Diastolic ventricular properties in patients during coronary revascularization

Diastolic Dysfunction After Coronary Artery Bypass Grafting?The Effect of Glucose-Insulin-Potassium Infusion

BACKGROUND

Glucose-insulin-potassium (GIK) infusion improves clinical outcome after coronary artery bypass surgery (CABG). The mechanism of benefit is unclear, but GIK limits ischemia and reperfusion injury. This study was designed to assess whether the clinical benefit of perioperative GIK infusion is mediated through reduction in the severity of diastolic dysfunction that occurs after CABG.

METHODS AND RESULTS

Thirty-one patients undergoing CABG were randomized to GIK infusion (n = 14) or no-GIK (n = 17). Left ventricular compliance, using pressure-area relationships, was assessed by simultaneous transesophageal echocardiographic measurement of LV end-diastolic area (LVEDA) and pulmonary capillary wedge pressure (PCWP) at baseline prior to CABG, early post cardiopulmonary bypass (CPB), after sternal closure, and 3 hours postoperatively. Measures of LVEDA were made at a constant PCWP and a decrease in LVEDA reflects a leftward shift in the pressure-area relationship consistent with decreased compliance. Both study groups demonstrated progressive and consistent worsening of LV compliance, as evidenced by a reduction of LVEDA from 17.0 +/- 3.9 cm(2) at baseline to 15.3 +/- 3.6 cm(2) after CPB, 14.6 +/- 2.9 cm(2) after sternal closure, and 14.1 +/- 3.2 cm(2) (p < 0.0001) at three hours postoperatively. LVEDA decreased from a baseline of 16.3 +/- 2.8 to 13.8 +/- 2.9 cm(2) in the GIK group, while the non-GIK group demonstrated a reduction of LVEDA from 17.5 +/- 4.6 to 14.3 +/- 3.5 cm(2). Doppler transmitral E wave deceleration time shortened as well, which is consistent with more restrictive LV filling due to rapid equilibration of LA and LV pressures. GIK infusion did not alter either measure of diastolic function significantly.

CONCLUSION

Diastolic dysfunction occurs nearly universally after CABG, worsens with chest closure, persists for up to 3 hours postoperatively, and is unaffected by GIK. Despite theoretical reasons why GIK might limit ischemia and reperfusion injury, the clinical benefits do not appear to be related to amelioration of diastolic dysfunction.

SUPPORT

The study was partially supported by Agilent Technologies/Philips Imaging.

Imaging and diagnostic testing: diastolic dysfunction after coronary artery bypass grafting: a frequent finding of clinical significance not influenced by intravenous calcium

BACKGROUND

Diastolic dysfunction is common immediately after coronary artery bypass surgery (CABG). The duration of this phenomenon is unknown. Intravenous calcium is frequently administered during separation from cardiopulmonary bypass (CPB). We sought to determine whether intravenous calcium influences perioperative diastolic function and whether diastolic dysfunction persists into the postoperative period.

METHODS AND RESULTS

Patients undergoing first-time elective CABG (n = 29) were randomly assigned to receive intravenous calcium chloride (n = 13) or placebo (n = 16) during separation from CPB. Diastolic function was assessed by the pressure-area relation with transesophageal echocardiography and pulmonary capillary wedge pressure (PCWP) measured simultaneously. Left ventricular end-diastolic area (LVEDA) and Doppler indexes were measured at comparable PCWP (within 2 mm Hg) at baseline, after separation from CPB, after sternal closure, and 3 hours after surgery. After CABG, both groups had a significant decrease in LVEDA and mitral E-wave deceleration time that persisted at 3 hours. Because there were no significant differences between the calcium and control groups at any time point, the data for the entire study cohort was analyzed. The LVEDA decreased (stiffness increased) progressively from 16.9 +/- 3.4 cm2 at baseline to 15.8 +/- 2.9 cm2 after CPB, 14.9 +/- 2.5 cm2 after sternal closure, and 14.3 +/- 3.1 cm2 at 3 hours after surgery (P <.0001). The mitral E-wave deceleration time measured at the same time points was 168 +/- 47 ms, 136 +/- 25 ms, 137 +/- 36 ms, and 111 +/- 44 ms (P =.0001).

CONCLUSIONS

An increase in left ventricular diastolic chamber stiffness is nearly universal after CABG, and it persists for at least 3 hours after surgery. An intravenous bolus of calcium chloride given during separation from CPB has no measurable negative effect on diastolic function. In the setting of increased chamber stiffness, the PCWP alone does not adequately reflect the volume status and effective preload of the left ventricle.

Milrinone, not epinephrine, improves left ventricular compliance after cardiopulmonary bypass

OBJECTIVE

To compare the effects of milrinone versus epinephrine administered after cardiopulmonary bypass (CPB) on left ventricular compliance.

DESIGN

Prospective and randomized.

SETTING

University-affiliated hospital.

PARTICIPANTS

Twenty consenting adult patients.

INTERVENTIONS

Patients undergoing aortocoronary bypass surgery were randomized to receive 50 microg/kg of milrinone (group M; n = 10) or 0.03 microg/kg/min of epinephrine (group E; n = 10) shortly after separation from CPB. Left ventricular compliance was assessed by observing changes in left ventricular end-diastolic area (LVEDA) in the short-axis view with transesophageal echocardiography, while maintaining a constant left atrial pressure. Measurements were performed (1) before CPB, (2) after separation from CPB, and (3) after either milrinone or epinephrine.

MEASUREMENTS AND MAIN RESULTS

Baseline LVEDA decreased by 20% after CPB in the milrinone group (from 16.6 +/- 3.1 cm2 to 14.3 +/- 2.4 cm2; p < 0.05) and by 22% in the epinephrine group (from 19.4 +/- 4.1 cm2 to 17.2 +/- 3.8 cm2; p < 0.05). LVEDA increased by 15% after milrinone (from 14.3 +/- 2.4 cm2 to 15.6 +/- 2.8 cm2; p < 0.05) but remained unchanged after epinephrine (from 17.2 +/- 3.8 cm2 to 17.1 +/- 4.2 cm2; p = ns).

CONCLUSIONS

Left ventricular compliance was decreased after CPB. The administration of milrinone, but not epinephrine, was associated with a partial return to prebypass values. The exact mechanism of action remains to be determined.

Iatrogenic myocardial edema: increased diastolic compliance and time course of resolution in vivo

BACKGROUND

Perfusion-induced edema reduces diastolic compliance in isolated hearts, but this effect and the time for edema to resolve after blood reperfusion have not been defined in large animals.

METHODS

Edema was induced by coronary perfusion with Plegisol (750 mL, 289 mOsm/L) during a 1-minute aortic occlusion in 6 pigs. This was followed by whole blood reperfusion, inotropic support, and circulatory assistance until sinus rhythm and contractile function were restored. A control group (n = 6) was treated similarly, with 1 minute of electrically induced ventricular fibrillation and no coronary perfusion. Recorded data included electrocardiogram, left ventricular pressure and conductance, aortic flow, and two-dimensional echocardiography. Preload reduction by vena caval occlusion was used to define systolic and diastolic properties. Data were recorded at baseline and at 15-minute intervals for 90 minutes after reperfusion.

RESULTS

In the edema group, average left ventricular mass (132 +/- 7 [standard error of the mean] versus 106 +/- 4 g) and ventricular stiffness constant (0.15 +/- 0.02 versus 0.05 +/- 0.01) increased after Plegisol versus baseline (p < 0.05), returning to normal after 45 minutes of reperfusion. In controls, mass (118 +/- 6 versus 116 +/- 4 g) and ventricular stiffness (0.06 +/- 0.01 versus 0.05 +/- 0.01) did not change significantly. There was no significant change in systolic function. Myocardial water content at the end of the study was not different for the two groups.

CONCLUSIONS

Crystalloid-induced edema and diastolic stiffness resolve after 45 minutes in pigs. This suggests that edema caused solely by cardioplegia during cardiac operations should not cause significant perioperative ventricular dysfunction.

Blood cardioplegia in the senescent heart

As an increasingly aged population undergoes cardiac surgery, myocardial protective strategies must address the fundamental differences between adult and senescent myocardium. In a test of the hypothesis that senescent myocardium is less tolerant of cardioplegic arrest, adult (0.5 to 1.0 years) and senescent (6 to 9 years) sheep underwent 55 minutes of hypothermic blood cardioplegic arrest. A 5-minute dose of terminal warm blood cardioplegic solution was administered followed by 30 minutes of vented reperfusion. Left ventricular volume was monitored by means of sonomicrometric crystals in three orthogonal planes. Myocardial function was assessed with the preload recruitable stroke work relationship. Diastolic function was assessed with two techniques: the "stiffness" coefficient (beta), derived from the exponential end-diastolic pressure-volume relationship, and the time constant of isovolumic left ventricular pressure decay (tau). Data were acquired before arrest and after the reperfusion period. Contractility in the adult hearts was well preserved (preload recruitable stroke work: 63.7 +/- 6.1 versus 56.8 +/- 4.1 mJ/beat per milliliter per 100 gm, prearrest versus postarrest, p = not significant). In contrast, senescent heart contractility was poorly preserved (56.8 +/- 4.1 versus 35.4 +/- 4.2 mJ/beat per milliliter per 100 gm, p < 0.025). Early diastolic relaxation (tau) was prolonged in the adult hearts (42.5 +/- 3.3 versus 48.8 +/- 3.5 msec prearrest versus postarrest, p < 0.05), whereas the senescent hearts were essentially unchanged (49.3 +/- 3.1 versus 52.3 +/- 4.5 msec. p = 0.35). Myocardial stiffness (beta) was unchanged in both groups. When compared with adult hearts, contractility in senescent hearts is poorly preserved after cold blood cardioplegic arrest. Active diastolic relaxation, however, is more prolonged in adult hearts. Passive diastolic properties are unchanged in both groups. Because there are specific age-related differences in tolerance to cardioplegic arrest, extrapolation of myocardial protective strategies from studies in adult hearts to elderly patients may not be appropriate.

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.

Validation of pressure-volume data obtained in patients by initial transit radionuclide angiocardiography

In order to validate the measurement of pressure-volume loops and stroke work in humans, simultaneous digital subtraction ventriculography (DSA) and first-pass radionuclide angiocardiography (RNA) coupled with high-fidelity micromanometer left ventricular pressure measurements were undertaken in 34 patients, mean age 75 +/- 9 years, with aortic stenosis. Twenty-nine patients had a repeat study after balloon valvuloplasty, for a total of 63 DSA and RNA pressure-volume loops. All data were analyzed in a systemic fashion in order to minimize intra- and interobserver error. Linear regression analysis was used to calculate the degree of agreement between the two technologies. Left ventricular ejection fraction (RNA: 0.47 +/- 0.17, DSA: 0.49 +/- 0.18) had a correlation coefficient of 0.96; left ventricular end-diastolic volume (RNA: 171 +/- 42 ml, DAS: 168 +/- 52 ml) and end-systolic volume (RNA: 95 +/- 50 ml, DSA: 89 +/- 50 ml) had correlation coefficients of 0.89 and 0.95, respectively. Left ventricular stroke volume (RNA: 75 +/- 26 ml, DSA: 75 +/- 27 ml) had a correlation coefficient of 0.92, while integrated pressure-volume loop or stroke work (RNA: 15.6 +/- 6.6 ergs 10(6), DSA: 15.9 +/- 6.3 ergs 10(6] had a correlation coefficient of 0.89. These data demonstrate that RNA measurements of left ventricular chamber dynamics concur with that obtained with DSA. With semiautomated data analysis, the portable first-pass RNA pressure-volume data are also less labor-intensive. Moreover, multiple measurements of ventricular performance during hemodynamic manipulations in the catheterization laboratory or operating room would allow for a more precise estimation of left ventricular performance.

The physiological basis of left ventricular diastolic dysfunction

Overall cardiac pump function requires adequate ventricular diastolic filling as well as normal systolic ejection. Abnormalities of the rate or extent of myocardial relaxation (diastolic dysfunction) have been described in a large variety of clinical conditions, including hypertrophy, ischemia, and after cardiac surgery. Diastolic and systolic dysfunction can be readily distinguished by analysis of pressure volume loops and utilization of echocardiography or nuclear cardiology gated blood pool scans. The mechanisms by which diastolic dysfunction can occur may be structural (hypertrophy, fibrosis) or dynamic (hypoxia, ischemia, alteration of diastolic cytosolic calcium levels). Hypertrophied myocardium is particularly susceptible to diastolic dysfunction by virtue of both structural changes (increased LV mass and interstitial fibrosis) and greater susceptibility to develop impaired myocardial relaxation during hypoxia or ischemia than nonhypertrophied myocardium.

Immediate enhancement of left ventricular relaxation by coronary artery bypass grafting: intraoperative assessment

We investigated the effect of coronary artery bypass grafting on the rate of left ventricular relaxation as defined by the time constant for isovolumetric relaxation, T, measured in milliseconds. Completeness of relaxation at rapid heart rates was determined by comparison of the relationship between left ventricular pressure and echocardiographic left ventricular cross-sectional cavity area during rapid ventricular pacing with that obtained after a prolonged diastole when the ventricle was maximally relaxed. Twelve patients with coronary artery disease had significantly higher T values (94.5 +/- 6.2) than six patients without coronary artery disease who were undergoing other open heart procedures (39.5 +/- 5.0, p less than .001). T was significantly reduced after coronary artery bypass grafting (68.2 +/- 5.1, p = .007), but was unchanged in the six control patients after cardiopulmonary bypass (37.8 +/- 4.5, p = .54). Similar changes were found during rapid pacing to 100, 120, and 140/min. Incomplete relaxation was detected in three of 10 (heart rate 120 beats/min) and nine of 11 (heart rate 140 beats/min) patients with coronary artery disease and this decreased to 0 of 10 (heart rate 120 beats/min) and six of 11 (heart rate 140 beats/min) patients after coronary artery bypass. Incomplete relaxation before bypass at a heart rate of 120 beats/min averaged 0.9 +/- 0.3 mm Hg. At a heart rate of 140 beats/min, incomplete relaxation averaged 5.6 +/- 1.6 mm Hg before and 1.4 +/- 0.5 mm Hg after bypass. Intake of beta-blockers or calcium-channel blockers, body temperature, and systolic blood pressure were not found to be related to these changes. We conclude that immediately after coronary artery bypass relaxation of left ventricular muscle is enhanced and incomplete relaxation at rapid heart rates is less likely. The most probable cause of this improvement in ventricular relaxation after coronary artery bypass grafting is relief of ischemia.

Surgical ablation of ventricular tachycardia with sequential map-guided subendocardial resection: electrophysiologic assessment and long-term follow-up

A new operative technique of sequential map-guided subendocardial resection (SER) was used in 45 consecutive patients for the treatment of sustained ventricular tachycardia due to coronary artery disease. This technique is characterized by map-guided SER or cryothermic ablation during normothermic cardiopulmonary bypass, followed by repeated sequences of programmed stimulation to assess adequacy of resection. The patients' mean age was 59 +/- 10 years and the mean left ventricular ejection fraction was 34 +/- 12%. Twenty-five (56%) patients had a history of myocardial infarction within the previous 2 months. After ventriculotomy, 34 patients (76%) had inducible monomorphic ventricular tachycardia. These patients underwent repeated sequences of ventricular tachycardia induction and mapping during normothermic bypass followed by successive SER or cryothermic ablation until sustained monomorphic ventricular tachycardia was no longer inducible. Twenty-seven patients had a total of 60 discrete, mappable tachycardias induced and seven patients had 10 discrete tachycardias that were too fast to accurately map. In the remaining 11 patients, no ventricular tachycardia was inducible after ventriculotomy and SER, which included all visually identifiable scar, was performed. The mean cardiopulmonary bypass time was 102 +/- 27 min. Forty-one of 45 patients (91%) survived to hospital discharge, and 35 of 41 patients (85%) had no inducible ventricular tachycardia at postoperative electrophysiologic evaluation performed in the absence of all antiarrhythmic drugs. The remaining six patients had no inducible ventricular tachycardia with drug therapy. All four operative nonsurvivors had refractory cardiac collapse preoperatively. Over 19 +/- 12 months of follow-up, there were four sudden cardiac deaths and no nonfatal recurrences of ventricular tachycardia. There were seven additional cardiac deaths. Actuarial cardiac survival was 0.57, and freedom from arrhythmic events was 0.76 at 42 months. Thus, in the absence of cardiogenic shock, the technique of sequential map-guided SER achieves: (1) a high operative survival with acceptable perfusion times, (2) excellent long-term arrhythmia control, and (3) survival comparable to that in patients with similar left ventricular function and no history of ventricular tachyarrhythmia.

Acute alterations in diastolic left ventricular chamber distensibility: mechanistic differences between hypoxemia and ischemia in isolated perfused rabbit and rat hearts

Changes in diastolic chamber distensibility (DCD) during hypoxemia and ischemia were studied in isolated-buffer-perfused rabbit hearts. Two minutes of hypoxemia (low PO2 coronary flow) resulted in a shift of the diastolic pressure-volume curve to the left, i.e., distensibility was decreased (hypoxemic contracture). In contrast, 2 minutes of ischemia (zero coronary flow) resulted in an initial shift of the diastolic pressure-volume curve to the right indicating increased distensibility, which was followed by a later (30 minutes) shift to the left (ischemic contracture). Two minutes of ischemia superimposed on hypoxemia caused complete reversal of contracture. A quick stretch and release applied to the myocardium reversed late ischemic contracture but did not effect early hypoxemic contracture. The role of intracellular pH in modulating changes in DCD during hypoxia and ischemia was studied using phosphorus-31 nuclear magnetic resonance spectroscopy of isolated-buffer-perfused rat hearts that demonstrated changes in DCD similar to rabbit hearts during hypoxemia and ischemia. Intracellular pH decreased from 7.03 +/- 0.02 to 6.87 +/- 0.03 (p less than .01) during 2 minutes of ischemia but did not change significantly during 4 minutes of hypoxemia. When 2 minutes of ischemia were superimposed on hypoxemia, pH decreased from 6.99 +/- 0.01 during hypoxemia to 6.88 +/- 0.02 after 2 minutes of ischemia (p less than .01), concomitant with the complete reversal of hypoxemic contracture. These results suggest different mechanisms for late ischemic and early hypoxemic contracture and also suggest an explanation for the opposite initial changes in DCD seen after brief periods of ischemia and hypoxemia. The early development of contracture during hypoxemia and rapid redevelopment of diastolic tension after quick stretching are consistent with the hypothesis that hypoxemic contracture results from persistent Ca++-activated diastolic tension secondary to impaired calcium resequestration by the sarcoplasmic reticulum. In contrast, the late development of contracture during global ischemia and reversal by quick stretching is compatible with rigor bond formation. The initial increase in distensibility during early ischemia and the reversal of hypoxemic contracture by a brief period of superimposed ischemia probably is the result of two factors present during ischemia but not during hypoxemia: the collapse of the coronary vasculature and loss of the "erectile" effect and, the rapid development of intracellular acidosis, which has been shown to affect myofibrillar calcium sensitivity, and this may lead to a decrease in Ca++ activated diastolic tension.

Myocardial preservation

The principles used to develop techniques for myocardial preservation in cardiac surgery have been successfully applied to the protection of the donor heart in transplant surgery. This article reviews the latest advances in myocardial preservation during cardiac surgery and shows how they have been adopted in current cardiac transplant techniques.

Ultrastructure of the human myocardium after intermittent ischemia compared to cardioplegia

A lot of reports informed about the detrimental effects of intermittent ischemia nevertheless this method is still used during coronary surgery. We investigated the myocardial protection due to cardioplegic arrest compared to intermittent ischemia in 120 patients undergoing coronary surgery. In all patients we took myocardial biopsies from the left ventricle before and after ischemia. Electron microscopic studies of all biopsies were performed and the degree of ultrastructural alteration was determined. The ischemic period in the cardioplegic group was 61 +/- 15 minutes and in the group with intermittent ischemia the total ischemic time was 45 +/- 21 minutes. After ischemia the myocardium showed most time only damage of moderate or light degree, while after intermittent ischemia the most biopsies showed severe ultrastructural damage. From our results we conclude, that intermittent ischemia is unable to protect the myocardium in a sufficient amount and should therefore no longer be used as a method of myocardial protection.

The effect of adding mannitol or albumin to a crystalloid cardioplegic solution: a prospective, randomized clinical study

To determine if the myocardial protection afforded by a cold crystalloid potassium cardioplegic solution could be improved by the addition of either mannitol or albumin, a prospective clinical study was undertaken in which 58 patients undergoing elective aortocoronary bypass were randomized to one of three groups. Each group featured a different cardioplegic solution. The solutions were a standard potassium crystalloid solution, a solution containing mannitol sufficient to raise the osmolality by 20 to 30 mOsm, and a solution containing 5% albumin. Preoperative, intraoperative, and postoperative evaluation included serial measurements of ejection fraction, myocardial-specific isoenzyme, and hemodynamic indexes of performance. Electrocardiographic evaluation for perioperative myocardial infarction and the need for postoperative inotropic and mechanical support were also included. No differences were found among the groups. Therefore, although the use of mannitol or albumin has been shown to be beneficial in an experimental setting, superiority of either additive could not be demonstrated clinically.

Recent advances in cardiopulmonary bypass and the clinical application of myocardial protection

Basic scientific research has provided the impetus to develop cardioplegic solutions that offer excellent myocardial preservation. Future research will continue to develop methods for better delivery of cardioplegia to all myocardial regions. In addition, earlier detection of evolving ischemic damage during aortic cross-clamping might provide a basis for earlier intervention to reverse developing myocardial injury. At the present time, the cardiac surgeon has many cardioplegic solutions and delivery systems from which to choose. Only by understanding the principles involved in myocardial preservation will the surgeon be able to develop a system that will work best in his or her clinical practice.