Ali A. Mehdirad

Electrophysiologic characteristics of accessory atrioventricular connections in an inherited form of Wolff-Parkinson-White syndrome.

EP Characteristics in Familial WPW. Introduction: A familial form of Wolff‐Parkinson‐White syndrome (WPW) occurs in association with hypertrophic cardiomyopathy and intraventricular conduction ahnormalities. This syndrome, demonstrating autosomal dominant inheritance and segregating with a high degree of penetrance but variable expressivity, has been genetically linked to chromosome 7q3. The purpose of this study is to detail the electrophysiologic characteristics of accessory atrioventricular connections (AC) in four members of a kindred with this syndrome.

Temperature Controlled RF Ablation in Canine Ventricle and Coronary Sinus using 7 Fr or 5 Fr Ablation Electrodes

The safety and lesion volume of temperature controlled radiofrequency ablation (TCRFA) in the right ventricle (RV), left ventricle (LV), and coronary sinus (CS) comparing long 5 Fr to standard tip electrodes have not been previously reported In 1O canines, TCRFA was delivered at a 70°C set point for 30 seconds. Lateral and septal RV lesions were made with either a 5 Fr/5 mm or 7 Fr/4 mm tip. Lateral and septal LV lesions were made with either a 5 Fr/7 mm or 7 Fr/4 mm tip. Proximal and distal CS lesions were made with either a 7 Fr/4 mm, 5 Fr/5 mm or 5 Fr/7 mm tip. Gross and histologic examination of the lesions was completed. Lesion size, tip temperature and power required are related to electrode surface area (SA) when ablating in the RV, LV or CS. 5 Fr/7 mm tips (SA = 36 mm2) tended to create larger lesions than 7 Fr/4 mm tips (SA = 29 mm2) in the LV. 7 Fr4 mm tips tended to create larger lesions than 5 Fr/5 mm tips (SA ‐ 26 mm2) in the RV. 7 Fr/4 mm LV lesions exceeded 7 Fr/4 mm RV lesions due to thicker LV walls. In the CS, 5 Fr/7 mm tips tended to create the largest lesions. In the RV, LV and CS, tips with larger SA tended to have lower temperatures and require higher power. No high temperature or high impedance shutdowns were observed. In conclusion, varying 5 Fr tip length can safely produce larger or smaller lesions compared to those created with 7 Fr/4 mm tips.

Clinical characteristics of sudden death victims in heritable (chromosome 1p1-1q1) conduction and myocardial disease

OBJECTIVES The purpose of this study was to identify the clinical characteristics of family members at risk of sudden death. BACKGROUND The significance of sudden death in heritable cardiac disorders with delayed expression is incompletely understood. Additional insights come from a four-decade experience of seven generations of a family of German origin with autosomal dominant (chromosome 1p1-1q1) cardiac conduction and myocardial disease. METHODS AND RESULTS A total of 38 family members (20 males; 18 females) were identified with sudden death. Twenty-eight family members (mean age 48+/-8 years) from earlier generations had no pacemaker at the time of sudden death. In this group, 15 subjects were asymptomatic prior to sudden death. Ten family members with sudden death, from later generations, had chronically implanted pacemakers for high grade atrioventricular block. This group was older (mean age 57+/-2 years), with decreased functional status (New York Heart Association class II to IV), enlarged left atria, dilated left ventricles with reduced systolic function and documented ventricular fibrillation in three members. Twenty-eight family members with sudden death were descendants of sib lineages 2 or 6; 21 family members with sudden death were offspring of a parent who also suffered sudden death. CONCLUSION Sudden death is an important late outcome in heritable (chromosome 1p1-1q1) cardiac conduction and myocardial disease. Pacemaker therapy is important for the treatment of symptomatic bradycardia, but it does not prevent sudden death. Family members who are beyond the third decade of life with reduced functional capacity, left ventricular dysfunction, pacemakers and who are the offspring of a parent with sudden death appear to be at greatest risk

Drug and defibrillator interactions

We reviewed the interactions of drugs and defibrillators, with emphasis on implantable cardioverter defibrillators. Articles were identified by searching MEDLINE from 1966 to the present; additional sources were identified from reference lists in these articles. Drugs have the potential for both beneficial and harmful interactions with electrical therapy. Beneficial interactions include reductions in the energy required to defibrillate the heart and in the occurrence of arrhythmia resulting in decreased shock frequency, prolonged device longevity, and improved patient comfort. Potentially harmful interactions include altering the detection of ventricular tachycardia; altering the pacing threshold, resulting in interference with bradycardia or anti‐tachycardia pacing; development of incessant ventricular tachycardia; and increasing the energy required to defibrillate the heart. As the use of implantable cardioverter defibrillators increases, pharmacists should be aware of the potential for drug‐device interactions.

Improved Clinical Efficacy of External Cardioversion by Fluoroscopic Electrode Positioning and Comparison to Internal Cardioversion in Patients with Atrial Fibrillation

Background: Despite using different electrode positions, “conventional” external DC cardioversion in patients with atrial fibrillation is ineffective in 6%–50% of cases. An alternative when DC cardioversion is not successful is low energy internal cardioversion, which is performed at increased risk. We tested the hypothesis that optimization of electrode pad position under fluoroscopy to encompass as much atrial muscle as possible might improve the success rate of external cardioversion and thus minimize the need for internal cardioversion. Methods: Fifteen (9 males, 6 females) patients (age: 54 ± 15 years, weight: 124 ± 35 kg) with chronic atrial fibrillation (> 8 weeks) who had undergone unsuccessful conventional external cardioversion entered the study. Repeat conventional external cardioversion with electrodes in standard (right anterior and left posterior) positions was followed by “optimized” external cardioversion by positioning electrodes under fluoroscopy (using metallic markers). In case of failure, internal cardioversion was performed. Results: All 15 patients had undergone unsuccessful conventional external cardioversion with 360‐J shocks. Eight patients (group A) reverted to sinus rhythm with one or two 360‐J shocks using fluoroscopy‐guided pad placement (53%). Six of the remaining 7 (86%) patients (group B) had successful internal cardioversion with biphasic shocks (12 ± 3 J). The body weight and body mass index were statistically lower in group A vs group B (106 ± 27 vs 145 ± 33 kg, p = 0.03 and 35 ± 8 vs 45 ± 8 kg/m2, P = 0.48, respectively). There was no statistically significant in age, height, body surface area, duration of atrial fibrillation, amiodarone therapy, ejection fraction, or underlying heart disease. Conclusion: Unsuccessful external DC cardioversion, in some patients, is in part due to suboptimal conventional positioning of electrode pads that can be improved under fluoroscopic guidance by achieving the best possible vector encompassing the right and left atria. The optimized external cardioversion technique may minimize the need for internal cardioversion, which remains an effective approach when external cardioversion fails.

Implantable Defibrillators Impedance Measurement Using Pacing Pulses Versus Shock Delivery with Intact and Modified High Voltage Lead System

At present the only method for measuring the high voltage system lead impedance in patients with an ICD is to deliver a low energy test shock. This is painful, requires sedation, and carries a risk of ventricular fibrillation induction. We sought to assess the shock lead and electrode function by calculating IMP using low voltage pacing pulses, and compared it to the measured impedance of a shock through the same lead. This was performed in both an intact and a modified lead system in order to mimic common clinical scenarios that alter lead system IMP (e.g., lead fracture). In an anesthesized canine model (n = 12) a standard (S) transvenous defibrillation lead (TDL), a modified (M) TDL (two‐thirds of coil covered with heat‐shrunk tubing), an active can (AC), and a M epicardial patch (EP) (two of four coils were disconnected) were used. Three configurations (C) were tested: C1: S/TDL→AC;, C2: M/TDL→AC;, and C3: M/TDL→MEP. A measured IMP was obtained by an ICD using a 5‐J shock as control. IMP was calculated using a 5‐J shock, pacing pulses of 10‐, 5‐, 2‐, and 1‐V amplitude, as well as from a square wave drive train of low amplitude/high frequency signals (1 and 0.2 V, at 10 kHz) in all Cs. Ohms law (V = IR) was utilized for measuring calculated IMP. As the surface area of the high voltage lead system decreased, the mean measured IMP (control) increased from C 1 to 3 (63 ± 10, 95 ± 4, and 127 ± 20 Ω, respectively). The correlation of calculated IMP from all Cs to measured impedance (control) remained high throughout the IMP range (range of correlation coefficient (r): 0.921–0.981). Calculated IMP using delivery of pacing pulses is highly correlated to IMP measured during shock delivery. This correlation remains high over a clinically significant range of high voltage lead system IMP changes. This study suggests that pacing pulses can be used to predict the IMP changes in the high voltage lead system which may occur clinically, reducing the need to deliver a shock for IMP measurement.

ALTERNATING CURRENT ELECTROCUTION DETECTION AND TERMINATION BY AN IMPLANTABLE CARDIOVERTER DEFIBRILLATOR

A patient with an ICD accidentally grasped a power line and was electrocuted. He was unable to release the cable during electrocution though he remained conscious. After receiving a shock from his ICD. the powerline was released. ICD interrogation revealed inappropriate detection of alternating current and delivery of a shock.

The Influence of Specific and Nonspecific Potassium Current Blockade on the Defibrillation Energy Requirement of Biphasic Shock

Block of delayed rectifier potassium current (IK) is known to decrease defibrillation energy requirements (DERs). We tested the hypothesis that there would be no difference in DER reduction with a nonspecific IK (IKr+ IKS) blocker, ambasilide, and a specific IKr blocker, dofetilide. Methods: An anesthetized canine model (n = 30) of internal transvenous defibrillation with biphasic shocks was used. Ambasilide (n = 9; dose: 4.8 mg/kg, then 9.6 mg/kg/hour), dofetilide (n = 10; dose: 10 (μg/kg, then 3.6 (μg/kg/hour), or matched placebo (n = 11) were administered. DERs (J) were determined in triplicate using an increment‐decrement protocol at baseline and during each treatment. ECG intervals were measured at baseline and during each treatment. ANOVA with post‐hoc Bonferroni test was used for statistical analysis. Results: Ambasilide resulted in a +23.5 ± 4.06% prolongation of the QTc interval, while dofetilide resulted in a +20.5%± 3.76% prolongation of the QTc interval. Thus, the two drugs resulted in comparable prolongation of the QTc interval (P < 0.05 compared to placebo). Both drugs significantly reduced the DER (‐17.7%± 5.33% reduction by ambasilide, and ‐21.9%± 5.21% reduction by dofetilide, P < 0.05 compared to placebo). There was no difference in the magnitude of DER reduction between the two treatments. Conclusions: Administration of equipotent doses (as indicated by QTc changes) of ambasilide or dofetilide had comparable effects on DERs. Selectivity of IK blockade has no significant effect on the magnitude of reduction in DERs.

Preliminary clinical results of a biphasic waveform and an RV lead system.

Biphasic defibrillation waveforms have provided a reduction in defibrillation thresholds in transvenous ICD systems. Although a variety of biphasic waveforms have been tested, the optimal pulse durations and tilts have yet to be identified. A multicenter clinical study was conducted to evaluate the performance of a new ICD biphasic waveform and new RV active fixation steroid eluting lead system. Fifty‐three patients were entered into the study. Mean age was 63 years with a mean ejection fraction of 36.8%. Primary indication for implantation was monomorphic ventricular tachycardia alone (54.7%). Forty‐eight patients (90.6%) were implanted with an RV shocking lead and active can alone as the anodal contact. The ICD can was the cathode. In four cases (7.5%), an additional SVC or CS had was used due to a high DFT with the RV lead alone. In an additional case, a chronic SVC lead was used although the RV‐Can DFT was acceptable. DFT for all cases at implant was 9.8 ± 3.7 J. Repeat testing at 3 months for a subset of patients showed a reduction in DFT (7.4 ± 3.0 J), P value = 0.03. Sensing and pacing characteristics of the RV lead system remained excellent during the study period (acute 0.047 ± 0.005 ms at 5.4 V and 9.9 ± 6.2 mV R wave; chronic 0.067 ± 0.11 ms at 5.4 V and 9.3 ± 5.4 mV R wave). It is concluded that this lead system provides good acute and chronic sensing and pacing characteristics with good DFT values in combination with this waveform.

Retrograde migration of the site of functional block: a mechanism underlying resolution of functional retrograde bundle branch block during AV reentrant tachycardia.

Retrograde Migration of Functional Block. Introduction: Functional bundle branch blocks during supraventricular tachycardia have been described, and their sustainment has been attributed to concealed conduction. Such blocks frequently resolve spontaneously, but the electrophysiologic mechanism of resolution bas not been well described. This report describes the resolution of functional bundle branch block through proximal migration of the site of block.