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Biomedical subjects

L Littmann

Publications and source records attributed to L Littmann.

At least 55 records · Page 3Linked to original sources
PubMed1991

Optical properties of normal, diseased, and laser photocoagulated myocardium at the Nd: YAG wavelength.

Laser photocoagulation of the myocardium effectively destroys arrhythmogenic foci. The purpose of this study was 1) to compare the optical properties of canine myocardium before and after photocoagulation, 2) to compare the canine model with clinical cases by measuring the optical properties of human myocardium, and 3) to assess the optical properties of human myocardial scar and epicardial fat tissue. Measured optical properties were the absorption coefficient, mu a; scattering coefficient, mu s; and scattering anisotropy factor, g. Optical measurements were performed at 1064 nm wavelength on thin plane parallel tissue slices using the integrating sphere method with glass hemispheres on either side of the sample. The study showed 1) an increase of the scattering coefficient by 40% and a two- to threefold increase in reduced scattering coefficient as a result of photocoagulation; 2) that the mu a (0.035 +/- 0.024 mm-1) and mu s (17.9 +/- 3.8 mm-1) of human myocardium were not significantly different from mu a (0.043 +/- 0.021 mm-1) and mu s (17.3 +/- 2.2 mm-1) of canine myocardium, whereas the human g (0.964 +/- 0.005) was slightly different from the canine g (0.974 +/- 0.008); and 3) that the mu a (0.021 +/- 0.016 mm-1) of epicardial fat and mu s (13.8 +/- 1.1 mm-1) of myocardial scar were significantly lower than those of normal myocardium. A dynamic model of laser-tissue interaction incorporating these changes and inhomogeneities is necessary to better describe light distribution during laser photocoagulation.

Animals↗
PubMed1991

Electrophysiologic characteristics of manifest and latent retrograde conduction in dogs.

Atrioventricular (AV) nodal reentry requires intact retrograde ventriculoatrial (VA) conduction. The purpose of this study was to assess the contribution of various pacing and pharmacologic techniques to uncover VA conduction during apparent unidirectional VA block, and to evaluate the role of several biologic and electrophysiologic factors in concealment of retrograde conduction. Forty healthy dogs underwent catheter-electrophysiologic studies of AV and VA conduction. Group I (20 animals) had intact VA conduction. Group II (six animals) had VA dissociation with ventricular pacing initiated during sinus rhythm, but the presence of VA conduction was confirmed by isoproterenol infusion or by premature ventricular stimulation. In group III (14 animals), the above techniques failed to uncover VA conduction. Eight of 14 group III animals underwent thoracotomy and crushing or freezing of the sinoatrial (SA) node. Ventricular pacing initiated during sinus standstill was associated with 1:1 VA conduction in each experiment. VA conduction time and retrograde Wenckebach cycle length, both in the baseline state and during isoproterenol infusion, were significantly longer in the eight animals in group III than in those in group I. Age, gender, weight, breed, sinus cycle length, and anterograde AV conduction properties were not significantly different between groups I, II, and III. The data suggest that (1) in normal dogs, complete unidirectional VA block probably does not exist; (2) in the presence of anterograde input to the AV node, even sophisticated pacing and pharmacologic maneuvers may fail to uncover the presence of VA conduction; (3) although anterograde input is essential for concealment of VA conduction, the phenomenon is more closely associated with depressed retrograde than with anterograde AV nodal characteristics.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Functional role of the epicardium in postinfarction ventricular tachycardia. Observations derived from computerized epicardial activation mapping, entrainment, and epicardial laser photoablation.

BACKGROUND: Conventionally, monomorphic sustained ventricular tachycardia in patients with remote myocardial infarction is believed to originate from the subendocardium. In a previous study, we demonstrated that electrical activation patterns during ventricular tachycardia occasionally suggest a subepicardial rather than subendocardial reentry. METHODS AND RESULTS: This study prospectively evaluated the functional role of the epicardium in postinfarction ventricular tachycardia with complex intraoperative techniques including computerized electrical activation mapping, entrainment, observation of changes in activation pattern during successful epicardial laser photoblation, and histological study. Five of 10 consecutive patients undergoing intraoperative computerized activation mapping had 10 ventricular tachycardia morphologies displaying epicardial diastolic activation These 10 "epicardial" ventricular tachycardias revealed the following global activation patterns: monoregional spread (two), figure-eight activation (five), and circular macroreentry (three). Entrainment of ventricular tachycardia using epicardial stimulation was successfully performed from an area of slow diastolic conduction in four tachycardia morphologies. During entrainment, global activation remained undisturbed with recordings showing a long stimulus to QRS interval, unchanged QRS morphology, and pacing capture of all components of the reentry circuit. Neodymium:yttrium aluminum garnet laser photocoagulation was delivered during ventricular tachycardia to epicardial sites of presumed reentry. Epicardial photoablation terminated five of five figure-eight tachycardias, two of three circular macroreentry tachycardias but not the monoregional tachycardias. Electrophysiological recordings during epicardial laser photocoagulation demonstrated progressive prolongation of ventricular tachycardia cycle length and apparent interruption of the presumed reentrant circuit. Histological evaluation of the reentrant region (three patients) showed a rim of surviving myocardium under the epicardial surface. CONCLUSIONS: This study suggests that 1) chronic postinfarction ventricular tachycardia may result from subepicardial macroreentry, 2) slow conduction within the reentry circuit can be localized by computerized mapping and epicardial entrainment, and 3) ventricular tachycardia interruption by laser photocoagulation results from conduction delay and block within critical elements of the reentrant pathway. Viable subepicardial muscle fibers may constitute the underlying pathology.

Diagnosis, Computer-Assisted↗
PubMed1991

Effects of vascular runoff on myointimal hyperplasia after mechanical balloon or thermal laser arterial injury in dogs.

BACKGROUND: Clinical evidence suggests that poor vascular runoff reduces the long-term success rate of femoral angioplasty procedures. The purpose of this experimental study was to examine myointimal hyperplasia of dog femoral arteries after balloon denudation, thermal laser arterial injury, or sham operation in normal and reduced vascular runoff conditions. METHODS AND RESULTS: Before mechanical balloon injury or transluminal heated laser probe motion, the peripheral vascular runoff of dogs was reduced by ligating the femoral artery below its three distal side branches, decreasing the femoral flow rate from 114 +/- 9 to 52 +/- 5 ml/min (mean +/- SEM). Endothelial denudation with a predominantly intact elastic internal membrane and circumferential structural changes in the media were noted by light microscopy 1 hour after balloon injury. Focal completely necrotic lesions of intima and media were found 1 hour after thermal laser arterial injury. After 8 weeks, the maximal thickness of neointima plus media of the site of previous intervention was greater after balloon injury (0.45 +/- 0.03 mm) and thermal laser injury (0.54 +/- 0.03 mm) than after sham operation (0.40 +/- 0.01 mm; p less than 0.001) in normal runoff dogs. Reduced vascular runoff augmented myointimal hyperplasia both in the balloon-injured and thermally damaged arteries; the wall thickness increased from 0.45 +/- 0.03 to 0.93 +/- 0.10 mm and from 0.54 +/- 0.03 to 0.65 +/- 0.05 mm, respectively (p less than 0.001). The neointimal and medial wall area of the balloon-injured arteries contributed 48% to the area encompassed by the external elastic membrane compared with an 81% portion when vascular runoff was reduced (p less than 0.01). A 47% neointimal and medial wall area was found in thermally injured arteries with normal runoff compared with 63% after runoff reduction (p less than 0.05). CONCLUSION: This study suggests that hemodynamic factors associated with poor vascular runoff play an important role in extending myointimal hyperplasia independent of method and severity of the arterial injury during angioplasty.

Animals↗
PubMed1990

Termination of ventricular tachycardia with epicardial laser photocoagulation: a clinical comparison with patients undergoing successful endocardial photocoagulation alone.

Electrical activation-guided laser photocoagulation was used intraoperatively to terminate ventricular tachycardia in patients with ischemic heart disease. During ventricular tachycardia, laser irradiation was delivered to mapped sites with local diastolic activation. In 30 long-term survivors, 85 ventricular tachycardia configurations were terminated by ablation; 72 (84.7%) were terminated by endocardial photocoagulation. Thirteen (15.3%) required epicardial photocoagulation; however, these 13 ventricular tachycardias occurred in 10 (33%) of the 30 patients. An aneurysm was present in 70% of patients with successful endocardial photocoagulation, but in only 10% of patients requiring epicardial photocoagulation for at least one ventricular tachycardia configuration; 90% of all patients requiring epicardial laser photocoagulation had no aneurysm and had either a right or a left circumflex coronary artery-related infarction. In this group, epicardial activation data were similar to those described for ventricular tachycardia with an "endocardial" origin and included 1) delayed potentials during sinus rhythm, 2) presystolic or pandiastolic activation sequences during ventricular tachycardia, and 3) regions of block near the presumed region of reentry during ventricular tachycardia. This study suggests that the critical anatomic substrates supporting reentry in postinfarction ventricular tachycardia may occur at intramural or epicardial sites, particularly in patients with right or circumflex coronary artery-related infarction and no aneurysm.

Cardiac Pacing, Artificial↗
PubMed1990

Modification of sinus node function by epicardial laser irradiation in dogs.

This study tested the feasibility of neodymium:YAG laser photocoagulation of selected sinus node areas to depress sinus rate responsiveness. In 14 open-chest dogs, origin of the sinus impulse (O point) was electrically mapped from the epicardium before and during isoproterenol infusion. Epicardial laser photocoagulation was applied to the O point observed during isoproterenol infusion and stepwise to remapped new O points until a 30 +/- 5% decrease in heart rate occurred. Long-term effects were assessed by Holter monitoring and electropharmacologic testing preoperatively and up to 10 weeks or 6 months. Mean (+/- SEM) percent decreases were observed at 10 weeks in the following parameters: average 24-hour heart rate, 17.4 +/- 5.0%; maximum heart rate on Holter, 30.5 +/- 3.5%; heart rate during pharmacologic autonomic blockade, 32.7 +/- 3.5%; and maximum heart rate on isoproterenol, 23.1 +/- 4.6% (all p less than 0.01). Curves with pacemaker recovery time plotted against control cycle length remained unchanged. Holter monitoring did not show excessive bradycardic episodes even after administration of propranolol. In three control dogs (sham operation), sinus node function remained unchanged. Histologic study of the irradiated area showed replacement by inflammatory cells, fibrosis, and cartilage formation with surrounding normal cells and occasional cells resembling pacemaker-like cells at the caudal end of the sinoatrial node. This study suggests that 1) map-guided graded laser photocoagulation of sinus node regions showing earliest activation during catecholamine stimulation successfully limits maximum heart rates without causing significant bradycardia, 2) the effects are long lasting, and 3) the remaining pacemaker behaves like the sinus node. Laser modification of sinus node function could become a form of nonpharmacologic heart rate control in patients with coronary artery disease undergoing surgery and in the syndrome of inappropriate sinus tachycardia.

Animals↗
PubMed1989

The complex posterior septal space in the Wolff-Parkinson-White syndrome. Surgical experience with 47 patients.

Forty-seven consecutive patients with the Wolff-Parkinson-White syndrome due to posterior septal accessory pathways were operated on from August 3, 1983 to March 23, 1989. Seven of these patients had Ebstein's anomaly, another three coronary sinus aneurysms, one a persistent left superior vena cava, and five others complex multiple pathway combinations. Two additional patients required surgery following unsuccessful catheter ablation and one after failed surgery at another institution. Thus nineteen of forty-seven patients (40%) had additional difficulty factors which tend to complicate the operative dissection in this already complex anatomical area. The surgical anatomy of the posterior septal space as well as the essential operative principles and techniques are reviewed. Each of the frequently encountered additional difficulty factors is described with emphasis on the coronary sinus aneurysm, a recently recognized entity.

Adolescent↗
PubMed1988

The effects of probucol on QT/QS2 relation and systolic time intervals.

The QT, QTc, QS2 intervals, pre-ejection period-left ventricular ejection time ratios and serum lipoprotein levels were measured in 8 patients with primary hypercholesterolemia before and after a 3-month therapy with probucol, 1 g/day. Both QT and QTc intervals increased significantly, whereas no significant changes were observed between the pre- and post-treatment QT/QS2 and pre-ejection period-left ventricular ejection time ratios. These results help to explain why treatment with probucol, while effecting a prolongation of the QTc interval, does not result in serious arrhythmias in man.

Adult↗
PubMed1988

Two-to-one sinoatrial block. Normalization by carotid massage.

In a clinical case of 2:1 sinoatrial block, carotid massage, paradoxically, released the sinoatrial block and doubled the manifest sinus rate. This resulted from a deceleration of the sinus discharge rate which allowed consecutive sinus impulses to traverse the sinoatrial junction.

Aged↗
PubMed1987

A study of modulated ventricular parasystole by programmed stimulation.

To analyze the phase-dependent sensitivity of the parasystolic pacemaker to nonparasystolic beats, 11 patients with modulated ventricular parasystole were studied using the ventricular extrastimulus method. The intrinsic parasystolic cycle lengths ranged from 1,100 to 1,800 ms. Premature stimuli altered the duration of the parasystolic cycle lengths by amounts that depended on timing of the test impulses within the parasystolic cycles. Premature impulses delivered during the first part of the parasystolic cycles prolonged the parasystolic cycle lengths to 107 to 151% of the intrinsic parasystolic cycle lengths and impulses applied during the second part abbreviated them to 70 to 81% of the intrinsic parasystolic cycle lengths. In 10 patients the accelerating effects were of greater magnitude than the decelerating effects. Transition from the accelerating to slowing phases was progressive or unstable in 9 patients and abrupt in 2. Changes induced by individual stimuli were short-lived and the parasystolic pacemakers returned immediately to their original rates. In 1 patient the biphasic sensitivity of parasystole to premature stimuli was shown to sustain for 21 days.

Aged↗
PubMed1987

Gap in bundle-branch conduction elicited by programmed His bundle stimulation.

The gap phenomenon in right bundle-branch conduction was elicited during programmed stimulation of the His bundle. Premature beats with short and long coupling intervals showed undisturbed intraventricular conduction, while the premature beat with intermediate coupling interval blocked within the right bundle branch. The electrophysiologic mechanism of "supernormal" conduction of the earliest beats was conduction delay at a proximal site within the His bundle which allowed recovery of the right bundle branch. This study shows that programmed His bundle stimulation is a valuable method in analyzing conduction characteristics of the distal atrioventricular conduction system in cases where atrioventricular nodal refractoriness would preclude this by atrial stimulation.

Adult↗
PubMed1987

Severe symptomatic atrioventricular block induced by pilocarpine eye drops.

An 89-year-old man with chronic glaucoma received hourly pilocarpine eye drops for seven hours, when he developed third-degree atrioventricular block with a slow idioventricular escape rate. After discontinuing the pilocarpine, the atrioventricular block gradually disappeared. The site of pilocarpine-related block was most likely within the His-Purkinje system.

Aged↗