Electrophysiologic Spectrum of Atrioventricular Nodal Behavior in Patients with Atrioventricular Nodal Reentrant Tachycardia Undergoing Selective Fast or Slow Pathway Ablation

AV Nodal Behavior After Ablation. Introduction; The objective of this report is to delineate the atrioventricular (AV) nodal electrophysiologic behavior in patients undergoing fast or slow pathway ablation for control of their AV nodal reentrant tachycardia (AVNRT).
Methods and Results: One hundred sixteen consecutive patients with symptomatic AVNRT were included. Twenty-two patients underwent fast pathway ablation with complete abolition of AVNRT in all and development of complete AV block in five patients. Of 17 patients with intact AV conduction postablation, 12 had demonstrated antegrade dual pathway physiology during baseline study, which was maintained in three and lost in nine patients postablation. Two patients with successful fast pathway ablation developed uncommon AVNRT necessitating a slow pathway ablation. Twenty-one patients demonstrated both common and uncommon forms of AV nodal reentry during baseline study. The earliest site of atrial activation was close to the His-bundle recording site (anterior interatrial septum) during common variety and the coronary sinus ostium (posterior interatrial septum) during the uncommon AV nodal reentry in all 21 patients. Ninety-six patients underwent successful slow pathway ablation. Among these, the antegrade dual pathway physiology demonstrable during baseline study (60 patients) was maintained in 25 and lost in 35 patients postablation.
Conclusion: These data suggest that: (1) dual pathway physiology may persist after successful ablation, which might be a reflection of multiple reentrant pathways in patients with AVNRT: and (2) the retrograde pathways during common and uncommon AVNRT have anatomically separate atrial breakthroughs. These findings have important electrophysiologic implications regarding the prevailing concept of the AV nodal physiology in patients with AVNRT.     

Ventriculoatrial Conduction Time During Bundle Branch Reentrant Beat Initiating Orthodromic Tachycardia: A Simple and Reliable Method for Localization of Accessory Pathways

VA Interval Via Accessory Pathway During Bundle Branch Reentry. Bundle branch reentrant (BBR) complex is commonly induced during programmed ventricular stimulation with single ex-trastimulus. In patients with atrioventricular accessory pathway, BBR beat frequently triggers orthodromic tachycardia. This study was designed to determine whether evaluation of the ventriculoatrial conduction time during BBR (VA_BBR) induced with right ventricular extrastimulation (i.e., left bundle branch block morphology) can separate left free-wall (LFW) accessory pathways from left posteroseptal (LPS) or right-sided pathways. Thirty-eight patients with single atrioventricular accessory pathways were included. There were 28 men and 10 women with a mean age of 26 years. The accessory pathway was localized in LFW in 23 patients (group I) and LPS in seven (group ID. Eight patients (group III) had pathways located in the right side. In each patient, VA_BBR was determined and compared with the following: (1) V₂A₂ interval exclusively via accessory pathway; and (2) ventriculoatrial conduction time during orthodromic tachycardia with narrow QRS complex (VA_NQ), left bundle branch block plus normal axis (VA_LB-NA) or left axis (VA_LB-LA). In group I, VA_BBR values (170–245 msec, mean 196.1 ± 20.5 msec) were 0–25 msec longer than V₂A₂ (170–245 msec, mean 191.3 ± 19.1 msec) and 45–125 msec greater than VA_NQ (100–155 msec, mean 125.6 ± 14.1 msec). VA_BBR was identical to VA_LB-LA but 25–55 msec greater than VA,_LB-NA (140–205 msec, mean 160.9 ± 20.8 msec). In group II, VA_BBR values (100–140 msec, mean 118.6 ± 14.3 msec) were 15–30 msec shorter than V₂A₂ (125–165 msec, mean 140.7 ± 14.3 msec) and 15–25 msec longer than VA_NQ (85–120 msec, mean 100.7 ± 12.0 msec). Comparing VA_BBR with VA_LB-NA or VA_LB-LA did not show any statistically significant difference. In group III, VA_BBR values were consistently shorter than V₂A₂ and identical to VA_NQ. Thus, assessment of VA_BBR is a simple and useful method that can be reliably utilized to differentiate LFW pathways from LPS or right-sided pathways. Furthermore, these data provide new insights into the electrophysiological characteristics of bundle branch reentry. (J Cardiovasc Electrophysiol, Vol. 1, pp. 121–131, April 1990)     

Regression Equation Predicts Dietary Phosphorus Intake from Estimate of Dietary Protein Intake

Objective To develop a predictive equation for dietary phosphorus intake.

Design In this clinic-based, cross-sectional study, a dietitian-administered food frequency questionnaire provided dietary intake estimates for a population of patients with chronic renal failure. A prediction equation for dietary phosphorus intake was developed and was validated on another sample of patients with CRF from the same clinic.

Subjects Outpatients treated for chronic renal failure at the E. Wolfson Medical Center Institute of Nephrology in Holon, Israel, participated in the study (N=104, 73 men and 31 women, mean AGE=65.6 years). The validation sample consisted of 53 outpatients with chronic renal failure (38 men and 15 women, mean AGE=64.2 years) from the same clinic.

Main outcome measures Dietary variables (ie, energy, protein, carbohydrate, fat, phosphorus) were examined in terms of crude intake, as percentage of total energy intake, and per kilogram of body weight.

Statistical analyses performed Stepwise linear regression analysis and Student's t tests were used to examine relationships between dietary phosphorus and other variables. Results Dietary phosphorus (milligrams)=128+14 (protein intake [grams]) was the best-fitting equation and explained 84% of the variance in dietary phosphorus intake.

Applications The prediction equation for dietary phosphorus intake is especially useful for renal dietitians who calculate patient diets by hand. J Am Diet Assoc. 1996; 96:1268-1270.     

Complete Atrioventricular Block Induced by Methyldopa

We present two patients who developed complete heart block due to treatment with methyldopa. After discontinuing methyldopa, conduction disturbances completely disappeared and recurred upon rechallenge with the medication. It is assumed that methyldopa can impair the myocardial conduction system by its central sympatholytic effect. Conduction anomalies should be excluded prior to treatment with methyldopa, and during treatment with the medication, the patients should be routinely screened for the presence of conduction anomalies.     

Flecainide Toxicity: Reversal of Drug Effects by Isoproterenol Infusion

Partial Reversal of Flecainide Toxicity by Isoproterenol. Introduction : Toxic levels of flecainide can cause life-threatening electrophysiologic and hemodynamic changes. Isoproterenol is known to reverse therapeutic drug effects in patients with ventricular and supraventricular tachycardias. In a single cell preparation it appears that isoproterenol increases inward Na current and it is conceivable that isoproterenol may also be capable of decreasing the electrophysiologic effects of flecainide toxicity. This study was aimed at detailed characterization of the electrophysiologic changes induced by toxic levels of flecainide, the extent that isoproterenol may reverse these changes, and the effect of beta blockade on these changes. Methods and Results : In this experimental model, using the strength-interval stimulation method, conduction time, and epicardial activation times, we defined the changes in conduction, refractoriness, and excitability caused by toxic levels of flecainide (> 3 μg/mL), during infusions of flecainide and isoproterenol, and lastly, these infusions and propranolol. In nine dogs, using atrial and ventricular stimulation at pacing rates of 120 and 210 beats/min, atrioventricular conduction, right ventricular refractoriness, and conduction changes were evaluated at baseline and following isoproterenol infusion (0.09 μg/kg/min), flecainide infusion (4 mg/kg followed by 5 mg/kg/hr), flecainide combined with isoproterenol infusion, and lastly, flecainide, isoproterenol, and propranolol (0.2 mg/kg). Compared to baseline, toxic levels of flecainide (3.71-3.86 μg/mL) produced a 64% and 93% increase in the atrial-His interval at pacing rates of 120 and 210 beats/minute, respectively. Isoproterenol reversed 15% and 55% of this prolongation. The His-ventricular conduction was prolonged by 82% and 124% after flecainide at 120 and 210 beats/min, respectively. These changes were reversed by 29% and 53% with isoproterenol. With flecainide, the relative and effective refractory periods of the ventricular myocardium (during right ventricular pacing) were lengthened by 16% and 19%, respectively, and reversed to baseline values following isoproterenol. None of the ventricular electrophysiologic parameters altered by flecainide were significantly affected with increasing pacing rate. The QRS complex duration increased by 59% with flecainide, and isoproterenol reversed 30% of this increase. Left ventricular (LV) activation time during right ventricular (RV) pacing increased by 88% with flecainide, 59% of which was reversed by isoproterenol. Propranolol resulted in complete elimination of the isoproterenol-produced partial reversal of flecainide toxicity. RV diastolic pacing threshold was raised by 61% with flecainide, but this effect was not reversed with isoproterenol. Conclusion : It is concluded that at least 30% of the toxic effects of flecainide can be reversed by isoproterenol. Such reversal may be useful in treating flecainide toxicity. Pacing threshold, however, does not improve with isoproterenol, and all the isoproterenol effects are abolished by propranolol. The electrophysiologic effects of toxic levels of flecainide were further aggravated with the addition of propranolol.     

When Is it Safe not to Replace an Implantable Cardioverter Defibrillator Generator?

In most reports on patients receiving implantable cardioverter defibrillators. shocks were received mainly during the first 2 to 3 years. Thus, the question had been raised as to the need for device replacement after 3 or 4 years if no shocks had been received. In order to answer this question, shock experience in 184 putients receiving the implantable cardioverter defibrillator was analyzed. Patients were followed for a mean of 24 ± 18.7 months. A patient's shock was judged to be appropriate if there was electrocardio-graphic documentation of sustained ventricular tachyarrhythmia at the time of shock or if it was preceded by sudden onset of presyncopal or syncopal symptoms. The majority of patients had coronary artery disease. In approximately two-thirds of patients, left ventricular ejection fraction was below 40%. One hundred fourteen patients had inducible sustained monomorphic ventricular tachycardia. On follow-up, there were 29 deaths, five of which were sudden. Sixty-eight patients received an appropriate shock during follow-up (37%). Over 90% of these 68 received their first shock within the 2 years after implant. The actuarial risk of receiving an appropriate shock by the fifth year after implant was 69%. Conversely, 31% of patients who survived 5 years had not received an appropriate shock. Hazard analysis indicates that there is a high incidence of first appropriate shock during the year following implant. Subsequently, the incidence dropped to a relatively steady rate with a rise in this rate during the fifth year. This analysis suggested a bimodal distribution of appropriate shocks. The results indicate that implantable cardioverter defibrillator generators should be replaced even up to the fifth year despite the fact that a patient had not received an appropriate shock.     

The Anatomical Determinants for the Design of Intracardiac Mapping and Ablation Catheters

An important factor in the efficient and successful completion of the ablation procedure is the design characteristics of the mapping/ablation catheters. These procedures are often hampered by the inability to maneuver the catheter to the desired location, in part because the catheters only have a single plane deflection capability and are not designed for the specific cardiac anatomical structures that contain the arrhythmogenic substrate. Single and Biplane Deflectable Catheters: Using measurements taken from six normal human cadaver hearts, ablation catheter design characteristics are presented for posterior, posterior septal, lateral, and posterior lateral pathways for retrograde and transseptal approaches. Three catheter designs based on anatomical characteristics were also evaluated. Pigtail Catheter: This catheter adapts to the atrial side of the mitral ring and improves positioning and stability for mapping and ablation of left-sided accessory pathways. Loop Catheter: This catheter is positioned at the perivalvular tricuspid ring and provides simultaneous mapping and aNation capabilities without the need to move the catheter or the need for additional catheters. Rotating Tip Catheter: The tip of this catheter is made up of three elongated teeth, which were curved 120° apart into the rotating tip electrode. This electrode was designed to negotiate the surfaces of the atrial and intraventricular chambers. It is capable of discrete movements and has a large electrode-tissue contact area for the ablation of atrial and ventricular arrhythmias. Catheter designs presented in this article are based on the ability of the catheter to adapt to the anatomical location of the arrhythmogenic tissue as well as the maneuverability of the catheter's mapping and ablation elec-trodes. An anatomical approach to the design of ablation catheter technology is likely to reduce the x-ray radiation exposure for patient and operator, and may further increase the success rate of the procedure.