Search PubMed⌕ Search

Biomedical subjects

B Lown

Publications and source records attributed to B Lown.

306 records · Page 17Linked to original sources
PubMedDate not supplied

Ventricular postextrasystolic potentiation in the dog. A study using list mode radionuclide ventriculography.

The first and second postextrasystolic sinus beats (PESB) were isolated and analyzed in five open-chested dogs with the aid of list mode radionuclide ventriculography. Ventricular stimulation was delivered using a coupling interval of 150 msec from electrodes positioned at two (in two animals) or five (in three animals) different ventricular sites. There were marked increases in both left ventricular ejection fraction (41.5 +/- 4% vs. 56.8 +/- 3.9%; control vs. PESB, p less than 0.001) and stroke volume (+ 51.6 +/- 16.8%; PESB vs. control, p less than 0.001) in all first postextrasystolic sinus beats. Concomitant decreases in end-systolic volumes (-16.2 +/- 5.2%; PESB vs. control beat, p less than 0.001) confirmed the increased inotropy seen during these beats. During the second postextrasystolic sinus beats a mild but statistically significant increase in ejection fraction (+ 1.6 +/- 1.6%; PESB vs., control, p less than 0.01) was also seen despite a small decrease in end-diastolic volume (-2.8 +/- 2.5%; PESB vs control, p less than 0.01). In the dog postextrasystolic potentiation affects mostly the first PESB and causes only a mild increase in inotropy during the subsequent sinus beat. List mode radionuclide ventriculography is a useful and reproducible method for assessing changes in ventricular function following ventricular ectopics that have a fixed coupling interval to the preceding QRS complex.

Animals↗
PubMedDate not supplied

Postextrasystolic potentiation during spontaneous ventricular ectopy in man. Associated left ventricular volume changes determined by list mode radionuclide ventriculography.

Five patients with spontaneously arising frequent ventricular ectopia were studied by list mode radionuclide ventriculography. Changes in left ventricular volumes reflected the increased inotropy of the postextrasystolic sinus beats: stroke volume increased by +36.0 +/- 32.8% (P less than 0.05) and end-systolic volumes decreasing by 13.6 +/- 7.3% (P less than 0.02) leading to an increased ejection fraction (+31.1 +/- 23.8%; P less than 0.05). There were no significant increases in end-diastolic volumes (+2.2 +/- 5.4%; P:NS). The reproducibility of the left ventricular volume estimates was confirmed by comparing the control sinus beats with the interrupted sinus beats. There were no significant changes in end-diastolic (+1.8 +/- 5.5%), end-systolic (+1.8 +/- 3.7%) and stroke volumes (+5.4 +/- 14.6%). List mode radionuclide ventriculography can be used to accurately monitor left ventricular volume changes associated with spontaneously arising ventricular ectopia. In these patients, the contribution of Frank-Starling mechanism to postextrasystolic potentiation was minimal.

Adult↗
PubMedDate not supplied

Semiautomated data reduction of ventricular ectopic activity: methodology and clinical application.

A semiautomated ventricular premature beat (VPB) detector was developed which detects VPBs based upon a logical combination of prematurity, amplitude, and width. This system utilizes technicians to define sensitivity and criteria of VPB detection and to monitor the system's performance using a unique feedback system. Technician-assisted semiautomated scanning was found superior both to the system using preselected criteria and sensitivity of the detectors, and to traditional Holter scanning for the detection of single and repetitive VPBs. Ninety percent confidence limits of VPB frequency per hour have been established for this system.

Arrhythmias, Cardiac↗