The effect of dofetilide on ventricular defibrillation thresholds.

INTRODUCTION: High defibrillation threshold (DFT) with an inadequate defibrillation safety margin remains an infrequent but troubling problem associated with defibrillator implantation. Dofetilide is a selective class III antiarrhythmic drug that reduces DFTs in a canine model. We hypothesized that dofetilide would reduce DFTs in humans, obviating the need for complex lead systems. METHODS AND RESULTS: Sixteen consecutive patients with DFTs > or =20 J delivered energy at implant-received dofetilide therapy and underwent follow-up DFT testing acutely following drug loading and/or chronically (128 +/- 94 days). Amiodarone was discontinued in four patients at implantation. With dofetilide, DFTs decreased from 28 +/- 4 J to 19 +/- 7 J (P < 0.0001), resulting in a safety margin of 15 +/- 8 J for the implanted devices. Five patients subsequently had spontaneous arrhythmias terminated successfully with shocks. CONCLUSION: Dofetilide reduces DFTs sufficiently to prevent the need for more complex lead systems. This strategy should be considered when an inadequate defibrillation safety margin is present.

Sustained ventricular tachycardia following alcohol septal ablation for hypertrophic obstructive cardiomyopathy.

A 49-year-old man with a history of hypertrophic obstructive cardiomyopathy (HOCM) presented in sustained monomorphic ventricular tachycardia (SMVT) 8 days post-alcohol septal ablation. A dual chamber implantable cardioverter defibrillator ICD was implanted and the patient experienced another episode of VT 3 weeks later, which was terminated by an ICD shock. This case demonstrates probable scar-induced reentrant VT post-alcohol septal ablation, a likely rare but hypothesized complication of this procedure.

Electroanatomic mapping of the right atrium with a right atrial basket catheter and three-dimensional intracardiac echocardiography.

The ablation of arrhythmias progresses towards an approach based upon application of linear lesions between nonconducting anatomic/electrical areas. Hence the identification of detailed anatomy together with electrical behavior becomes increasingly important. This study aims to achieve true electroanatomic mapping by the use of three-dimensional intracardiac imaging of the right atrium combined with use of a right atrial basket to obtain detailed electrical information. We studied nine patients, seven requiring atrial flutter ablation. A 9 Fr, 9 MHZ intracardiac echo catheter was pulled back from SVC to IVC using respiratory and ECG gating. The images, recorded on a Clearview ultrasound machine, were reconstructed using commercially available software. The intracardiac basket was placed into the atrium using the markers and fluoroscopy to allow orientation. Isochronal maps were obtained from the basket in sinus rhythm, pacing from different sites within the atrium and in atrial flutter. Isochronal maps were constructed and superimposed on the ICE image. The maps with pacing were consistent with that which was expected, confirming the validity of this approach. We were able to visualize changes in activation sequence following the placement of bidirectional isthmus block. True electroanatomic mapping is possible by the use of three-dimensional ICE reconstruction of the right atrium with electrical activation obtained from an intracardiac basket. This has significance for anatomically based arrhythmia ablations such as the ablation of atrial flutter, atrial fibrillation, with transcatheter MAZE procedures and pulmonary vein isolation. Further developments in software will allow such maps to be produced simultaneously with greater rapidity.

Occurrence of atrial fibrillation after flutter ablation: the significance of intra-atrial conduction and atrial vulnerability.

Atrial vulnerability and intra-atrial conduction delay are important substrates for paroxysmal atrial fibrillation (AFib); however, their significance is unknown in patients undergoing atrial flutter ablation. Antegrade (high right atrium to coronary sinus: HRA-CS) and retrograde (CS-HRA) intra-atrial conduction times and AFib inducibility were assessed in 61 patients undergoing ablation for type I atrial flutter. Twenty-three patients had structural heart disease and 18 AFib before the procedure. After 16 +/- 12 months of follow-up 17 patients experienced AFib, 5 of which progressed into chronic AFib. During the study, AFib was easily inducible in 14 patients, 7 of which developed AFib (P =.03). Patients with post- ablation AFib were older (59 +/- 11 vs. 44 +/- 15 years, P =.001), had longer intra-atrial conduction times before (98 +/- 17 ms vs. 68 +/- 20 ms, P <.001) and after ablation (91 +/- 19 ms vs. 73 +/- 21 ms, P =.01) than those without AFib. Discriminant analysis revealed that only age, previous AFib and inta-atrial conduction delay (>90 ms) were independent predictors of postablation AFib. Patients without a history of AFib and with normal intra-atrial conduction had a 3% risk of AFib, while patients with both factors had a 90% risk of AFib after ablation. Intra-atrial conduction delay is an important electrophysiological factor predicting atrial fibrillation after successful flutter ablation.

A randomized prospective study of single coil versus dual coil defibrillation in patients with ventricular arrhythmias undergoing implantable cardioverter defibrillator therapy.

ICD implantation is standard therapy for malignant ventricular arrhythmias. The advantage of dual and single coil defibrillator leads in the successful conversion of arrhythmias is unclear. This study compared the effectiveness of dual versus single coil defibrillation leads. The study was a prospective, multicenter, randomized study comparing a dual with a single coil defibrillation system as part of an ICD using an active pectoral electrode. Seventy-six patients (64 men, 12 women; age 61 +/- 11 years) were implanted with a dual (group 1, n = 38) or single coil lead system (group 2,n = 38). The patients represented a typical ICD cohort: 60% presented with ischemic cardiomyopathy as their primary cardiac disease, the mean left ventricular ejection fraction was 0.406 +/- 0.158. The primary tachyarrhythmia was monomorphic ventricular tachyarrhythmia in 52.6% patients and ventricular fibrillation in 38.4%. There was no significant difference in terms of P and R wave amplitudes, pacing thresholds, and lead impedance at implantation and follow-up in the two groups. There was similarly no difference in terms of defibrillation thresholds (DFT) at implantation. Patients in group 1 had an average DFT of 10.2 +/- 5.2 J compared to 10.3 +/- 4.1 J in Group 2, P = NS. This study demonstrates no significant advantage of a dual coil lead system over a single coil system in terms of lead values and defibrillation thresholds. This may have important bearing on the choice of lead systems when implanting ICDs.

Coronary ischemia induced by radiofrequency ablation in the left atrium.

INTRODUCTION: We report three cases of transient, reversible coronary ischemia occurring after radiofrequency ablation in the left atrium. METHODS AND RESULTS: A 56-year-old man with a left atrial tachycardia that was mapped to the septum and roof of the atrium using a noncontact mapping developed 5-mm ST elevation in the anterolateral leads. Coronary angiography showed an occluded diagonal that was opened using intracoronary nitrate, which led to resolution of the ST changes. A 57-year-old man undergoing right upper pulmonary vein ablation developed 6-mm ST elevation in leads V1-V4, II, III, and aVF. Coronary angiography showed normal coronaries with slow flow into the left anterior descending artery, which resolved with nitrates. A 50-year-old man undergoing left lower pulmonary vein ablation developed 3-mm reversible inferior ST elevation. All patients were adequately anticoagulated after transseptal access to the left atrium. CONCLUSION: Ablation in the left atrium, at the roof, septum, and left inferior wall, can cause transient coronary ischemia, possibly due to spasm, which can be reversed with intracoronary nitrates. This phenomenon has not been previously described.

Can we predict which patients with implantable cardioverter defibrillators receive appropriate shock therapy? A study of 155 patients.

BACKGROUND: Appropriate shock therapy (AST) occurs in the minority of patients with implantable cardioverter defibrillators (ICDs). We assessed which patients received AST and whether there were any predictive factors. METHODS: We retrospectively analysed data from 155 patients implanted with ICDs at our institution from a period from February 1984 to February 2001. Stored electrogram data were analysed. We sub-divided patients on the basis of underlying cardiac disease. Various clinical echocardiographic and electrophysiological variables were studied. RESULTS: AST occurred in 53 (34%) of patients (Group 1) and no AST in 102 (64%) of patients (Group 2). Impaired LV function was significantly associated with AST. Group 1 patients had a lower ejection fraction (EF) compared to Group 2 (37.5+/-13% vs. 47.8+/-14%, P<0.0001). Seventy-two percent of patients with AST had an EF <40% vs. 35% of patients in Group 2 (P<0.0001). NYHA Class was also associated with AST, 42% of Group 1 were in NYHA Class III/IV vs. 12% in Group 2 (P<0.001). Programmed electrical stimulation (PES) was a predictor of AST. PES was positive in a greater proportion of patients in Group 1 vs. 2 (88% vs. 64%, P<0.0006). Sub-group analysis showed that patients with dilated cardiomyopathy (DCM) had a high incidence of AST (80%). In these patients PES was a poor predictor of AST being positive in only 25%. CONCLUSION: AST occurs in the minority of our patients. Certain pre-procedural variables predict AST. PES does not appear useful in predicting shock therapy in DCM patients and a negative PES should not preclude ICD implantation in this group.