Terminal warm blood cardioplegia improves cardiac function through microtubule repolymerization

Terminal warm blood cardioplegia in mitral valve replacement: prospective study

Terminal warm blood cardioplegia has had a profound impact on cardiac surgery, especially in coronary artery bypass surgery, but there have been few studies on its use in mitral valve replacement. The purpose of this study was to determine whether terminal warm blood cardioplegia offers any advantages in mitral valve replacement. Forty patients with mitral valve disease were prospectively randomized to one of two groups of 20 with different techniques of myocardial protection: group A had cold blood cardioplegia, and group B had cold blood cardioplegia with terminal warm blood cardioplegia. Intraoperative and postoperative variables were used to assess primary outcomes. Postoperative troponin T release was measured as a secondary outcome. Improved spontaneous recovery of sinus rhythm was observed in group B, but the difference was not significant. The maximum doses of inotropics, duration of inotropic support, intensive care unit stay, and postoperative left ventricular ejection fraction were similar in both groups. Troponin T release at 0 and 6 h postoperatively was not different between the two groups. This study did not find any benefit of terminal warm blood cardioplegia in either clinical outcome or troponin T release after mitral valve replacement.

A comparison of 250 and 500 mL of terminal warm blood cardioplegia after global myocardial ischemia: a prospective randomized study

BACKGROUND

Controlled reperfusion with terminal warm blood cardioplegia (TWBC) improves myocardial performance after global ischemia. However, the optimum volume required is unknown.

METHODS

Fifty patients undergoing elective coronary artery bypass graft surgery were prospectively randomized to receive either 250 or 500 mL of TWBC. During TWBC delivery, and for 10 minutes after cross-clamp removal, samples were taken from the aorta and coronary sinus to measure the hydrogen ion, lactate, and oxygen content.

RESULTS

At the end of TWBC delivery, the 500 mL group had significantly less hydrogen ion washout (p = 0.006) compared with the 250 mL group. Also, more hydrogen ions (p = 0.02) and lactate (p = 0.02) had been washed out during the entire period of TWBC delivery in the 500 mL group compared with the 250 mL, indicating better metabolic recovery. By 4 minutes after aortic cross-clamp removal, hydrogen ion and lactate washout, as well as oxygen extraction was similar in the two groups. However, the time to return to regular mechanical activity was prolonged in the 500 mL group, 5.8 (3) versus 4.6 (3) minutes in the 250 mL group (p = 0.05). Though there was no difference in postoperative Troponin T levels, eight patients in the 500 mL group versus four in the 250 mL group required ionotropic support (p = 0.1).

CONCLUSIONS

A total of 500 mL of hotshot achieves a better metabolic state after hotshot delivery. However, there is no clinical benefit or improvement in the postoperative Troponin T release suggesting that in a short ischemic time, 500 mL TWCB has a limited clinical benefit.

Microtubule disruption by colchicine reversibly enhances calcium signaling in intact rat cardiac myocytes

Using the whole-cell patch-clamp configuration in rat ventricular myocytes, we recently reported that microtubule disruption increases calcium current (I(Ca)) and [Ca(2+)](i) transient and accelerates their kinetics by adenylyl cyclase activation. In the present report, we further analyzed the effects of microtubule disruption by 1 micromol/L colchicine on Ca(2+) signaling in cardiac myocytes with intact sarcolemma. In quiescent intact cells, it is possible to investigate ryanodine receptor (RyR) activity by analyzing the characteristics of spontaneous Ca(2+) sparks. Colchicine treatment decreased Ca(2+) spark amplitude (F/F(0): 1.78+/-0.01, n=983, versus 1.64+/-0.01, n=1660, recorded in control versus colchicine-treated cells; P<0.0001) without modifying the sarcoplasmic reticulum Ca(2+) load and enhanced their time to peak (in ms: 6.85+/-0.09, n=1185, versus 7.33+/-0.13, n=1647; P<0.0001). Microtubule disruption also induced the appearance of Ca(2+) sparks in doublets. These alterations may reflect RyR phosphorylation. To further investigate Ca(2+) signaling in cardiac myocytes with intact sarcolemma, we analyzed [Ca(2+)](i) transient evoked by field stimulation. Cells were loaded with the fluorescence Ca(2+) indicator, Fluo-3 cell permeant, and stimulated at 1 HZ: [Ca(2+)](i) transient amplitude was greater and its decay was accelerated in colchicine-treated, field-stimulated myocytes. This effect is reversible. When colchicine-treated myocytes were placed in a colchicine-free solution for 30 minutes, tubulin was repolymerized into microtubules, as shown by immunofluorescence, and the increase in [Ca(2+)](i) transient was reversed. In summary, we demonstrate that microtubule disruption by colchicine reversibly modulates Ca(2+) signaling in cardiac cells with intact sarcolemma.