Michael Shehata

Using the Upper Limit of Vulnerability to Assess Defibrillation Efficacy at Implantation of ICDs

The upper limit of vulnerability (ULV) is the weakest shock strength at or above which ventricular fibrillation (VF) is not induced when the shock is delivered during the vulnerable period. The ULV, a measurement made in regular rhythm, provides an estimate of the minimum shock strength required for reliable defibrillation that is as accurate or more accurate than the defibrillation threshold (DFT). The ULV hypothesis of defibrillation postulates a mechanistic relationship between the ULV—measured during regular rhythm—and the minimum shock strength that defibrillates reliably. Vulnerability testing can be applied at implantable cardioverter defibrillator (ICD) implant to confirm a clinically adequate defibrillation safety margin without inducing VF in 75%–95% of ICD recipients. Alternatively, the ULV provides an accurate patient‐specific safety margin with a single fibrillation–defibrillation episode. Programming first ICD shocks based on patient‐specific measurements of ULV rather than programming routinely to maximum output shortens charge time and may reduce the probability of syncope as ICDs age and charge times increase. Because the ULV is more reproducible than the DFT, it provides greater statistical power for clinical research with fewer episodes of VF. Limited evidence suggests that vulnerability testing is safer than conventional defibrillation testing.

Electrophysiological characteristics of focal atrial tachycardia surrounding the aortic coronary cusps.

Background— Catheter ablation of atrial tachycardia (AT) arising near the coronary cusps has been reported in limited numbers of patients. We investigated the electrophysiological characteristics of these ATs in 22 consecutive patients. Methods and Results— This study included 22 patients (mean age±SD, 53±11 years; 86% female) with ATs arising near the aortic coronary cusps who underwent successful ablation. Activation mapping was performed during tachycardia to identify the earliest activation site. All patients achieved successful ablation through either a retrograde aortic (n=19) or a transseptal (n=3) approach. The successful ablation sites were located in the noncoronary cusp (NCC) (n=16), including 3 near the junction between the NCC and right coronary cusp. The remaining 6 cases were ablated from the left coronary cusp (LCC) (n=3) or the left atrium posterior to the LCC (n=3). For most tachycardias, there were distinctive P-wave morphological features recorded for each cusp location. Furthermore, analysis of the electrogram morphological features recorded during tachycardia at successful ablation sites revealed an atrial/ventricular (A/V) ratio >1 in 14 of 16 NCC ATs; the remaining 2, from the NCC near the junction with the right coronary cusp, showed an A/V ratio ⩽1. At ablation sites in the LCC, the A/V ratio was <1 (4 of 6 patients) or 1 (remaining 2 patients). During a follow-up duration of 30±13 months, all patients were free of arrhythmias without antiarrhythmic drugs. Conclusions— ATs surrounding the aortic coronary cusps can be safely and effectively ablated, with good long-term outcomes. In addition to the P-wave morphological features, the A/V ratio of the local electrogram recording during tachycardia facilitated the localization of successful sites.

Correlation of Scar in Cardiac MRI and High‐Resolution Contact Mapping of Left Ventricle in a Chronic Infarct Model

Endocardial mapping for scars and abnormal electrograms forms the most essential component of ventricular tachycardia ablation. The utility of ultra‐high resolution mapping of ventricular scar was assessed using a multielectrode contact mapping system in a chronic canine infarct model.

Macroreentrant Loop in Ventricular Tachycardia From the Left Posterior Fascicle: New Implications for Mapping and Ablation

Background—The underlying mechanisms of reentry during left posterior fascicular ventricular tachycardia (LPF-VT) remain unclear. The purpose of this study is to describe the components of LPF-VT reentry circuit and their electrophysiological properties. Methods and Results—Fourteen consecutive patients with LPF-VT underwent electrophysiology study and radiofrequency ablation. Via a multipolar electrode catheter placed from a retrograde aortic approach, a sharp inflection, high-frequency potential (P1) was detected in 9 patients (64%). The ranges of length and velocity of recorded P1 were 9 to 30 mm and 0.5 to 1.2 mm/ms, respectively. Macroreentry involving the ventricular myocardium was confirmed to be the mechanism in all patients by premature ventricular stimuli delivery or entrainment of LPF-VT with progressive fusion, or both. During LPF-VT, the earliest left posterior fascicle (LPF, P2) was considered to be the site of connection between P1 and P2, and the site of the earliest P2 along the left posterior ventricular septum correlated well with the His-ventricular interval during tachycardia. Radiofrequency ablation focused on the P1 potentials (9 patients with a recorded P1) or earliest P2 (5 patients without a recorded P1) was successful in all 14 patients. After 4.5±3.0 months of follow-up, no patients had recurrence of LPF-VT. Conclusions—The LPF-VT macroreentrant loop involves the ventricular myocardium, a part of the LPF, a slow conduction zone, and in certain cases, a specially conducting P1 fiber. The His-ventricular interval during LPF-VT correlates with multiple electrophysiological measures and is a useful marker for identification of the optimal ablation site.

Spectrum of issues detected by an ICD diagnostic alert that utilizes far-field electrograms: Clinical implications

BACKGROUNDnImplantable cardioverter-defibrillator (ICD) lead failure is one of the major causes of inappropriate shocks. Algorithms have been developed by manufacturers to identify ICD lead failure and avoid inappropriate shocks. The SecureSense RV Lead Noise Discrimination (St Jude Medical, St Paul, MN) algorithm is designed to differentiate oversensing due to lead failure from ventricular arrhythmias and withhold inappropriate therapies. Several non-lead failure-related issues can trigger the SecureSense automated algorithm.nnnOBJECTIVEnOur objective was to explain the SecureSense algorithm in a detailed fashion, highlighting examples of SecureSense alerts triggered by non-lead failure-related issues.nnnMETHODSnThis is a nonrandomized observational case series. SecureSense-triggered alerts from 3 ICD device clinics were analyzed, and representative examples of SecureSense triggers due to non-lead failure-related issues were chosen to explain the function and malfunction of this algorithm.nnnRESULTSnThe series includes 8 cases of SecureSense alerts triggered by non-lead failure-related issues---myopotential oversensing (1), P-wave oversensing (1), T-wave oversensing (1), loss of capture (1), R-wave undersensing (1), timing cycle issues (2), and cross talk (1)---and 1 case of failure of the algorithm to appropriately identify lead failure and prevent ICD shocks.nnnCONCLUSIONnLead failure detection algorithms such as the one assessed in this study have an inherent risk of false-positive and false-negative detections. The latter might have fatal consequences. The true accuracy of these algorithms needs to be evaluated in large-scale real-life prospective clinical studies.

Automatic Determination of Timing Intervals for Upper Limit of Vulnerability Using ICD Electrograms

Background: Implantable cardioverter defibrillator (ICD) implant testing based on the upper limit of vulnerability, or vulnerability testing, permits assessment of defibrillation safety margins without inducing ventricular fibrillation (VF) in most patients. Vulnerability testing requires that T‐wave shocks be timed at the most vulnerable intervals of the cardiac cycle, defined as intervals at which the strongest shock induces VF. Our goal was to develop and test an automated method to select these timing intervals using ICD intracardiac electrograms (EGMs).

Atrioventricular block during slow pathway ablation: entirely preventable?

Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common regular supraventricular tachycardia. Slow pathway (SP) modification has evolved as the first-line treatment,1,2 with acute success rates of 95% to 98%. A sensitive sign for success of the procedure is observation of accelerated junctional rhythm (JR) during ablation.3 The serious complication of AV block (AVB) can occur, and affects ≈1% to 2.3% of patients during or after catheter ablation procedures.2,4 Some studies have demonstrated that loss of VA conduction during radiofrequency application predicts impending AVB during ablation.5,6 From this illustrative series of cases assembled from 4 large tertiary care centers during a period of 3 years, we analyze some possible reasons for occurrence of AVB, and suggest methods to prevent this complication during SP modification procedures.nnEditor’s Perspective see p 745 nnA 58-year-old woman with a history of paroxysmal supraventricular tachycardia was refractory to medical therapy and referred for ablation. The baseline AH and HV intervals were 80 and 50 ms, respectively. Atrial pacing at 600 ms demonstrated fast pathway conduction and jump to SP conduction with a single echo beat (Figure 1A, left). A narrow QRS tachycardia with the same retrograde conduction sequence was induced during isoproterenol infusion, by atrial programmed stimulation (Figure 1A, right), which was diagnosed as AVNRT with cycle length (CL) of 380 ms, AH of 280 ms, HV of 50 ms, and VA of 50ms. No further pacing maneuvers were performed during tachycardia and SP modification was performed guided by fluoroscopy with a power setting of 30 W, temperature 60°C and total duration of 35 s. During radiofrequency delivery, JR with 1:1 retrograde conduction was observed during radiofrequency application with a CL between 500 and 600 ms, and 4 beats of sinus rhythm with …

Intramural outflow tract ventricular tachycardia: anatomy, mapping, and ablation.

Idiopathic ventricular tachycardia (VT) originating from the outflow tract has been treated with a relatively high success rate by radiofrequency catheter ablation. However, a small percentage of failure in these patients may be because of an inaccessible site of origin from an intramural location. The region of the interventricular septum between the right (RVOT) and left ventricular outflow tracts (LVOT) can be mapped by using thinner multielectrode catheters advanced via the septal perforating venous tributaries of the great cardiac vein (GCV).1,2 The following case series is a description of these intramural VTs and the anatomic analysis in this region.nnSee Editor’s Perspective p 982nn### Case 1nnA 56-year-old man with a history of high-burden premature ventricular contractions (PVCs) that were refractory to medical therapy underwent catheter ablation. The morphology of the PVC by ECG showed a rS wave with S wave notch at lead I and a rS wave in V1 (Figure 1A). The earliest ventricular activation timing at the RVOT was −19 ms. Mapping of the GCV and vein tributaries was then performed using a 3.5-mm irrigated ablation catheter guided by venography (Figure 1B). The GCV and lateral veins of the GCV were mapped with no optimal early ventricular activation located. However, the earliest activation was located at a septal perforating branch (SPB) vein of the GCV with a timing of −39 ms. Pace mapping at the target area completely matched with the clinical PVC. Ablation was performed at the earliest SPB vein site using an irrigated catheter with 15 W and an infusion rate of 17 mL/min with impedance …

Catheter Ablation of Idiopathic Left Posterior Fascicular Ventricular Tachycardia: Predicting the Site of Origin via Mapping and Electrocardiography

Background: We report the 12-lead ECG morphology of left posterior fascicular ventricular tachycardia (LPF-VT) and the relationship between His-ventricular (HV) interval and site of origin in LPF-VT. Methods and Results: We studied 41 patients who underwent successful catheter ablation of LPF-VT with HV interval >0 ms (n=8; proximal-LPF group), HV interval 0 to −15 ms (n=15; middle-LPF group), and HV interval <–15 ms (n=18; distal-LPF group). The earliest mapped presystolic potential (PP)-QRS interval was 34.1±4.2, 24.5±3.2, and 19.4±2.8 ms in proximal-, middle-, and distal-LPF groups. The earliest PP ratio (PP-QRS interval during VT/HV interval during sinus rhythm) was 0.59±0.05, 0.45±0.07, and 0.31±0.05 in the proximal-, middle-, and distal-LPF groups. There were statistically significant differences between the 3 groups in earliest PP ratio, and there was close correlation between the HV interval during LPF-VT and earliest PP ratio. The QRS duration in the proximal-LPF group (114±6 ms) was significantly narrower compared with the middle-LPF group (128±5 ms) and distal-LPF group (140±6 ms). In leads I and V6, the ratio of R/S tended to be greater in the proximal-LPF group compared with the other 2 groups. QRS duration, the ratio of R/S in leads V6, and lead I could predict a proximal or distal origin site of LPF-VT with high sensitivity and specificity. Conclusion: The HV interval and 12-lead ECG morphology of LPF-VT may help predict the successful site of origin and prove useful in guiding an effective ablation strategy.

Mechanisms of Posterior Fascicular Tachycardia: The Relationship Between High Frequency Potentials and the Ventricular Myocardium

### Case 1nnA 17-year-old man presented with a history of palpitations and surface ECG demonstrating wide QRS tachycardia (QRS duration=140 ms) with a right bundle branch block pattern and left-axis deviation (Figure 1A). The 12-lead ECG was normal during sinus rhythm.nnnnFigure 1. nA , Surface ECG of tachycardia showed wide QRS complex (QRS duration=140 ms) with a right bundle branch block pattern and left-axis deviation. B , During sinus rhythm (left), A–H and H–V intervals were 57 and 55 ms, respectively. P2 was recorded with an antegrade conduction sequence from proximal to distal multielectrode catheter (MEC). The ventricular potentials at the mid MEC were earlier than proximal and distal ventricular potentials. During tachycardia (right), the H–V interval was −30 ms. P1 and P2 were recorded with opposite conduction sequences with P1 activated antegradely, and P2 activated retrogradely. P1 transition to P2 activation occurred toward the distal MEC. C , Right and left anterior oblique fluoroscopic images of catheter positions. The 20 pole MEC was positioned at the left septal ventricle via a retrograde aortic approach. CS indicates coronary sinus electrogram; HIS, His bundle electrogram; His, His bundle; LAF, left anterior fascicle; LAO, left anterior oblique; LPF, left posterior fascicle; LV, left ventricular electrogram; RAO, right anterior oblique; RB, right bundle; and RV, right ventricular electrogram.nnnnSee Editor’s Perspective by Asirvatham and Stevenson nnDuring electrophysiology study, mapping was performed using a 20 pole multielectrode catheter (MEC) via a retrograde aortic approach (Figure 1C). The baseline A–H and H–V intervals were 57 and 55 ms, respectively (Figure 1B, left). A wide QRS tachycardia identical to the clinical tachycardia was observed with cycle length of 320 ms, H–V interval of −30 ms (Figure 1B, right). This was consistent with a diagnosis of …