Is warm retrograde blood cardioplegia better than cold for myocardial protection?

Serial ultrastructural evaluation of myocardial ischemic injury after infusion of del Nido cardioplegia in the human heart

OBJECTIVES

The safe ischemic time after a single-dose del Nido cardioplegia (DNC) infusion has not yet been established. This study evaluated the progression of myocardial ischemic injury to establish the safe ischemic time after a single-dose DNC infusion in the human heart using a transmission electron microscope.

METHODS

Seven hearts extracted from heart transplant recipients after infusion of 1000 mL single-dose DNC were evaluated. Serial left ventricular myocardial tissue samples were collected every 30 minutes for 180 minutes. Ischemic injuries in the mitochondria and nuclei were scored from 0 to 3 (0 = normal, 0.5 = slight, 1 = moderate, 2 = severe, and 3 = irreversible).

RESULTS

At the time of extraction, 83.5% of the mitochondria were normal. The proportion of mitochondria with moderate ischemic injury increased gradually from 1.4% at extraction to 52.5% at 180 minutes. From 90 minutes to 180 minutes, the proportion of mitochondria with severe and irreversible injury increased from 0.8% to 4.4% and 0.3% to 1.3%, respectively. A significant linear correlation was identified between the average ischemic injury score of mitochondria and ischemic time (P < .001). Most nuclei showed moderate to severe ischemic injury at every time point (61.0%-85.2%). A significant linear correlation was also found between the average ischemic injury score of nuclei and ischemic time (P < .001).

CONCLUSIONS

Myocardial ischemic injury progresses gradually, and irreversible ischemic injury begins to occur 90 minutes after initial DNC infusion in the adult human heart. Therefore, redosing of DNC may be required after 90 minutes of aortic crossclamp time during adult cardiac surgery.

Minimal Invasive Pericardial Perfusion Model in Swine: A Translational Model for Cardiac Remodeling After Ischemia/Reperfusion Injury

Rationale

Adverse remodeling leads to heart failure after myocardial infarction (MI), with important impact on morbidity and mortality. New therapeutic approaches are needed to further improve and broaden heart failure therapy. We established a minimally invasive, reproducible pericardial irrigation model in swine, as a translational model to study the impact of temperature on adverse cardiac remodeling and its molecular mechanisms after MI.

Objective

Chronic heart failure remains a leading cause of death in western industrialized countries, with a tremendous economic impact on the health care system. Previously, many studies have investigated mechanisms to reduce infarct size after ischemia/reperfusion injury, including therapeutic hypothermia. Nonetheless, the molecular mechanisms of adverse remodeling after MI remain poorly understood. By deciphering the latter, new therapeutic strategies can be developed to not only reduce rehospitalization of heart failure patients but also reduce or prevent adverse remodeling in the first place.

Methods and Results

After 90 min of MI, a 12Fr dual lumen dialysis catheter was place into the pericardium via minimal invasive, sub-xiphoidal percutaneous puncture. We performed pericardial irrigation with cold or warm saline for 60 min in 25 female farm pigs after ischemia and reperfusion. After one week of survival the heart was harvested for further studies. After cold pericardial irrigation we observed a significant decrease of systemic body temperature measured with a rectal probe in the cold group, reflecting that the heart was chilled throughout its entire thickness. The temperature remained stable in the control group during the procedure. We did not see any difference in arrhythmia or hemodynamic stability between both groups.

Conclusion

We established a minimally invasive, reproducible and translational model of pericardial irrigation in swine. This method enables the investigation of mechanisms involved in myocardial adverse remodeling after ischemia/reperfusion injury in the future.

Disruption of desmin-mitochondrial architecture in patients with regurgitant mitral valves and preserved ventricular function

OBJECTIVE

Recent studies have demonstrated improved outcomes in patients receiving early surgery for degenerative mitral regurgitation (MR) rather than adhering to conventional guidelines for surgical intervention. However, studies providing a mechanistic basis for these findings are limited.

METHODS

Left ventricular (LV) myocardium from 22 patients undergoing mitral valve repair for American Heart Association class I indications was evaluated for desmin, the voltage-dependent anion channel, α-B-crystallin, and α, β-unsaturated aldehyde 4-hydroxynonenal by fluorescence microscopy. The same was evaluated in 6 normal control LV autopsy specimens. Cardiomyocyte ultrastructure was examined by transmission electron microscopy. Magnetic resonance imaging with tissue tagging was performed in 55 normal subjects and 22 MR patients before and 6 months after mitral valve repair.

RESULTS

LV end-diastolic volume was 1.5-fold (P < .0001) higher and LV mass-to-volume ratio was lower in MR (P = .004) hearts versus normal hearts and showed improvement 6 months after mitral valve surgery. However, LV ejection fraction decreased from 65% ± 7% to 52% ± 9% (P < .0001) and LV circumferential (P < .0001) and longitudinal strain decreased significantly below normal values (P = .002) after surgery. Hearts with MR had a 53% decrease in desmin (P < .0001) and a 2.6-fold increase in desmin aggregates (P < .0001) versus normal, along with substantial, intense perinuclear staining of α, β-unsaturated aldehyde 4-hydroxynonenal in areas of mitochondrial breakdown and clustering. Transmission electron microscopy demonstrated numerous electron-dense deposits, myofibrillar loss, Z-disc abnormalities, and extensive granulofilamentous debris identified as desmin-positive by immunogold transmission electron microscopy.

CONCLUSIONS

Despite well-preserved preoperative LV ejection fraction, severe oxidative stress and disruption of cardiomyocyte desmin-mitochondrial sarcomeric architecture may explain postoperative LV functional decline and further supports the move toward earlier surgical intervention.

The right ventricular annular velocity reduction caused by coronary artery bypass graft surgery occurs at the moment of pericardial incision

Background

Right ventricular (RV) long-axis function is known to be depressed after cardiac surgery, but the mechanism is not known. We hypothesized that intraoperative transesophageal echocardiography could pinpoint the time at which this happens to help narrow the range of plausible mechanisms.

Method

Transthoracic echocardiography was conducted in 33 patients before and after elective coronary artery bypass graft. In an intensively monitored cohort of 9 patients, we also monitored RV function intraoperatively using serial pulsed wave tissue Doppler (PW TD) transesophageal echocardiography.

Results

There was no significant difference in myocardial velocities from the onset of the operation up to the beginning of pericardial incision, change in RV PW TD S′ velocities 3% ± 2% (P = not significant).

Within the first 3 minutes of opening the pericardium, RV PW TD S′ velocities had reduced by 43% ± 17% (P < .001). At 5 minutes postpericardial incision, 2 minutes later, the velocities had more than halved, by 54% ± 11% (P < .0001). Velocities thereafter remained depressed throughout the operation, with final intraoperative S′ reduction being 61% ± 11% (P < .0001).

One month after surgery, in the full 33-patient cohort, transthoracic echocardiogram data showed a 55% ± 12% (P < .0001) reduction in RV S′ velocities compared with preoperative values.

Conclusions

Minute-by-minute monitoring during cardiac surgery reveals that, virtually, all the losses in RV systolic velocity occurs within the first 3 minutes after pericardial incision. Right ventricular long-axis reduction during coronary bypass surgery results not from cardiopulmonary bypass but rather from pericardial incision.

Predictors and Outcomes of Coronary Artery Bypass Grafting in ST Elevation Myocardial Infarction

BACKGROUND

Treatment of ST-elevation myocardial infarction has undergone great evolution since introduction of percutaneous coronary intervention (PCI). The purpose was therefore to assess the outcome of patients with ST-elevation myocardial infarction undergoing surgical revascularization with coronary artery bypass grafting (CABG).

METHODS

A total of 138 consecutive patients with ST-elevation myocardial infarction underwent CABG therapy between January 2000 and January 2007 at our institution. Prospectively recorded preoperative, intraoperative, and postoperative data were retrospectively screened for in-hospital mortality and major adverse cardiac events (MACE).

RESULTS

The delay between the onset of ST-elevation myocardial infarction symptoms and CABG procedures was within 6 hours in 37 patients, 7 to 24 hours in 21, 1 to 3 days in 15, 4 to 7 days in 24, and 8 to 14 days in 41 patients. Cardiogenic shock (Killip class > or = III) was present in 38 patients (28%), and 37 patients (27%) were referred for CABG after failed PCI. Overall in-hospital mortality was 8.7%, but mortality varied between 10.8% (< or = 6 hours), 23.8% (7 to 24 hours), 6.7% (1 to 3 days), 4.2% (4 to 7 days), and 2.4% (8 to 14 days), depending on time interval from symptom onset to operation. Overall, more nonsurvivors were women (58% versus 23%; p < 0.01), had higher preoperative cardiac troponin I levels (13.2 +/- 9.8 versus 4.5 +/- 4.2 ng/ml; p < 0.0001), and were more frequently in cardiogenic shock (83% versus 22%; p < 0.0001). Unadjusted univariable and risk-adjusted multivariable logistic regression analysis revealed age, female sex, preoperative cardiac troponin I levels, and cardiogenic shock to be the most potent predictors of in-hospital death and MACE.

CONCLUSIONS

CABG in ST-elevation myocardial infarction can be performed with acceptable risk by incorporating adequate management strategies. However, female sex, preoperative cardiac troponin I level, preoperative cardiogenic shock, and time to operation are major variables of mortality and morbidity results.

Normothermic versus hypothermic hyperkalemic cardioplegia: effects on myocyte contractility

BACKGROUND

This study was designed to determine the effects of prolonged hyperkalemic cardioplegic arrest under normothermic or hypothermic conditions with respect to left ventricular myocyte contractile performance and beta-adrenergic responsiveness.

METHODS

Isolated left ventricular porcine myocytes were randomly assigned to one of three groups: (group 1) normothermic control, (group 2) hypothermic cardioplegic arrest, or (group 3) normothermic cardioplegic arrest. Myocyte contractility was evaluated by high-speed video microscopy at baseline and after beta-adrenergic stimulation with isoproterenol (25 nmol/L).

RESULTS

Myocyte velocity of shortening was decreased after both hypothermic and normothermic cardioplegic arrest (68 +/- 2 and 69 +/- 2 microns/s, respectively) compared with normothermic control values (96 +/- 2 microns/s; p < 0.05). This relative reduction in baseline contractile function was equivalent in both cardioplegia groups (p = 0.5356). With beta-adrenergic stimulation, myocyte velocity of shortening was 186 +/- 4 microns/s in the hypothermic and 176 +/- 3 microns/s in the normothermic cardioplegia groups (p = 0.0563). However, myocyte contractility with beta-adrenergic stimulation was reduced in both cardioplegia groups compared with normothermic controls (205 +/- 4 microns/s; p < 0.05, respectively).

CONCLUSIONS

Hyperkalemic cardioplegic arrest under either normothermic or hypothermic conditions resulted in an equivalent reduction in baseline myocyte contractile function with reperfusion/rewarming. Hypothermic cardioplegic arrest may have provided mild protective effects on beta-adrenergic responsiveness. Nevertheless, these results suggest that an important contributory factor for diminished myocyte contractility after simulated cardioplegic arrest was prolonged exposure to a hyperkalemic environment.