Clinical Experience with Expanded Polytetrafluoroethylene Gore-Tex® Surgical Membrane for Pericardial Closure: A Study of 110 Cases

Complete closure of the pericardium after cardiac operations has the advantage of avoiding injury of the heart and great vessels during reoperation. Between 1985 and 1987, the pericardium was closed with Gore-Tex Surgical Membrane (SM) in a selected series of 110 patients 1 month to 76 years of age. Fifty-three patients had congenital heart lesions and 57 patients had acquired heart disease. Overall hospital mortality was 3/110 cases. In no instance was there a relationship between occurrence of death and pericardial closure with SM. There was one episode of cardiac tamponade on the seventh postoperative day. One patient developed fever and leukocytosis due to a mediastinal hematoma. During a mean follow-up of 15 months, four patients had to be reoperated upon three, four, eight weeks, and eight months after primary operation. The anterior wall of the heart had no adhesion with the SM and the other parts of pericardium could be dissected easily. Scanning electron microscopic examination of the explanted SM patches showed neither cellular ingrowth nor immunocompetent cellular elements. The Gore-Tex Surgical Membrane has the advantages of easy availability and lack of reaction between its surface and the epicardium and pericardium. We believe its routine use should be encouraged in patients with high probability of reoperation after repair of complex cardiac anomalies, implantation of bioprostheses, coronary revascularization for one- or two-vessel disease, and repair of degenerative disease of the ascending aorta.     

Polarity Reversal Improves Defibrillation Efficacy in Patients Undergoing Transvenous Cardioverter Defibrillator Implantation with Biphasic Sbocks

The purpose of this study was to determine the influence of polarity reversal on DFT in patients undergoing implantation of nonthoracotomy defibrillators with biphasic shocks. Previous studies have shown higher defibrillation efficacy with using the distal electrode as anode in implantation of nonthoracotomy defibrillators and monophasic shocks. However, it is as yet unclear whether biphasic shock defibrillation will also be influenced by polarity reversal. Using a transvenous lead system with a proximal electrode in the superior caval vein and a distal electrode in the RV apex, 27 patients undergoing defibrillator implantation were randomized to DFT testing with "initial" (distal electrode = cathode) or "reversed" polarity (distal electrode = anode). Defibrillation energy was reduced stepwise until defibrillation failure occurred. At this point, polarity was switched and testing continued until the lowest energy requirement was determined for both polarities. With reversed polarity, DFT was 11.1 ± 5.7 J versus 13.3 ± 5.8 J with initial polarity (P = 0.033). This means a 17% reduction of the DFT. In 10 patients, the threshold was lower with reversed, whereas in 3 patients it was lower with initial polarity. In conclusion, changing electrode polarity in transvenous implantable defibrillators with biphasic shocks may significantly influence defibrillation energy requirements. Therefore, polarity reversal should always be attempted before considering patch implantation.     

Normovolaemic haemodilution and hyperoxia have no effect on fractal dimension of regional myocardial perfusion in dogs

Hypervolaemic haemodilution makes myocardial perfusion more homogenous as reflected by reduced fractal dimension of regional myocardial perfusion. The clinically more commonly performed acute normovolaemic haemodilution, however, has not yet been studied in this respect. Hyperoxic ventilation with 100% oxygen is used in conjunction with haemodilution to compensate for low oxygen content by increasing physically dissolved oxygen in plasma. Since hyperoxia is known to cause disturbance in microcirculatory regulation we studied the effects of acute normovolaemic haemodilution to haematocrit (hct) 20 ± 1% and hyperoxia on regional myocardial perfusion heterogeneity in 22 anaesthetized dogs using fractal and correlation analysis. Regional myocardial perfusion was assessed with radioactive microspheres. The results of the study were that heart rate, blood volume and arterial pressure were unchanged during haemodilution. Cardiac index was 3.6 ± 0.7 L min^?1 m^?2 before and 4.6 ± 0.7 L min^?1 m^?2 after haemodilution (P < 0.05). Fractal dimension (D) of regional myocardial perfusion was 1.17 ± 0.10 at baseline. Neither haemodilution (D = 1.19 ± 0.10) nor hyperoxia (D = 1.17 ± 0.10) altered fractal properties of regional myocardial perfusion. Spatial correlation of blood flow to adjacent tissue samples before haemodilution was 0.58 ± 0.15. Haemodilution and hyperoxia did not significantly influence spatial correlation (0.57 ± 0.12 vs. 0.60 ± 0.09; ns). We conclude that neither acute normovolaemic haemodilution nor haemodilution in combination with hyperoxic ventilation alter physiological myocardial perfusion heterogeneity.     

Influence of Polarity Reversal on de-fibrillation Success with Biphasic Shocks and a Transvenous/Subcutaneous Defibrillator System in a Porcine Animal Model

Clinical studies show that polarity reversal affects de-fibrillation success in transvenous monophasic defibrillators. Current devices use biphasic shocks for de-fibrillation. We investigated in a porcine animal model whether polarity reversal influences de-fibrillation success with biphasic shocks. In nine anesthetized, ventilated pigs, the de-fibrillation efficacy of biphasic shocks (14.3 ms and 10.8 ms pulse duration) with “initial polarity” (IP, distal electrode = cathode) and “reversed polarity” (RP, distal electrode = anode) delivered via a transvenous/subcutaneous lead system was compared. Voltage and current of each defibrillating pulse were recorded on an oscilloscope and impedance calculated as voltage divided by current. Cumulative de-fibrillation success was significantly higher for RP than for IP for both pulse durations (55% vs 44%, P = 0.019) for 14.3 ms (57% vs 45%, P < 0.05) and insignificantly higher for 10.8 ms (52% vs 42%, P = n.s.). Impedance was significantly lower with RP at the trailing edge of pulse 1 (IP: 44 ± 8.4 vs RP: 37 ± 9.3 with 14.3 ms, P < 0.001 and IP: 44 ± 6.2 vs RP: 41 ± 7.6 Ω with 10.8 ms, P < 0.001) and the leading edge of pulse 2 (IP: 37 ± 5 vs RP: 35 ± 4.2 Ω with 14.3 ms, P = 0.05 and IP: 37.5 ± 3.7 vs RP: 36 ± 5 Ω with 10.8 ms, P = 0.02). In conclusion, in this animal model, internal de-fibrillation using the distal coil as anode results in higher de-fibrillation efficacy than using the distal coil as cathode. Calculated impedances show different courses throughout the shock pulses suggesting differences in current flow during the shock.     

Cardiogenic oscillations in spontaneous breathing airway signal reflect respiratory system mechanics

Background: Heartbeat‐related pressure oscillations appear at the airway opening. We investigated whether these cardiogenic oscillations (COS) – extracted from spontaneous breathing signals – reflect the compliance of the respiratory system. Methods: Fifteen volunteers breathed spontaneously at normal or reduced chest wall compliance, i.e. with and without thorax strapping, and at normal or reduced lung compliance, induced by positive end‐expiratory pressure (PEEP). COS‐related signals were extracted by averaging the flow and pressure curve sections, temporally aligned to the electrocardiogram signal. Results: COS‐related airway pressure and flow curves correlated closely for each subject (r²=0.97±0.02, P<0.0001). At the unstrapped thorax, the oscillation's amplitudes were 0.07±0.03 cmH₂O (pressure) and 22±10 ml/s (flow). COS‐related pressure amplitudes correlated closely with the ratio of tidal volume divided by pressure amplitude (r²=0.88, P<0.001) and furthermore increased with either thorax strapping (P<0.001) or with increasing PEEP (P=0.049). Conclusion: We conclude that COS extracted from the pressure and flow signal reflect the compliance of the respiratory system and could potentially allow estimating respiratory system mechanics during spontaneous breathing.     

Hyperosmotic-hyperoncotic solutions during abdominal aortic aneurysm (AAA) resection

A largely positive perioperative fluid balance during both elective and emergency abdominal aortic aneurysm repair (AAA) may put patients at risk of developing left ventricular failure and may thus contribute to morbidity. In the present paper we report on a prospective study using hyperosmotic-hyperoncotic solutions (HHS) infused during clamping of the aorta, for the prevention of declamping shock, and the associated reduction in perioperative fluid requirements. The major aim of this paper was to determine the efficacy of an HHS infusion when given over 20 minutes and to detect possible adverse effects of HHS. For perioperative fluid replacement 12 patients received crystalloid solutions with HHS [250 ml of 7.2% NaCl combined with either 6% Dextran (n=3), 6% Hydroxyethylstarch (HES, n=4) or 10% HES (n=5)]. In 16 controls, crystalloids with 1000 ml of HES 10% were infused. Patients were invasively monitored and hemodynamic parameters frequently assessed during the operation, which were statistically analyzed in relation to the start of the fluid loading during clamping of the aorta. One patient showed an anaphylactoid reaction to HES, otherwise no side effects of HHS were observed during infusion (no hypotension, no pathological EKG changes). Plasma sodium and chloride concentration as well as osmolality rose resulting in an osmotic gradient and a desired intravascular volume expansion. Prior to declamping pulmonary capillary wedge pressure had increased to the desired value of > 13 mmHg and <18 mmHg. Oxygen delivery was significantly elevated upon HHS and remained so post declamping, whereas no change was observed in controls. During clamping systemic vascular resistance was significantly decreased, but was unchanged in controls. The perioperative fluid balance of patients receiving HHS was 2471.0±948.6 ml, which was significantly less than +3386.7±1247.9 ml of controls (P < 0.01). We suggest that HHS opens new perspectives in perioperative fluid management of both elective and emergency AAA repair, since hemodynamic parameters are improved and the overall fluid balance is less positive, thus decreasing the likelihood of edema formation. Moreover, the previously described positive microcirculatory effects of HHS may be particular beneficial in some high-risk patients.     

Optimized Pulse Durations Minimize the Effect of Polarity Reversal on Defibrillation Efficacy with Biphasic Shocks

There are conflicting results on the effect of polarity change on the defibrillation efficacy of biphasic shocks possibly caused by different shock durations. The goal of the present study was to investigate the influence of polarity reversal on defibrillation efficacy for different biphasic shock durations in a porcine animal model. In eight anesthesized pigs using a transvenous/submuscular lead system DFTs for 4 phase 1 durations were determined: 8.1 ms, 6 ms, 3.8 ms and 1.7 ms. The phase 1/phase 2 ratio was constant at 60%/40%. For cathodal shocks, the defibrillation coil in the right ventricular apex was the cathode during phase 1 and for anodal shocks it was the anode. For both polarities, the strength-duration curve revealed a DFT minimum at 3.8 ms (cathodal shocks: 21.3 +/- 6.4 J, P < 0.001; anodal shocks: 21.9 +/- 8 J, P = 0.05). For anodal shocks and phase 1 durations of 1.7, 3.8, and 6 ms there was no significant difference of the stored energy at the DFT compared to cathodal shocks. In contrast, significantly lower DFTs were observed for anodal shocks with a phase 1 duration of 8.1 ms (28.8 +/- 6.4 J compared to 33.1 +/- 5.9 J for cathodal shocks, P = 0.006). The effect of lower defibrillation energy requirements with polarity reversal depends on the total biphasic shock duration; for the pulse duration with the lowest DFT, polarity reversal does not increase defibrillation efficacy of biphasic shocks.     

HISTAMINE RELEASE IN HUMAN SUBJECTS BY MODIFIED GELATIN (HAEMACCEL) AND DEXTRAN: AN EXPLANATION FOR ANAPHYLACTOID REACTIONS OBSERVED UNDER CLINICAL CONDITIONS?

Histamine release by modified gelatin (Haemaccel) and dextran(Macrodex) has been demonstrated in volunteers by direct andindirect methods. In a pilot study of Haemaccel, histamine releasewas observed in six of seven volunteers. The highest plasmahistamine concentration was 4.8 ng/ml, the lowest 1.7 ng/ml:two of the subjects showed slight allergic reactions. UsingHaemaccel batch 2551, 10 out of 12 subjects reacted to the rapidinfusion of Haemaccel with increased plasma histamine concentrations,whereas none reacted to Ringer’s solution. None of the10 subjects had an allergic reaction, but an increase in gastricsecretion was observed in eight. Changes in the venous basophilgranulocyte count were found in both those who reacted and thosewho did not react to Haemaccel. After the rapid infusion ofdextran the highest plasma histamine concentration was 5.0 ng/ml,the lowest 1.3 ng/ml. The withdrawal of blood had no influenceon plasma histamine concentration. The incidences of histaminerelease produced by Haemaccel varied with different batches.Thus, it seems unlikely that immunological mechanisms are principallyresponsible. Nine instances of allergic and anaphylactoid reactionsto plasma substitutes have been reported, seven after Haemaccelinfusion, and two after dextran administration. One of the patientswho received dextran died. Histamine release was always associatedwith Haemaccel infusion and corresponded in extent to the clinicalsymptoms observed, but there was no significant histamine releaseassociated with the reactions to dextran.     

Prostacyclin aerosol and inhaled nitric oxide fail to reverse pulmonary vasoconstriction induced by thromboxane analogue in dogs

Inhalation of either prostacyclin (PGI₂) as an aerosol or nitric oxide (NO) has been shown to elicit selective pulmonary vasodilation during hypoxic pulmonary vasoconstriction in dogs. Hypoxia may produce cardiovascular changes confounding interpretation of drug effects. Therefore, we investigated the effects of PGI₂-aerosol and inhaled NO (50 p.p.m.) on pulmonary pressure-flow relationships (P/Q_ plots) during thromboxane analogue (U46619) induced pulmonary vasoconstriction. In eight anaesthetized dogs infusion of U46619 (0.33 ± 0.18 μg kg_¹ min^-1) increased the slope (3.5 ± 1.1 to 8.4 ± 1.7 mmHg L^-1 min^-1, P < 0.001) and the intercept (4.4±2.3 to 10.2 ± 4.6 mmHg, P < 0.01) of P/Q plots indicating pulmonary vasoconstriction. Inhalation of both aerosolized PGI₂ solution (10μgmL^-1) and NO (50 p.p.m.) reduced neither the slope nor the intercept of the P/Q_ plots. Increasing the concentration of the aerosolized PGI₂ solution to 50 μg mL^-1: (n= 3) did not enhance the effect on pulmonary circulation but systemic vascular resistance fell by 23%. Oxygenation and intrapulmonary shunt remained unchanged during both PGI₂-aerosol and inhaled NO. The failure of PGI₂-aerosol to induce pulmonary vasodilation indicates that during aerosolization PGI₂-concentrations at receptor sites on pulmonary vessels were insufficient to surmount U46619 induced vasoconstriction; this notion is supported by unchanged arterial plasma concentrations of the PGI₂ degradation product 6-keto-PGF_lα. Considering that NO inhaled at comparable concentrations in sheep reversed U46619 induced pulmonary vasoconstriction, species differences may account for the failure of both PGI₂-aerosol and NO to dilate pulmonary vessels in dogs.