Permanent Pacemaker Implantation Following Cardiac Surgery: Indications and Long-Term Follow-Up

Background: Conduction disturbances requiring permanent pacemaker implantation after heart surgery occur in about 1.5% of patients. Early pacemaker implantation may reduce morbidity and postoperative hospital stay. We reviewed our experience with patients undergoing surgery to try and identify predictors for pacemaker requirements and patients who will remain pacemaker dependent.
Methods: We performed a retrospective review of 4,999 patients undergoing surgery between the years 1993 and 2005. Patient age was 64 ± 12 years, and 71% were males. Coronary bypass was performed in 4,071 (81%), aortic valve replacement in 675 (14%), and mitral valve replacement in 968 (18%) patients.
Results: Seventy-two patients (1.4%) required implantation of a permanent pacemaker after surgery. Indications for pacemaker implantation included complete atrioventricular block in 59, symptomatic bradycardia/slow atrial fibrillation in nine, second-degree atrioventricular block in two, and other conduction disturbances in two patients. Predictors for pacemaker requirement by multivariate analysis were left bundle branch block and aortic valve replacement (P < 0.001). Late follow-up was available in 58 patients, at 72 ± 32 months. Thirty-seven (63%) were pacemaker dependent. Predictors for late pacemaker dependency were third-degree atrioventricular block after surgery and preoperative left bundle branch block (P < 0.001).
Conclusions: Patients at high risk for pacemaker implantation after heart surgery include those with preexisting conduction disturbances, and those undergoing aortic valve replacement. Of those receiving a pacemaker, about one-third will recover at late follow-up. For patients in the high-risk group who are pacemaker dependent after surgery, we recommend implanting a permanent pacemaker at 5 days after surgery, thus enabling early mobilization and early discharge.     

Stereospecificity of hydrogen transfer by the NADP-linked alcohol dehydrogenase from the thermophilic bacterium Thermoanaerobium brockii

Class A and class B NAD(H):NADP(H) coenzyme-dependent dehydrogenases distinguish between the diastereotopic hydrogens pro-R and pro-S at position 4 of the cofactor. We investigated the stereochemistry of hydride transfer in reactions catalyzed by an unusual thermophilic, zinc-containing, NADP-linked enzyme Thermoanaerobium brockii alcohol dehydrogenase (TBAD). Using proton NMK spectroscopy of monodeuterated alcohols and coenzymes we found that TBAD is a class A enzyme that transfers the pro-R hydrogen from the pyridine 4 position of the reduced coenzyme. This stereospecificity is stable over (a) a broad range of temperatures up to 70° C. (b) different concentrations of the coenzyme (catalytic or stoichiometric) and (c) a wide scope of substrates. Although NAD ⁺ is not an effective coenzyme for TBAD, NADP ⁺ and its synthetic analogs, 3-acetqlpyridine-ADP ⁺ and thio-NADP ⁺, can be used successfully.     

The streaming liver

ABSTRACT— Twenty male adult rats weighing 200 g were injected with tritiated thymidine (³HTdR). The animals were then killed in groups of five, at the following times: 1 h, 1, 3 and 5 weeks. Autoradiograms of sections through the liver were prepared. The distances between labelled cells and the portal space rim were measured. One hour after labelling most labelled cells were confined to a region extending from the portal space rim up to a distance of 700 μm, which roughly corresponds to Rappaport's hepatic acinus zones-1 and -2. Throughout the experiment lasting 5 weeks labelled cells entered zone-3 and advanced toward the terminal hepatic vein. Hepatocytes travelled at a daily velocity of 1.44 μm, covering daily 0.324% of the acinus diameter. During the experiment acinus size did not change appreciably. The estimated mean hepatocyte cell cycle time was 37 days and its life expectation, 201 days. These experiments show that the liver is essentially a slowly renewing cell population. Hepatocytes nascent at the portal space gradually stream toward the terminal hepatic vein where they are probably eliminated by apoptosis. Their journey lasts 201 days. Since hepatocytes are glued together with tight junctions, all have to advance toward their terminal hepatic veins en masse. During their voyage, they traverse the three acinus zones, and since in each they produce different enzymes, each zone represents a differentiation state of the advancing cell. It is suggested further that the streaming hepatocyte carries with it its nerve supply and is accompanied by sinusoidal endothelium and Kupffer cells.