Cardiac Ischemia Reperfusion Injury Following Instillation of 20 nm Citrate-capped Nanosilver

BACKGROUND

Silver nanoparticles (AgNP) have garnered much interest due to their antimicrobial properties, becoming one of the most utilized nano-scale materials. However, any potential evocable cardiovascular injury associated with exposure has not been reported to date. We have previously demonstrated expansion of myocardial infarction after intratracheal (IT) instillation of carbon-based nanomaterials. We hypothesized pulmonary exposure to Ag core AgNP induces a measureable increase in circulating cytokines, expansion of cardiac ischemia-reperfusion (I/R) injury and is associated with depressed coronary constrictor and relaxation responses. Secondarily, we addressed the potential contribution of silver ion release on AgNP toxicity.

METHODS

Male Sprague-Dawley rats were exposed to 200 μl of 1 mg/ml of 20 nm citrate-capped Ag core AgNP, 0.01, 0.1, 1 mg/ml Silver Acetate (AgAc), or a citrate vehicle by intratracheal (IT) instillation. One and 7 days following IT instillation the lungs were evaluated for inflammation and the presence of silver; serum was analyzed for concentrations of selected cytokines; cardiac I/R injury and coronary artery reactivity were assessed.

RESULTS

AgNP instillation resulted in modest pulmonary inflammation with detection of silver in lung tissue and alveolar macrophages, elevation of serum cytokines: G-CSF, MIP-1α, IL-1β, IL-2, IL-6, IL-13, IL-10, IL-18, IL-17α, TNFα, and RANTES, expansion of I/R injury and depression of the coronary vessel reactivity at 1 day post IT compared to vehicle treated rats. Silver within lung tissue was persistent at 7 days post IT instillation and was associated with an elevation in cytokines: IL-2, IL-13, and TNFα and expansion of I/R injury. AgAc resulted in a concentration dependent infarct expansion and depressed vascular reactivity without marked pulmonary inflammation or serum cytokine response.

CONCLUSIONS

Based on these data, IT instillation of AgNP increases circulating levels of several key cytokines, which may contribute to persistent expansion of I/R injury possibly through an impaired vascular responsiveness.

High-fat diet induces Ikkbeta and reduces insulin sensitivity in rats with low running capacity

Rats bred for a high-capacity to run (HCR) do not develop insulin resistance on a high-fat diet (HFD) vs. those bred for a low-capacity for running (LCR). Recently, a link between obesity and insulin resistance has been established via IKKbeta action and IRS-1 Ser (312/307) phosphorylation. This study measured IkappaBalpha and IRS-1 pSer (307) in mixed gastrocnemius muscle in HCR and LCR rats challenged with a 12-wk HFD. HFD treatment resulted in significantly higher glucose and insulin levels in LCR vs. HCR rats. IkappaBalpha levels, an inverse indicator of IKKbeta activity, were lower in LCR vs. HCR rats maintained on chow diet and were reduced further following HFD in LCR rats only. IRS-1 pSer (307) in the LCR rats increased on the HFD vs. chow. We conclude that differences in glucose tolerance between LCR and HCR rats are at least partly explained by differences in IKKbeta activity and pSer (307) levels.

A carotid stenosis model in canines

A carotid stenosis model was developed in canines in order to study the effects of systemic blood pressure and hemodilution on cerebrovascular perfusion and metabolism during cardiopulmonary bypass in the setting of significant coexistent inflow stenosis. Under general anesthesia, through a low midline neck incision, the carotid sheath was entered and the carotid artery was isolated and retracted medially. The vertebral artery could be identified posterolaterally. After ligating the vertebral artery with a 00 silk tie, carotid stenosis was created by tying bilateral carotid arteries over an 18-gauge needle using a 00 silk tie. The needle was then removed, leaving a tight stenosis. To determine the degree of stenosis, arteriograms were performed, revealing high-grade lesions of greater than 90% stenosis in the carotid arteries and absence of flow through the vertebral arteries. Cerebral blood flow studies during cardiopulmonary bypass (CPB) were performed, revealing a significant decline. Carotid arteries were harvested at the conclusion of the experiments, revealing tight lesions on direct inspection. The mean gradient measured across stenotic segments was >25 mm Hg. In conclusion, a carotid stenosis model can be created successfully in dogs by ligating the vertebral arteries bilaterally and simply using the shaft of a needle to standardize the lumen size of the carotid arteries. We found the diameter of an 18-gauge needle sufficient to produce stenoses of greater than 90% as evidenced by arteriograms.

Transformation of nonvascular acellular tissue matrices into durable vascular conduits

BACKGROUND

Prosthetic grafts commonly used for vascular reconstruction are limited to synthetics and cross-linked tissue grafts. Within these devices, graft infections are common, compliance mismatch is significant, and handling qualities are poor. Natural biological tissues that are unfixed have been shown to resist infections and be durable and compliant. A natural biological matrix that could be remodeled appropriately after implantation would be a desirable graft for vascular reconstruction.

METHODS

SynerGraft tissue engineering strategies have been used to minimize antigenicity and produce stable unfixed vascular grafts from nonvascular bovine tissues. These grafts have replaced the abdominal aortas of 8 dogs that have been followed for up to 10 months.

RESULTS

Early evaluation indicates rapid recellularization by recipient smooth muscle actin positive cells, which become arranged circumferentially, into the media. Arterioles were present in the adventitial areas and endothelial cells were seen to cover lumenal surfaces. After 10 months, grafts were patent and not aneurysmal.

CONCLUSIONS

These data indicate that SynerGraft processing of animal tissues is capable of producing stable vascular conduits that exhibit long-term functionality in other species.

Differences in myocardial and peripheral VEGF and KDR levels after acute ischemia

BACKGROUND

Recent clinical use of vascular endothelial growth factor (VEGF) in the treatment of both myocardial and peripheral ischemia has suggested the possibility of tissue specific coregulation of VEGF and its receptors (eg, kinase domain region [KDR]). The present study was performed to detect the relationship between VEGF and KDR protein levels after acute myocardial and peripheral ischemia.

METHODS

Eleven dogs were divided into two groups: peripheral ischemia (n = 6, ligation of major limb arteries) and myocardial ischemia (n = 5, circumflex artery ligation). Muscle biopsy specimens were taken from the perfusion territories of the occluded circumflex artery and limb arteries 3 hours and 6 hours after ligation. Protein levels were determined using Western blot analysis.

RESULTS

In myocardium, VEGF levels increased on average eightfold from baseline (p < 0.05) both 3 hours and 6 hours after occlusion, whereas myocardial KDR levels dropped by about 60% at 3 hours and 80% at 6 hours (p < 0.05). With limb ischemia, both VEGF and KDR levels were significantly elevated at 3 hours.

CONCLUSIONS

In acute ischemia, regulation of VEGF and KDR may be controlled differently in cardiac and skeletal muscle. Myocardial KDR levels showed a significant decrease from baseline compared with a significant rise with peripheral ischemia.

Regional left ventricular systolic function in humans during off-pump coronary bypass surgery

BACKGROUND

Controversy exists as to whether off-pump CABG with local occlusion results in clinically significant myocardial ischemia during the occlusion period. This study was undertaken to delineate the effects of transient local coronary artery occlusion on regional systolic function.

METHODS AND RESULTS

Eight consenting patients undergoing left internal mammary to left anterior descending coronary artery (LAD) bypass were instrumented with a left ventricular pressure catheter and 2 subepicardial cylindrical ultrasonic dimension transducers placed in the minor axis dimension in the region served by the LAD. A digital sonomicrometer was used to collect data before, during, and after coronary occlusion from which percent systolic shortening and pressure-dimension loops were derived. Measuring devices were removed immediately after the final time point. All patients tolerated the procedure well, and there were no complications. Average duration of local occlusion needed for CABG was 15.9+/-4.4 minutes (range, 12 to 26 minutes). Local occlusion was associated with a decrease in peak systolic shortening from 5.8+/-0.8% to 1.8+/-0.8%. In all cases, function returned to baseline after restoration of flow. Pressure-dimension loops confirmed these findings and no evidence of diastolic creep. Linear repression analysis of degree of stenosis versus change in segmental shortening revealed a significant inverse correlation.

CONCLUSIONS

Local occlusion of the LAD resulted in a transient decrease in myocardial function during occlusion with complete recovery during reperfusion. This change was less significant with increasing degrees of coronary stenosis. These data suggest that local occlusion is not associated with permanent myocardial injury but that ischemic changes do occur that may be clinically significant, especially in patients with lesser degrees of coronary stenosis.

Minimally invasive cardiac operation: adapting cardioprotective strategies

BACKGROUND

Minimally invasive heart operation differs from traditional cardiac operations through the omission of a sternotomy, cardiopulmonary bypass, or both. Current concerns with minimally invasive operation include: operative safety, learning curve, operative times, arrest times, and adequacy of myocardial protection. While many of the protective strategies used for traditional procedures may be applied to minimally invasive cardiac operations, the safe applications of minimally invasive operations require unique techniques of myocardial protection.

METHODS AND RESULTS

Omission of extracorporeal perfusion may benefit patients through attenuation of systemic inflammatory response, decrement in neurologic insults, and reduced bleeding complications. As a counterbalance, surgeons must consider long-term operative quality and level of myocardial protection provided during beating heart coronary operation. Current issues that must be addressed include: pharmacologic management, coronary collateralization and ischemic preconditioning, the utility of intraluminal coronary shunts, and technical adequacy of the anastomosis. Nonsternotomy cardiopulmonary bypass methods utilize alternative incisions and "port-access" technology, and may render more rapid patient recovery including: decreased pain, shortened hospital stay, and more rapid return to work. Altered strategies of myocardial protection in a closed chest environment must address: method of cannulation, technique of aortic occlusion, rapidity and maintenance of cardiac arrest, and cardiac de-airing techniques.

CONCLUSIONS

Previous obstacles to minimally invasive cardiac operations included limitations in operative exposure, inadequate perfusion technology, and inability to provide myocardial protection. Recent advances in videoscopic visualization and evolving mechanisms of myocardial protection may justify the expanding application of minimally invasive techniques.

A paradox of cerebral hyperperfusion in the face of cerebral hypotension: the effect of perfusion pressure on cerebral blood flow and metabolism during normothermic cardiopulmonary bypass

BACKGROUND

The purpose of this study was to determine the impact of perfusion pressure on cerebral blood flow (CBF) and metabolism during normothermic cardiopulmonary bypass (CPB) and after weaning.

MATERIALS AND METHODS

Two groups of mongrel dogs were studied (Group A, CPB perfusion at 50 mm Hg, n = 6; and Group B, CPB perfusion at 100 mm Hg, n = 6). All animals underwent 2 h of normothermic bypass at cardiac indexes >2.1 L/min/m2 and were weaned from pump, maintained at pressures >75 mm Hg, and followed for an additional 2 h.

RESULTS

In both groups CBF increased over 85% from baseline, in proportion to the hemodilution during the initiation of CPB. Intracranial pressure increased moderately in both groups during CPB, compromising CBF at 1 h in Group A, but not in Group B. The Group A cerebral metabolic rate for oxygen (CMRO2), however, remained unchanged as the percentage of oxygen extraction increased to compensate for the decreased CBF. During recovery, temperature, mean arterial pressure, and cerebral perfusion pressure were not significantly different between the two groups. However, the CBF, percentage of oxygen extracted, and CMRO2 were significantly lower in Group A.

CONCLUSIONS

Normothermic CPB initiated with a crystalloid prime and performed at the lower end of a 50-70 mm Hg perfusion window resulted in a highly significant increase in CBF in order to compensate for hemodilution, while at the same time reduced the perfusion pressure available to supply the increased CBF. Together, these two events create a hemodynamic paradox of hyperperfusion in the face of hypotension. The reduction in CMRO2 in Group A is yet to be explained but seems to remain coupled to CBF and could represent a previously undescribed protective mechanism of hibernating cerebral tissue, similar to the phenomena of ischemic preconditioning in the heart, where cerebral tissue is stimulated to lower metabolism in response to inadequate CBF.

Video-assisted minimally invasive mitral valve surgery

OBJECTIVE

This study was done to determine the potential benefits of minimally invasive mitral surgery performed with intraoperative video assistance.

METHODS

From May 1996 until March 1997, a minithoracotomy and video assistance were used in 31 consecutive patients undergoing mitral repair (n = 20) and replacement (n = 11). Their ages ranged from 18 to 77 years (59 +/- 2.6 years; mean +/- standard error of the mean). Ejection fractions were 35% to 62% (55% +/- 1.5%). Operations were done with either antegrade/retrograde (n = 10) or antegrade (n = 19) cold blood cardioplegia and a new transthoracic crossclamp or with ventricular fibrillation (n = 2). Peripheral arterial cannulation (n = 28) and pump-assisted right atrial drainage (n = 26) were used most often.

RESULTS

No hospital deaths occurred, but the 30-day mortality was 3.2%. Complications included deep venous thrombosis and a phrenic nerve palsy in one patient each. No patient had a stroke or required reoperation for bleeding. Postoperative echocardiography showed excellent valve function in all but one patient. Cardiopulmonary bypass and arrest times averaged 183 +/- 7.2 and 136 +/- 5.5 minutes, respectively. Compared with 100 patients having conventional mitral valve operations, these patients had significantly shorter hospitalization times (8.6 +/- 0.5 vs 5.1 +/- 0.9 days, p = 0.05). Moreover, 81% of the later cohort were discharged between day 3 and 5 (3.6 +/- 0.2 days). Hospital charges (decreases 27%, p = 0.05) and costs (decreases 34%, p < 0.05) were less than in conventional operations. Patient follow-up suggested minimal perioperative pain and rapid recovery.

CONCLUSIONS

Early results suggest that video-assisted minimally invasive mitral operations can be done safely. These methods may benefit patients through less morbidity, earlier discharge, and lower cost.

Successful small diameter arterial grafting using cryopreserved allograft arteries

Intimal hyperplasia (IH) limits the long-term success of veins as arterial grafts. IH occurs in veins partly as an adaptive process to arterial pressure conditions. The authors have previously reported early success with cryopreserved (CP) saphenous veins as aortocoronary bypass grafts, and they have hypothesized that CP arterial segments were already structurally adapted for arterial conditions. Six femoral arterial segments were harvested from three adult donor dogs, and cryopreserved. The segments were thawed and implanted into six recipient dogs, in end-to-end fashion, as interpositional grafts in the femoral artery. A similar length of native femoral artery was removed from the implant site and grafted in the contralateral femoral artery of the same animal to serve as native autograft-matched controls. Grafts were harvested bilaterally after 2 (n = 3) and 4 weeks (n = 3), perfusion fixed (80 mmHg, 15 min), and analyzed histologically. All grafts were patent at harvest, and flows distal to the grafted segments were not significantly different between grafts within an animal either at implant or subsequent harvest. Although CP arterial grafts still showed slight but significant dilation compared with native autograft, the dilation was much less than seen previously with either CP or native venous segments. No evidence of inflammation or IH was seen in CP arterial grafts. The absence of early IH or inflammation suggests that CP small diameter arteries may perform better than many currently available allograft tissues and synthetic prosthetics.

The temporal expression of transforming growth factor-beta 1 in early aortocoronary vein grafts

The success of coronary reconstructive procedures is limited by the high incidence of restenosis secondary to intimal hyperplasia (IH). Transforming growth factor-beta 1 (TGF-beta 1) is a growth factor which has been shown to be important in the early development of IH in arteries and peripheral vein grafts. To date, there is little information concerning the early remodeling in aortocoronary vein grafts (ACVG). The purpose of this study was to characterize the expression of TGF-beta 1 expression in early aortocoronary vein grafts. Eighteen mongrel dogs underwent aortocoronary vein bypass grafting. Vein grafts were excised at 2 hr, 4 hr, and 7 days after implantation, snap frozen, and processed for ribonuclease protection assays (RPA) using 32P-labeled riboprobes for TGF-beta 1 and 18 S rRNA. TGF-beta 1 expression was quantified by densitometric analysis of autoradiographs which were expressed as a ratio TGF-beta 1/rRNA. Representative vessel rings were also collected for histology. There was a significant rise in TGF-beta 1 expression in the 2-hr vein grafts (0.42 +/- 0.04 compared to control saphenous vein (0.21 +/- 0.05, P < 0.02). In addition, there was significant downregulation of TGF-beta 1 at 4 hr (0.28 +/- 0.05) and at 7 days (0.18 +/- 0.01) when compared to 2 hr (P < 0.05). Histological specimens showed minimal intimal hyperplasia at 7 days. These results show for the first time an acute rise in TGF-beta 1 expression in ACVG. This upregulation quickly subsides by 4 hr and gene expression approaches control values by 7 days. By understanding this temporal relationship of expression one could better target potential therapeutic modalities to attenuate IH.

In-line leukocyte filtration during bypass. Clinical results from a randomized prospective trial

Leukocyte mediated pulmonary injury may delay recovery after cardiac surgery, and leukocyte depletion during bypass has been suggested. Two groups of patients were randomly, prospectively assigned from 50 sequential patients to undergo open heart surgery using cardiopulmonary bypass, either with (n = 25) or without (n = 25) leukocyte filters. The two groups were not significantly different regarding age, gender, race, pre-operative ejection fraction, pump time, or cross-clamp time. Post operative arterial blood gases (pO2: 173 +/- 66 vs 192 +/- 107; pCO2: 30.2 +/- 8.2 vs 30.8 +/- 8.0), pulmonary vascular resistance (PVR 105 +/- 45 vs 112 +/- 50 dyne cm-5), time on ventilator (17.8 +/- 6.4 vs 19.7 +/- 8.6 hr), and length of hospital stay (7.65 +/- 4.57 vs 8.52 +/- 5.87 days) were not different between groups (mean +/- SD, with vs without filters, respectively). Arterial oxygenation was somewhat poorer, and PVR was somewhat lower in the leukocyte filtered group. However, these trends did not produce significant decreases in total ventilator time or length of hospital stay. In-line filtration did remove leukocytes, but did not reduce circulating leukocyte count. In effect, leukocyte filtration produced an effective leukocyte concentration at the filter site. These data do not support routine incorporation of in-line leukocyte filtration during bypass.

Extracardiac adjustment of mitral chordae replacement

This study was designed to determine the feasibility of completing mitral chord repair externally when the heart was weaned from bypass. Ten anesthetized dogs (22.9 +/- 4.6 kg) were placed on cardiopulmonary bypass through a left thoracotomy. The left atrium was opened and one or two marginal chords of the anterior mitral leaflet were divided. A double-armed 2-O polypropylene suture was placed in the margin of the mitral leaflet, and both suture ends were brought outside of the ventricle through the anterior papillary muscle, but were not anchored. Production of mitral incompetence was verified when the animals were weaned from bypass. Mean left atrial pressure (LAPm), the v wave of the left atrial pressure (LAPv), systolic billowing of the anterior leaflet into the left atrium above the mitral closure line (two-dimensional echocardiography, long axis), and function curves (left atrial-aortic systolic pressure, LAPv-AoSP) were used to determine valve competence and functionality of the repair. All values are expressed as means +/- SE. Acute mitral incompetence in this model was associated with severe left atrial bulging, left atrial billowing of the anterior leaflet (7-12 mm, 9.6 +/- 1.6 mm), significantly increased left atrial pressure [LAPv, 30.5 +/- 5.8; LAPm, 23.6 +/- 4.3 mm Hg; both P < 0.01 vs control (10.5 +/- 2.5 and 7.5 +/- 2.7 mm Hg, respectively)], and decreased systemic pressure development (AoSP, 84 +/- 8.8 vs 108 +/- 12.3 mm Hg; P < 0.01). The slope of the atrial-systemic pressure curve was decreased significantly, shifted to the right and reduced by more than half (2.1069 vs 0.9190; P < 0.05). External adjustment of the pledgeted suture ends returned all values to within control limits (LAPv, 12.7 +/- 4.1; LAPm, 9.8 +/- 4.3; AoSP, 104 +/- 10.5; LAP-AoSP slope, 2.0909; all P = n.s.), atrial bulging was not evident, and atrial displacement of the valve leaflet could no longer be visualized. These data suggest that mitral chord repair is feasible through a thoracotomy and, more importantly, final adjustments to obtain optimal chord length can be completed externally, guided by changes in dynamic, physiologic parameters.

Complex valve operations: antegrade versus retrograde cardioplegia?

BACKGROUND

Increasingly complex cardiac procedures demand optimal myocardial protective techniques during the requisite interval of aortic cross-clamping. For complex procedures in which prolonged cross-clamp times are anticipated, we favor combined antegrade and retrograde cold blood cardioplegia. Advantages include rapid arrest, uniform distribution, and an uninterrupted operation.

METHODS

We retrospectively evaluated the cases of 194 consecutive patients who underwent complex cardiovascular procedures between January 1988 and October 1994. Procedures performed included valve repair and coronary artery bypass grafting (23.7%), valve replacement and coronary artery bypass grafting (19.1%), complex aortic arch and valve procedures (16.6%), valve repair only (16.5%), reoperative valve (9.8%), and multiple-valve replacements (9.3%). Cardioplegic arrest times averaged 113 +/- 38.5 minutes (range, 52 to 292 minutes).

RESULTS

Postoperative left and right ventricular function was evaluated using transesophageal echocardiography. The echocardiograms revealed a 3.1% incidence of new left ventricular dysfunction and no case of right ventricular dysfunction. Of the patients evaluated, 75.7% required little (< 3 micrograms.kg-1.min-1 of dopamine hydrochloride) or no inotropic support postoperatively. The 30-day mortality rate was 3.1%, and no death was due to cardiac failure.

CONCLUSIONS

We conclude that myocardial protection using a combined antegrade and retrograde cardioplegia technique permits excellent myocardial protection during complex cardiovascular procedures requiring long arrest times.

Allopurinol improves myocardial reperfusion injury in a xanthine oxidase-free model

The ability of allopurinol to protect against reperfusion injury in the heart has usually been attributed to its xanthine oxidase (XO)-inhibiting properties. Human myocardium however, has exhibited low levels of XO activity. To investigate the effects of allopurinol in an XO-free model and determine whether pretreatment is necessary, 12 domestic pigs (15 kg to 20 kg) underwent occlusion of the left circumflex for 8 minutes followed by reperfusion for 4 hours. One group received allopurinol infusion (5 mg/kg IV) at occlusion over 45 minutes and a control group (n = 6) received a saline infusion (same volume). Left ventricular and aortic pressure, electrocardiograms, and regional wall motion (sonomicrometry) were monitored throughout the process. Regional blood flow (microspheres) were obtained before, during, and 5, 10, and 30 minutes after ischemia. Occlusion decreased transmural flow at the midpapillary level by 75% (0.28 versus 1.10 mL/minute/g). The allopurinol-treated group exhibited a mild, generalized hyperemia at 5 minutes (ischemic zone: 1.44 versus 1.10 mL/min/g, which returned to control levels at 10 and 30 minutes. In contrast, the control group was associated with only 80% restoration of resting blood flow at 5 minutes (0.84 versus 1.10 mL/min/g), which stabilized at 63% of control levels at 10 and 30 minutes. When evaluated for the propensity of arrhythmias using an arbitrary arrhythmia score, the allopurinol group demonstrated no myocardial ectopy when compared with the focal ectopy routinely encountered in the control group at all time intervals.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cocaine on left ventricular function. Relation to increased wall stress and persistence after treatment

BACKGROUND

To determine whether alterations in left ventricular (LV) function after a cocaine infusion are due to reduced myocardial contractility or changes in loading conditions, we examined LV function in 30 morphine-sedated, closed-chest dogs. We also wanted to determine the time course of the effects of cocaine on LV function after the infusion was stopped.

METHODS AND RESULTS

Two-dimensional echocardiography and hemodynamics provided LV fractional shortening and end-systolic wall stress data. Radionuclide ventriculography was also performed. Four groups of dogs received saline or cocaine infusions of 10, 30, or 100 micrograms.kg-1.min-1. Cocaine was infused for 90 minutes with ECG and arterial pressure monitoring. Animals were monitored for an additional 120 minutes after the infusion ended. Arterial pressure rose over the course of the experiment in all four groups, but saline and cocaine 10 micrograms.kg-1.min-1 did not significantly change ejection fraction. Cocaine 30 and 100 micrograms.kg-1.min-1 acutely increased arterial pressure and heart rate but decreased ejection fraction from 0.64 +/- 0.06 to 0.45 +/- 0.08 and from 0.65 +/- 0.10 to 0.46 +/- 0.11, respectively. Additionally, cocaine 100 micrograms.kg-1.min-1 decreased fractional shortening from 36 +/- 9% to 23 +/- 12%. However, cocaine 30 and 100 micrograms.kg-1.min-1 also increased wall stress from 42 +/- 15 to 65 +/- 11 g/cm2 and from 37 +/- 15 to 90 +/- 33 g/cm2, respectively. These results were analyzed by use of the relation between wall stress and fractional shortening as an index of contractility. Fractional shortening after cocaine infusion was displaced downward as a result of increased wall stress rather than changes in contractility. In addition, alteration of afterload with phenylephrine (6 micrograms/kg) and sodium nitroprusside (10 micrograms/kg) before and during infusion of cocaine 100 micrograms.kg-1.min-1 showed similar regression lines for wall stress to fractional shortening.

CONCLUSIONS

Ejection-phase indexes of LV function were reduced by cocaine in this model of conscious, sedated dogs, but effects were attributable to increased wall stress rather than to reduced myocardial contractility. These effects persisted for at least 2 hours after the infusion was stopped.

Experimental supplemental vein grafting and hypoperfusion syndrome

An additional saphenous vein graft (SVG) sometimes is required to the same coronary system if acute internal thoracic artery (ITA) graft flow is inadequate. These experiments were conducted to determine the consequences produced by ITA-SVG dual grafting. Fourteen dogs each received two coronary grafts (without bypass, using local occlusion) to the proximal circumflex coronary artery, using the ITA and an SVG, and then the circumflex artery was ligated proximally. Simultaneous flow in both grafts was determined at rest and after pharmacologic (adenosine, phenylephrine) or physiologic (cardiac pacing) stimulation. Serial angiography was performed during the first 4 weeks after grafting to determine patency patterns of the ITAs and SVGs. In the resting heart, flow was 7.5 +/- 1.6 mL/min (17.5%) in the ITA graft and 35.3 +/- 5.2 mL/min (82.5%) in the SVG (mean +/- standard deviation [% total distal perfusion]), and the combined flow was not significantly different from the original native flow. Intravenous adenosine (0.2 mg.kg-1.min-1) preferentially increased both the total ITA flow and its fractional contribution to total distal perfusion (18.4 +/- 3.2 [31.1%]; p < 0.05 versus rest). Saphenous vein graft flow was not changed significantly (40.3 +/- 6.0 mL/min), in part due to a modest decrease in arterial pressure. In contrast, intravenous phenylephrine (0.003 mg.kg-1.min-1) decreased both absolute ITA flow and its relative contribution to distal perfusion (6.1 +/- 1.1 [10.9%]; p < 0.05 versus rest), despite an increased systemic perfusion pressure, which increased SVG flow significantly (50.1 +/- 4.8 [89.1%]; p < 0.05 versus rest).(ABSTRACT TRUNCATED AT 250 WORDS)

Distal flow determinants in canine myocardium perfused through internal thoracic artery bypass grafts

The dynamic reactivity and the acute, recruitable flow capacity of an internal thoracic artery (ITA) graft remains unclear. These experiments were conducted in 20 anesthetized dogs with the left ITA grafted to the circumflex artery, off pump, using a brief local occlusion. The left main coronary artery was occluded, rendering the entire left ventricle, including anterior descending artery and circumflex regions, totally dependent on the ITA graft. When the left main coronary artery was occluded, the ITA flow immediately increased more than fivefold (93.4 +/- 9.6 mL/min; mean +/- standard deviation), representing an absolute flow value three times higher than ITA flow measured in situ on the chest wall (27.5 +/- 9.6 mL/min; p < 0.05 versus control), and the ITA graft provided total resting flow requirements (93.4 +/- 9.6 mL/min) for both left anterior descending and circumflex coronary artery perfusion territories at levels comparable with measured native flow values (y = (0.9555)x + 21.9272; r = 0.976; p < 0.05). Pharmacologic challenge with adenosine (0.2 mg.kg-1.min-1 intravenously) significantly increased the graft flow (120.3 +/- 18.7 mL/min; p < 0.05 versus control), but also significantly decreased the mean arterial pressure (85.4 +/- 5.0 versus 74.6 +/- 6.1 mm Hg; p < 0.05). Phenylephrine (0.003 mg.kg-1.min-1 intravenously) significantly decreased ITA graft flow (81.2 +/- 9.0 mL/min; p < 0.05 versus control) despite significantly increased perfusion pressure (84.8 +/- 6.3 versus 108.2 +/- 8.6 mm Hg; p < 0.05 versus control).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac pacing induced flow responses in internal thoracic artery and saphenous vein coronary artery bypass grafts

The flow reactivity of an internal thoracic artery (ITA) graft and a vein graft for multiple coronary beds in response to different modes of cardiac pacing remains unclear. These experiments were conducted in 14 anesthetized dogs with the ITA or the vein grafted to the circumflex coronary artery, off pump, using a brief local occlusion. The left main coronary artery was occluded, rendering the entire left ventricle totally dependent upon the ITA graft or the vein graft. When the left main coronary artery was occluded and the heart rate was 120 beats per min, graft flow was 93.4 +/- 9.6 ml per min in the ITA, and 96.1 +/- 10.4 ml per min in the vein graft. Atrial pacing to increase heart rates 25% to 150 beats per min increased both the ITA graft flow (110.3 +/- 9.7 ml per min, p < 0.05 versus flow in sinus rhythm) and the vein graft flow (109.8 +/- 7.9 ml per min, p < 0.05 versus flow in sinus rhythm). The increases in flow in both cases were not attributable to changes in perfusion pressure. In contrast, ventricular pacing to the same heart rate decreased systemic pressure slightly, but insignificantly. Despite the slight decrease in perfusion pressure, ventricular pacing increased ITA flow (107.9 +/- 8.4 ml per min, p < 0.05 versus flow in sinus rhythm), but the increase in vein graft flow was not significant compared with flow in sinus rhythm (102.1 +/- 7.3 ml per min, p = ns versus flow in sinus rhythm).(ABSTRACT TRUNCATED AT 250 WORDS)

Bilateral vs single internal thoracic artery grafting for left main coronary artery occlusion

This study was conducted to compare the coronary flow distributed by single and bilateral internal thoracic artery (ITA) grafts in the setting of the left main coronary occlusion. Ten dogs underwent coronary artery bypass grafting through a left thoracotomy, off pump, using a brief local occlusion to perform the anastomosis. Dogs were randomly assigned to receive either a single left ITA (LITA) graft to the circumflex coronary artery (CFX), or bilateral ITA grafts, with additional placement of the right ITA (RITA) to the left anterior descending artery (LAD). After the grafts were placed, the left main coronary artery was ligated. Electromagnetic flows were obtained in the LAD and the CFX proximally and distally to ITA grafts in both groups before grafting and after grafting. ITA flow in situ was also measured before rotation from the chest wall. Total left ventricular flow requirements were satisfied equally well by either a single LITA graft (116.7 +/- 11.6 mL/min) or bilateral ITA grafts (total, 116.8 +/- 9.6 mL/min divided as LITA, 55.9 +/- 7.4 mL/min; RITA, 60.9 +/- 12.0 mL/min). When two grafts were replaced, competitive flow in the proximal regions of both native vessels was noted, although basal flow requirements were maintained. When an individual graft was occluded in the bilaterally grafted system, the remaining graft immediately recruited the additional flow, demonstrating that either right or left ITA can support flow demands five to six times higher than in situ chest wall flow (RITA, 21.9 +/- 3.1 mL/min; LITA, 22.3 +/- 4.9 mL/min). These data suggest that in this canine model, a single ITA graft can support the entire flow requirements of the left ventricle. Assuming no intervening stenosis is present in native coronary systems, bilateral ITA grafting may provide a margin of safety, but under resting conditions, provides no perfusion advantages over a single ITA graft.

Modification of De Vega's tricuspid annuloplasty for experimental tricuspid regurgitation

We propose a new experimental model of tricuspid annular dilatation and provide some modifications to De Vega's tricuspid annuloplasty to treat this condition. Tricuspid annular dilatation was done by creating ten 1.5-mm incisions around the circumference of the tricuspid annulus. The annulus became significantly dilated from 7.6 cm to 9.4 cm (p < 0.01). After dilatation, 2-0 polypropylene stitches were placed circumferentially around the tricuspid annulus and the suture ends were brought outside the heart through the right atrial wall. After cardiac resuscitation, the following hemodynamic variables were measured as preload was increased incrementally: mean right atrial pressure, v wave of atrial pressure, right ventricular end-diastolic pressure, and cardiac output. Measurements were obtained and preload-output curves were constructed for three time periods: before annular dilatation (Control); after dilatation, but before external adjustment (Before); and after external modification of the annulus (After). Following cardiac resuscitation, right atrial and ventricular pressures were significantly higher after annular dilatation, compared to control values. The preload-output curve was shifted to the right, and cardiac output could not be increased above 0.9 L/min. Once the extracardiac adjustment was accomplished, these pressures were returned to control values, and the preload-output relationship was returned to normal curve.

Masking of heparin activity in the activated coagulation time (ACT) by platelet procoagulant activity

The effect of platelet procoagulant activity in the Activated Coagulation Time (ACT) was measured in whole blood anticoagulated with various levels of heparin before or after reversal with protamine. Similar studies were carried out on blood anticoagulated with hirudin to distinguish procoagulant activity from heparin neutralization in platelet preparations. At 0.5-1.0 units/mL antithrombin activity with heparin or hirudin, the ACT was lowered progressively by the addition of increasing concentrations of lysed platelets to as much as 20 seconds below the baseline clotting time obtained with unanticoagulated blood samples. Neutralization of higher concentrations of heparin with protamine produced an ACT below baseline in the presence of lysed platelets. Aprotinin (400 KIU/mL) prolonged the ACT slightly in heparinized whole blood, but did not prevent the lowering of the ACT by lysed platelets to baseline or below. Recirculation of heparinized whole blood in a simulated cardiopulmonary bypass circuit generated platelet microparticles detected by flow cytometry. An increase in platelet microparticles was associated with a decrease in the amount of protamine needed to reach the baseline ACT in blood samples removed from the circuit at various time points during recirculation. A chromogenic anti-Factor Xa assay of heparin did not show a change with increasing microparticle concentration during recirculation. These findings indicate a masking of heparin activity by the procoagulant activity of platelet membrane microparticles that could affect reversal of heparin based on the ACT.

Effect of chronic native flow competition on internal thoracic artery grafts

Residual competitive flow from the native coronary artery has been proposed as a mechanism that reduces flow in an internal thoracic artery graft (ITA), resulting in narrowing and ultimately failure of the graft. Results from acute experiments have indicated that competitive flow from a fully patent native artery did not abolish ITA graft flow. The present study was designed to examine the consequences of dynamic flow competition between the native vessel and the ITA graft in a chronic model. Fifteen mongrel dogs underwent coronary artery bypass grafting using the pedicled left ITA anastomosed to the normal, fully patent circumflex (CFX) coronary artery. The procedure was performed through a sterile thoracotomy, without systemic cardiopulmonary bypass, using a brief local occlusion to construct the anastomosis. Intraoperatively, ITA flow was measured in situ on the chest wall, before the pedicle was mobilized. Internal thoracic artery graft and distal CFX flow were measured after the anastomosis was completed, with and without brief occlusion of the proximal CFX. Angiography was performed 72 hours, 4 weeks, and 8 weeks later; graft patency and diameter were evaluated. After 8 weeks, open-chest direct flow measurements comparable with the intraoperative assessment were obtained. Two grafts (13%) occluded early, the technical result of poor anastomotic construction. In the 13 remaining animals, all grafts were widely patent at all time points. Internal thoracic artery flow in situ averaged 10.9 +/- 7.8 mL/min (mean +/- standard deviation), and was maintained after grafting (11.5 +/- 4.4 mL/min; p = not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Multicenter trial of automated nitroprusside infusion for postoperative hypertension. Titrator Multicenter Study Group

Hypertension is common after a cardiac operation and may result in postoperative hemorrhagic and other complications. Most often this problem has been treated using manually controlled doses of intravenous sodium nitroprusside. To evaluate the clinical impact of an automated closed-loop administration system on patients after cardiotomy, a prospective trial was conducted at nine clinical centers. Patients with hypertension were managed by either manual nitroprusside titration (n = 532) or a closed-loop automated titration system (n = 557). Patient groups were not significantly different in age, weight, or height. Moreover, the types of surgical procedures were comparable: primary coronary artery bypass grafting, 59.2% and 58.9%, manual group versus automated group; repeat coronary artery bypass grafting, 10.5% and 8.6%, respectively; valve procedures, 11.3% and 15.1%, respectively; and other cardiac procedures, 19.0% and 17.4%, respectively (all p = not significant). The automated group showed a significant reduction in the number of hypertensive episodes per patient (1.8 +/- 0.2 versus 0.6 +/- 0.07; p = 0.0001. At the same time, the number of hypotensive episodes per patient was reduced with automated closed-loop titration (0.40 +/- 0.05 versus 0.30 +/- 0.03; p = 0.02). Chest tube drainage (866 +/- 37 mL versus 693 +/- 23 mL [mean +/- standard error of the mean]; p = 0.0001), percentage of patients receiving transfusion (40.0% versus 33.0%; p = 0.02), and total amount transfused (2.4 +/- 0.12 units versus 2.0 +/- 0.10 units; p = 0.0003) were all reduced significantly by the use of an automated titration system.(ABSTRACT TRUNCATED AT 250 WORDS)

Competitive flow from a fully patent coronary artery does not limit acute mammary graft flow

The shriveled, stenotic mammary graft sometimes observed after internal mammary artery (IMA) to coronary artery bypass grafting has been attributed to competitive flow from the insufficiently stenosed native coronary vessel. To study further the effects of native coronary artery competing flow on IMA graft flow, 10 dogs (mean weight, 23.5 +/- 3.69 kg) underwent coronary artery bypass grafting using the pedicled left IMA anastomosed to a normal, fully patent proximal circumflex (CFX) coronary artery. The procedure was performed through a left thoracotomy, off pump, using a brief local occlusion to perform the anastomosis. Native in situ IMA flow, CFX flow distal to the anastomosis, and IMA graft flow were measured using calibrated electromagnetic flow probes. When the CFX proximal to the anastomosis was occluded transiently, IMA flow increased to supply 100% of the previously measured distal CFX flow (60.2 +/- 7.9 mL/min). When both the IMA graft and CFX proximal to the anastomosis were patent, total distal perfusion was maintained (58.9 +/- 7.8 mL/min) and relative IMA graft flow (26.5 +/- 3.3 mL/min) was proportional to the relative diameter of the IMA graft to the native coronary artery (r = 0.96). The mean flow in the IMA in situ on the chest wall before its division was 23.8 +/- 8.1 mL/min. These results suggest that, at least acutely in a canine model, IMA graft flow is maintained above in situ levels even when grafted to a completely patent coronary artery and that acute competitive flow probably does not cause mammary artery shriveling.

Internal mammary artery use. Sternal revascularization and experimental infection patterns

We have described previously the acute sternal devascularization produced by mobilization of one or both internal mammary arteries (IMAs). The present experiments were conducted to examine the time course of sternal revascularization and infection patterns after IMA use. Twenty-four 8-week-old domestic pigs were obtained from a herd in which active Streptococcus faecalis had been detected in recent litters. After control blood flow procedures (microspheres) were completed, each pig underwent a median sternotomy; one or both IMAs were mobilized as a pedicle, and the sternotomy was repaired. Repeat blood flow determinations were made in half the pigs at 1 week and in the remainder after 2 weeks. The pigs were killed, the wound was examined, cultures were taken as indicated, and tissue was harvested for blood flow analysis. Despite the retention of an intact IMA on the contralateral side, persistent, significant sternal ischemia existed 2 weeks after repair. However, when both IMAs were used, the extent of devascularization was exaggerated, and revascularization was impaired further. Revascularization of intercostal muscle occurred more rapidly and was essentially returned to normal 2 weeks after sternotomy and IMA harvest. Active mediastinitis with erosion of the sternum was found in one (17%) of six pigs at 1 week and in four (67%) of six pigs at 2 weeks when the IMAs had been rotated bilaterally. No wound infections were detected in the single IMA resection group. These data suggest that bilateral IMA mobilization may delay an already slow revascularization process and predispose to infectious complications.

Surgical management of renal cell carcinoma with extensive intracaval involvement using a venous bypass system suitable for rapid conversion to total cardiopulmonary bypass

Renal cell carcinoma involves the vena cava in approximately 4% of the patients. Presently surgical extirpation is the only form of therapy that can result in cure. Recently management of extensive vena caval involvement has involved the use of cardiopulmonary bypass with circulatory arrest and hypothermia. We describe a technique using a venous bypass pump system (femoral vein to right atrium) for resection of renal cell carcinoma with suprahepatic vena caval extension (type II), which avoids the risks and complications of cardiac arrest and hypothermia but allows for rapid conversion to total cardiopulmonary bypass should the intraoperative need arise.

Feasibility of intraoperative aortic root angiography in the identification of critical coronary lesions

Early revascularization is critical for the treatment of acute myocardial infarction (AMI) because the ischemic myocardium begins to suffer irreversible damage after 4 h from the onset of symptoms. However, to make a diagnosis, perform coronary angiography, and prepare for operative revascularization usually takes longer than 4 h. Also, once a patient develops severe cardiogenic shock, coronary angiography is often impossible. Without angiography, the patient is no longer a candidate for surgical repair. To circumvent this problem, we designed this experiment to determine whether intraoperative aortic root angiography after cardiopulmonary bypass and cardioplegic arrest could satisfactorily substitute for angiographic examination in the identification of critical coronary lesions. The feasibility of this approach was tested in dog hearts in which one or tow of the major coronary arteries were ligated. The ascending aorta was then clamped, contrast material was injected, and continuous real-time fluoroscopic images were obtained and recorded on videotape. The videotape was then analyzed by three physicians independently, each without prior knowledge of the lesion locations. Lesions of the left anterior descending artery, the circumflex coronary artery, and the right coronary artery were identified with 94, 91, and 94% accuracy, respectively, for an overall identification rate of 92%. We conclude that aortic root angiography reliably demonstrates coronary artery lesions, and refinements in this technique may allow certain patients to undergo coronary operations without preoperative catheterization.

Improvement in thoracic aortic pressure after proximal aortic cross-clamping by balloon occlusion of the distal aorta

Spinal cord hypoperfusion injury is a devastating complication of cross-clamping the proximal thoracic aorta. The collateral circulation around the cross-clamp is generally poorly developed, and the run-off is immense, resulting in extremely low thoracic aortic and spinal cord perfusion pressures. The authors postulated that balloon occlusion of the abdominal aorta might confine this reduced collateral flow around the cross-clamp to the thoracic aorta. In 8 of 16 dogs subjected to aortic cross-clamping of the aorta just beyond the arch vessels, the abdominal aorta was also occluded by a balloon. Thoracic aortic pressure and spinal cord perfusion pressure were significantly higher in the animals with aortic balloon occlusion than in those without balloon occlusion (77 +/- 8 mm Hg versus 26 +/- 1 mm Hg, p less than 0.01, and 67 +/- 8 mm Hg versus 18 +/- 2 mm Hg, p less than 0.01, at 10 minutes after cross-clamping). Abdominal aortic balloon occlusion increases thoracic aortic pressure after the aorta is cross-clamped proximally. Further studies are necessary in primates to assess the effect of this procedure in spinal cord perfusion and the rate of paraplegia.

Donor-specific tolerance permits burn allografting without increased sepsis

Early excision and allografting of massive burns is beneficial. However, chronic immunosuppression, utilized to prolong allograft survival, increases the potential risk of infection. We have previously shown long-term skin allograft survival in mice with a 30% total body surface area (TBSA) burn by inducing donor-specific tolerance (DST) using only perigrafting administration of antithymocyte globulin (ATG) and donor bone marrow (DBM). Chronic immunosuppression is avoided. This study tests whether induction of DST compromises host resistance to infection. Resistance to a septic challenge created by cecal ligation and puncture (CLP) 10 days after a 30% TBSA burn was investigated in the following groups of mice: [table: see text] Positive blood cultures were documented for 97% of mortalities. Burn excision and grafting significantly (P less than or equal to 0.05) decreased mortality. No increased mortality was seen in allografted mice receiving ATG or ATG and DBM compared to isografted mice receiving no immunosuppression. These studies suggest that skin allografting with DST may permit the benefits of burn excision without the risks of infection seen with chronic immunosuppression.

Reappraisal of the mechanism for cerebrospinal fluid hypertension during aortic surgery

Cerebrospinal fluid (CSF) hypertension during aortic surgery is a poorly understood, multifactorial event that may increase the risk of spinal cord injury. To assess the factors that may contribute to changes in CSF pressure during aortic surgery, measurements of ascending arterial and CSF pressures were made in 17 anesthetized mongrel dogs. Changes in CSF patterns were monitored under several conditions tested in random sequence. These included systemic hypertension produced by an infusion of phenylephrine, cross-clamping of the descending thoracic aorta, and manual, superior displacement of the transverse aortic arch (arch elevation), either alone or in conjunction with the cross-clamp. Hypertension, cross-clamping, and cross-clamping combined with arch elevation all produced significant increases in ascending mean arterial pressure (204 +/- 20, 170 +/- 8, and 158 +/- 11 mm Hg, respectively, vs. 117 +/- 8 mm Hg [control]; (p less than 0.01). Small, nonsignificant increases in CSF pressure were detected in the cross-clamp group, but none were detected with hypertension alone, despite significant increases in ascending arterial blood pressure in both groups. Thus, neither arterial hypertension nor cross-clamping alone could be demonstrated directly to cause significant CSF hypertension. However, when aortic elevation (displacement) was combined with cross-clamping, the rise in CSF pressure increased to significant levels, even though the ascending arterial hypertension was least severe in this group. In contrast, arch elevation alone did not produce any significant increase in ascending arterial pressure but did produce an approximately 114% increase in CSF pressure (15.2 +/- mm Hg vs. 7.7 +/- 1 mm Hg [control]; p less than 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)

Improved protection of chronically inflow-limited myocardium with retrograde coronary sinus cardioplegia

The effects of retrograde coronary sinus cardioplegia (CSC) and conventional aortic route cardioplegia (ARC) on reperfusion blood flow patterns were compared in 18 mongrel dogs having ameroid-induced coronary collaterals. Animals were placed on cardiopulmonary bypass and cooled systemically. The aorta was clamped, and the hearts were arrested with a bolus infusion of hypothermic (4 degrees C) hyperkalemic cardioplegic solution delivered either into the aortic root or through a balloon catheter placed in the coronary sinus. After 45 minutes of ischemic arrest, hearts were reperfused, and blood flow patterns were measured at 1, 5, 10, and 60 minutes. In the normal region, a significant hyperemia occurred with both CSC and ARC. However, the peak reactive transmural flow was 120% more with ARC than with CSC (4.55 +/- 0.45 vs. 2.12 +/- 0.19 ml/min/g, respectively; p less than 0.05) and remained elevated after 60 minutes of reperfusion, when CSC flows had returned to control levels. In the collateral-dependent region, a significant hyperemia was observed with ARC that persisted throughout reperfusion. However, with CSC, no significant changes in blood flow were detected at any time during reperfusion. Thus, the decreased hyperemic response after arrest suggests a reduced energetic debt with CSC compared with ARC and may indicate superior myocardial protection with CSC. This is particularly evident in chronically inflow-restricted myocardial regions.

Postextrasystolic potentiation: analysis of methods of induction

Studies were conducted in 15 patients with coronary artery disease to determine if the type of pacing used to induce an extrasystole had a bearing on subsequent postextrasystolic potentiation (PESP) and if the fact that these were evaluated in jeopardized or nonjeopardized portions of the ventricle altered the ability to assess PESP. Two types of pacing were used. In the first group, all beats in the test sequence (basic heart rate, extrasystole, and postextrasystole) were delivered from a programmed external pacemaker. This group was termed the "all-paced" (AP) group, and the postextrasystole was introduced before a compensatory pause could occur, so that loading conditions within the ventricle at the last regular beat and after the extrasystole were not different. In the second group, the extrasystole was coupled to the sensed intrinsic heart rate of the patient, and the postextrasystole was allowed to occur spontaneously. This group was termed the "sensed-paced" (SP) group. Despite differences in basic heart rates and postextrasystolic intervals between the two groups, comparable results were obtained with the two techniques. However, the postextrasystole in the SP group occurred much earlier than expected, probably due to intrinsic cardioacceleration during ventriculography. The net result was that loading conditions in this group before and after the extrasystole were also not different from each other. Results from the pacing techniques were not influenced by whether they were obtained from jeopardized or nonjeopardized segments.(ABSTRACT TRUNCATED AT 250 WORDS)

Postextrasystolic potentiation: regional wall motion before and after revascularization

We evaluated the augmentation of contractility which follows an extrasystole (postextrasystolic potentiation: PESP) in patients before and after coronary revascularization surgery for angina pectoris. PESP was induced by methods which result in essentially identical loading conditions of the ventricle for the beat before the extrasystole and the beat after the extrasystole. We evaluated regional ventricular function before and after revascularization in "jeopardized" segments (supplied by a coronary vessel with significant coronary disease) and "nonjeopardized" segments (supplied by a vessel without significant disease). All coronary lesions were proximal to all three anterior or all posterior segments. Those jeopardized segments with patent grafts which had augmented with PESP improved their baseline function following revascularization. Conversely, those jeopardized segments which failed to augment with PESP decreased their basic function following revascularization. Those segments in which the grafts were occluded failed to augment with PESP after attempted revascularization. Perioperative myocardial infarction resulted in a drop in ejection fraction and a failure to augment with PESP. The nonjeopardized segments responded to PESP similarly to the ischemic augmenting segments. The results of this study suggest that PESP does detect ventricular segments which will improve basic function following revascularization. Those segments which fail to augment with PESP are most likely more ischemic than the augmenting segments, will not improve, and may even decrease function following revascularization.

Applicability of echocardiography in volume determinations in experimental animals

A method is described for the use of echocardiography in volume determinations in the experimental animal. Suitability of the technique in both acute and chronically implanted animals was tested. Stroke volumes derived from calculations based on echo data were compared with those obtained by an electromagnetic flow probe placed around the aorta. High correlation was found in both the acute (r = 0.96, P less than 0.001) and the chronic (r = 0.89, P less than 0.001) preparations. Cardiac output computed from echocardiographic data and compared with those based on either flow probe or indicator-dilution techniques also showed a high degree of correlation in both the acute (r = 0.91 and 0.95, respectively; P less than 0.001) and chronic (r = 0.98 and 0.94, respectively, P less than 0.001) preparations. It is suggested that echocardiography, because of the potential to measure many indicators of myocardial function in addition to volume, represents a significant improvement in the techniques available for basic cardiovascular experimentation.

Use of a programmable calculator for rapid, low-cost processing of echocardiographic records

A comparative study was performed to determine the accuracy of a programmable calculator with supplemental digitizer in echocardiographic analysis. Twenty separate measurements were collected per heart beat from five different dogs, taking five heart beats from each dog. The measurements were made by an echocardiographic technician (ET), echocomputer (EC), and by a programmable calculator (HP). In a triple comparison (ET-HP, ET-EC, HP-EC) there were no significant differences in the values obtained, suggesting that the programmable calculator can provide a highly accurate and rapid means of processing echocardiographic measurements, thereby providing the advantages of the echocomputer without the cost of such a device.

Cardiac taurine levels during endotoxemia

Three hours after dogs were given an intravenous injection of Escherichia coli endotoxin significant decreases in cardiac taurine levels were observed in the apex and epicardial regions of the right ventricle and in all regions sampled from the left ventricle. A decrease in taurine was seen in all regions of the heart (including the atria) by 90 min after endotoxin treatment but the results were not statistically significant. Echocardiography and left ventricular cannulation were used in a separate group to confirm that the dose of endotoxin used was adequate to produce depression of cardiac output and force of contraction.

Postextrasystolic potentiation and contractile reserve: requirements and restrictions

These studies were conducted to examine the basic characteristics of postextrasystolic potentiation (PESP) and the relationship of loading effects to PESP. Measurements of left ventricular (LV) and aortic pressures, the rate of pressure rise, and echocardiographically determined LV dimensions were made in anesthetized open-chest dogs. The hearts were paced, and timed extrasystoles were introduced that were followed by postextrasystoles (PES). PES's were elicited after an interval equal to either a full compensatory pause or a time when the diastolic properties of the LV could not be distinguished from control (isolength). Potentiation of contraction for the PES's introduced after an isolength pause was dependent on both the heart rate and the extrasystolic interval, whereas the PES's that occurred after a full pause showed no dependence on either of these intervals. PESP elicited during the isolength period was not dependent on either preload and afterload. It is concluded that PESP depends on the combination of heart rate and extrasystolic and postextrasystolic intervals. Further, PESP may be inaccurate in assessing contractile reserve unless the heart rate and extrasystolic interval are known and the PES is introduced after an isolength pause.