Initial Clinical Experience with a Rate Responsive Pacemaker

Prism-CLR is a new single chamber unipolar pace, bipolar or unipolar sense, rate responsive pacemaker that utilizes a closed-loop system based on the analysis of the evoked potential for rate adjustment. It also has an automatic output regulation feature for capture verification and threshold search. Five patients in whom this pacemaker was implanted exhibited an appropriate rate increase with exercise and psychological stress. Automatic output regulation functioned appropriately in three of five patients. Preliminary data suggest that Prism-ClR is an effective pacemaker for patients who may benefit from rate responsive pacing. The automatic output regulation recognition algorithm may need modification in some patients.     

Centrofacial lentiginosis

Forty patients with centrofacial lentiginosis have been studied. A greater than normal number of bone abnormalities, malformations due to dysraphia, endocrine dysfunctions, and neurological diseases, but not psychiatric impairment, were found.     

Multiple Accessory Pathways: A Combined Electrophysiological and Radionuclide Study

Electrophysiological study in a patient with Wolff-Parkinson-White syndrome revealed multiple accessory pathways: Kent bundle and Mahaim nodoventricular and fasciculoventricular fibers. Radionuclide phase imaging disclosed two distinct ventricular activation sequences during sinus rhythm or slow atrial pacing and during fast atrial pacing. The third activation pattern could be recorded after injection of ajmaline, which abolished signs of preexcitation in the electrocardiogram. Phase image in combination with pacing and pharmacological interventions can, at least in some cases, detect complex preexcitation syndromes noninvasively.     

Activation and Repolarization Patterns are Governed by Different Structural Characteristics of Ventricular Myocardium:

Activation and Repolarization Patterns. Introduction : Substantial progress has been made in our understanding of transmural activation across ventricular muscle through studies of excitation patterns and potential distributions. In contrast, repolarization sequences are poorly understood because of experimental difficulties in mapping action potential durations (APDs) using extracellular electrodes.
Methods and Results : Langendorff-perfused guinea pig hearts and isolated coronaryperfused left ventricular sheet preparations were stained with the voltage-sensitive dye RH-421 and optical APs were recorded with a photodiode array. Epicardial maps were constructed using a triangulation method applied to matrices of activation and repolarization times determined from (dF/dt)_max and (d²F/dt²)_max' respectively. Numerical simulations were carried out based on: (1) a modified Luo-Rudy model; (2) the three-dimensional architecture of ventricular fibers; and (3) the intrinsic spatial distribution of APDs. In ventricular sheets, epicardial stimulation elicited elliptical activation patterns with the major axis aligned with the longitudinal axis of epicardial fibers. When the pacing electrode was progressively inserted from epicardium to endocardium, the major axes rotated gradually, clockwise by 45°, and the eccentricity decreased from 2 to 1.14. Repolarization showed a relatively uniform pattern, independent of pacing site, beginning at the apex and spreading to the base.
Conclusion : In experiments and simulations, the helical rotation of epicardial excitation isochrones caused by pacing at increasing depth in the myocardium correlated with the helical three-dimensional architecture of ventricular fibers. In contrast, repolarization was independent of the activation sequence and was mainly guided by spatial differences in APDs between apex and base.     

Nonpharmacological Therapy of Supraventricular Arrhythmias: Surgery and Catheter Ablation Techniques

Treatment of supraventricular tachyarrhythmias has undergone substantial change and development over the past decade. Pharmacological approaches to management of supraventricular arrhythmias have been supplanted by nonpharmacological techniques. These nonpharmacological techniques are the subject of the present review. The first part of this review will concentrate on the nonpharmacological techniques available for the treatment of supraventricular tachycardia, excluding Wolff-Parkinson-White syndrome, whereas Part 2 will concentrate on the surgical and the ablative procedures for management of tachycardias associated with Wolff-Parkinson-White syndrome. Pacing techniques for termination of supraventricular tachycardias are beyond the scope of this article and will not be included in the discussion.     

Diagnosis and treatment of accidental root perforations

A review of endodontic and periodontal aspects on the prognosis, diagnosis, prevention, and treatment of accidental root perforations is presented. Successful treatment depends mainly on proper diagnosis and immediate sealing of the perforation to eliminate risk of infection. A classification of root perforations is presented in the review to assist the clinician in making a proper choice of treatment protocol.     

The Automatic Implantable Cardioverter Defibrillator: T Wave Sensing in the Newest Generation

The AICD uses an automatic gain control amplifier for detecting the small electrograms during ventricular fibrillation. The latest generation of the AICD appears to have a more sensitive lock on gain amplifier, as 6 of 76 patients implanted with the new AICD had double counting of the QHS-T wave complex resulting in asymptomatic discharges. Solutions to the problem of limiting these asymptomatic discharges are difficult and include slowing of the heart rate with beta blockers, changing the lead system, or replacement of the device. One of the six patients was treated with beta blockers. Three patients had their device changed, two patients requested the inactivation of their device until a rate programmable unit was available. The potential for T wave sensing in a lock on gain amplifier represents the unique dilemma between detecting small electrograms of ventricular fibrillation, and detecting diastolic events which occur shortly after the QRS complex.