Gordon N. Olinger

The implanted defibrillator: relation of defibrillating lead configuration and clinical variables to defibrillation threshold

Forty-two defibrillating lead systems for the automatic implantable defibrillator were implanted and tested in 41 patients. Two basic lead configurations were used: 1) spring-patch, consisting of a transvenous superior vena cava spring electrode as the anode and an apical or left lateral ventricular patch electrode (either small [13.9 cm2] or large [27.9 cm2]) as the cathode; and 2) patch-patch, consisting of an anterior right ventricular patch as the anode and a posterior left ventricular patch as the cathode. Of the 42 lead systems, 10 were spring-patch and 32 were patch-patch combinations. The defibrillation threshold for the patch-patch combinations (9.8 +/- 6.5 J, mean +/- standard deviation) was significantly (p less than 0.01) lower than that for the spring-patch combinations (19.1 +/- 10.3 J). Subgroup analysis revealed the lowest defibrillation thresholds for patch-patch combinations with at least one large patch. Total surface area of defibrillating leads was strongly negatively correlated with the defibrillation threshold (p less than 0.005). Analysis of the relation of clinical variables to defibrillation threshold revealed that only amiodarone therapy was independently associated with a significantly (p less than 0.05) higher defibrillation threshold. Thus, surface area of the defibrillating leads is a critical determinant of the defibrillation threshold for the implanted defibrillator. Patch-patch lead systems with at least one large patch may provide an increased safety margin for defibrillation. Conversely, amiodarone therapy is associated with higher defibrillation thresholds and may decrease the margin of safety.

Increased tolerance of the chronically hypoxic immature heart to ischemia. Contribution of the KATP channel.

BACKGROUND Hypoxia from birth in immature rabbits increases the tolerance of isolated hearts to ischemia compared with age-matched normoxic rabbits. We determined whether this increased tolerance to ischemia was due to an alteration in the ATP-sensitive potassium (KATP) channel and whether increased KATP channel activation was associated with increases in intracellular lactate. METHODS AND RESULTS Isolated immature rabbit hearts (7 to 10 days old) were perfused with bicarbonate buffer at 39 degrees C in the Langendorff mode at a constant pressure. Saline-filled latex balloons were placed in the left and right ventricles for measurement of developed pressure. A KATP channel agonist (bimakalim) or a KATP channel antagonist (glibenclamide) was added 15 minutes before a global ischemic period of 18 minutes, followed by 35 minutes of reperfusion. Rabbits raised from birth in hypoxic conditions (FIO2 = 0.12) displayed significantly enhanced recovery of developed pressure. The right ventricle was more tolerant of ischemia than the left ventricle in normoxic and hypoxic hearts. Bimakalim (1 mumol/L) increased the recovery of left ventricular developed pressure in normoxic hearts to values not different from those of hypoxic controls (43 +/- 3% to 67 +/- 5%) and slightly increased developed pressure in hypoxic hearts (67 +/- 5% to 72 +/- 5%). Glibenclamide (3 mumol/L) abolished the cardioprotective effect of hypoxia (67 +/- 5% to 43 +/- 5%). Constant-flow studies indicated that the effects of bimakalim and glibenclamide were independent of their actions on coronary flow. Ventricular lactate and lactate dehydrogenase concentrations were elevated in hypoxic hearts compared with normoxic control hearts. CONCLUSIONS Increased tolerance to ischemia exhibited by chronically hypoxic rabbit hearts is associated with increased activation of the KATP channel. This increased KATP activity may be the result of increased intracellular concentrations of lactate.

Successful Implementation of a Novel Internet Hybrid Surgery Curriculum: The Early Phase Outcome of Thoracic Surgery Prerequisite Curriculum E-Learning Project

Background:The internet CD-ROM thoracic surgery (TS) e-learning system was implemented in 2001 as a prospective randomized trial testing resident acceptance and educational impact of a unique web-based curriculum system on prematriculated TS residents. The Prerequisite Curriculum (PRC) contains 75 segments organized with textbook and case-based navigational systems. Methods:Web-based technology tracked the PRC use for each resident. Of 142 residents, 138 thoracic surgery residents matching in 2001 for 2002 matriculation participated in a prospective randomized trial comparing the PRC system to a control group. Two sets of in-training exams, as well as resident and faculty knowledge/performance surveys, were used from July 2001 through January 2004 for ongoing, blinded multidimensional evaluation. Results:Most residents (55/69) responded to the written prematriculation surveys and indicated they used the PRC (43/55), averaging 1.45 hours weekly. The PRC was rated as easy to use (8.3/10), a valuable study guide (7.7/10), and superior to traditional texts and journals for preresidency preparation (7.9/10). Web-based tracking revealed that 47/69 actually used the PRC. Sessions averaged 23.3 minutes with an average of 148 sessions over the prematriculation year. The in-training exam performance when evaluated at 1 and 9 months into the TS residency revealed a positive correlation between examination performance and PRC use. After TS residency matriculation, the self-evaluated knowledge and performance satisfaction scores were superior among PRC users in all categories. Simultaneous TS faculty evaluations of the same resident groups demonstrated smaller, but significant group differences. Conclusion:The implementation of the TS PRC has been exciting and successful. Future multidisciplinary curricular progress will hopefully continue to build upon this e-learning strategy.

Long-term internal cardiac defibrillation threshold stability.

The automatic implantable cardioverter‐defibrillator is tested intraoperatively with defibrillation trials to ensure effectiveness. It is unknown if the energy requirement for internal defibrillation remains stable and that once demonstrated effective, if the device will continue to be effective in terminating lethal ventricular arrhythmias. In this study, the defibrillation energy requirement was compared in 56 patients at the time of lead implantation to that obtained at the time of generator replacement. Mean time to generator replacement was 17. ± 6.6 months. The defibrillation threshold was stable over that time (11. 9 ± 6.7 joules compared to 12.7 ± 8.4 joules, NS). There was no relation between transmyocardial impedance and defibrillation threshold. In addition, no effect on defibrillation threshold was demonstrated by the use of various cardiac medications, concomitant surgery or the occurrence of clinical shocks during follow‐up.

Prevention of lipid accumulation in experimental vein bypass grafts by antiplatelet therapy.

The ameliorative effect of antiplatelet therapy on atherogenesis of vein grafts was assessed in autologous cephalic veins grafted into femoral arteries of 16 normolipemic and 11 hyperlipemic stumptailed macaque monkeys. Before grafting, one half of each vein was distended at high pressure (700 mm Hg) and the other half at low pressure (350 mm Hg). Eight normolipemic monkeys were treated with aspirin, 80 mg/day, and dipyridamole, 50 mg/day, and eight were controls. When grafts were harvested at 12 weeks, tissue cholesterol and,8‐apoprotein content in grafts from untreated monkeys were significantly higher than in ungrafted, uninjured veins. Antiplatelet therapy eliminated the increase in lipid content of vein segments distended at low pressure, and significantly lowered lipid content of segments distended at high pressure, though not to the control levels of ungrafted veins. Seven of the 11 hyperlipemic monkeys received antiplatelet drugs and four did not. The lipid content of all graft segments was significantly higher than in grafted or ungrafted veins from normolipemic monkeys. Antiplatelet therapy again significantly reduced the lipid content in vein segments distended at both levels of pressure, and also reduced the elevated cholesterol content in ungrafted veins. Although this animal preparation differs in many ways from human coronary bypass operations, these observations may be pertinent to the prevention of atherosclerosis in human vein bypass grafts.

Mortality and neurologic morbidity after repair of traumatic aortic disruption

BACKGROUND Traumatic disruption of the thoracic aorta frequently results in death before operative repair. The determinants of mortality after repair, however, are uncertain. In addition, intraoperative strategies for reducing the incidence of spinal cord injury remain controversial. METHODS The records of 45 consecutive patients undergoing repair of traumatic disruption of the thoracic aorta at a single institution during a 9-year period were reviewed in a retrospective fashion. Patient age ranged from 15 to 81 years (mean age, 33.9 years). Twenty-two patients (49%) had multiple associated injuries, and 8 (18%) had isolated aortic injuries. Nine patients (20%) experienced preoperative hypotension (systolic blood pressure of less than 90 mm Hg). Repair was performed with partial bypass in 22 patients, a heparinized shunt in 2, and no distal perfusion (clamp and sew technique) in 21. RESULTS Nine patient (20%) died after operation. Multivariate logistic regression analysis of preoperative and intraoperative variables identified advancing age and preoperative hypotension as independent predictors of operative death. The presence of associated injuries was not an independent predictor of operative death. All 4 patients with injuries proximal to the aortic isthmus died. Ten patients were excluded from analysis of spinal cord injury either because of preoperative neurologic deficit or because of death before postoperative evaluation. Six (17%) of the remaining 35 patients had development of paraplegia: 5 of the 15 patients having the clamp and sew technique, 1 of the 2 with a shunt, and 0 of the 18 patients with bypass (p < 0.05, clamp and sew versus bypass). In the clamp and sew group, patients in whom paraplegia developed had significantly longer aortic clamp times than those without neurologic injury (40.6 +/- 4.4 minutes versus 28.7 +/- 2.9 minutes, respectively; p < 0.05). CONCLUSIONS Advancing age, preoperative hypotension, and perhaps injury location are important determinants of death after repair of traumatic disruption of the thoracic aorta. Adjunctive perfusion with partial bypass should be used during repair to reduce the incidence of spinal cord injury.

Long-term complications of implantable cardioverter defibrillator lead systems.

Over a period of 8.5 years in 255 patients with full-system implantable cardioverter defibrillators, lead-specific complications requiring reoperation developed in 32 patients. A total of 36 leads were affected. Lead fracture was the cause of failure in half of these patients. Refinement and improvement in structural designs of these leads, use of endocardial leads, and attention to technical details during implantation should decrease the incidence of these complications.

Mitral valve prolapse requiring surgery. Clinical and Pathologic study

The clinical, hemodynamic, surgical, and pathologic findings in 30 patients who required mitral valvular surgery and who had a preoperative diagnosis of mitral valve prolapse were reviewed. The mean age of the patients was 59.5 years; 28 patients were over 45 years of age and 10 were over 60 years. Surprisingly, 20 were males. A long history of systolic murmur was common, whereas symptoms of heart failure were of abrupt onset. At the time of surgery, a local holosystolic murmur typical of mitral regurgitation was present, although a mid- to late systolic click was not heard in any of the patients. Electrocardiographic abnormalities were present in all patients, with 13 patients demonstrating atrial fibrillation. Only four patients had a normal heart size radiographically. Echocardiography confirmed the radiographic findings, in that 27 patients demonstrated left atrial and ventricular enlargement. All 29 patients undergoing cardiac catheterization and angiography demonstrated a prolapsing mitral valve with severe regurgitation. Surgical and pathologic examination revealed findings characteristic of a myxomatous valve in all patients, with 19 also demonstrating ruptured chordae tendineae. This study demonstrates that heart failure requiring valvular surgery occurs in a subset of patients with mitral valve prolapse. In this subset, males predominate and most are over 50 years of age. These patients may be asymptomatic for many years, demonstrating mild to moderate mitral valvular regurgitation, before heart failure develops.

Long-term survival after prehospital sudden cardiac death

One hundred thirty-nine survivors of prehospital sudden cardiac death were followed after their hospital discharge. Eighty patients were studied with coronary angiography and cardiac catheterization; 34 of these underwent coronary bypass surgery. After a maximum follow-up of 105 months, 89 patients were still alive. The probability of survival at 6 months, 1 year, 2 years, 3 years, 4 years, and 5 years was 88%, 86%, 78%, 70%, 63%, and 59%, respectively. Of the 43 cardiac deaths, 37 (86%) were secondary to documented recurrent ventricular fibrillation or occurred suddenly. Twelve percent of the total population had recurrent ventricular fibrillation in the first year following the initial cardiac arrest, 16% within 2 years, and 22% within 3 years. Of the 37 survivors dying from recurrent ventricular fibrillation, 32% died within the first 3 months following hospital discharge, 46% in the first year, 64% within 2 years, and 78% within the first 3 years. Most survivors were capable of resuming normal activities after hospital discharge. Only 7% demonstrated permanent neurologic impairment. Sixty-eight percent of the patients who were employed at the time of their prehospital sudden cardiac arrest returned to full-time employment. In the subset of 34 surgically treated patients, there have been six (18%) cardiac deaths. Four of these deaths were related to recurrent ventricular fibrillation, with one of these deaths occurring in the immediate postoperative period. The other three deaths related to recurrent ventricular fibrillation occurred 36 months (two deaths) and 49 months following the initial prehospital cardiac arrest.

Vasodilator effects of the sodium acetate in pooled protein fraction.

Paradoxical hypotension during rapid infusion of plasma protein fraction (PPF) has been attributed to yasodilation by bradykinin in PPF. This study employed a canine, controlled right heart bypass preparation to assess changes in systemic vascular resistance and venous capacitance during infusion of PPF and other possibly vasoactive mediators. Plasma protein fraction caused consistent vasodilation, whereas purified human albumin did not. This vasodilation could be ascribed entirely to acetate, present in PPF as a buffer. Bradykinin in PPF had no effect during venous infusion. Acetate is used widely as a buffer in intravenous and dialysate solutions. Its vasoactive properties must be recognized when such solutions are administered to patients with limited capacity to compensate for sudden vasodilation.