James E. Jordan

Gradual Reperfusion Reduces Infarct Size and Endothelial Injury but Augments Neutrophil Accumulation

BACKGROUND Reperfusion causes injury to the coronary artery endothelium primarily by neutrophil-mediated mechanisms. However, factors other than neutrophils may govern the extent of myocardial necrosis. This study tests the hypothesis that gradual initiation of reflow will reduce reperfusion injury and preserve postischemic endothelial function. METHODS In 16 anesthetized dogs, the left anterior descending artery was ligated for 60 minutes. In one group, reperfusion was initiated abruptly (abrupt, n = 8), whereas in the gradual reperfusion group (ramp, n = 8), flow was slowly initiated during the first 30 minutes of reperfusion. After reperfusion, coronary artery segments were isolated to assess postischemic endothelial function. RESULTS Infarct size (area of necrosis/area at risk) was significantly reduced in the ramp group (28.2% +/- 2.0%) compared with abrupt (41.6% +/- 1.4%). Neutrophil accumulation (myeloperoxidase) in the area at risk was significantly greater in the ramp group compared with abrupt (8.0 +/- 1.3 versus 3.5 +/- 0.8 U/g tissue). In isolated postischemic left anterior descending arterial rings, the concentration of acetylcholine that elicited a response 50% of the maximum possible response was significantly greater in abrupt (-6.88 +/- 0.04 log [mol/L]) than ramp (-7.62 +/- 0.04 log [mol/L]) and control (-7.68 +/- 0.003 log [mol/L]), suggesting endothelial dysfunction. The concentration of A23187 that elicited a response 50% of the maximum possible response was similarly greater in abrupt (-7.24 +/- 0.03 log [mol/L]) versus ramp (-7.62 +/- 0.03 log [mol/L]) and control (-7.8 +/- 0.04 log [mol/L]). Smooth muscle dysfunction (response to sodium nitrite) also occurred in the abrupt rings. CONCLUSIONS Gradual reperfusion of an ischemic area reduces infarct size and preserves endothelial function but paradoxically increases neutrophil accumulation within the area at risk.

Novel Approach to Early Detection of Doxorubicin Cardiotoxicity by Gadolinium-Enhanced Cardiovascular Magnetic Resonance Imaging in an Experimental Model

Background —To determine if cardiovascular magnetic resonance (CMR) measures of gadolinium (Gd) signal intensity (SI) within the left ventricular (LV) myocardium are associated with future changes in LV ejection fraction (LVEF) after receipt of doxorubicin (DOX). Methods and Results —Forty Sprague-Dawley rats were divided into 3 groups scheduled to receive weekly intravenous doses of: normal saline (NS) (n=7), 1.5 mg/kg DOX (n=19), or 2.5 mg/kg DOX (n=14). MR determinations of LVEF and myocardial Gd-SI were performed before and then at 2, 4, 7, and 10 weeks after DOX initiation. During treatment, animals were sacrificed at different time points so that histopathological assessments of the LV myocardium could be obtained. Within group analyses were performed to examine time-dependent relationships between Gd-SI and primary events (a deterioration in LVEF or an unanticipated death). Six of 19 animals receiving 1.5 mg/kg of DOX and 10/14 animals receiving 2.5 mg/kg of DOX experienced a primary event; no NS animals experienced a primary event. In animals with a primary event, histopathological evidence of myocellular vacuolization occurred (p=0.04), and the Gd-SI was elevated relative to baseline at the time of the event (p<0.0001) and during the measurement period prior to the event (p=0.0001). In all animals (including NS) without an event, measures of Gd-SI did not differ from baseline. Conclusions —After DOX, low serial measures of Gd-SI predict an absence of a LVEF drop or unanticipated death. An increase in Gd-SI after DOX forecasts a subsequent drop in LVEF as well as histopathologic evidence of intracellular vacuolization consistent with DOX cardiotoxicity.Background—We sought to determine whether cardiovascular magnetic resonance measures of gadolinium (Gd) signal intensity (SI) within the left ventricular myocardium are associated with future changes in left ventricular ejection fraction (LVEF) after receipt of doxorubicin (DOX). Methods and Results—Forty Sprague-Dawley rats were divided into 3 groups scheduled to receive weekly intravenous doses of normal saline (n=7), 1.5 mg/kg DOX (n=19), or 2.5 mg/kg DOX (n=14). Magnetic resonance determinations of LVEF and myocardial Gd-SI were performed before and at 2, 4, 7, and 10 weeks after DOX initiation. During treatment, animals were euthanized at different time points so that histopathologic assessments of the left ventricular myocardium could be obtained. Within-group analyses were performed to examine time-dependent relations between Gd-SI and primary events (deterioration in LVEF or an unanticipated death). Six of 19 animals receiving 1.5 mg/kg DOX and 10 of 14 animals receiving 2.5 mg/kg DOX experienced a primary event; no normal saline animals experienced a primary event. In animals with a primary event, histopathologic evidence of myocellular vacuolization occurred (P=0.04), and the Gd-SI was elevated relative to baseline at the time of the event (P<0.0001) and during the measurement period before the event (P=0.0001). In all animals (including normal saline) without an event, measures of Gd-SI did not differ from baseline. Conclusions—After DOX, low serial measures of Gd-SI predict an absence of an LVEF drop or unanticipated death. An increase in Gd-SI after DOX forecasts a subsequent drop in LVEF as well as histopathologic evidence of intracellular vacuolization consistent with DOX cardiotoxicity.

Early Detection of Doxorubicin Cardiotoxicity Using Gadolinium Enhanced Cardiovascular Magnetic Resonance Imaging

Background —To determine if cardiovascular magnetic resonance (CMR) measures of gadolinium (Gd) signal intensity (SI) within the left ventricular (LV) myocardium are associated with future changes in LV ejection fraction (LVEF) after receipt of doxorubicin (DOX). Methods and Results —Forty Sprague-Dawley rats were divided into 3 groups scheduled to receive weekly intravenous doses of: normal saline (NS) (n=7), 1.5 mg/kg DOX (n=19), or 2.5 mg/kg DOX (n=14). MR determinations of LVEF and myocardial Gd-SI were performed before and then at 2, 4, 7, and 10 weeks after DOX initiation. During treatment, animals were sacrificed at different time points so that histopathological assessments of the LV myocardium could be obtained. Within group analyses were performed to examine time-dependent relationships between Gd-SI and primary events (a deterioration in LVEF or an unanticipated death). Six of 19 animals receiving 1.5 mg/kg of DOX and 10/14 animals receiving 2.5 mg/kg of DOX experienced a primary event; no NS animals experienced a primary event. In animals with a primary event, histopathological evidence of myocellular vacuolization occurred (p=0.04), and the Gd-SI was elevated relative to baseline at the time of the event (p<0.0001) and during the measurement period prior to the event (p=0.0001). In all animals (including NS) without an event, measures of Gd-SI did not differ from baseline. Conclusions —After DOX, low serial measures of Gd-SI predict an absence of a LVEF drop or unanticipated death. An increase in Gd-SI after DOX forecasts a subsequent drop in LVEF as well as histopathologic evidence of intracellular vacuolization consistent with DOX cardiotoxicity.Background—We sought to determine whether cardiovascular magnetic resonance measures of gadolinium (Gd) signal intensity (SI) within the left ventricular myocardium are associated with future changes in left ventricular ejection fraction (LVEF) after receipt of doxorubicin (DOX). Methods and Results—Forty Sprague-Dawley rats were divided into 3 groups scheduled to receive weekly intravenous doses of normal saline (n=7), 1.5 mg/kg DOX (n=19), or 2.5 mg/kg DOX (n=14). Magnetic resonance determinations of LVEF and myocardial Gd-SI were performed before and at 2, 4, 7, and 10 weeks after DOX initiation. During treatment, animals were euthanized at different time points so that histopathologic assessments of the left ventricular myocardium could be obtained. Within-group analyses were performed to examine time-dependent relations between Gd-SI and primary events (deterioration in LVEF or an unanticipated death). Six of 19 animals receiving 1.5 mg/kg DOX and 10 of 14 animals receiving 2.5 mg/kg DOX experienced a primary event; no normal saline animals experienced a primary event. In animals with a primary event, histopathologic evidence of myocellular vacuolization occurred (P=0.04), and the Gd-SI was elevated relative to baseline at the time of the event (P<0.0001) and during the measurement period before the event (P=0.0001). In all animals (including normal saline) without an event, measures of Gd-SI did not differ from baseline. Conclusions—After DOX, low serial measures of Gd-SI predict an absence of an LVEF drop or unanticipated death. An increase in Gd-SI after DOX forecasts a subsequent drop in LVEF as well as histopathologic evidence of intracellular vacuolization consistent with DOX cardiotoxicity.

Basal nitric oxide expresses endogenous cardioprotection during reperfusion by inhibition of neutrophil-mediated damage after surgical revascularization ☆ ☆☆ ★ ★★ ♢

Ischemia-reperfusion damages endothelium and impairs basal production of nitric oxide. Basally released nitric oxide is cardioprotective by its inhibition of neutrophil activities. Loss of endogenous nitric oxide with endothelial injury may occur during two phases: cardioplegic ischemia and reperfusion (aortic declamping). This study tested the hypothesis that inhibition of endogenously released nitric oxide in hearts subjected to regional ischemia, cardioplegic arrest, and reperfusion (1) restricts endogenous cardioprotection and permits neutrophil-mediated damage and (2) expresses damage during the reperfusion phase. L-Nitro-arginine was used to block basal nitric oxide production. In 22 anesthetized dogs, the left anterior descending artery was ligated for 90 minutes followed by 1 hour of arrest with cold multidose (every 20 minutes) blood cardioplegia. Dogs were divided into three groups: the first group received standard unsupplemented blood cardioplegia (group 1, n = 8), in the second group L-nitro-arginine was administered as an additive to blood cardioplegic solution (1 mmol) and as an infusion during reperfusion (34 mg/kg) (group 2, n = 7), and in the third group L-nitro-arginine was administered only at reperfusion (group 3, n = 7). The ligature was released during the second infusion of cardioplegic solution. Infarct size (triphenyltetrazolium chloride) was increased in group 3 (L-nitro-arginine only at reperfusion) compared with that in group 1 (standard blood cardioplegia) (49% +/- 6% vs 34% +/- 2%, respectively), but was not further extended in group 2 (L-nitro-arginine as an additive to blood cardioplegic solution and at reperfusion) (56% +/- 3%, p > 0.05 vs group 3), which suggests primarily a reperfusion process. Polymorphonuclear neutrophil-specific myeloperoxidase activity in the area at risk was elevated comparably in groups 2 and 3 (group 2: 2.9 +/- 0.5 units/gm tissue, p = 0.06 vs group 1; group 3: 3.9 +/- 1.0 units/gm tissue, p < 0.05 vs group 1) compared with that in the standard blood cardioplegia group (1.7 +/- 0.3 units/gm tissue), suggesting polymorphonuclear neutrophil accumulation occurs primarily during reperfusion. Polymorphonuclear neutrophil adherence in ischemic-reperfused left anterior descending artery segments was comparably greater in group 2 (L-nitro-arginine as an additive to blood cardioplegic solution and at reperfusion: 195 +/- 21 polymorphonuclear neutrophils/mm2 of artery, p < 0.05 vs group 1) and group 3 (L-nitro-arginine only at reperfusion: 224 +/- 20 polymorphonuclear neutrophils/mm2 of artery, p < 0.05 vs group 1) relative to that in group 1 (108 +/- 19 polymorphonuclear neutrophils/mm2 of artery). There was no significant adherence to nonischemic circumflex arteries. We conclude that blockade of endogenous nitric oxide augments postischemic injury mediated by polymorphonuclear neutrophils, and this damage is expressed primarily during the reperfusion phase.

Endothelialization of Heart Valve Matrix Using a Computer-Assisted Pulsatile Bioreactor

Although calcification remains as the main clinical concern associated with bioprosthetic heart valve replacement surgery, there is evidence that tissue deterioration leads to thromboembolism. In such instances, measures that prevent thrombosis may be beneficial. To minimize thrombosis, endothelialization of the valve surface before implantation has been proposed to facilitate coverage. In this study we aimed to define the optimal flow parameters for the endothelialization of decellularized heart valves using endothelial progenitor cell (EPC)-derived endothelial cells (ECs). We assessed the thrombogenic characteristics of the endothelialized heart valve surface using a bioreactor. EPC-derived ECs were seeded on decellularized porcine valve scaffolds. A computer-controlled bioreactor system was used to determine the optimal flow rates. Successful endothelialization was achieved by preconditioning the cell-seeded valves with stepwise increases in volume flow rate up to 2 L/min for 7 days. We show that decellularized valve scaffolds seeded with EPC-derived ECs improved the anti-thrombotic properties of the valve, whereas the scaffolds without ECs escalated the coagulation process. This study demonstrates that preconditioning of ECs seeded on valve matrices using a bioreactor system is necessary for achieving uniform endothelialization of valve scaffolds, which may reduce thrombotic activity after implantation in vivo.

Bioreactors for Development of Tissue Engineered Heart Valves

Millions of people worldwide are diagnosed each year with valvular heart disease, resulting in hundreds of thousands of valve replacement operations. Prosthetic valve replacements are designed to correct narrowing or backflow through the valvular orifice. Although commonly used, these therapies have serious disadvantages including morbidity associated with long-term anticoagulation and limited durability necessitating repeat operations. The ideal substitute would be widely available and technically implantable for most cardiac surgeons, have normal hemodynamic performance, low risk for structural degeneration, thrombo-embolism and endocarditis, and growth potential for pediatric patients. Tissue engineered heart valves hold promise as a viable substitute to outperform existing valve replacements. An essential component to the development of tissue engineered heart valves is a bioreactor. It is inside the bioreactor that the scaffold and cells are gradually conditioned to the biochemical and mechanical environment of the valve to be replaced.

Timing of adding blood to prime affects inflammatory response to neonatal cardiopulmonary bypass.

Complications from systemic inflammation are reported in neonates following exposure to cardiopulmonary bypass. Although the use of asanguinous primes can reduce these complications, in neonates, this can result in significant haemodilution, requiring addition of blood. This study investigates whether the addition of blood after institution of bypass alters the inflammatory response compared with a blood prime. Neonatal swine were randomised into four groups: blood prime, blood after bypass but before cooling, blood after cooling but before low flow, and blood after re-warming. All groups were placed on central bypass, cooled, underwent low flow, and then re-warmed for a total bypass time of 2 hours. Although haematocrit values between groups varied throughout bypass, all groups ended with a similar value. Although they spent time with a lower haematocrit, asanguinous prime groups did not have elevated lactate levels at the end of bypass compared with blood prime. Asanguinous primes released less tumour necrosis factor α than blood primes (p=0.023). Asanguinous primes with blood added on bypass produced less interleukin 10 and tumour necrosis factor α (p=0.006, 0.019). Animals receiving blood while cool also showed less interleukin 10 and tumour necrosis factor α production than those that received blood warm (p=0.026, 0.033). Asanguinous primes exhibited less oedema than blood primes, with the least body weight gain noted in the end cool group (p=0.011). This study suggests that using an asanguinous prime for neonates being cooled to deep hypothermia is practical, and the later addition of blood reduces inflammation.