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

Heart failure in the twenty-first century: is it a coronary artery disease or hypertension problem?

Hypertension and coronary disease are major risk factors for the incidence and progression of heart failure. These two risk factors frequently coexist, and have additive and synergistic effects that promote both left ventricular remodeling and heart failure in the general population. The relative contributions of these two risk factors to heart failure burden in the community may vary based on age, gender, and race. In general, attribution of heart failure in the community to solely one of these two risk factors is inappropriate. Prevention of both hypertension and coronary disease is important for preventing heart failure in the twenty-first century.

A Rapid Hemodynamic Monitor of Acute Ischemia during Cardiac Procedures: Changes in Relaxation via a Continuous Left Ventricular Pressure-Derivative Loop

BACKGROUND

Procedures that induce ischemic pre-conditioning during cardiac surgery will require a rapidly visualized hemodynamic monitor of acute ischemia. This study investigated the utility of a continuous loop tracing of left ventricular pressure (LVP) plotted against its derivative (dP/dt) as a visual beat-to-beat monitor of acute changes in myocardial relaxation due to global ischemia.

MATERIALS AND METHODS

In 11 dogs, LVP, recorded via a micromanometer-tip catheter, was plotted against dP/dt as a continuous loop. The angle of the loop during relaxation is inversely related to tau, the time constant of isovolumic relaxation. The angle was measured before and during: infusion of dextran to increase pre-load, infusion of nitroprusside to reduce after-load, and a 30-s occlusion of the left main coronary artery to induce temporary global ischemia.

RESULTS

The relaxation angle of the loop did not change with dextran or nitroprusside infusion. During left main occlusion, the angle increased from 57 +/- 7 degrees to 92 +/- 3 degrees (P < 0.001), reflecting markedly impaired relaxation. In five of nine cases, the angle became greater than 90 degrees, rendering the monoexponential model of pressure decay inapplicable. However, the beat-to-beat progression of the angle could easily be followed visually.

CONCLUSIONS

The LVP-dP/dt loop is a readily visualized, continuous display of beat-to-beat changes in myocardial relaxation. It provides a dynamic and specific display of immediate changes in relaxation during global ischemia, even when the exponential model of pressure decay is not applicable. The loop may be useful for guiding procedures that induce ischemic pre-conditioning or post-conditioning during cardiac surgery.

Effects of Milrinone Versus Epinephrine on Left Ventricular Relaxation After Cardiopulmonary Bypass Following Myocardial Revascularization: Assessment by Color M-Mode and Tissue Doppler

OBJECTIVE

The purpose of this study was to evaluate the left ventricular lusitropic effects of epinephrine versus milrinone after cardiopulmonary bypass.

DESIGN

Prospective randomized study.

SETTING

Single institution, university teaching hospital.

PARTICIPANTS

Adult patients undergoing coronary artery bypass grafting under cardiopulmonary bypass.

INTERVENTIONS

After separation from cardiopulmonary bypass, patients were randomized to receive intravenous epinephrine by continuous infusion (0.03 microg/kg/min) or milrinone (50 microg/kg followed by 0.5 microg/kg/min). Transesophageal echocardiographic evaluation of left ventricular diastolic function, with emphasis on relaxation, was performed before and after bypass and after the administration of either epinephrine or milrinone.

MEASUREMENTS AND MAIN RESULTS

Measurements included pulse-wave Doppler analysis of mitral inflow and pulmonary vein and left ventricular outflow tract velocities. Left ventricular inflow velocity of propagation measured with color M-mode and tissue Doppler assessment of early mitral annulus velocity were used to evaluate left ventricular relaxation. Values of velocity of propagation and mitral annulus velocity improved significantly after bypass, suggesting improved relaxation. The administration of either epinephrine or milrinone did not result in further improvement in left ventricular relaxation.

CONCLUSIONS

After cardiopulmonary bypass, left ventricular relaxation was significantly improved. Neither epinephrine nor milrinone exhibited favorable lusitropic effects after bypass.

Coronary artery disease and prevention of heart failure

Coronary artery disease is a major contributor to the progression of left ventricular systolic dysfunction and heart failure (HF). Recognizing that coronary artery disease is a leading cause of HF in the United States is critical to reducing mortality resulting from this condition. Although some patients may be candidates for mechanical revascularization to improve left ventricular function, all patients are candidates for aggressive secondary prevention strategies. This review discusses the prevalence of coronary artery disease, prognostic significance and pathophysiology, risk factor modifications, pharmacologic treatments, and the role of revascularization.

New insights into diastolic heart failure: role of diabetes mellitus

Heart failure affects nearly 5 million people in the United States and is a major contributor to mortality, hospitalization, and medical costs. Approximately 40% of patients with heart failure have preserved left ventricular systolic function, thus exhibiting diastolic heart failure. More common in women and the elderly, this condition is associated with hypertension, coronary artery disease, and/or atrial fibrillation. With the exception of the Digitalis Investigation Group (DIG) and the Candesartin in Heart Failure: Assessment of Reduction in Mortality and Morbidity (CHARM)-Preserved trials, no completed large randomized clinical trial has addressed the management of such patients. Symptomatic treatment involves administration of diuretics and nitrates, but long-term management with angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, aldosterone antagonists, beta-blockers, and calcium channel blockers targets the underlying disorders. Recent studies found that diabetes mellitus produces functional, biochemical, and morphologic myocardial abnormalities independent of coronary atherosclerosis and hypertension. These abnormalities may result in impaired left ventricular diastolic function, contributing importantly to heart failure with normal systolic function. Although tight glycemic control decreases the risk of heart failure in patients with diabetes, the effects of different diabetic treatment regimens on heart failure with normal systolic function are unknown and remain subject to future investigation.

Perioperative Assessment of Left Ventricular Function by Pressure-Volume Loops Using the Conductance Catheter Method

Interpretation of perioperative measurements of cardiac function during cardiac surgery is complicated by changes in loading conditions induced by anesthesia, cardiopulmonary bypass (CPB), and the surgical procedure itself. Quantification of left ventricular (LV) function by pressure-volume relations as obtained by the conductance catheter would be advantageous because load-independent indices can be determined. Accordingly, we evaluated methodological aspects of the conductance-catheter technique and documented LV function before and after CPB in eight patients undergoing coronary artery bypass grafting. LV pressure-volume loops by transesophageal echocardiography-guided transaortic application of the conductance catheter were obtained at steady-state and during preload reduction by temporary occlusion of the inferior cava. All patients remained hemodynamically stable, and no complications occurred. Complete data were acquired within 15 min before and after CPB. Cardiac output (5.2 +/- 1.3 L/min to 6.0 +/- 1.4 L/min) and LV ejection fraction (46% +/- 17% to 48% +/- 19%) did not change, but end-diastolic pressure increased significantly after CPB (8 +/- 2 mm Hg to 16 +/- 7 mm Hg; P < 0.05). Load-independent systolic indices remained constant (end-systolic elastance: 1.31 +/- 1.20 mm Hg/mL to 1.13 +/- 0.59 mm Hg/mL). Diastolic function changed significantly after CPB, as the relaxation time constant decreased from 64 +/- 6 ms to 52 +/- 5 ms (P < 0.05) and the chamber stiffness constant increased from 0.016 +/- 0.014/mL to 0.038 +/- 0.016/mL (P < 0.05). We conclude that the conductance catheter method provides detailed data on perioperative myocardial function and may be useful for evaluating the effects of new surgical and anesthetic procedures.

IMPLICATIONS

Pressure-volume loops provide on-line quantification of intrinsic systolic and diastolic myocardial function in a load-independent fashion. This study shows the feasibility of perioperative pressure-volume analysis by use of the conductance-catheter method. This method provides detailed data about the immediate effects of surgery and may be used to evaluate complex cardiac procedures.

Intraoperative assessment of diastolic function: utility of echocardiography

PURPOSE OF REVIEW

This review discusses the current and future applications of different echocardiographic modalities in evaluating diastolic function intraoperatively.

RECENT FINDINGS

Normal diastolic function is required for optimal cardiac performance. There is sufficient evidence to support the significant prevalence of preoperative diastolic dysfunction and its incidence following cardiac surgery, however controversy still exists regarding the impact of diastolic dysfunction on adverse outcomes. Echocardiography provides a relatively safe, practical and noninvasive means to evaluate perioperative diastolic function, however conventional measures may be limited by the impact of changes in heart rate, rhythm and loading conditions. Newer echocardiographic modalities are reportedly less sensitive to acute changes in loading conditions, and may therefore complement the use of conventional echocardiographic techniques in the perioperative period.

SUMMARY

The availability of effective technology for diagnosing the presence and progression of perioperative diastolic function should assist in the identification of high-risk cardiac surgical patients who may benefit from appropriate triaging and therapeutic intervention.

Early patency of the infarct-related artery after myocardial infarction preserves diastolic filling

A patent infarct-related artery (IRA) following myocardial infarction has been associated with lower mortality, increased systolic function, decreased left ventricular remodeling, and electrical stability. The purpose of this study was to determine whether coronary artery patency early after myocardial infarction is associated with greater early diastolic filling than a closed artery. Radionuclide ventriculograms were performed at a central laboratory on 167 patients who received alteplase for an acute myocardial infarction and had infarct artery patency determined by cardiac catheterization. The peak early filling rate (PEFR) was assessed by 4 different methods: (1) PEFR (EDV/s)--normalized to the end-diastolic volume; (2) PEFR (SV/s)--normalized to the stroke volume; (3) PEFR (ml/s/m(2))--an absolute diastolic filling rate; and (4) PEFR (PER)--normalized to the peak ejection rate. Patients with a closed IRA (n = 16, Thrombolysis In Myocardial Infarction [TIMI] 0 or 1 flow) and patients with an open IRA (n = 151, TIMI 2 or 3 flow) had similar ages, ejection fractions, and cardiac volumes. However, among patients with an occluded IRA, the PEFR was decreased by 12% to 18% by the 4 measures of diastolic filling (3 of 4 methods, p <0.05). PEFR (EDV/s) was 1.69 +/- 0.9 in the occluded group versus 2.06 +/- 0.4 EDV/s in the open artery group (p = 0.005). By multivariate analysis, IRA patency was an independent predictor of the PEFR by all 4 methods. Early coronary artery patency after an acute myocardial infarction preserves diastolic filling. Improved diastolic function may in part explain part of the long-term benefits of a patent IRA after thrombolytic therapy when there is no documented improvement in the ejection fraction.

Determinants of aortic pressure variation during positive-pressure ventilation in man

STUDY OBJECTIVES

To define the relation between systolic arterial pressure (SAP) changes during ventilation and left ventricular (LV) performance in humans.

DESIGN

Prospective repeat-measures series.

SETTING

University of Pittsburgh Medical Center Operating Room.

PATIENTS

Fifteen anesthetized cardiac surgery patients before and after cardiopulmonary bypass when the mediastinum was either closed or open.

INTERVENTIONS

Positive-pressure ventilation.

MEASUREMENTS AND RESULTS

SAP and LV midaxis cross-sectional areas were measured during apnea and then were measured for three consecutive breaths. SAP increased during inspiration, this being the greatest during closed chest conditions (p < 0.05). Changes in SAP could not be correlated with changes in either LV end-diastolic areas (EDAs), end-systolic areas, or stroke areas (SAs). If SAP decreased relative to apnea, the decrease occurred during expiration and was often associated with increasing LV EDAs and SAs. SAP often decreased after a positive-pressure breath, but the decrease was unrelated to SA deficits during the breath. Increases in SAP were in phase with increases in airway pressure, whereas decreases in SAP, if present, followed inspiration. No consistent relation between SAP variation and LV area could be identified.

CONCLUSIONS

In this patient group, changes in SAP reflect changes in airway pressure and (by inference) intrathoracic pressure (as in a Valsalva maneuver) better than they reflect concomitant changes in LV hemodynamics.

Early effects of coronary artery bypass surgery and cold cardioplegic ischemia on left ventricular diastolic function: evaluation by computer-assisted transesophageal echocardiography

OBJECTIVE

Although left ventricular (LV) systolic function undergoes a temporary decrease after cardiopulmonary bypass (CPB) in patients undergoing coronary artery bypass grafting (CABG), data on the effects of CABG and cardioplegic arrest on LV diastolic function are contradictory. The objective of the present study was to further evaluate the effects of CABG and CPB on LV diastolic function.

DESIGN

A prospective study.

SETTING

A multi-institutional investigation at a university hospital.

PARTICIPANTS

20 patients on beta-receptor antagonists, scheduled for CABG and with a preoperative ejection fraction over 0.5.

INTERVENTIONS

Central hemodynamic measurements, transesophageal LV short-axis images, and mitral Doppler flow profiles were obtained before and after volume loading that in turn was performed both before surgical incision and after weaning from CPB.

MEASUREMENTS AND MAIN RESULTS

Heart rate, cardiac output, and peak atrial filling velocity increased; systemic vascular resistance decreased; whereas stroke volume, LV area ejection fraction, deceleration rate and slope of early diastolic filling, time-velocity integral of early diastolic filling, and the ratio between early and atrial peak filling velocity were unchanged post-CPB compared with pre-CPB. LV end-diastolic stiffness that was calculated for each patient pre-CPB and post-CPB using the formula: P = B*eS*A), where P is the LV filling pressure and A is the end-diastolic short-axis area, was unchanged post-CPB compared with pre-CPB.

CONCLUSIONS

Both the active and passive components of LV diastolic function are well maintained shortly after CABG and cardioplegic arrest in patients with a good preoperative systolic LV function.

Digital subtraction high-frame-rate echocardiography in detecting delayed onset of regional left ventricular relaxation in ischemic heart disease

BACKGROUND

Because left ventricular (LV) diastolic function is impaired before systolic function in patients with ischemic heart disease and because ischemic heart disease is constituted of regional rather than global abnormalities of the left ventricle, measures of LV regional diastolic dysfunction, if possible, should provide the most sensitive assessment of the coronary involved region. The objectives of this study are to clarify whether high-frame-rate two-dimensional echocardiography, combined with digital subtraction image processing, may be used to visualize regional LV relaxation abnormalities in patients with ischemic heart disease and to clarify whether this technique provides a measure for the noninvasive assessment of the coronary involved region.

METHOD AND RESULTS

In 30 normal subjects and 59 patients with ischemic heart disease, two-dimensional echocardiograms obtained at a rate of 60 frames per second were provided on line for digital subtraction analysis, with which digitized images were continuously subtracted on a frame-by-frame basis. The subtracted images were analyzed to determine the onset of the segmental outward motion of the LV wall in early diastole in each of 16 segments per subject. Regional relaxation index, defined as the interval from the second heart sound to the onset of outward wall motion, was significantly prolonged in the coronary involved segments compared with the normal segments (36.3 +/- 18.0 versus 101.2 +/- 34.0 ms, P < .01). The prolongation in the regional relaxation index was observed even in the coronary involved segments without reduction in systolic wall motion. When a cutoff level of 50.0 ms was used, coronary involved segments could be distinguished from normal or border segments with a sensitivity of 92% and a specificity of 81%.

CONCLUSIONS

Digital subtraction high-frame-rate echocardiography may be used to visualize regional LV relaxation abnormalities in patients with ischemic heart disease. The time interval from the second heart sound to the onset of the segmental outward motion of the LV wall (regional relaxation index) obtained with this technique provides a noninvasive and accurate measure for assessing coronary involved regions.

Serial changes in left ventricular function after coronary artery bypass: implications in viability assessment

Improvement in left ventricular (LV) performance after coronary artery bypass surgery remains the gold standard in myocardial viability assessment. The time-related changes, however, are not well known. This study examined the LV ejection fraction (EF) by gated blood pool imaging early (6 +/- 4 days) and late (62 +/- 24 days) after surgery in patients with normal preoperative EF (group 1, n = 12) and those with LV dysfunction (group 2, n = 15). There were no changes in the clinical status between the early and late studies, and all patients had normal sinus rhythm. Group 1 had no significant change in EF (preoperatively 62%, early postoperatively 64%, late postoperatively 63%; p = NS). In group 2, EF was 26% +/- 8% preoperatively; 30% +/- 10% early postoperatively; and 34% +/- 8% late postoperatively (p < 0.05). Postoperatively there was > or = 5% improvement in EF in 4 patients early and 11 patients late (p < 0.05). Patients who showed early improvement continued to do so in the late study but, additionally, 7 patients showed improvement only in the late study. Thus the timing of EF measurement after surgery is important in patients with LV dysfunction but not in patients with normal LV function. Early assessment may underestimate the prevalence and degree of recovery.

Left ventricular diastolic filling during coronary artery bypass surgery in patients with diabetes mellitus and/or hypertension

To evaluate left ventricular diastolic filling (DF) using transesophageal Doppler echocardiography in 40 patients with or without diabetes mellitus and/or hypertension, we measured DF after induction of anesthesia, before and after cardiopulmonary bypass (CPB), and at the end of coronary artery bypass surgery (CABS). In 13 patients with complete measurements, there was no significant change in DF but diastolic filling time became shorter and peak velocity during atrial contraction increased significantly following CPB. In the other patients, the assessment of DF could be performed accurately in CABS patients without diabetes and/or hypertension, but not in CABS patients with these disorders because of a high incidence of fusion of the E-A waves, which is an indicator of impaired DF. When heart rate (HR) was more than 75 beats·min^-1 (RR interval of less than 800 ms), the incidence of fusion points was significantly higher in patients with diabetes and/or hypertension than without (13 of 29s 1 of 9,P<0.05). It is suggested that a slower HR (less than 75 beat·min^-1) is desirable in CABS patients with these disorders to avoid impairment of DF due to either prolonged systolic time or isovolumic relaxation time.

Three-dimensional transesophageal echocardiography for depiction of regional left-ventricular performance: initial results and future directions

To assess the potential of a prototype transesophageal echocardiography probe for evaluating left-ventricular wall motion in three dimensions, we acquired images under anesthesia in 15 patients who had akinesia or dyskinesia and 8 patients who had normal function demonstrated on preoperative ventriculography. Short-axis, oblique transgastric scans were obtained in 16 of the patients and four-chamber, long-axis oblique scans were obtained in 12 patients, with five patients (22%) yielding good-quality scans of both types. Off-line, we outlined the endocardial borders manually and used the outlines to make computer-generated three-dimensional models of the endocardial surfaces, color-tiled according to regional ejection fraction. Compared with contrast ventriculograms, the regional ejection fraction histograms derived from these models showed 86% concordance for detecting dyssynergy. However, the concordance between the ventriculograms and the color-tiled models in localizing the dyssynergy was only 67% overall. Uncertainty in rotational alignment between the reconstructions and the ventriculograms appeared to contribute to misreading the location of dyssynergy. In addition, the apical region appeared to have been missed in 8 (50%) of the short-axis scans, whereas it was visualized in all long-axis scans. We conclude that three-dimensional analysis of the location, extent, and degree of left-ventricular dyssynergy is feasible from transesophageal echocardiograms and could have wide application in the study of regional ventricular function. However, improvements are necessary to enable the transducer to scan the cardiac apex more reliably from the short-axis viewpoint and to have a means for spatially orienting the images with respect to an external frame of reference.

Reversal of chronic ischemic myocardial dysfunction after transluminal coronary angioplasty

From a cohort of patients referred for elective transluminal coronary angioplasty, a subset of patients was evaluated to determine whether revascularization using coronary angioplasty could salvage chronically ischemic myocardium. Reversible chronic ischemic left ventricular dysfunction was identified by a severe wall motion abnormality at rest and at least one of the following: 1) persistent angina pectoris; 2) postextrasystolic ventricular contraction potentiation of motion in the asynergic zone on baseline ventriculogram; and 3) thallium-201 uptake in the asynergic zone. Twelve patients were identified as having reversible chronic ischemia and underwent coronary angioplasty. Their mean age was 63 +/- 11 years and duration of symptoms 8.3 +/- 9.7 weeks. Immediate pre- and postangioplasty left ventriculograms were obtained. Regional wall motion was analyzed using a radial axis model, and global ejection fraction was calculated. After angioplasty, tension development (heart rate-systolic pressure product) increased in the absence of an increase in left ventricular end-diastolic pressure. Global ejection fraction increased from 46 +/- 20 to 62 +/- 19% (p less than 0.005). The percent of left ventricular diastolic perimeter showing asynergy decreased from 29 +/- 11 to 10 +/- 13% (p less than 0.005). During follow-up ranging from 6 to 51 months, sudden death occurred in one patient who had had no improvement in wall motion after angioplasty, repeat angioplasty was performed in three patients and eight patients remained asymptomatic. Application of easily obtainable clinical data identifies a subset of patients with chronically ischemic myocardium. Coronary angioplasty in such patients is useful in salvaging hibernating myocardium.