Guidance for Rebooting Electrophysiology Through the COVID-19 Pandemic From the Heart Rhythm Society and the American Heart Association Electrocardiography and Arrhythmias Committee of the Council on Clinical Cardiology: Endorsed by the American College of Cardiology.

Coronavirus disease 2019 (COVID-19) has presented substantial challenges to patient care and impacted health care delivery, including cardiac electrophysiology practice throughout the globe. Based upon the undetermined course and regional variability of the pandemic, there is uncertainty as to how and when to resume and deliver electrophysiology services for arrhythmia patients. This joint document from representatives of the Heart Rhythm Society, American Heart Association, and American College of Cardiology seeks to provide guidance for clinicians and institutions reestablishing safe electrophysiological care. To achieve this aim, we address regional and local COVID-19 disease status, the role of viral screening and serologic testing, return-to-work considerations for exposed or infected health care workers, risk stratification and management strategies based on COVID-19 disease burden, institutional preparedness for resumption of elective procedures, patient preparation and communication, prioritization of procedures, and development of outpatient and periprocedural care pathways.

Differentiating Ventricular From Supraventricular Arrhythmias Using the Postpacing Interval After Failed Antitachycardia Pacing.

BACKGROUND: Implantable cardioverter defibrillator arrhythmia discrimination algorithms often are unable to discriminate ventricular from supraventricular arrhythmias. We sought to evaluate whether the response to antitachycardia pacing (ATP) in patients with an implantable cardioverter defibrillator could further discriminate ventricular from supraventricular arrhythmias in patients receiving ATP. METHODS AND RESULTS: All episodes of ventricular or supraventricular tachycardia where ATP was delivered in patients enrolled in RAFT (Cardiac-Resynchronization Therapy for Mild-to-Moderate Heart Failure Trial) were included. RAFT randomized 1798 patients with New York Heart Association class II/III heart failure, left ventricular ejection fraction ≤30%, and QRS duration of ≥120 ms to a implantable cardioverter defibrillator±cardiac resynchronization therapy. The tachycardia cycle lengths (TCLs) before and after the delivery of ATP and the postpacing intervals were assessed. Overall, 10 916 ATP attempts were reviewed for 8150 tachycardia episodes in 924 patients. After excluding tachycardias where ATP terminated the episode or where the specific mechanism of the tachycardia was uncertain, we analyzed 3676 ATP attempts delivered for 2046 tachycardia episodes in 541 patients. A shorter difference between postpacing interval and TCL (PPI-TCL) was more likely to be associated with ventricular tachycardia than with supraventricular tachyarrhythmia (138.1±104.2 versus 277.4±126.9 ms; p<0.001). Analysis of the receiver operator curve for the PPI-TCL revealed an area under the curve of 0.803 (p<0.001; 95% confidence interval, 0.784-0.822). The majority of tachycardias with a PPI-TCL >360 ms were supraventricular with a PPI-TCL value of ≤360 ms having a sensitivity of 97.4% and specificity of 28.3% for ventricular tachycardia. CONCLUSIONS: The ATP response, specifically the PPI-TCL, can further discriminate ventricular from supraventricular arrhythmias in patients with implantable cardioverter defibrillators when the currently available discriminators fail. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov. Unique identifier: NCT00251251.

Differential sequential septal pacing: a simple maneuver to differentiate nodal versus extranodal ventriculoatrial conduction.

BACKGROUND: Distinguishing retrograde nodal conduction from extranodal conduction using an accessory pathway (AP) can sometimes be challenging. OBJECTIVE: To distinguish nodal from extranodal ventriculoatrial (VA) conduction regardless of AP location by proposing a simple method. This method is based on the principle that moving the pacing site progressively from the basal region toward the entrance of the His-Purkinje system should shorten VA time for nodal but not for AP conduction. METHODS: Sixty-seven patients with supraventricular tachycardia were prospectively recruited. Quadripolar catheters were placed at the right ventricular (RV) apex, right atrium, and His and coronary sinus. The RV septum was sequentially paced at 4 sites: (1) basal, (2) high midventricle, (3) low midventricle, and (4) apex at a cycle length 100 ms shorter than the resting cycle length. The stimulus-to-atrial (SA) interval was measured by using the proximal coronary sinus atrial electrogram. RESULTS: Group 1 (n = 33) had nodal VA conduction; all patients had typical atrioventricular nodal reentrant tachycardia. Group 2 (n = 34) had extranodal VA conduction via an AP: 19 left-sided, 6 right-sided, and 9 posteroseptal. In group 1, the SA interval decreased significantly as pacing site moved closer toward the apex (site 1: 166 ± 35 ms, site 2: 153 ± 32 ms, site 3: 149 ± 32 ms, site 4: 154 ± 33 ms, P < .001, respectively, at sites 2-4 compared with site 1). In contrast, in group 2, the SA interval increased significantly toward the apex (site 1: 149 ± 45 ms, site 2: 158 ± 43 ms, site 3: 161 ± 43 ms, and site 4: 163 ± 40 ms, P < .001, respectively, at sites 2-4 compared with site 1). The SA interval at the high midventricular site (site 2) - SA interval at the base (site 1) ≤ 0 ms for nodal and > 0 ms for extranodal conduction had optimal sensitivity and specificity (nodal: selectivity = 97.0% and specificity = 85.3%; extranodal: selectivity = 85.3% and specificity = 97.0%). CONCLUSIONS: Differential sequential pacing of the RV septum reliably distinguishes retrograde atrioventricular nodal conduction from AP conduction.

Ventricular fibrillation induced by spontaneous hypothermia in a patient with early repolarization syndrome.

INTRODUCTION: The early repolarization (ER) pattern on ECG was originally described in the context of hypothermia. CASE SUMMARY: We present the case of a 34-year-old male with cardiac arrest in the context of spontaneous hypothalamic mediated thermal dysregulation after intracranial hemorrhage. Ventricular fibrillation with a marked ER pattern recurred with therapeutic hypothermia. Spontaneous hypothermia due to hypothalamic dysregulation was observed to enhance the amplitude of the ER pattern and was contemporaneous with recurrent ventricular fibrillation during follow-up. CONCLUSIONS: Hypothermia is an important trigger of VF in the setting of early repolarization syndrome, and warrants assessment as an environmental trigger of spontaneous events.

Voltage-guided ablation technique for cavotricuspid isthmus-dependent atrial flutter: refining the continuous line.

Ablation of the cavotricuspid isthmus has become first-line therapy for "isthmus-dependent" atrial flutter. The goal of ablation is to produce bidirectional cavotricuspid isthmus block. Traditionally, this has been obtained by creation of a complete ablation line across the isthmus from the ventricular end to the inferior vena cava. This article describes an alternative method used in our laboratory. There is substantial evidence that conduction across the isthmus occurs preferentially over discrete separate bundles of tissue. Consequently, voltage-guided ablation targeting only these bundles with large amplitude atrial electrograms results in a highly efficient alternate method for the interruption of conduction across the cavotricuspid isthmus. Understanding the bundle structure of conduction over the isthmus facilitates more flexible approaches to its ablation and targeting maximum voltages in our hands has resulted in reduction of ablation time and fewer recurrences.

Latent microvolt T-wave alternans in survivors of unexplained cardiac arrest unmasked by epinephrine challenge.

BACKGROUND: The arrhythmogenic substrate in survivors of unexplained cardiac arrest (UCA) has not been defined. OBJECTIVES: To test the hypothesis that patients with UCA have latent repolarization abnormalities, in particular T-wave alternans (TWA), which may be unmasked with epinephrine (EPI) challenge. METHODS: We prospectively studied 10 UCA survivors (46 ± 9 years) and 11 first-degree relatives (FDRs) of sudden death victims (37 ± 14 years). Patients with UCA underwent standard clinical testing, which was normal. FDRs had normal clinical history and testing. All subjects underwent an EPI infusion (0.05, 0.1, and 0.2 µg/(kg·min), 5 minutes each dose) while recording continuous digital 12-lead electrocardiograms. Corrected QT interval and QT variability index were evaluated at each EPI dose. TWA magnitude (V(alt)) was assessed at each dose by using the spectral method. Positive (+) TWA at each dose was defined as V(alt) > 0 with k ≥ 3 in 1 or more 128-beat segment in ≥2 electrocardiogram leads. A novel metric, TWA burden, reflecting V(alt) integrated over time (s), was also evaluated for each EPI dose. RESULTS: There was no difference between UCA survivors and FDRs with respect to heart rate, QT, corrected QT interval, or QT variability index at baseline or during EPI. At baseline, +TWA was similar between UCA survivors and FDRs (10% vs 0%; P = NS). During EPI, +TWA was more prevalent in UCA survivors than in FDRs (80% vs 18%; P = .009). TWA burden was greater in UCA survivors than in FDRs during EPI 0.1 (P = .039) and EPI 0.2 µg/(kg·min) (P = .009). CONCLUSIONS: UCA survivors are more likely to demonstrate latent TWA compared with FDRs, which becomes manifest with EPI. This novel finding provides evidence for an arrhythmogenic substrate in UCA survivors.

Tachycardia induction with ventricular extrastimuli differentiates atypical atrioventricular nodal reentrant tachycardia from orthodromic reciprocating tachycardia.

BACKGROUND: Differentiating atypical atrioventricular nodal reentrant tachycardia (AVNRT) from septal orthodromic reentrant tachycardia (ORT(Septal)) is challenging in nonsustained tachycardia. When sustained, the postpacing interval minus tachycardia cycle length following entrainment (PPI(Entrainment) - TCL) and stimulation to atrial interval minus ventriculoatrial interval (Stim-A(Entrainment) - VA) are utilized. OBJECTIVE: We hypothesized that the first tachycardia cycle after tachycardia induction with right ventricular apical extrastimulation would yield comparable information to entrainment, precluding the need for sustained tachycardia. METHODS: Twenty-four patients with AVNRT (age 47 ± 18 years), 19 with ORT(Septal) (age 42 ± 17 years), and 15 with ORT over a left lateral accessory pathway (ORT(Left)) (age 41 ± 16 years) were included. The ventricular extrastimulus to atrial depolarization at tachycardia initiation (Stim-A(Initiation)) and tachycardia VA interval were measured to establish the Stim-A(Initiation) minus VA interval (Stim-A(Initiation) - VA). The ventricular extrastimulus to the subsequent right ventricular apical depolarization (postpacing interval at initiation, PPI(Initiation)) was utilized to obtain the PPI(Initiation) minus TCL (PPI(Initiation) - TCL). The AH interval associated with the PPI(Initiation) minus the AH in tachycardia was utilized to establish a corrected PPI(Initiation) minus TCL (cPPI(Initiation) - TCL). RESULTS: The intervals after tachycardia initiation were longer for AVNRT than for ORT: mean PPI(Initiation) - TCL (193 ± 44 vs 91 ± 73; P <.001), cPPI(Initiation) - TCL (174 ± 44 ms vs 88 ± 50 ms; P <.001), and Stim-A(Initiation) - VA (161 ± 45 ms vs 69 ± 53 ms; P <.001). The correlation coefficient for Stim-A(Initiation) minus VA against Stim-A(Entrainment) minus VA was 0.79 and for cPPI(Initiation) minus TCL against PPI(Entrainment) minus TCL was 0.71. cPPI(Initiation) minus TCL <115 ms or Stim-A(Initiation) - VA <85 ms was observed only in ORT. The converse was observed in AVNRT but also in ORT(Septal) over decremental accessory pathways and ORT(Left). CONCLUSION: Stim-A(Initiation) - VA < 85 ms or cPPI(Initiation) - TCL < 115 ms excludes AVNRT.

Entrainment for distinguishing atypical atrioventricular node reentrant tachycardia from atrioventricular reentrant tachycardia over septal accessory pathways with long-RP [corrected] tachycardia.

BACKGROUND: The response to right ventricular (RV) entrainment is useful to distinguish atypical AV node reentrant tachycardia from AV reentrant tachycardia using a septal accessory pathway. Whether entrainment can differentiate between AV node reentrant tachycardia and AV reentrant tachycardia in patients with long-RP tachycardia has not been systematically validated. METHODS AND RESULTS: Twenty-four patients with concealed septal accessory pathways who had an electrophysiology study between January 1, 2000, and January 1, 2010, were included (age, 38 ± 17 years; men, 17). Entrainment was performed from the RV apex pacing at cycle length 20 to 40 ms shorter than tachycardia cycle length (TCL). The mean TCL was 390 ± 80 ms, the mean AH interval during tachycardia was 151 ± 57 ms, and the mean ventriculoatrial (VA) time was 182 ± 103 ms. Twelve patients had typical accessory pathways (VA/TCL <40%), and 12 had slowly conducting accessory pathways (VA/TCL ≥ 40%). In all patients with typical accessory pathways, the postpacing interval minus the TCL (PPI-TCL) was <115 ms and the difference in the VA interval during pacing and tachycardia (StimA-VA) was <85 ms. On the other hand, in 6 of the 12 patients in the slowly conducting group, the PPI-TCL was >115 ms, and the StimA-VA was > 85 ms. CONCLUSIONS: Slowly conducting accessory pathways frequently yield RV entrainment criteria traditionally attributable to AV node reentry. Distinguishing AV node reentry from AV reentry in patients with long-RP tachycardia requires other criteria.

Complete antral encirclement is not required for pulmonary vein isolation.

BACKGROUND: Complete circumferential antral ablation may not be necessary for successful pulmonary vein (PV) isolation in patients with paroxysmal atrial fibrillation (AF). OBJECTIVE: We examined the feasibility of a noncircumferential approach limited to segments of the antra required for PV-atrial conduction. METHODS: During ablation for paroxysmal AF, each PV antrum was divided into six segments, and ablation was sequentially targeted to antral segments with the earliest activity until bidirectional isolation was achieved. Ablation at the ostium was avoided. Patients requiring complete circumferential ablation (circumferential group) were compared with those undergoing incomplete antral ablation (noncircumferential group) with respect to freedom from symptomatic atrial arrhythmia, procedure, and ablation times. RESULTS: Ninety-nine patients underwent ablation with successful isolation of PVs (n = 37 circumferential; n = 62 noncircumferential). There were no significant differences in age, gender, AF duration, or LA size. Procedure time (202 ± 45 vs. 185 ± 47 minutes; P = .06) and ablation time (51 ± 15 vs. 41 ± 14 minutes; P = .004) were shorter in the noncircumferential group. During follow-up (12 ± 6 months), freedom from symptomatic recurrence was 73% in both groups (P = .97), with organized atrial tachycardia being more common in the circumferential group (P = .06). In 22 patients undergoing repeat study, PV reconnection was demonstrated in 82% and 81% of PVs in each group. Reconnection in the noncircumferential group occurred in previously ablated segments in 10 (77%) of 13 cases. CONCLUSIONS: Noncircumferential antral ablation achieves similar success rates with shorter procedure and ablation times than circumferential ablation. Greater attention should be focused on producing permanent lesions rather than on completing antral encirclement after isolation is achieved.

Reduction of complex ventricular ectopy and improvement in exercise capacity with flecainide therapy in Andersen-Tawil syndrome.

Andersen-Tawil syndrome (ATS) is a rare inherited autosomal disorder characterized by the clinical triad of ventricular arrhythmias, hypokalaemic periodic paralyses, and skeletal developmental abnormalities, resulting in dysmorphic features. Although ATS patients have a high incidence of ventricular arrhythmias, the occurrence of sudden cardiac death is rare. In this report, we describe the successful use of flecainide in an ATS patient with a considerable ventricular arrhythmia burden who had not demonstrated any response to conventional beta-blocker therapy used in conjunction with potassium (K(+)) supplementation.

Effect of defibrillation testing on management during implantable cardioverter-defibrillator implantation.

BACKGROUND: Verification of defibrillation efficacy by defibrillation threshold (DFT) testing during implantable cardioverter-defibrillator implantation is the current standard. Generally, defibrillation of ventricular fibrillation at 10 J below the maximum output of a device is felt to establish an adequate safety margin. Nonetheless, DFT testing adds to cost and carries some potential for morbidity, whereas its impact on outcomes in the modern era of defibrillator technology is unclear. We aimed to determine the frequency that DFT testing resulted in a change at device implant and to identify clinical and echocardiographic predictors of the need for DFT testing. METHODS: We reviewed all implantable cardioverter-defibrillators that were implanted at the London Health Sciences Centre (Ontario, Canada) from June 1999 to August 2003 and used multivariate analysis to determine variables associated with DFT test failures and elevated DFT values. When a defibrillation failure was not observed, a lowest energy to defibrillate (LED) was recorded. RESULTS: Among 168 implants, DFT testing was successful with a minimum 10-J safety margin in 152 (90%), whereas the remaining 16 required changes at device implant. In a multivariate analysis, use of amiodarone was independently associated with DFT failure (odds ratio, 4.6; 95% confidence interval, 1.2-17.0). Significantly higher mean DFT/LED values were observed among patients on amiodarone (1.36 J; P = .0041). Those with nonischemic cardiomyopathy had a higher mean DFT/LED compared with those with ischemic cardiomyopathy (1.44 J; P = .028). CONCLUSIONS: Use of amiodarone is associated with a 4-fold increase in risk of DFT failure and subsequent need for changes at implant to achieve a safe threshold. Defibrillation threshold testing appears to be most useful for patients taking amiodarone.

Utility and cost effectiveness of temporary pacing using active fixation leads and an externally placed reusable permanent pacemaker.

Active-fixation leads and externally placed permanent pacemakers for temporary pacing may be beneficial because they allow for greater patient mobility and comfort and increased reliability of lead placement. The relative cost of this form of pacing may be prohibitive unless markedly prolonged pacing is required. Twenty patients (63 +/- 15 years of age, 15 men) underwent external "temporary permanent" pacing. Pacing duration and associated complications were recorded. Cost models were then constructed using data from the London Health Sciences Center business unit to compare the cost of traditional temporary pacing and this technique using a Medtronic KSR903 pacemaker and 5,076 leads. Direct costs were calculated based on the 2005 Ontario Health Insurance Plan fee schedule, combined with calculation of labor and materials. Pacing was undertaken for a median of 2 days (range 2 to 83). There were no complications during implantation or pacing or after system removal. Sensing was lost in only 1 instance, which was reprogrammed uneventfully. Cost comparison showed that, although active-fixation lead placement was initially more costly ($798.71 vs $471.91), the added reliability of the permanent system allowed ward telemetry instead of cardiac care unit monitoring. This resulted in cost equivalence after only 18 hours and conferred a cost savings of $456 per 24-hour period thereafter. As a result, a savings of $585.20 is projected for a modeled patient after 48 hours of temporary pacing. In conclusion, temporary pacing using this technique is a reliable and comfortable alternative to traditional temporary pacing and appears to be a cost-effective temporary pacing option after 18 hours.

Using the net benefit regression framework to construct cost-effectiveness acceptability curves: an example using data from a trial of external loop recorders versus Holter monitoring for ambulatory monitoring of "community acquired" syncope.

BACKGROUND: Cost-effectiveness acceptability curves (CEACs) describe the probability that a new treatment or intervention is cost-effective. The net benefit regression framework (NBRF) allows cost-effectiveness analysis to be done in a simple regression framework. The objective of the paper is to illustrate how net benefit regression can be used to construct a CEAC. METHODS: One hundred patients referred for ambulatory monitoring with syncope or presyncope were randomized to a one-month external loop recorder (n = 49) or 48-hour Holter monitor (n = 51). The primary endpoint was symptom-rhythm correlation during monitoring. Direct costs were calculated based on the 2003 Ontario Health Insurance Plan (OHIP) fee schedule combined with hospital case costing of labour, materials, service and overhead costs for diagnostic testing and related equipment. RESULTS: In the loop recorder group, 63.27% of patients (31/49) had symptom recurrence and successful activation, compared to 23.53% in the Holter group (12/51). The cost in US dollars for loop recording was 648.50 dollars and 212.92 dollars for Holter monitoring. The incremental cost-effectiveness ratio (ICER) of the loop recorder was 1,096 dollars per extra successful diagnosis. The probability that the loop recorder was cost-effective compared to the Holter monitor was estimated using net benefit regression and plotted on a CEAC. In a sensitivity analysis, bootstrapping was used to examine the effect of distributional assumptions. CONCLUSION: The NBRF is straightforward to use and interpret. The resulting uncertainty surrounding the regression coefficient relates to the CEAC. When the link from the regression's p-value to the probability of cost-effectiveness is tentative, bootstrapping may be used.

Hybrid approach for minimally-invasive operative therapy of arrhythmias.

The failure of linear radiofrequency lesions to effectively replace operative therapy for atrial fibrillation (AF) is largely related to the inability to produce complete lines of conduction block. While pulmonary vein ablation enjoys success in patients with paroxysmal AF, patients with persistent AF and permanent AF fair less well. As such, a minimally-invasive, preferably "off pump" robotically-assisted procedure for complex arrhythmias like AF remains highly desirable. The shift to access from a mini-thoracotomy or port access will limit visualization and direct access to the ablation target. For the most part, the tools to overcome these limitations are not yet developed. As these develop, it is critical for the electrophysiologic effects of the delivered lesions to be assessed. With the development of non-fluoroscopic mapping systems and advances in imaging, a hybrid operative, electrophysiology (EP) suite can be equipped to provide full support for the surgeon and electrophysiologist. This will provide the opportunity to assess the efficacy and safety of ablation lesions, ideally with direct feedback to the surgeon. A hybrid approach will provide the opportunity to gain insights into the success and failure of specific ablation tools, approaches and lesions. This step will be crucial in understanding why specific procedures ultimately fail to cure AF and other complex arrhythmias.