads and deliver dynamically R-wave triggered pacing stimuli during the absolute refractory period. They examined the ability of this system to control repolarization alternans and reduce arrhythmia susceptibility, in vivo. R-wave trigger pacing can induce repolarization alternans, the magnitude of which can be modulated by varying the amplitude, pulse width, or size of the pacing vector. Using a swine model (n = 9), the authors demonstrated that to induce 1 microvolt change in the alternans voltage on the body surface, coronary sinus or left ventricle, requires a delivery charge of 0.04, 0.05 and 0.06 microcoulombs, respectively, while to induce one unit change of the case score requires a delivery charge of 0.93, 0.32 and 0.33 microcoulombs, respectively. For all body surface and intracardiac leads a Delta alternans voltage and Delta K score between baseline and R-wave triggered pace peaks increases consistently with an increase in the pacing pulse amplitude, pulse width and vector spacing. Additionally, the author showed that the proposed method can be used to suppress spontaneously occurring alternans (n = 7), in the presence of myocardial ischemia. Suppression of repolarization alternans by pacing during the absolute refractory period results in a significant reduction in arrhythmia susceptibility, evidenced by lower S rank score during program ventricular stimulation compared to baseline prior to ischemia.

In a perspective outlining the cardiovascular effects of chloroquine and hydroxychloroquine, Ohad Oren and associates describe their belief that the use of chloroquine and hydroxychloroquine in COVID-19 should be limited to randomized, controlled trials. For critically ill patients, unable to enroll in a trial, selective in-hospital use could be considered with careful clinical monitoring in keeping with the FDA's emergency use authorization. The authors suggested that studies evaluating chloroquine and hydroxychloroquine should systematically collect baseline demographic data, results from electrocardiographic and echocardiographic monitoring prior to and during treatment and rates of adverse cardiovascular events in both the near and long-term.

In a research letter, Federico Migliore and Alessandro Zorzi and associates found a 28% decrease in the number of urgent pacemaker implantations during the six weeks after the first COVID-19 case, from 122 to 88 (P = 0.02), compared to the six weeks before the first COVID-19 case. The proportion of female patients requiring urgent pacemaker implantation after the COVID-19 outbreak decreased from six out of 122 (49%) to 30 out of 88 (34%) (P = 0.03).

In a special report Stephanie Kochav and associates described 4 cases of cardiac arrhythmias in COVID-19, including AV block, atrial fibrillation, polymorphic ventricular tachycardia, and pulseless electrical activity arrest.

In a year in review, Suraj Kapa and associates discuss a number of the many advances in our understanding of arrhythmia mechanisms, diagnosis, and new therapies in the past year. Data suggests that secretoneurin may be a marker for patients at risk of ventricular arrhythmias, while natriuretic peptide receptor C may have a role in atrial fibrosis. In atrial specific 2-pore potassium channel TASK-1 may be a therapeutic target for atrial fibrillation. Sensory neurons may play a key role in sleep apnea related to atrial fibrillation. Bariatric surgery is associated with improved atrial fibrillation outcome. Artificial intelligence applied to electrocardiography has yielded estimates of age, gender, and overall health. We've seen new tools for collection of patient centered outcomes following catheter ablation. There's been significant advances in the ability to identify ventricular tachycardia termination sites through high density mapping of deceleration zones. We've learned that right ventricular dysfunction may be a predictor of survival benefit after ICD implantation in non ischemic cardiomyopathy patients. We've seen further insights in the role of his bundle pacing on improving outcomes. As our understanding of cardiac laminopathies advance, we have new tools to predict arrhythmic event rates in gene carriers. And finally, we've seen numerous advances in the treatment of arrhythmias in patients with congenital heart disease.

That's it for this month. We hope that you'll find the journal to be the go-to place for everyone interested in the field. See you next time. This program is copyright American Heart Association 2020.

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