Left ventricular dysfunction and disturbed O(2)-utilization in stunned myocardium: influence of ischemic preconditioning

Excellent Restoration of Left Ventricular Compliance After Prolonged Del Nido Single-Dose Cardioplegia in an In Vivo Piglet Model

Del Nido cardioplegia (DN) is used in congenital heart surgery and recently in adults, a single dose has been administered. However, the tolerable ischemic time has not been established. The objective is to evaluate the left ventricular (LV) function recovery and accompanying biochemical and histologic markers to clarify the tolerable ischemic time in an in vivo cardiopulmonary bypass (CPB) piglet model. Twenty-one piglets were subjected to either 90 minutes (with or without topical cooling; TC) or 120 minutes (with TC) of global ischemia induced by single-dose DN, while the other 7 served as the control group (CPB only). The CPB temperature was established with a perfusion temperature of 30°C. The LV function recovery was assessed by the percent change in end-systolic elastance (Ees) and the end-diastolic pressure-volume relationship (EDPVR). Creatine kinase-MB (CK-MB) levels and the mitochondrial score were also assessed. LV contractility assessed by %Ees after 90 and 120 minutes of ischemia (89.3 ± 20.6% and 57.9 ± 17.8%) was lower compared with the control group (122.6 ± 35.8%, P = 0.001). Conversely, LV compliance assessed by %EDPVR was preserved in both groups (102.7 ± 28.2% and 88.5 ± 24.0%), which was comparable to the control group (105.8 ± 36.9%, P = 0.531). There was no change in LV contractility after 90 minutes of ischemia with or without TC (89.3 ± 20.6% or 84.8 ± 16.2%, P = 0.657), whereas LV compliance was lower but not statistically different without TC (102.7 ± 28.2% vs 78.0 ± 38.9%). CK-MB and the mitochondrial score were equivalent between all groups. The proposed single-dose ischemic time for redosing is 90 minutes using TC.

Post-resuscitation hemodynamics and relationship to the duration of ventricular fibrillation

OBJECTIVE

We have observed consistent hemodynamic patterns after restoration of spontaneous circulation (ROSC) after ventricular fibrillation (VF) cardiac arrest. We sought to characterize the time-course of these patterns, and to determine whether these differed based on duration of the VF insult.

METHODS

We performed a retrospective review of data from a randomized animal experiment that was conducted in an AAALAC-approved animal laboratory. We used mixed-breed domestic swine of either sex. Animals were anesthetized and instrumented for continuous recording of ECG and blood pressures. VF was induced electrically and allowed to progress for various times ranging from brief (22s) to moderate (less than 3 min) to prolonged (3-10 min). All animals were initially shocked (150J) up to three times. If ROSC was not achieved on the three initial shocks, a standardized treatment protocol was followed. We defined cardiovascular collapse as a SBP<90 mmHg sustained for 1 min. For statistical purposes, we classified animals as having VF of <3 min, or >3 min duration. Data were analyzed with Fisher's exact test and survival analysis.

RESULTS

A hyperdynamic phase, consisting of very high-blood pressures and tachycardia, was seen in all animals immediately after ROSC. This lasts from 1 to 4 min. Post-resuscitation cardiovascular collapse occurred in 2/7 (29%) animals in the <3 min group and 13/14 in the >3 min group (93%) p=0.006. Onset of cardiovascular collapse was highly related to duration of VF (log-rank p=0.004).

CONCLUSIONS

There are two distinct phases of hemodynamic change after resuscitation of VF. The first phase is a brief hyperdynamic phase. The second phase is either stabilization or cardiovascular collapse. When VF is brief, blood pressures often return to normal without exogenous support. When VF was prolonged animals were rescued with exogenous pressor. Healthcare providers should be prepared to provide pressor support for patients having ROSC after prolonged VF.

Delayed preconditioning via Angiotensin-converting enzyme inhibition: pros and cons from an experimental study

1. Bradykinin B(2) receptor activation confers preconditioning from ischaemic injury. In the present study, we tested whether an angiotensin-converting enzyme (ACE) inhibitor (captopril) could mediate delayed preconditioning and, thus, cardioprotection. 2. New Zealand white rabbits received 15 mL infusion of either saline (control group; n = 7) or drugs (0.3 mg/kg captopril (CAP group; n = 7) or 0.3 mg/kg captopril + 0.1 mg/kg HOE 140 (CAPHOE group; n = 7)) via a marginal ear vein over 30 min. After 24 h, hearts were connected to a Langendorff apparatus and buffer perfused. The experimental protocol consisted of 20 min global normothermic hypoxia, followed by 120 min reperfusion. 3. Compared with baseline, the mean (SEM) contractile state (= dP/dt(max)) at 120 min reperfusion was decreased to 42 +/- ;23, 72 +/- ;16 (*P < 0.05 vs control) and 49 +/- ;22% in the control, CAP and CAPHOE groups, respectively. Early relaxation (= dP/dt(min)) was reduced to 55 +/- ;28, 73 +/- ;15 (*P < 0.05 vs control) and 52 +/- ;19% in the control, CAP and CAPHOE groups, respectively. The estimate for myocardial oxygen consumption (MVO(2)= rate-pressure product) was decreased to 52 +/- ;15, 69 +/- ;24 (*P < 0.05 vs control) and 56 +/- ;15% in the control, CAP and CAPHOE groups, respectively. Similarly, coronary flow was decreased in the control, CAP and CAPHOE groups to 49 +/- ;20, 67 +/- ;18 and 46 +/- ;19%, respectively. In contrast, ventricular extrasystoles during reperfusion were significantly elevated in both the CAP and CAPHOE groups (1.3 +/- ;0.2 and 1.1 +/- ;0.3 /min, respectively) compared with control (0.4 +/- ;0.2 /min). 4. Captopril confers delayed preconditioning against stunning via a B(2) receptor-mediated pathway. This pharmacological preconditioning protects against systolic and diastolic stunning, against vascular stunning and preserves cardiac metabolism. In addition to its accepted cardioprotective effects in early preconditioning, captopril should induce delayed preconditioning (e.g. for routine interventional cardiology or in elective cardiac surgery).