Subendocardial ischemia after cardiopulmonary bypass

Augmentation of central arterial pressure in Type 2 diabetes

AIMS

Aortic systolic blood pressure has been shown to be augmented in Type 1 diabetes, indicative of more rapid pulse wave reflection due to increased arterial stiffness. This abnormality is more pronounced in diabetic males. The aim of this study was to examine the effects of diabetes on augmentation of aortic systolic pressure in subjects with Type 2 diabetes.

METHODS

Radial artery pressure waveforms were obtained non-invasively by applanation tonometry. A central aortic waveform can be derived using a transfer function obtained from previous studies during cardiac catheterization. A total of 88 subjects with Type 2 diabetes (51 men and 37 women, aged 55.8 years (interquartile range (IR) 49.7-64.1), duration of diabetes 7.5 years (IR 2.4-12.4), HbA1c 7.6% (IR 6.6-8.7)) and 85 controls subjects (40 men and 45 women, aged 55.3 years (IR 44.2-66.4)) were studied. The central aortic waveform allowed determination of the: (i) aortic augmentation index and (ii) subendocardial viability ratio.

RESULTS

Similar to Type 1 diabetic subjects, patients with Type 2 diabetes had a significantly higher aortic augmentation index (136.1 +/- 18.0% vs. 128.3 +/- 19.2%, t = 2.8, P = 0.006) and lower subendocardial viability ratio (137.4 +/- 25.0% vs. 155.1 +/- 25.9%; t = 4.6, P = 0.0001) compared with controls. Multivariate analysis identified diabetes as an important determinant of aortic augmentation index (t = 4.0, P = 0.0001). The higher aortic augmentation index was due mainly to the male cohort (t = 2.6; P = 0.01) and was not apparent for females with diabetes (P = 0.2).

CONCLUSIONS

Type 2 diabetes is characterized by higher augmentation of aortic systolic pressure and unfavourable ratio of myocardial perfusion to cardiac workload. These results are consistent with increased arterial stiffness. The age-related progression of arterial stiffness is similar in Type 1 and Type 2 diabetes. Anti-hypertensive agents that reduce wave reflection and augmentation may help to prevent systolic hypertension and cardiac hypertrophy in diabetes.

Influence of arterial pulse and reflected waves on blood pressure and cardiac function

An integrated view of the role of arterial blood pressure in cardiovascular physiology should consider both the steady (mean blood pressure) and pulsatile (systolic, diastolic, and pulse pressures) components. This brief overview describes the important factors influencing these components, with emphasis on the consequences of arterial stiffening. In addition to their conduit function, arteries also perform a cushioning function that transforms the pulsatile flow generated by contraction of the left ventricle into steady flow at the periphery. Arterial compliance is a principal determinant of arterial blood pressure and is both pressure dependent and affected by vascular biomechanics. Other important factors that affect the steady and pulsatile components of blood pressure include ventricle performance, peripheral resistance, pulse wave velocity, and the timing of pulse wave reflections. Ageing and hypertension are important factors that contribute to reductions in arterial compliance. Important functional effects of this are that both the amplitude of the arterial pulse wave and pulse wave velocity increase, causing an early return of reflected waves from the periphery to the aorta. This may boost aortic and left ventricular pressures during systole at the expense of diastolic pressure, which is reduced. Studies have shown that stiffening of arteries and the associated increase in systolic and pulse pressures are important cardiovascular risk factors. Patients with an increased risk of cardiovascular events associated with such changes should be identified and receive appropriate therapeutic interventions.

Large artery structure and function in hypertension and end-stage renal disease

The cardiovascular complications in hypertension are ascribed to two different but associated alterations, namely atherosclerosis and arteriosclerosis. Whereas the former disturbs principally the conduit function and the delivery of an adequate blood flow to peripheral organs and tissues, the latter disturbs the cushioning function of large arteries, inducing an inadequate increase in systolic and pulse pressure. Arteriosclerosis represents a clinical form of accelerated ageing process and is characterized by a diffuse dilation and hypertrophy of large conduit arteries and stiffening of arterial walls. Independently from the ageing, structural changes are associated with several haemodynamic alterations such as increased in blood flow and flow velocity, and increased parietal stress due to increased arterial diameters and/or intraarterial pressure. The principal consequences of arterial stiffening are: (1) an increased left ventricular afterload with development of left ventricular hypertrophy and increased myocardial oxygen demand; (2) altered coronary perfusion and blood flow distribution; and (3) decreased perfusion reserve during haemodynamic stress. In the absence of controlled studies, it is difficult to propose therapeutic interventions aimed to prevent or treat arterial abnormalities in hypertensive patients. It has been shown that long-term administration of either calcium channel blockers and angiotensin converting enzyme inhibitors led to an improvement of vessel wall elasticity. Nevertheless, these studies did not conclude whether the improvement of elastic properties were due only to decrease in blood pressure or to alterations in intrinsic properties of arterial walls. More investigations should be necessary to investigate this important problem.

Influence of body height on pulsatile arterial hemodynamic data

OBJECTIVES

This study sought to present evidence that short stature is a hemodynamic liability, which could explain in part the inverse relation between body height and cardiovascular risk.

BACKGROUND

Other explanations for the association of short stature with increased cardiovascular risk include advancing age, reduced pulmonary function, genetic factors, poor childhood nutrition and small-caliber coronary arteries. This study adds another factor-the physiologic effects of reduced body height on the arterial tree, which increase left ventricular work and jeopardize myocardial perfusion.

METHODS

Four hundred two subjects were studied: 149 with end-stage renal disease and 253 with normal renal function. Measurements included blood pressure, body height, cardiac cycle length, carotid to femoral artery pulse wave velocity, carotid artery pulse waves (by applanation tonometry) and the arrival time of reflected waves. Calculations included the carotid augmentation index, carotid artery compliance and the diastolic to systolic pressure-time ratio (an index of myocardial supply and demand).

RESULTS

On linear and stepwise multiple regression, body height correlated with all variables except mean blood pressure.

CONCLUSIONS

The early systolic arrival of reflected waves in short people in this group acts to stiffen the aorta and increase the pulsatile effort of the left ventricle, even at the same mean blood pressures. Short stature also induces a faster heart rate, which increases cardiac minute work and shorten diastole. Stiffening lowers the aortic diastolic pressure and, coupled with a shortened diastole, could adversely influence myocardial supply. Although indirect, this evidence supports a physiologic hypothesis for the body height-cardiovascular risk association.

Gender-related differences in the central arterial pressure waveform

OBJECTIVES

This study investigated the effect of age and gender on central arterial hemodynamic variables derived from noninvasive tonometric carotid pressure waveforms.

BACKGROUND

Women have a greater age-related increase in left ventricular (LV) mass than do men and are more likely to experience symptomatic heart failure after infarction despite their higher ejection fraction. In studies of these changes, ventricular afterload is incompletely defined by brachial blood pressure (BP) measurements. We hypothesized that there exist gender differences in pulsatile vascular load, as revealed by pressure waveform analysis, which may produce suboptimal afterload conditions in women.

METHODS

Data from 350 healthy normotensive subjects (187 female) aged 2 to 81 years were analyzed in decade groups. Augmentation index (AIx, the difference between early and late pressure peaks divided by pulse pressure) was used as an index of pulsatile afterload, and the ratio of diastolic to systolic pressure-time integral gave a subendocardial viability index. Heart rate, BP, ejection duration and maximal rate of pressure rise (dP/dt(max)) were also determined.

RESULTS

Male subjects had a slightly higher systolic pressure until age 50. Female subjects had higher systolic pressure augmentation after the 1st decade, a difference that was significant after age 30 (p < 0.005 for each decade). In both males and females there was a strong age dependence for AIx (r = 0.77, p < 0.001 for females, r = 0.66, p < 0.001 for males). Although males had a larger body size and higher systolic pressure, systolic pressure-time integral was similar in males and females across all age groups. Diastolic pressure-time integral was consistently lower in females because of their shorter diastolic period. Subendocardial viability index was lower in females across the entire group. Differences in stature and heart rate may contribute to these findings.

CONCLUSIONS

These new data may help to explain previous findings in women of an age-related increase in LV mass and excess symptomatic heart failure that are not explained by differences in brachial BP.

Cardiac disease in chronic uremia: pathogenesis

Cardiomyopathy in chronic uremia results from pressure and volume overload. The former causes concentric left ventricular [LV] hypertrophy, results from hypertension and aortic stenosis, and is also associated with diabetes mellitus and anemia. Volume overload causes LV dilatation, results from arteriovenous shunting, salt and water overload, and anemia, and is also associated with ischemic heart disease, hypertension, and hypoalbuminemia. Decreased major arterial compliance and an early return of arterial wave reflections are also associated with the extent of LV hypertrophy. Cardiomyopathy predisposes to diastolic and systolic dysfunction. The latter results from myocyte death, and predisposing factors include ischemic heart disease and the uremic environment. Ischemic heart disease may be atherosclerotic or nonatherosclerotic in origin. Multiple factors contribute to the vascular pathology of chronic uremia, including injury to the vessel wall, dyslipidemia, prothrombotic factors, increased oxidant stress, and hyperhomocysteinemia. Ischemic risk factors include hypertension, LV hypertrophy, hypoalbuminemia, and perhaps hyperparathyroidism. The clinical consequences of cardiomyopathy include heart failure, ischemic heart disease, dialysis hypotension, and arrhythmias. The adverse impact of ischemic heart disease is probably mediated through the development of cardiac failure.

Cardiac and arterial interactions in end-stage renal disease

Although cardiac hypertrophy is a frequent complication of end-stage renal disease (ESRD), relatively little is known about large arterial geometry and function in vivo in these patients, and the relationship between arterial changes and cardiac hypertrophy is unknown. Common carotid artery (CCA) intima-media thickness and internal diameter and left ventricular geometry and function were determined by ultrasound imaging in 70 uncomplicated ESRD patients and in 50 age-, sex-, and blood pressure-matched controls. Arterial distensibility and compliance were determined from simultaneously recorded CCA diameter and stroke changes in diameter and CCA pressure waveforms, obtained by applanation tonometry, and also by the measurement of carotid-femoral pulse wave velocity. Compared with control subjects, ESRD patients had greater left ventricular diameter (P < 0.01), wall thicknesses and mass (P < 0.001), increased CCA diameter (6.25 +/- 0.87 vs. 5.55 +/- 0.65 mm; P < 0.001), larger CCA intima-media thickness (777 +/- 115 vs. 678 +/- 105 microns; P < 0.001) and intima-media cross-sectional area (17.5 +/- 4.5 vs. 13.4 +/- 3.3 mm2; P < 0.001). In uremic patients, arterial hypertrophy was associated with decreased CCA distensibility (17.8 +/- 8.8 vs. 24.0 +/- 12.7 kPa-1.10(-3); P < 0.001) and compliance (5.15 +/- 2 vs. 6.0 +/- 2.5 m2.kPa-1.10(-7); P < 0.05), accelerated carotid-femoral pulse wave velocity (1055 +/- 290 vs. 957 +/- 180 cm/seconds; P < 0.001), early return and increased effect of arterial wave reflections (20.5 +/- 15.4 vs. 9.2 +/- 18.4%; P < 0.001). The latter phenomenons were responsible for increased pulsatile pressure load in CCA (58.3 +/- 21 vs. 48 +/- 17 mm Hg; P < 0.01) and were associated with a decreased subendocardial viability index (157 +/- 31 vs. 173 +/- 30%; P < 0.001). The CCA diameter was correlated with the left ventricular diameter (P < 0.01), and a significant correlations existed between CCA wall thickness or CCA intima-media cross-sectional area and left ventricular wall thicknesses and/or left ventricular mass (P < 0.01). In multivariate analysis, these relationships were independent regarding age, sex, blood pressure and body surface area. The present study documents parallel cardiac and vascular adaptation in ESRD, and demonstrates the potential contribution of structural and functional large artery alterations to the pathogenesis of left ventricular hypertrophy and functional alterations.

Beneficial effects of prostacyclin treatment on reperfusion of the myocardium

A total of 20 patients with coronary artery disease were studied in order to assess the benefits of prostacyclin administration on reperfusion of the ischaemic myocardium after cardiopulmonary bypass. Ten received prostacyclin (25 ng/kg per min) while ten were untreated controls. There was no difference between groups with regard to age, preoperative ejection fraction and aortic cross-clamping times. There were no in-hospital deaths in either group. The administration of prostacyclin significantly altered the metabolic side effects of reperfusion followed by hypothermic cardioplegic arrest. Myocardial oxygen consumption after cardiopulmonary bypass was significantly higher in the prostacyclin-treated group than in controls (18.5 ml versus 13 ml; P < 0.01). Prostacyclin treatment significantly reduced the leucocyte activity: leukotriene B4 concentrations were 58 pmol/l in prostacyclin-treated patients compared with 93 pmol/l in controls (P < 0.01). Such recovery of metabolic status during reperfusion resulted in better haemodynamic function in patients receiving prostacyclin.

Heterogeneity of myocardial blood flow

Myocardial blood flow is heterogeneous, whether considered by chamber, by layers of the ventricular walls, or by microregions within layers. There is also variability of myocardial flow reserve, particularly in layers and microregions, even when the heart is arrested. The variability of flow during arrest may be associated with the resistance pathways to each region, but the variability of flows in the beating heart with vascular tone is probably due to regional differences in work and thus oxygen demand. Heterogeneity by layer may be responsible for the subendocardial ischemia that is common to many forms of heart disease. Microheterogeneity may account for the patchy necrosis that occurs with chronic ischemia.

Increased left ventricular diastolic chamber stiffness immediately after coronary artery bypass surgery

OBJECTIVES

The aim of this study was to assess the incidence and severity of left ventricular diastolic dysfunction immediately after coronary artery bypass surgery by utilizing simultaneous transesophageal echocardiographic and hemodynamic monitoring.

BACKGROUND

Left ventricular diastolic dysfunction has been documented after coronary bypass surgery, but its measurement has been technically difficult to acquire and limited by dependence on loading conditions.

METHODS

End-diastolic pressure-area curves were constructed before and immediately after coronary bypass surgery in 20 patients. Transesophageal echocardiographic images at the midpapillary level of the left ventricle and hemodynamic data were recorded. Volume status was manipulated to alter loading conditions, and multiple measurements were taken at each loading condition.

RESULTS

Diastolic function worsened in all patients, as manifested by a postoperative leftward shift of the end-diastolic pressure-area curve. At a comparable preload, mean end-diastolic area +/- SEM decreased by 15% from 17.6 +/- 0.8 to 14.9 +/- 0.8 cm2 postoperatively (p = 0.0001).

CONCLUSIONS

Left ventricular diastolic chamber stiffness frequently increases immediately after coronary artery bypass surgery. Simultaneous hemodynamic and transesophageal echocardiographic monitoring, through the construction of end-diastolic pressure-area curves, is a useful method to evaluate diastolic function and guide management after cardiac surgery.

Minimal coronary stenoses and left ventricular blood flow during CPR

STUDY OBJECTIVE

To assess the effect of a 33% coronary stenosis on myocardial blood flow during normal sinus rhythm and CPR.

DESIGN

Prospective, before and after cardiac arrest and CPR; before and after creation of a 33% stenosis.

SETTING

The University of Arizona Resuscitation Research Laboratory.

SUBJECTS

Ten domestic closed-chest swine with patent coronary stenoses.

INTERVENTIONS

A Teflon cylinder was placed in the mid-left anterior descending coronary artery to create a 33% stenosis. Myocardial blood flow was measured with colored microspheres both proximal and distal to the stenosis during normal sinus rhythm and during CPR.

MEASUREMENTS AND MAIN RESULTS

During normal sinus rhythm, the stenosis did not alter the amount of myocardial blood flow distribution or quantity. Proximal to the stenosis the endocardial/epicardial flow ratio was 1.49 +/- 0.33, and distal to the stenosis it was 1.50 +/- 0.50. Likewise, during normal sinus rhythm, blood flow proximal and distal to the stenosis did not differ for either the epicardium (79 +/- 9 versus 66 +/- 13 mL/min/100 g) or the endocardium (111 +/- 27 versus 83 +/- 19 mL/min/100 g). However, the distribution of myocardial blood flow was markedly altered during CPR. The resultant endocardial/epicardial flow ratios were significantly less than during normal sinus rhythm, 0.49 +/- 0.11 (three minutes of CPR) and 0.74 +/- 0.07 (eight minutes of CPR) proximal to the stenosis and 0.39 +/- 0.15 (three minutes of CPR) and 0.49 +/- 0.14 (eight minutes of CPR) distal to the stenosis (P less than .05 versus normal sinus rhythm). In the presence of a 33% mid-left anterior descending coronary artery stenosis, endocardial blood flow at eight minutes of CPR was significantly lower distal to the stenosis compared with proximal to the stenosis (23 +/- 7 mL/min/100 g versus 74 +/- 18 mL/min/100 g; P less than .02).

CONCLUSION

Minimal coronary lesions that do not diminish myocardial perfusion during normal physiologic conditions appear to significantly decrease subendocardial blood flow during cardiac arrest and CPR.

Left ventricular diastolic dysfunction in coronary artery disease: effects of coronary revascularization

Left ventricular diastolic dysfunction was studied globally and regionally in patients with coronary artery disease, and the effects of coronary revascularization were evaluated. A total of 25 patients with angina pectoris who had a stenotic lesion (greater than or equal to 90%) in only left anterior descending branch underwent coronary revascularization [percutaneous transluminal coronary angioplasty (PTCA) in 13 patients and coronary artery bypass graft (CABG) in 12]. Nine patients with normal coronary artery were studied as controls. Left ventricular volume and radial axes were measured on serial frames of one cardiac cycle by cine left ventriculography. The radial axes were drawn from the left ventricular gravity to left ventricular wall at every 20 degrees. Left ventricular filling fraction and distension rate of radial axes were calculated at the times of 25%, 50%, 75%, and 100% of diastolic period, 100% being end-diastole. Although there were no significant changes of the systolic function by revascularization, the filling fraction increased from 11.2 +/- 2.6 to 14.5 +/- 3.5% (p less than 0.001) at 25% time of diastole, from 29.9 +/- 4.9 to 32.5 +/- 5.0% (p less than 0.05) at 50% time in the PTCA group, and from 11.8 +/- 3.7 to 13.4 +/- 3.8% (p less than 0.01) at 25% time in the CABG group. The distension rate of radial axis to the anterior wall also increased significantly at 25% and 50% time of diastole after revascularization, and the change was marked in the PTCA group. However, these increases did not apply to the control patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of adenosine triphosphate on the postischemic left ventricular function of the immature myocardium

In this study, the effect of exogenous adenosine triphosphate (ATP) on the immature myocardium was evaluated. Isolated working neonatal rabbit hearts were perfused aerobically for 15 min with Krebs-Henseleit buffer (KHB) at 37 degrees C, and then arrested with St. Thomas solution (STS) in group 1 and STS containing 500 mumol/L of ATP in group 2 at 4 degrees to 6 degrees C and maintained at 10 degrees to 14 degrees C for 60 min. Hearts were reperfused with KHB aerobically at 37 degrees C for 15 min. Each heart served as its own control before and after arrest. Systolic function was significantly depressed in group 1 compared with group 2. There was a significant decrease in the peak left ventricular (LV) systolic pressure in group 1 (preischemia mean [PIM] 54 mm Hg to postischemia mean [PoIM] 42 mm Hg, Student's t test p = 0.007) than in group 2 (PIM 66 to PoIM 62 mm Hg, p = 0.5). The LV pulse pressure decreased in group 1 (PIM 72 to PoIM 54 mm Hg, p = 0.02) but not in group 2 (PIM 84 to PoIM 86 mm Hg, p = 0.9) and the rate of rise of LV pressure (dP/dT) in group 2 improved (PIM 5718 to PoIM 6926 mm Hg, p = 0.4) compared with group 1 (PIM 7021 to PoIM 4125 mm Hg, p = 0.008). The PoIM LV flow (LVF) was greater in group 2 than group 1 (LVF group 1 = 2.7 ml/min, group 2 = 4.5 ml/min). Diastolic pressures were not significantly different in the two groups. Our findings suggest that the incorporation of ATP in STS has a significant effect in improving postischemic LV systolic function in neonatal rabbit hearts.

Cross-sectional area index of left ventricular myocardium as a risk factor influencing early and late postoperative survival in aortic regurgitation

Late cardiogenic death after aortic valve replacement in aortic regurgitation is still a most important unresolved problem. We studied how the extent of cross-sectional area index (CSAI) relates to early and late cardiogenic deaths after aortic valve replacement (AVR) in aortic regurgitation with normal coronary artery. Forty-one patients were classified into two groups: Group I having CSAI greater than 20 cm2/m2 (18 patients), and Group II, in whom CSAI was less than 20 cm2/m2 (23 patients). All preoperative factors in patients with CSAI greater than or equal to 20 cm2/m2 showed poor values compared with patients with CSAI less than 20 cm2/m2 with a statistical difference of 63 +/- 6 versus 56 +/- 4% in cardiothoracic ratio, 72 +/- 9 versus 64 +/- 8 mm in diastolic dimension, 54 +/- 9 versus 43 +/- 7 mm in systolic dimension, 25 +/- 7 versus 32 +/- 6% in fractional shortening, 326 +/- 60 versus 209 +/- 63 ml/m2 in end-diastolic volume index, 177 +/- 52 versus 81 +/- 29 ml/m2 in end-systolic volume index, and 47 +/- 14 versus 58 +/- 5% in ejection fraction (mean +/- SD). In Group II, there were no postoperative cardiac deaths and no patient was subjected to intra-aortic balloon pumping (IABP). In contrast, in Group I, 17% died from postoperative low output syndrome and 33% were subjected to IABP. Concerning late deaths, there was no cardiac death in any CSAI patient with less than 20 cm2/m2; however, 22% of the patients with CSAI greater than or equal to 20 cm2/m2 died from cardiac causes.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonuniform blood flow in the canine left ventricle

In order to investigate the relationship between coronary perfusion pressure and blood flow distribution in the left ventricle (LV), we measured myocardial blood flow in small regions using radioactive microspheres in six anesthetized, open-chest dogs. Mean coronary perfusion pressure (CPP) was controlled with a femoral artery to left main coronary artery shunt which included a pressurized, servo-controlled blood reservoir. In each dog, we measured flow in 192 regions of the LV free wall (mean weight per region = 206 +/- 38 mg) at different perfusion pressures. At CPP = 80 mm Hg, blood flow to individual regions varied fourfold (0.30 to 1.18 ml/min/g; relative dispersion (RD) = 21.8 +/- 2.3%). At CPP = 50 mm Hg, flow varied over sevenfold (0.08 to 0.60 ml/min/g; RD = 42.8 +/- 10%; P less than 0.01 vs 80 mm Hg). This relationship between flow variability and CPP was present within individual LV layers as well between layers and is much higher than the error associated with the microsphere technique. We conclude that blood flow to small regions of the LV is markedly nonuniform. This heterogeneity becomes more profound at lower CPP. These findings suggest that (1) global measurements of coronary flow must be interpreted with caution, and (2) even in hearts with normal coronary arteries some regions of the LV are more susceptible to ischemia than others. In addition, these findings may help explain the patchy nature of myocardial damage that occurs following periods of low coronary pressure or inadequate myocardial protection during cardiopulmonary bypass.

Retrograde coronary sinus cardioplegia for aortic valve operations: a clinical report on 500 patients

Retrograde delivery of cardioplegic solutions has recently been the subject of renewed interest, but the reliability of this technique has not been assessed in large clinical series. From 1980 to 1989, we used retrograde coronary sinus perfusion as the exclusive means of cardioplegia delivery in 500 consecutive patients undergoing aortic valve replacement, either isolated (359 patients) or combined with another valve or coronary procedure (141 patients). The coronary sinus was always cannulated under direct vision after bicaval cannulation with snaring. Cold crystalloid cardioplegia was delivered retrogradely at an average flow rate of 100 mL/min in conjunction with topical and systemic (25 degrees C) hypothermia. The mean cross-clamp time was 83 +/- 23 minutes (+/- the standard deviation). There were 31 hospital deaths (6.2%), 20 of which were cardiac related. Transient hemodynamic instability (defined as a need for inotropic agents for less than 24 hours postoperatively) occurred in 16 patients (3.2%), whereas a true low-output syndrome developed in 60 patients (12%). The incidence of clinically significant supraventricular arrhythmias and of permanent conduction defects was 7.4% and 1.2%, respectively. There were three nonfatal coronary venous injuries during our early experience. We conclude that coronary sinus perfusion is a safe and effective means of delivering cardioplegia in aortic valve operations. While providing a degree of myocardial protection similar to that reported with anterograde cardioplegia, the coronary sinus technique offers distinct advantages, in particular, the avoidance of perfusion-related coronary artery complications and the opportunity to repeat cardioplegia administration without interrupting the procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Surgical hypothermia

Induced hypothermia is an interesting and useful adjunct to therapy in many areas of surgery and medicine. To paraphrase Professor Swan (1973), clinical hypothermia 'has a past and some promise for the future'.

Regional changes in myocardial acid production during ischemic arrest: a comparison of sanguineous and asanguineous cardioplegia

Regional differences in myocardial acid production have not been characterized during administration of either asanguineous or sanguineous cardioplegia. To investigate this, miniature glass pH electrodes were placed in the right ventricular (RV) myocardium, the left ventricular subendocardial (LV endo) region, and the subepicardial (LV epi) region in a canine model. Multiple doses of either blood cardioplegia (Group 1; N = 11) or crystalloid cardioplegia (Group 2; N = 11) were administered during 4 hours of aortic cross-clamping. The accumulation of hydrogen ions during the cross-clamp period was greater in Group 2 than Group 1 in the LV endo region (629 +/- 79 nm/L versus 66 +/- 31 nm/L; p less than 0.001), the LV epi region (623 +/- 66 nm/L versus 72 +/- 32 nm/L; p less than 0.001), and the RV myocardium (814 +/- 296 nm/L versus 150 +/- 54 nm/L; p less than 0.05). Within each group, the time course of myocardial pH and the accumulation of hydrogen ions did not differ among the LV endo region, LV epi region, and the RV myocardium (p = not significant). These data indicate that transmural and interventricular differences in myocardial pH and hydrogen ion accumulation are not produced in the vented, arrested canine heart. In addition, when compared with asanguineous cardioplegia, blood cardioplegia globally and transmurally reduces acid accumulation during ischemic arrest.

Dipyridamole reduced myocardial platelet and leukocyte deposition following ischemia and cardioplegia

Urgent coronary revascularization for acute myocardial ischemia results in an increased mortality and morbidity. Deposition of activated platelets and leukocytes into the ischemic myocardium during reperfusion may augment perioperative ischemic injury. Dipyridamole reduces platelet activation and may reduce myocardial deposition and prevent ischemic injury during reperfusion. The effects of dipyridamole on myocardial platelet and leukocyte deposition were evaluated in a canine model of acute regional myocardial ischemia with reperfusion during cardioplegia on cardiopulmonary bypass. Eight dogs underwent left anterior descending (LAD) coronary artery ligation for 45 min followed by cardiopulmonary bypass and release of the ligature during 60 min of cold crystalloid cardioplegic arrest to simulate urgent revascularization. Four dogs were randomized to receive an infusion of dipyridamole perioperatively (50 mg/hr) and 4 dogs served as controls. Autologous platelets were labeled with 111In, leukocytes with 99mTc, and erythrocytes with 51Cr. The labeled cells were infused immediately after cross-clamp release and myocardial biopsies were obtained at 10, 20, 30, and 60 min of reperfusion. Platelets were deposited in the myocardium during reperfusion and four times more platelets were found in the LAD region than the circumflex region. Leukocyte deposition was similar in the LAD and circumflex regions. Dipyridamole reduced both platelet and leukocyte deposition and the reduction was greater in the LAD than in the circumflex region. Myocardial platelet and leukocyte deposition was found after regional ischemia, cardioplegia, and cardiopulmonary bypass. Dipyridamole reduced myocardial platelet and leukocyte deposition and may reduce perioperative ischemic injury.

Transmural myocardial perfusion

The predilection for subendocardial underperfusion and ischemia is great and must be considered in the management of any patient, especially if there is coronary artery disease or ventricular hypertrophy. Although the mechanisms of subendocardial ischemia remain to be fully defined, they are clearly associated with the transmural distribution of intramyocardial systolic pressures. Even though almost all the myocardium is perfused in diastole, a reduction of diastolic perfusion pressure or duration will result in subendocardial ischemia. The factors that produce subendocardial ischemia are all associated with a reduction or loss of coronary flow reserve, and as our ability to measure flow reserve in humans improves, it is likely that we will be able to select medical or surgical therapy that will minimize or abolish subendocardial ischemia. For example, it will someday become possible to choose a time for valve replacement in an asymptomatic patient to obtain maximal protection of the myocardium or to select the right combination of therapies for the immediate post-operative period so that as much myocardium as possible will be spared. The more we learn to understand the mechanisms of subendocardial ischemia, the sooner will we be able to achieve these desired ends.

Evidence against systolic intramural forces as the primary cause of subendocardial preponderance of ischemia

Verification of the current view that subendocardial preponderance of ischemia is due to greater forces generated in the deep myocardial layer during systole was undertaken. In anesthetized mongrel dogs transient ischemia was produced in two different situations of altered systolic forces. First, in order to remove that part of the systolic force which is related to intracavitary pressure, left ventricular bypass was created and the left ventricle vented. Second, in order to even out the transmural distribution of the remaining part of the forces, which is due directly to distortion and displacement of contracting fibers, ventricular fibrillation was induced in addition to venting under conditions of total cardiopulmonary bypass. In both series of experiments the ischemic area was then reperfused, normal circulation re-established and the animal allowed to survive for 3-5 days. After sacrifice, ischemic necrosis was found almost exclusively in the subendocardium. The persistence of subendocardial preponderance of ischemia under conditions of left ventricular venting and absence of coordinated contraction shows that uneven distribution of intramural forces generated during systole is not the primary cause of this preponderance.

A computer evaluation of the ratio of the diastolic pressure-time index to the time-tension index from three arterial sites in dogs

The ratio of the area under the diastolic portion of the arterial pulse pressure trace (diastolic pressure-time index; DPTI) to the area under the systolic component of the arterial pulse pressure trace (time-tension index; TTI) has been used to predict the relationship of myocardial blood supply to oxygen demand. Since introduction of the DPTI-to-TTI ratio as a measurement of this relationship, the accepted critical DPTI:TTI value below which subendocardial ischemia may occur has decreased by almost 50%. This lower critical value has come about as more clinical experience has been gained, particularly in patients with an arterial catheter in the arm. To investigate a potential cause for this decrease, we studied a canine model by pulse transduction from the central aorta (the site traditionally used for these ratio determinations), as well as the femoral artery and the median forepaw artery. Following inotropic and ventricular loading interventions, the changes in the DPTI:TTI, calculated by a special-purpose computer, were exaggerated by approximately 25% in the peripheral arterial measurements. The peripheral arterial sites had consistently higher systolic waveforms and consistently lower, broader diastolic waveforms than those for the central aortic site. This type of configurational change is probably a major cause of the differences among ratios from the three sites in our study, and it helps to explain why the value of the critical ratio has been a subject of controversy.

Optimum dose of cold potassium cardioplegia for patients with chronic aortic valve disease: determination by left ventricular mass

Twenty-eight patients with chronic aortic valve disease and left ventricular (LV) hypertrophy who underwent aortic valve replacement were studied. Angiographically obtained LV mass ranged from 113 to 580 gm (average, 292 gm). In 14 patients, the LV mass per square meter of body surface area was 200 gm or more. Cold glucose-insulin-K+ cardioplegic solution was infused to obtain a myocardial temperature of less than 15 degrees C. The initial dose of cardioplegic solution was increased to as much as 25 mL per kilogram of body weight when LV hypertrophy was severe. The initial dose was standardized by LV mass and ranged from 1.0 to 3.6 ml/gm (average, 2.7 ml/gm). Postoperative peak levels of the myocardial-specific isoenzyme of creatine phosphokinase (CPK-MB) showed no significant relationship to aortic cross-clamp time, but were related significantly to LV mass (r = 0.457, p less than 0.02). The initial dose of cardioplegic solution per LV mass and the peak CPK-MB had an inverse relationship (r = -0.753, p less than 0.001). Also, peak CPK-MB was significantly lower in those patients with an initial dose of cardioplegic solution per LV mass of 2.5 ml/gm or more regardless of the size of the LV mass (300 gm or more and less than 300 gm) in spite of no significant difference in myocardial temperature. These results indicate that the dose determination of cardioplegic solution by LV mass seems desirable for patients with chronic aortic valve disease and LV hypertrophy even when myocardial temperature is monitored.

Does prostacyclin (PGI2) cardioplegic infusion improve myocardial protection after ischemic arrest?

To determine whether prostacyclin (PGI2) plays a beneficial role in the blood-perfused heart undergoing global ischemia, 20 isolated canine hearts were studied after sustaining one hour of cardioplegic arrest under moderate hypothermia (27 degrees to 28 degrees C). Left ventricular function (peak systolic pressure, rate of rise of left ventricular pressure [dP/dt], and compliance change in left ventricular volume), myocardial edema, coronary blood flow, and oxygen content were measured during the preischemic period and at 15 and 30 minutes during reperfusion. Results showed an improved hemodynamic recovery (peak systolic pressure, p = 0.018 at 30 minutes; dP/dt, p = 0.020 at 15 minutes) in the group of hearts treated with PGI2 infusion compared with controls. There was no difference in ventricular compliance or myocardial edema between the two groups. This benefit was attributed to a significant increase in myocardial blood flow (p = 0.028 at 15 minutes) and oxygen delivery (p = 0.021 at 15 minutes) during the reperfusion period with PGI2. These data suggest a potential clinical role for PGI2 when applied to the globally ischemic heart in the improvement of myocardial resuscitation during the early reperfusion period.

Enhanced cardioplegic protection by a fluorocarbon-oxygenated reperfusate: a phosphorus-31 nuclear magnetic resonance study

Prolonged global ischemia results in a defect in oxygen extraction during early reperfusion. This study was thus undertaken to assess the effects of maintaining cardioplegia at the onset of reoxygenation in view of channeling available energy toward reparative cell processes rather than mechanical activity. Twenty-four isolated perfused rat hearts were subjected to 120 min of 15 degrees C ischemia. Group I (control) was reperfused with the standard Krebs perfusion medium whereas in groups II and III the initial reperfusate consisted of an oxygenated alkaline cardioplegic solution prior to the resumption of Krebs perfusion. Oxygenation of the cardioplegic reperfusate was ensured by fluorocarbons at a concentration of 10% (O2 content: 5.5 vol %; group II) or 20% (O2 content: 9 vol %; group III). In addition to hemodynamical determinations, high-energy phosphates and intracellular pH were monitored serially by phosphorus-31 nuclear magnetic resonance spectroscopy. After 30 min of reperfusion postischemic recovery of aortic flow was better in group II (74.0 +/- 5.9% of control) than in group I (59.1 +/- 5.4% of control, P less than 0.05). This functional improvement correlated with a higher postischemic increase in phosphocreatine levels (103.21 +/- 11.21% vs 74.12 +/- 3.59%, at 3 min of reperfusion, P less than 0.05) without significant differences in total ATP content. Group III hearts exhibited a slow recovery as evidenced by a severe depression in aortic flow, coronary arteriovenous difference, and total phosphate content during the 15 initial minutes of reperfusion. These results show that the protection provided by cardioplegia can be improved by a fluorocarbon-oxygenated cardioplegic reperfusate.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between perfusion pressure and myocardial microcirculation in the beating empty or spontaneously fibrillating heart

The influence of graded perfusion pressure (30, 60, and 90 mmHg) at cardiopulmonary bypass were studied on beating empty hearts (BEH) or spontaneously fibrillating hearts (SFH) in the normothermic state. The adequacy and distribution of coronary flow and the myocardial oxygen consumption (MVO2) were examined using the tracer microsphere technique in twelve mongrel dogs. In the SFH, the left ventricular (LV) endocardium (ENDO)/epicardium (EPI) flow ratio indicated significant decrease at 30 and 60 mmHg (0.83 +/- 0.05 and 0.86 +/- 0.06, p less than 0.005, respectively), but was recovered to control value at 90 mmHg (1.01 +/- 0.13). In the BEH, these low perfusion pressures did not result in an abnormal flow distribution in the LV (1.03 +/- 0.03 at 30 mmHg). The flow distribution to the right ventricle (RV) relatively increased in both the BEH and the SFH (p less than 0.001). The ENDO/EPI ratio of the RV did not decrease at 30 mmHg in both groups (1.11 +/- 0.03 in BEH and 1.16 +/- 0.08 in SFH). Coronary blood flow and MVO2 were significantly higher in the SFH than in the BEH. Coronary blood flow increased significantly with increase in the perfusion pressure, in both groups. The MVO2 was constant in the BEH, regardless of the perfusion pressure, but increased in the SFH at increasing pressure. These results show that in the SFH, subendocardial underperfusion of the LV is induced at the perfusion pressure of 30 and 60 mmHg.

The effect of nitroglycerin cardioplegia on myocardial cooling in patients undergoing myocardial revascularization

The effect of intracoronary administration of nitroglycerin on the distribution of cardioplegia and myocardial cooling was assessed in 45 patients undergoing elective myocardial revascularization. The patients were divided into three groups. Myocardial temperature was measured over the right and left coronary artery distributions in Group 1 after the infusion of 1 liter of potassium blood cardioplegic solution (20 mEq of potassium per liter). Similar temperature measurements were made in Group 2 after the addition of 300 micrograms of nitroglycerin to the cardioplegic solution and in Group 3 after the addition of 1,000 micrograms of nitroglycerin. Nitroglycerin did not affect myocardial cooling, and large temperature gradients persisted after delivery of cardioplegia in patients with occlusive coronary artery disease. Unexpectedly, however, the rate of cardioplegia delivery increased by 134%, within the same range of infusion pressures, in patients receiving nitroglycerin. Although nitroglycerin cardioplegia does not affect the regional disparity in the distribution of cardioplegia in patients with severe coronary artery disease, intracoronary administration of nitroglycerin reduces the time required for administration of cardioplegia and thereby decreases the total ischemia time.

Should ventricular fibrillation be induced prior to the infusion of cardioplegic solution?

The present study evaluates the metabolic effects on the left ventricular energy stores of a clinically used cardioplegic solution that was infused into the ascending aorta of pigs while the heart was either fibrillating (induced ventricular fibrillation) or in normal sinus rhythm prior to aortic clamping. Fibrillating hearts had lower stores of glycogen in the epicardium and endocardium compared with hearts in normal sinus rhythm. There was no difference in the stores of creatine phosphate between the hearts for both the epicardium and endocardium, but stores of adenosine triphosphate (ATP) in both layers were lower in fibrillating hearts. These results indicate that for ideal myocardial protection the cardioplegic solution should be infused while the heart is beating under cardiopulmonary bypass, and that ventricular fibrillation induced and maintained prior to cross-clamping may cause myocardial damage.

The hemodynamic and metabolic effects of cardioplegic rearrest in the pig

The hemodynamic and metabolic effects of two consecutive 1-hour periods of cardioplegic arrest with a 20-minute interval of reperfusion or cardioplegic rearrest were evaluated in pig hearts. This model was designed to recreate in the laboratory a situation occasionally encountered during open-heart operation. Results indicate that at the end of 40 minutes of reperfusion following cardioplegic rearrest and 20 minutes after cardiopulmonary bypass (CPB), the stores of glycogen, adenosine triphosphate and total adenine nucleotides were lower than those found in hearts beating under CPB for an identical period of time. These stores were, however, sufficient to permit hemodynamic recovery, and they compared favorably with those found in hearts subjected to a single hour of cardioplegic arrest and reperfusion. The laboratory data and our previous clinical experience suggest that cardioplegic rearrest is a feasible alternative when surgical difficulties demand a second period of aortic cross-clamping after an initial period of cardioplegic arrest and reperfusion.

Biopsy assessment of preservation during open-heart surgery with cold cardioplegic arrest

The efficacy of cold cardioplegic arrest as a method of myocardial preservation has been evaluated by cytochemical and biophysical assessments made on needle biopsies taken from 150 patients undergoing open-heart surgery (e.g., aortic valve replacement, aortic and mitral valve replacement, mitral valve replacement, coronary artery bypass graft, repair of atrial or ventricular septal defects). Comparison of endo- and epicardial preservation showed improved endocardial preservation with cardioplegia compared with that achieved with the previous method used--continuous coronary perfusion at 32 degrees C; however, care had to be taken to ensure adequate cooling of the epicardium. Biopsies also showed the need for repeated infusions of cardioplegic solution if the aorta was occluded for more than 70 min. Preservation of right and left ventricle has also been compared.

Correlation among water content, left ventricular function, coronary blood flow, and myocardial metabolism after hypothermic ischemic cardiac arrest

Subendocardial ischemia is a common cause of death following ischemic cardiac arrest. We studied relationships among myocardial water content (WC), left ventricular function, coronary blood flow, and myocardial metabolism following ischemic cardiac arrest. Under cardiopulmonary bypass with hypothermia, 120 min of aortic occlusion was employed, and myocardial temperature was kept around 20 degrees C in 10 mongrel dogs. Left ventricular function (peak LVP, max dp/dt, LVEDP, LVSWI), coronary blood flow, myocardial enzymes (m-GOT, total CPK, MB-CPK), myocardial ATP and creatine phosphate (CP), and WC of the subendocardium of the left ventricle were measured. Data were obtained in the control state and immediately and 30 and 60 min after aortic unclamping. Significant negative correlations were obtained between WC and max dp/dt (r = -0.8384), coronary blood flow (r = -0.9928), ATP (r = -0.7038), and CP (r = -0.7835). Significant positive correlations were obtained between WC and LVEDP (r = 0.7525), m-GOT (r = 0.7638), and total CPK (r = 0.7079). These data suggest that myocardial edema results in depression of left ventricular function and metabolism.

Myocardial responses to acute global ischemia and reperfusion

Effects of 15 to 120 minutes of global myocardial ischemia without coronary occlusion followed by 60 minutes of reperfusion were examined in anesthetized dogs on total coronary bypass. Thirty minutes or less of global ischemia was found to be fully recoverable, while longer periods of ischemia were associated with irreversible damage. Total and regional myocardial flows and myocardial oxygen consumption did not recover in animals subjected to 60 minutes of global ischemia, while hemodynamic dysfunction became apparent only after 90 minutes of global ischemia. These results indicate that global myocardial ischemia, like coronary artery ligation, will produce functional impairment during reperfusion which is dependent on the duration of the insult.

The limit of application of intraaortic balloon pumping (IABP) on canine myocardial infarction

The limit of application of intraaortic balloon pumping was evaluated in cases of canine myocardial infarction produced by either ligation of the descending coronary artery and of branches in the right coronary artery or establishment of stenosis in the left main coronary artery. The limit of application of intraaortic balloon pumping was confirmed to be as follows: 1) stenosis of seventy-five per cent or more in left main coronary artery, 2) over 45 per cent infarction of the entire left ventricular free wall, 3) endocardial viability ratio of less than 0.65, 4) blood flow of less than 18 ml/min/100 g in the left circumflex coronary artery when the left descending coronary artery was ligated, 5) and less than 0.69 in the ratio of inside blood flow to outside of the left ventricular free wall, as related to regional myocardial blood flow.

Coenzyme Q10: the prophylactic effect on low cardiac output following cardiac valve replacement

A randomized, prospective study of the effectiveness of preoperative administration of coenzyme Q10 on the prophylaxis of postoperative low cardiac output state was performed in 50 patients with acquired valvular diseases necessitating valve replacement. There were 25 patients in the treatment group and 25 in the control group. Patients in the treatment group received 30 to 60 mg of coenzyme Q10 orally for six days before operation. Preoperative clinical variables, operative procedures, total cardiopulmonary bypass time, and aortic cross-clamping time were similar for the two groups. Postoperatively, mild to severe low cardiac output state developed in 28 of 50 patients (56%) and necessitated the administration of considerable amounts of inotropic agent. The treatment group showed a significantly lower incidence of low cardiac output state during the recovery period than the control group (p less than 0.05). These results suggest that preoperative administration of coenzyme Q10 will increase the tolerance of human hearts to ischemia during aortic cross-clamping.

Transmural gradient in high-energy phosphate content in patients with coronary artery disease

In 16 patients undergoing elective coronary artery bypass, transmural biopsies were performed during bypass but before global ischemia. Subendocardial and subepicardial halves were separately assayed in each sampled tissue. Adenosine triphosphate (ATP) levels, total adenine nucleotide content (sigma Ad), and creatine phosphate (CP) content were significantly higher (p less than 0.005) in the subepicardium than the subendocardium in regions of the heart distal to major occlusions: 35.36 +/- 2.12 nmole/mg versus 28.7 +/- 1.7 (ATP), 42.24 +/- 2.04 versus 35.6 +/- 1.6 (sigma Ad), and 29.99 +/- 4.32 +/- versus 16.35 +/- 3.48 (CP). The opposite was true in two hearts with normal coronary arteries, in which high-energy phosphates tended to be higher in the subendocardium than the subepicardium. A transmural metabolic gradient therefore exists in regions of the myocardium distal to significant coronary occlusive disease. The subendocardium's relative depression in metabolic reserve cold determine its susceptibility to ischemic damage and influence techniques designed to preserve the heart during ischemia.

Nonrandomized matched pair analysis of intermittent ischemic arrest versus potassium crystalloid cardioplegia during myocardial revascularization

The quest for the ideal method of myocardial preservation during coronary artery bypass graft (CABG) surgery continues at a rapid pace. Nevertheless, in the present clinical practice of cardiac surgery, the choice is chiefly between hypothermic intermittent ischemic arrest and hypothermic potassium cardioplegia. This study applies newer technics in radionuclear cardiology, as well as more conventional enzymatic, electrocardiographic, and hemodynamic determinations, to the evaluation of the effectiveness of the previously mentioned modes of myocardial protection. Serial assessments are made preoperatively as well as during the first ten days postoperatively. We find that the perioperative incidence of myocardial damage and changes in left ventricular performance are almost identical using either method in patients with relatively normal preoperative left ventricular performance who do not have severe preoperative refractory ischemia or necrosis.

Beneficial effects of nitroprusside administration on left ventricular dysfunction and myocardial ischemia in severe aortic stenosis

Although surgical therapy is effective for reducing excessive left ventricular (LV) afterload in valvular aortic stenosis (AS), salutary short-term medical treatment has been lacking. Since we have shown LV systolic pressure (SP) is altered concordant with arterial SP in AS by vasopressors, the present study evaluated efficacy of nitroprusside (NP) on LV function, energetics, and perfusion in 15 severe AS patients. NP infusion (average 33 micron/min) proved beneficial in each: LVSP 192 mm Hg was reduced to 164; arterial SP decrement equaled LVSP change; LV end-diastolic pressure 19 mm Hg declined to 10: cardiac index (2.73 L/min/m2) and heart rate were unaltered; total systemic vascular resistance 1433 dsc-5 decreased to 1201; elevated LV stroke work index 92 gm.m/m2 was diminished to 74. Simultaneously, LV O2 consumption fell, LV diastolic flow was unchanged, while subendocardial perfusion increased. Thus cautious NP therapy with careful monitoring provided marked reduction of LV affected and improved LV function, energetics, and coronary flow distribution.