Coronary and systemic vascular resistance during reperfusion after global myocardial ischemia

Reperfusion strategy after regional ischaemia: comparative study of reperfusion conditions and compositions

We investigated the effects of pressure, temperature and additives on aortic root reperfusion success. Cardiopulmonary bypass and heart arrest were initiated in mongrel dogs and sudden uncontrolled normothermic (group 1), pressure controlled substrate enriched normothermic (group 2a), pressure controlled unmodified normothermic (group 2b) and pressure controlled unmodified tepid (group 3) reperfusion compared. In group 1, the first cardiac rhythm was ventricular fibrillation, but dogs in the other groups showed spontaneous sinus rhythm. Recovery times were significantly longer and cardiac output levels significantly decreased in group 1 compared with the other groups. Prolonged lactate production and oxygen uptake failure were observed in group 1 compared with the other groups; oxidative stress markers and microscopic studies confirmed significant tissue injury in group 1. All parameters were similar between groups 2a, 2b and 3, indicating that low reperfusion pressure in the first 2 min is the most effective component of reperfusion.

The effects of cardioplegia on coronary pressure-flow velocity relationships during aortic valve replacement

OBJECTIVE

The acute physiological response of the coronary circulation to aortic valve replacement (AVR) has not been fully elucidated. This study aimed to characterize the changes in coronary perfusion pressure-flow velocity relationships, and to test whether this relationship is affected by cardioplegic method.

METHODS

Nineteen patients (mean age 67 +/- 12 (SD) years, 9 males) undergoing aortic valve replacement who received either cold blood cardioplegia (CBC, n = 9) or warm blood cardioplegia (WBC, n = 10), were prospectively studied before and 30 min after the operation, using transesophageal Doppler echocardiography combined with high fidelity left ventricular (LV) and aortic pressures. We thus determined: (1) Diastolic flow velocities in proximal anterior descending coronary artery (LAD), and simultaneous aorta to LV pressure differences. (2) The slope (LAD proximal linear resistance) and pressure intercept (zero flow pressure) of this relationship. (3) Overall LAD linear resistance as the ratio of mean diastolic flow velocity to mean pressure difference between aorta and left ventricle. (4) LV myocardial stroke work.

RESULTS

Following operation, myocardial stroke work fell from 5.2 +/- 2.7 to 3.0 +/- 1.7, mJ cm(-3) (P = 0.001), LAD mean diastolic flow velocity increased from 47 +/- 19 to 74 +/- 21, cm s(-1) (P = 0.0002). LAD overall linear resistance fell (0.75 +/- 0.24 vs. 1.26 +/- 0.26, mmHg cm(-1) s, P = 0.001). LAD proximal linear resistance, however, remained unchanged (P = 0.21), but the zero flow pressure fell (18 +/- 12.6 vs. 27 +/- 12.2, mmHg above LV end diastolic pressure, P = 0.013). With similar fall in myocardial work postoperatively, there was a greater fall in zero flow pressure after WBC than CBC (48 +/- 28 vs. 19 +/- 13,% of pre-op, P = 0.012), and a greater increase in flow velocity time integral (127 +/- 81 vs. 53 +/- 59,%, P = 0.039).

CONCLUSION

Instantaneous diastolic LAD pressure-flow velocity relations in the early postoperative period can be explained more satisfactorily in terms of zero flow pressure and proximal linear resistance than simple resistance alone. The fall in zero flow pressure alone explains the increase in LAD flow velocity immediately after aortic valve replacement. The extent of this fall is greater after warm rather than cold blood cardioplegia.

Warm or cold continuous blood cardioplegia provides similar myocardial protection

BACKGROUND

This study was performed to investigate the effect of temperature of blood cardioplegia on the recovery of postischemic cardiac function.

METHODS

Pigs on cardiopulmonary bypass were subjected to global ischemia (30 minutes), followed by cold (n = 10) or warm (n = 11) continuous antegrade blood cardioplegia (45 minutes) delivered at 55-60 mm Hg.

RESULTS

Global left ventricular function, evaluated by preload recruitable stroke work, decreased with cold cardioplegia from 91 (85-103) [mean (quartile interval)], at baseline, to 73 (55-87) erg x 10(3)/mL postbypass (p = 0.03), but was unchanged after warm cardioplegia; 110 (80-132) to 109 (71-175) erg x 10(3)/mL (p > 0.5). However, the difference between treatment effects was not significant (p = 0.25). Diastolic function, evaluated by end-diastolic pressure-volume relation, deteriorated without any difference between groups. Mean cardioplegic flow was similar between groups. Coronary vascular resistance increased at constant rate during warm cardioplegic delivery, but remained unchanged with cold cardioplegia (p = 0.001 between regression coefficients).

CONCLUSIONS

No significant difference was found in postischemic functional recovery comparing cold and warm continuous blood cardioplegia. Cold cardioplegia is therefore preferred due to added safety of hypothermia.

Myocardial oxygenation during terminal warm blood cardioplegia

BACKGROUND

Terminal warm blood cardioplegia accelerates myocardial metabolic recovery. The process of myocardial oxygenation during terminal warm blood cardioplegia and its optimal administration are not clear.

METHODS

We measured the myocardial tissue oxygen saturation (SO2) during reperfusion using near-infrared spectroscopy. Twenty-four dogs underwent 1 hour of ischemic arrest with cold crystalloid cardioplegia. They were then divided into four equal groups. Group 1 dogs received normal blood reperfusion. The other dogs received 15 mL/kg of terminal warm blood cardioplegia at 80 mm Hg in group 2 or at 60 mm Hg in group 3, and 30 mL/kg of cardioplegia at 60 mm Hg in group 4, followed by blood reperfusion.

RESULTS

In group 1, the SO2 increased gradually during the early reperfusion and decreased transiently during the late reperfusion. In group 2, the SO2 increased rapidly but it decreased transiently during blood reperfusion. In groups 3 and 4, the SO2 increased rapidly and remained at high levels during the blood reperfusion. Reperfusion ventricular fibrillation occurred along with a SO2 decrease only in groups 1 and 2. The postischemic troponin-T levels of groups 3 and 4 were lower than that of group 1. The functional recovery in group 4 was better than those in the other three groups.

CONCLUSIONS

Terminal warm blood cardioplegia accelerates the early SO2 increase and abolishes the SO2 decrease during subsequent reperfusion and reduces the incidence of reperfusion arrhythmia, suggesting that it ameliorates reperfusion injury and consequently improves postischemic functional recovery.

Coronary vascular regulation during postcardioplegia reperfusion

BACKGROUND

This study extends previous investigations of global and regional myocardial blood flow during early postcardioplegia reperfusion. The hypothesis tested is that coronary vascular regulation becomes abnormal within 3 minutes after the start of postcardioplegia reperfusion.

METHODS

Pigs (n = 40) were supported by cardiopulmonary bypass and 38 degrees C blood cardioplegic solution was infused. A control preischemic microsphere injection (No. 1) was given in asystolic hearts. Groups 1 to 3 had 1 hour of hypothermic cardioplegic arrest. Group 4 (control group) had 1 hour of perfusion without cardioplegia. A blood cardioplegic solution at 38 degrees C and 70 mm Hg pressure was infused to maintain asystole during the initial 7 to 10 minutes of reperfusion in all groups. Left ventricular intracavitary pressures were set at 0, 10, 20, or 0 mm Hg in groups 1, 2, 3, and 4 (n = 10 pigs per group), respectively, during the initial 7 minutes of reperfusion. The ventricle was then decompressed. At 30 seconds, 3 minutes, and 6 minutes after reperfusion, microsphere injections 2, 3, and 4 were given in asystolic hearts. Microsphere injection No. 5 was given 10 minutes after reperfusion in beating vented hearts.

RESULTS

(1) Left ventricular distention during the initial 7 minutes of reperfusion after hypothermic cardioplegic arrest attenuates postischemic hyperemia. (2) Left ventricular intracavitary pressure of 20 mm Hg during reperfusion causes a decrease in endocardial blood flow relative to epicardial blood flow at 6 minutes after reperfusion. (3) Global myocardial blood flow during postcardioplegia reperfusion falls significantly below preischemic control values despite the return of electromechanical activity.

INFERENCE

Coronary vascular regulation (i.e., coronary resistance and metabolic flow recruitment) becomes abnormal within 3 minutes after the start of reperfusion after hypothermic blood cardioplegic arrest.

Improvement in functional recovery of the isolated guinea pig heart after hyperkalemic reperfusion with adenosine

The aim of this study was to examine the effect of initial hyperkalemic reperfusion (HKR), with and without added adenosine, on coronary flow, myocardial function, and endothelium-dependent and endothelium-independent coronary vascular function. Cardioplegic arrest was induced in 40 isolated guinea pig hearts by infusing oxygenated cardioplegic (high in potassium ion) Krebs solution for 5 minutes. Hearts were then stored at room temperature for 3.5 hours. On reperfusion, hearts were divided into four groups of 10 hearts each: control, reperfusion with regular Krebs solution (4.6 mmol/L potassium chloride); base hyperkalemic reperfusion, initial reperfusion with 37 degrees C oxygenated, cardioplegic Krebs solution for 5 minutes; hyperkalemic reperfusion with addition of 1 mmol/L adenosine during HKR; and hyperkalemic reperfusion with addition of 5 mmol/L adenosine. Coronary reserve (adenosine bolus 2 mmol/L) and responses to acetylcholine (1 mumol/L) and nitroprusside (100 mumol/L) were examined before and after ischemia and reperfusion. Flow did not return to preischemic values in any group after reperfusion. Adenosine treatment during initial reperfusion increased coronary flow (percentage of baseline +/- standard error of the mean) from 57% +/- 4% in control and 45% +/- 3% in hearts with hyperkalemic reperfusion to 79% +/- 3% and 83% +/- 5% in hearts with hyperkalemic reperfusion also treated with, respectively, 1 mmol/L adenosine and 5 mmol/L adenosine (p < 0.05). At 30 and 60 minutes of reperfusion, however, flow remained elevated only in the group treated with 5 mmol/L adenosine. Coronary reserve and responses to acetylcholine and nitroprusside were equivalently depressed in all groups after reperfusion. Recovery of left ventricular systolic and diastolic function was improved in all groups after hyperkalemic reperfusion (54% +/- 4% of preischemic value) compared with control (39% +/- 3%), and recovery was further enhanced in the group treated with 5 mmol/L adenosine (60% +/- 4%). In this ex vivo model, hyperkalemic reperfusion improved myocardial function after cardioplegic arrest and the addition of 5 mmol/L adenosine improved coronary flow. Adenosine may counteract the potassium chloride-induced vasoconstriction that occurs during hyperkalemic reperfusion and may thus improve coronary flow and myocardial function. Postischemic depression of endothelium-dependent or endothelium-independent vascular functions, however, was not alleviated by hyperkalemic reperfusion with or without adenosine.

Myocardial reperfusion injury: an assessment by the spasm of resistance vessel concept of ischemic heart disease

Myocardial reperfusion injury will be discussed in context to the spasm of resistance vessel concept of ischemic heart disease. This hypothesis attributes symptoms in this disorder directly to primary spasm of resistance vessels, and is based in part on a study of no-reflow which provided evidence that no-reflow is due to ischemia-induced injury-spasm of resistance vessels. Studies of no-reflow and reperfusion injury are rather similar, and the concept asserts that ischemia-induced injury-spasm causing no-reflow is involved in reperfusion injury. It is recognized that oxygen free radicals cause both myocardial and vascular injury during reperfusion injury, and the concept suggests that vascular injury contributes significantly to reperfusion injury by inducing the sequence of injury-spasm, no-reflow, fresh ischemia, and fresh ischemic reperfusion injury. In keeping with this, the possible involvement of spasm and no-reflow in reperfusion injury occasionally is mentioned. However, it seems to be generally accepted that reperfusion injury is due essentially solely to direct myocardial injury by free radicals, and possible reasons will be explored for a relative disinterest in spasm and no-reflow in reperfusion injury.

Controlled initial hyperkalemic reperfusion after cardiac transplantation: coronary vascular resistance and blood flow

The coronary vascular response to controlled initial hyperkalemic reperfusion after global ischemia during cardiac transplantation was studied in 11 patients. The mean global ischemic time was 206 minutes (range, 143 to 245 minutes). All donor hearts received initial hyperkalemic crystalloid cardioplegia and subsequent oxygenated crystalloid cardioplegia during implantation. Coronary blood flow was highest during the first one to two minutes of controlled reperfusion but remained normal throughout the first ten minutes of reperfusion. Coronary vascular resistance was less than normal throughout the first ten minutes of controlled reperfusion, but there was a gradual increase throughout this period. Systemic vascular resistance remained within normal limits. The time to effective contraction was highly variable, but a greater potassium load during initial reperfusion was generally associated with a longer time to effective contraction.

Factors determining in-hospital or late survival after aortic valve replacement

To ascertain incremental risk factors for in-hospital and late mortality of patients undergoing AVR with the bovine pericardial valve, multiple variables were analyzed in a group of 240 patients undergoing AVR between 1977 and 1983. Follow-up totaled 12,023 patient-months (mean, 52.7 +/- 1.7 patient-months) and was 100 percent complete. Univariate analysis of incremental risk factors for in-hospital mortality identified the following: age over 60 years (p = 0.015); and advanced preoperative NYHA class (p = 0.003). Multivariate analysis of risk factors for in-hospital mortality identified the following: age (p = 0.038); NYHA class (p = 0.018); and year of operation (p = 0.049). Incremental risk factors for late mortality were identified as age (p = 0.003), year of operation (p = 0.003), concomitant procedure (p = 0.047), and valvular lesion (regurgitation) (p = 0.053). Actuarial survival of patients (+/- SE) was 87 +/- 2 percent, 75 +/- 3 percent, and 61 +/- 5 percent at 2, 5, and 8.7 years, respectively. The actuarial survival of patients experiencing valve-related events was 62.6 +/- 10.1 percent at 8.7 years, compared to 55.4 +/- 7 percent for those who did not (p = 0.38).