Clinical evaluation of a thin bipolar pacing lead.

The main disadvantages of bipolar pacing leads have traditionally been related to their relative thickness and stiffness compared to unipolar leads. In a new "drawn filled tube" plus "coated wire" technology, each conductor strand is composed of MP35N tubing filled with silver core and coated with a thin ETFE polymer insulation material. This and parallel winding of single anode and cathode conductors into a single bifilar coil resulted in a bipolar lead (ThinLine, Intermedics) with a body diameter and flexibility similar to unipolar leads. The lead is tined, polyurethane, with the cathode and the anode made of iridium-oxide-coated titanium (IROX). The slotted 8-mm2 cathode tip is coated with polyethylene glycol, a blood soluble material. We present the clinical evaluation results from four pacemaker clinics, where 47 leads (23 atrial-J model 432-04 and 24 ventricular model 430-10) were implanted in 25 patients and followed for up to 2 years. The lead handling characteristics were found to be very satisfactory. Electrical parameters of the leads were measured at implant and noninvasively on postoperative days 1, 2, 21, 42, and months 3, 6, 12, and 24. Mean chronic pulse width thresholds at 2.5 V were 0.14 +/- 0.05 ms in the atrium and 0.10 +/- 0.02 ms in the ventricle, pacing impedances 443 +/- 104 omega and 520 +/- 241 omega, while median electrogram amplitudes were > or = 3.5 mV and > or = 7 mV, respectively. Pacing impedances and thresholds were found to be slightly but statistically significantly higher in unipolar than in bipolar configuration--the findings are explainable by the lead construction. One of 47 leads failed 3 weeks after implant; the conductors were short circuited due to an error during the manufacturing process. We conclude that the new lead thus far has demonstrated appropriate mechanical and electrical characteristics.

Does correction of acidosis influence microcirculatory blood flow during cardiopulmonary bypass?

We studied 15 patients undergoing cardiopulmonary bypass (CPB) to examine the effect of response to correction of acidosis on microcirculatory blood flow. Acidosis was defined when base excess was less than -10.0 mmol litre-1 while carbon dioxide partial pressure was within the normal range. CPB was carried out at almost normothermic temperature (smallest rectal temperature 35.2 (SD) 0.4 degrees C). Sodium bicarbonate (NaHCO3) was given to correct acidosis during steady state CPB. Skin microcirculatory blood flow was assessed using a double-channel laser Doppler flow (LDF) monitor. LDF was measured on the patient's forehead and forearm before infusion of NaHCO3 (baseline) and 30 s, 1, 3, 5, 7, 10 and 15 min later. Skin, blood, rectal and nasopharyngeal temperatures did not change during the investigation. Plasma viscosity, haemoglobin and carbon dioxide partial pressure also remained unchanged. Mean arterial pressure (MAP) and systemic vascular resistance (SVR) decreased slightly after infusion of NaHCO3 (MAP -29%; SVR -32%). A total of NaHCO3 99.4 (4.4) mmol litre-1 was given for correction of acidosis. pH and HCO3- were within the normal range shortly after the infusion of NaHCO3. LDF measured on both the forehead (+49%) and the forearm (+29%) increased significantly after infusion of NaHCO3. Changes in pH correlated positively with changes in LDF (analyses of co-variance, P < 0.02), but haemodynamic and other laboratory values did not correlate with LDF. We conclude that the microcirculatory response to correction of acidosis with NaHCO3 during CPB can be monitored using skin laser Doppler flowmetry. Infusion of NaHCO3 resulted in a significant improvement in skin microcirculatory perfusion.