Resin ionomer restorative materials: the new generation.
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Acrylic Resins↗
Biomedical subjects
J Summitt
Publications and source records attributed to J Summitt.
A comparison of standard and high-dose regimens for the initiation of amiodarone therapy.
The effects of two regimens for the initiation of amiodarone therapy were compared in 92 patients with inducible sustained ventricular tachycardia (VT) at baseline electrophysiologic testing. Two groups of 46 patients each received a total of 16.8 gm of oral amiodarone before follow-up electrophysiologic testing. Group A (standard dose) received 1200 mg/day for 14 days, and group B (high dose) received 2400 mg/day for 7 days. Amiodarone suppressed the induction of sustained VT in six subjects (13%) in group A versus 10 (22%) in group B (p = NS). In subjects who continued to have inducible VT after amiodarone loading, the mean increase in cycle length of induced VT was similar in group A (delta = 85 +/- 73 msec) and group B (delta = 78 +/- 59 msec). The mean increase in sinus cycle length, AH and HV intervals, paced QRS duration, and ventricular refractory periods was also not significantly different between the two groups. Side effects developed in 10 (22%) patients in group B but were serious only in one, and one patient required a reduction in dosage. Thus compared to the 14-day standard-dose regimen, the 7-day high-dose regimen was well tolerated and had similar effects on VT inducibility and electrophysiologic variables. Its use may significantly shorten the duration of hospitalization in patients with life-threatening inducible VT who are undergoing loading with amiodarone on an inpatient basis.
Aged↗
The effect of quinidine and mexiletine on the adaptation of ventricular refractoriness to an increase in rate.
The purpose of this study was to determine the effects of quinidine and mexiletine on the adaptation of ventricular refractoriness to a change in heart rate. The ventricular effective refractory period was measured at a basic drive cycle length of 500 msec with basic drive train durations of two beats, eight beats, 20 beats and 3 minutes. The ventricular refractory periods were measured in the baseline state and after oral treatment with quinidine or mexiletine in 20 subjects each. In the baseline state, there was progressive shortening of the ventricular refractory period as the drive train duration increased from two beats to 3 minutes. Quinidine prolonged refractoriness by 5% (p less than 0.001) at each drive train duration. Mexiletine did not affect the ventricular effective refractory period at any of the drive train durations. In a control group of 20 subjects, there were no significant differences between two determinations of refractoriness at each basic drive train duration. In conclusion, neither quinidine nor mexiletine affect the adaptation of ventricular refractoriness to an increase in rate. Although the ventricular effective refractory period measured with a conventional basic drive train duration of eight beats is often more than 20 msec longer than the actual ventricular effective refractory period measured with a drive train duration of 3 minutes, the effects of quinidine and mexiletine on the conventionally measured ventricular effective refractory period accurately reflect the effects of these drugs on the actual ventricular effective refractory period.
Adaptation, Physiological↗
Effect of basic drive cycle length on the yield of ventricular tachycardia during programmed ventricular stimulation.
The yield of sustained, monomorphic ventricular tachycardia (VT) induced by programmed ventricular stimulation was compared, using basic drive trains of 400 ms, 600 ms and sinus rhythm, to identify the most efficient sequence of basic drive trains to use during programmed stimulation. Fifty-five patients with coronary artery disease and inducible sustained monomorphic VT not requiring countershock to terminate underwent 81 electrophysiology tests in which 1 to 3 extrastimuli were introduced during sinus rhythm and after basic drive trains of 600 and 400 ms. In 72 electrophysiology tests, sustained, monomorphic VT was induced at the right ventricular apex. The yield of VT using a drive cycle length of 400 ms was 63 of 72 (88%), compared to 46 of 72 (64%) when the drive cycle length was 600 ms, and 23 of 72 (32%) when the extrastimuli were introduced during sinus rhythm (p less than 0.001 for all pairwise comparisons). In 14 electrophysiology tests in which VT was not induced using a 400 ms basic drive cycle length at the apex, the yield of VT was higher using a 400 ms drive cycle length at a second right ventricular site (12 of 14) than with a 600 ms drive cycle length (3 of 12) or sinus rhythm (4 of 12) at the apex (p less than 0.05). The yield of sustained, monomorphic VT induced by 1 to 3 extrastimuli increases as the basic drive cycle length shortens. Whereas programmed stimulation is conventionally started during sinus rhythm or with a drive cycle length of 600 ms, the present results suggest that starting with a drive cycle length of 400 ms may be more efficient.
Cardiac Pacing, Artificial↗
Effects of resting vagal tone on accessory atrioventricular connections.
The purpose of this study was to determine the effects of resting vagal tone on accessory atrioventricular (AV) connections. Atropine (0.04 mg/kg) was administered to 13 patients with the Wolff-Parkinson-White syndrome and was found to have the following effects on the accessory AV connection: the anterograde block cycle length shortened from 305 +/- 51 to 279 +/- 54 msec (mean +/- SD; p less than 0.001); the retrograde block cycle length shortened from 288 +/- 57 to 251 +/- 50 msec (p less than 0.001); and the effective refractory period measured at a basic drive cycle length of 400 msec shortened from 295 +/- 45 to 265 +/- 47 msec in the anterograde direction (p less than 0.001) and from 283 +/- 18 to 261 +/- 12 msec in the retrograde direction (p less than 0.01). During atrial fibrillation, the mean ventricular cycle length decreased from 434 +/- 88 to 352 +/- 56 msec (p less than 0.001), and the shortest preexcited RR interval decreased from 302 +/- 56 to 256 +/- 43 msec (p less than 0.01). In another seven patients, propranolol (0.2 mg/kg) was administered before atropine, and atropine lengthened the anterograde block cycle length and the effective refractory period of the accessory AV connection; the magnitude of these effects was similar to that in the patients who did not receive propranolol. In conclusion, these data demonstrate that resting vagal tone exerts a direct depressant effect on accessory AV connections that does not require background sympathetic activity to be manifest.
Adult↗
The effect of electrode configuration on the unipolar His-bundle electrogram.
Although "unipolar electrograms" recorded from the His-bundle position have been used to help position catheters for His-bundle ablation, the techniques used to record such electrograms have not been standardized. The effects of five anode locations (right chest wall, anterior chest wall, left chest wall, posterior chest wall, and inferior vena cava) on unipolar atrial, His bundle and ventricular electrograms recorded from the His-bundle position were examined in ten patients undergoing clinical electrophysiology studies. Electrograms were recorded at filter settings of 50-500 as well as 0.05-1000 Hz. The location of the anode had no consistent effect on the amplitude, duration or morphology of any of the electrograms at either filter setting, but signals recorded with the inferior vena cava anode had the highest signal-to-noise ratio. A filter setting of 50-500 Hz decreased the amplitude of atrial (0.72 to 0.33 mV-P less than 0.01), His bundle (0.38 vs 0.32 mV-P less than 0.01) and ventricular electrograms (3.71 vs 2.01 mV-P less than 0.001) compared to a filter setting of 0.05-1,000 Hz. The filter setting did not affect electrogram duration. We concluded that the use of an electrode catheter in the inferior vena cava as the anode when recording "unipolar electrograms" from the His-bundle position yields a better signal-to-noise ratio than a skin patch on the chest and appears to be the optimal method for recording unipolar electrograms.
Bundle of His↗