Peter Kabunga

Subclavian vein pacing and venous pressure waveform measurement for phrenic nerve monitoring during cryoballoon ablation of atrial fibrillation

AIMS The phrenic nerves may be damaged during catheter ablation of atrial fibrillation. Phrenic nerve function is routinely monitored during ablation by stimulating the right phrenic nerve from a site in the superior vena cava (SVC) and manually assessing the strength of diaphragmatic contraction. However the optimal stimulation site, method of assessing diaphragmatic contraction, and techniques for monitoring the left phrenic nerve have not been established. We assessed novel techniques to monitor phrenic nerve function during cryoablation procedures. METHODS AND RESULTS Pacing threshold and stability of phrenic nerve capture were assessed when pacing from the SVC, left and right subclavian veins. Femoral venous pressure waveforms were used to monitor the strength of diaphragmatic contraction. Stable capture of the left phrenic nerve by stimulation in the left subclavian vein was achieved in 96 of 100 patients, with a median capture threshold of 2.5 mA [inter-quartile range (IQR) 1.4-5.0 mA]. Stimulation of the right phrenic nerve from the subclavian vein was superior to stimulation from the SVC with lower pacing thresholds (1.8 mA IQR 1.4-3.3 vs. 6.0 mA IQR 3.4-8.0, P < 0.001). Venous pressure waveforms were obtained in all patients and attenuation of the waveform was always observed prior to onset of phrenic nerve palsy. CONCLUSION The left phrenic nerve can be stimulated from the left subclavian vein. The subclavian veins are the optimal sites for phrenic nerve stimulation. Monitoring the femoral venous pressure waveform is a novel technique for detecting impending phrenic nerve damage.

Systematic review of cardiac electrical disease in Kearns-Sayre syndrome and mitochondrial cytopathy.

Kearns-Sayre syndrome (KSS) is a mitochondrial disorder characterised by onset before the age of 20years, progressive external ophthalmoplegia, and pigmentary retinopathy, accompanied by either cardiac conduction defects, elevated cerebrospinal fluid protein or cerebellar ataxia. 50% of patients with KSS develop cardiac complications. The most common cardiac manifestation is conduction disease which may progress to complete atrioventricular block or bradycardia-related polymorphic ventricular tachycardia (PMVT). The management of cardiac electrical disease associated with KSS and mitochondrial cytopathy is systematically reviewed including the case of a 23year-old female patient with KSS who developed a constellation of cardiac arrhythmias including rapidly progressive conduction system disease and monomorphic ventricular tachycardia with myocardial scarring. The emerging role of cardiac magnetic resonance imaging (CMR) in detecting subclinical cardiac involvement is also highlighted. This review illustrates the need for cardiologists to be informed about this rare but emerging condition.

Systematic Review of Defibrillation Threshold Testing at De Novo Implantation

Background—Recent results from the largest multicenter randomized trial (Shockless IMPLant Evaluation [SIMPLE]) on defibrillation threshold (DFT) testing suggest that while shock testing seems safe, it does not reduce the risk of failed shocks or prolong survival. A contemporary systematic review of DFT versus no-DFT testing at the time of implantable cardioverter–defibrillator implantation was performed to evaluate the current evidence and to assess the impact of the SIMPLE study. Methods and Results—Electronic searches were performed using 6 databases from their inception to March 2014. Relevant studies investigating implant DFT were identified. Data were extracted and analyzed according to predefined clinical end points. Predefined outcomes for interrogation were all-cause mortality, composite end point of implantable cardioverter–defibrillator efficacy (arrhythmic deaths and ineffective shocks), and composite safety end point (the sum of complications recorded at 30 days). Meta-analysis was performed including 13 studies and 9740 patients. No significant differences between DFT versus no-DFT cohorts were found in terms of all-cause mortality (risk ratio, 0.90; 95% confidence interval, 0.71–1.15; P=0.41), composite efficacy outcome (risk ratio, 1.24; 95% confidence interval, 0.65–3.37; P=0.51), and 30-day postimplant complications (risk ratio, 1.18; 95% confidence interval, 0.87–1.60; P=0.29). No significant difference was found in the trends observed when the results of the SIMPLE study were excluded or included. Conclusions—This systematic review of contemporary data suggests a modest average effect of DFT, if any, in terms of mortality, shock efficacy, or safety. Therefore, DFT testing should no longer be compulsory during de novo implantation. However, DFT testing may still be clinically relevant in specific patient populations.

Defibrillator Threshold Testing at Generator Replacement: Is it Time to Abandon the Practice?

Rapid improvements in implantable cardioverter-defibrillator (ICD) technology in recent years have spurred the debate of whether defibrillation threshold (DFT) testing at the time of implantation is required.1–3 DFT testing was traditionally the gold standard for ensuring electrical integrity, reliable sensing, and reliable defibrillation by the ICD. However, there are concerns regarding the potential for serious adverse events related to DFT testing such as circulatory arrest,1 myocardial ischemia,4 refractory ventricular fibrillation (VF),27 respiratory depression, central nervous system hypoperfusion,25,26 and thromboembolism.5 Moreover, several cohort studies have reported no difference in clinical outcomes associated with routine DFT testing.1,6–8 This was confirmed in the recent Shockless IMPLant Evaluation (SIMPLE) trial.32 In light of these emerging data, routine DFT testing at the time of new ICD implants has been abandoned by many physicians.3,10 In parallel, there has been a growing reluctance among physicians to perform routine DFT at the time of ICD generator replacement.11 However, data regarding DFT testing during new ICD implants may not be directly applicable to generator replacement because chronically implanted ICD leads may develop integrity issues over time.12,13 Although several reports have cautioned against the abandonment of DFT testing during generator replacement,14–16 the issue has been sparingly addressed in the existing literature.

Loss of Biventricular Pacing During Exercise: What is the Mechanism?

Loss of Biventricular Pacing During Exercise: What Is the Mechanism? PETER KABUNGA, M.B.Ch.B., M.R.C.P.,∗ GEORGE J. KLEIN, M.D.,† EMILY HODKINSON, M.B.Ch.B., M.R.C.P.,∗ CHRIS SANDGREN, B.Sc.,‡ and RAYMOND W. SY, M.B.B.S., Ph.D.∗ From the ∗Department of Cardiology, Royal Prince Alfred Hospital, NSW, Australia; †University of Western Ontario, London, Ontario, Canada; and ‡Medtronic Technical Services Australasia, Sydney, NSW, Australia

Preferential conduction during focal atrial tachycardia arising from the noncoronary cusp

Ventricular arrhythmias arising from a single focus within the left ventricular outflow tract and aortic sinuses of Valsalva may exhibit different QRS morphologies owing to preferential conduction to multiple exits. We describe a case of an atrial tachycardia (AT) arising from the noncoronary aortic cusp (NCC) with different P-wave morphologies, presumably on the basis of preferential conduction.

Malignant Ventricular Arrhythmic Storm Triggered by Short-coupled Premature Ventricular Contractions Arising from the Anterolateral Papillary Muscle

Disclosure: Peter Kabunga, Caroline Medi, Laura Yeates and Raymond W Sy have nothing to disclose in relation to this article. No funding was received in the publication of this article. Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any noncommercial use, distribution, adaptation, and reproduction provided the original author(s) and source are given appropriate credit. Compliance with Ethics: All procedures were followed in accordance with the responsible committee on human experimentation and with the Helsinki Declaration of 1975 and subsequent revisions, and informed consent was received from the patient involved in this case study. Received: 22 February 2016 Accepted: 4 April 2016 Citation: European Journal of Arrhythmia & Electrophysiology, 2016;2(1):33–6 Correspondence: Raymond W Sy, Department of Cardiology, Royal Prince Alfred Hospital, Camperdown, New South Wales 2050, Australia. E: raymond.sy01@gmail.com