In 36 patients undergoing a permanent right atrial pacing for the treatment of sick sinus syndrome and/or atrioventricular block, the stimulation threshold was determined at a wide range of pacing rates (60 to 120 beats/min) 7 to 10 days after the lead implantation. Twenty-nine (80%) of these cases showed rate-dependent threshold changes, with significantly lower thresholds at higher than lower pacing rates (e.g., 2.91 +/- 1.01 mA at 70 beats/min and 2.32 +/- 0.75 mA at 120 beats/min, P less than 0.01). Thus, with a fixed, smaller current strength, the stimuli often failed to capture the right atrium at lower rates, but caused a 1:1 capture at higher rates. In an echocardiographic study in another series of eight patients, the end-diastolic diameter of the left atrium was decreased from 3.2 +/- 0.9 to 2.7 +/- 0.8 cm (P less than 0.01) when the pacing rate was increased from 60-70 beats/min to 100-120 beats/min. In experiments using two anesthetized, open-chest dogs, a rapid withdrawal of 500 mL of arterial blood reduced the right atrial dimension. This was accompanied by an increased amplitude of the right atrial endocardial electrogram, and the initially subthreshold stimuli became effective in capturing the atria. It was concluded that (1) rate-dependent threshold changes were commonly observed in the early stage of atrial pacing, and (2) fluctuations in the electrode contact with the endocardium appeared responsible for such threshold changes.
We present a 62-year-old man with mitral regurgitation whose posterior annulus had severe calcification. Mitral valve replacement was performed by anchoring the cuff on a double-plicated posterior leaflet, and reinforcing with an equine pericardium. The patient is doing well 13 years after surgery with echocardiography showing no problems.
Glassy-carbon-stented intraluminal grafts were used for the treatment of thoracic aortic aneurysms. As a stent, glassy carbon tubes 22 and 24 mm in outer diameter were cut to a length of 25 mm. The center of each tube was shaved by 5 mm in width and several notches were made. The stents were prepared for use in the assembly of intraluminal grafts, using conventional artificial vascular prostheses. Five cases of thoracic aortic aneurysm are presented as case reports. The location of the stents was always at the distal end of the aorta, but every proximal end-to-end anastomosis was performed with a conventional suture technique. The longest follow-up term is three years and more than one year in the other cases. Complications such as thromboembolism, graft detachment, and pseudoaneurysm formation have not been encountered to date. These new stents performed quite satisfactorily and showed a great advantage over commercially available intraluminal grafts.
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