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Asian Cardiovasc Thorac Ann 1998;6:250-256
© 1998 Asia Publishing EXchange Pte Ltd

ORIGINAL CONTRIBUTION

Recovery of Left Ventricular Diastolic Function After Coronary Bypass Surgery

Erkan Kuralay, MD, Ufuk Demirkiliç, MD, Ertugrul Özal, MD, Faruk Cingöz, MD, Hayrettin Karaeren, MD1, Harun Tatar, MD

Department of Cardiovascular Surgery
1 Department of Cardiology Gülhane Military Medical Academy Ankara, Turkey
For reprint information contact: Erkan Kuralay, MD Department of Cardiovascular Surgery Gülhane Military Medical Academy 60 Sokak No. 30 Emek, Ankara 06510, Turkey Tel: 90 312 322 3859 Fax: 90 312 426 2732 or 435 4732 Email:karaca{at}hitit.ato.org.tr

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Effects of myocardial revascularization in patients with preoperative left ventricular diastolic dysfunction have not been well characterized. The aim of this study was to evaluate the recovery of diastolic function following successful coronary artery bypass surgery. Forty-five patients with normal diastolic function were selected for comparison with 45 patients who had a pattern of diastolic dysfunction. Mitral flow peak velocity ratios and atrial filling fractions were measured by pulsed Doppler echocardiography 24 hours before surgery. Diastolic dysfunction was defined as a mitral flow peak velocity ratio of less than one. After coronary artery bypass graft surgery, patients who required hemodynamic support were excluded from further study. Group 1 consisted of 38 patients (mean age, 59 ± 9 years) with normal preoperative peak velocity ratios. Group 2 consisted of 33 patients (mean age, 52 ± 9) with preoperative diastolic dysfunction. In group 1, mitral flow peak velocity ratios decreased immediately after cardiopulmonary bypass and persisted for 24 hours, returning to normal at 72 hours. In group 2, peak velocity ratios decreased immediately after cardiopulmonary bypass and persisted for 10 days. Similar changes occurred in atrial filling fractions in the 2 groups. These findings indicate that recovery of left ventricular diastolic function is prolonged in patients with preoperative dysfunction, which may reflect the time required for reversal of the effects of chronic myocardial ischemia.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Left ventricular diastolic dysfunction is often present in patients with significant coronary artery disease, even in the absence of regional or global left ventricular systolic dysfunction.1 It has been suggested that abnormalities in left ventricular diastolic function may precede systolic dysfunction and, therefore, serve as an early and sensitive marker of ischemia.2 Pulsed Doppler echocardiography is a reliable noninvasive technique to assess left ventricular diastolic filling.3 Use of this method to describe ventricular filling characteristics in coronary artery disease has gained increasing clinical acceptance based on the results of hemodynamic, cineangiographic, and radionuclide studies.4–6

It has been well documented that global and regional systolic left ventricular function improves after revascularization.7,8 Much less has been published regarding the reversibility of ischemia-related alterations in left ventricular diastolic filling dynamics. Reversal of diastolic dysfunction both at rest and during exercise in some patients after coronary angioplasty have been demonstrated in radionuclide studies.9,10 Some studies have demonstrated a prompt improvement in left ventricular diastolic filling by Doppler echocardiography after successful coronary angioplasty in patients with stable angina pectoris.5,11 A recent investigation in patients with preoperatively normal diastolic function has shown reversible deterioration in left ventricular filling patterns after coronary artery bypass surgery.12 However, the effects of successful coronary artery bypass surgery in patients with preoperative left ventricular diastolic dysfunction have not been well characterized. The aim of this study was to assess the impact of relieving myocardial ischemia on left ventricular filling and diastolic function in patients who underwent successful coronary artery bypass surgery.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Between January and May 1996, we routinely performed preoperative echocardiographic examinations on 215 consecutive patients with coronary artery disease referred for coronary artery bypass graft surgery at the cardiovascular surgery clinic in Gülhane Military Medical Academy. Ninety patients were selected for this study and divided into 2 groups according to: atrial filling fraction (AFF); mitral flow peak velocity ratio (E/A) calculated as the ratio of maximal early inflow velocity (E) to maximal atrial inflow velocity (A); the ratio of systolic pulmonary venous forward flow velocity to reverse flow velocity in diastole (S/D); and peak pulmonary reverse flow velocity at atrial contraction (A-pv). The 45 patients in group 1 were considered to have normal diastolic function (AFF less than 35%, E/A greater than 1, S/D greater than 1, A-pv less than 20). The 45 patients in group 2 were considered to have some degree of impairment of diastolic function (AFF greater than 35%, E/A less than 1, S/D greater than 1, A-pv greater than 20). Patients were excluded from the study if they had mitral regurgitation evaluated by color Doppler echocardiography or contrast ventriculography, or obstructive lung disease. Patients with heart failure, hypertension, left ventricular hypertrophy, left ventricular aneurysm, and prior myocardial infarction were also excluded. All patients were in sinus rhythm and none had systolic dysfunction. Preoperative medication consisted of aspirin in 39 and 31 patients in groups 1 and 2 respectively, dipyridamole in 17 and 11 patients, nitrates in 22 and 16, angiotensin-converting enzyme inhibitors in 6 and 8, calcium channel blockers in 8 and 15, beta blockers in 7 and 12, antiarrhythmics in 2 and 1, and no therapy in4 and 1. All medications were discontinued 12 hours before the study. Informed consent was obtained from each patient.

After placement of thermodilution pulmonary artery and radial artery pressure catheters, general anesthesia was induced and maintained with alfentanil (10 to 20 mg·kg–1) and atracurium (0.2 to 1.0 mg·kg–1). All patients were mechanically ventilated. A 5-MHz Omni-plane transesophageal transducer was inserted (Sonos 1000 system; Hewlett-Packard, Andover, MA, USA). Following a median sternotomy, cardiopulmonary bypass (CPB) was performed using crystalloid cardioplegia(St. Thomas' Hospital no. 2 solution) at 4°C and a single aortic cross-clamp period. Patients were cooled to a core temperature of 26°C and an intramyocardial temperature of less than 12°C. Characteristics of the patients selected for the complete study are summarized in Table 1Go. There were no significant differences in the number of bypass grafts, CPB time, or other characteristics between the two groups.


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  		Table 1. Patient Characteristics*
 
Echocardiographic studies were performed 24 hoursbefore and 2 hours after CPB, and repeated at 6, 24, and 72 hours, and on the 10th day after surgery. Echocardiographic measurements were carried out at 2 and 6 hours after CPB by transesophageal Doppler echocardiography, whereas before CPB and later than 6 hours postoperatively they were obtained by transthoracic Doppler echocardiography. The first two measurements in the postoperative period were obtained while the patients were still mechanically ventilated. All measurements were performed at end-expiratory apnea to minimize the effects of mechanical ventilation. Transthoracic examinations were conducted with the patient in the supine or left lateral decubitus position. The left ventricle was imaged in the standard parasternal long-axes and short-axes and apical 4-chamber views. The transmitral flow velocity profile was assessed by pulsed Doppler recordings using the apical 4-chamber view in transthoracic Doppler echocardiography. Left atrial pulsed Doppler recordings of diastolic transmitral flow velocity profiles were taken from the apical 4-chamber view with the sample volume located at the tips of the mitral leaflets. All measurements represented the average of 3 to 5 consecutive cardiac cycles in normal sinus rhythm. Flow velocity was not corrected for angle deviation but care was taken to align the sample volume as perpendicular as possible to the mitral annulus in 4-chamber view in transesophageal echocardiography. The sample volume was located at the coaptation point of the mitral leaflets. The transducer orientation was adjusted for optimal spectral display (highest velocity with least spectral dispersion). Sample volume depth was noted and carefully maintained throughout all studies. Diastolic filling characteristics were more predictive of diastolic function than the absolute values alone.12 E/A peak velocity ratio and AFF were calculated from the following equations: E/A = E ÷ A, where E = maximal early inflow velocity, A = maximal atrial inflow velocity; AFF = (TVI A) ÷ [(TVI E) + (TVI A)], where (TVI A) = atrial time velocity integral, (TVI E) = early diastolic time integral.

To assess the reproducibility of Doppler measurements, 32 of the 90 recordings were randomly selected and analyzed on 2 separate occasions for intraobserver variability, and blindly by a second echocardiographer for interobserver variability. Both intra- and interobserver variabilities were minimal; correlations were 0.97 and 0.99 for E/A peak velocity ratio and 0.94 and 0.97 for atrial filling fraction. Patients had simultaneous measurement of heart rate, arterial blood pressure, pulmonary artery wedge pressure (PAWP), and cardiac index by the thermodilution method using the pulmonary artery catheter. During pressure measurements, the external transducer was at the level of the right atrium. Left ventricular stroke work index (LVSWI) was calculated from the following equation: LVSWI = 1.36 x (mean arterial pressure – PAWP) x stroke index ÷ 100.

Radial and pulmonary artery catheters remained in place during the first 3 days of the study. On the 10th day after surgery, measurements of PAWP were made by pulmonary artery catheter via the femoral vein in only 10 patients in each group (informed consent was obtained from these patients). Left atrial pressure is one of the most important determinants of E and A wave velocity and integrals.10,11 Left atrial pressure was monitored by PAWP. Either volume infusion [to increase pulmonary capillary wedge pressure (PCWP)] or Trendelenburg position (to decrease PCWP) was used to maintain PCWP at a steady state of 10 ± 2 mm Hg for each patient during each study period.

Statistical analyses were made using the Student t test for independent samples and the chi-squared test. Analysis of variance was carried out on repeated measurements of echocardiographic and hemodynamic data. A p value of less than 0.05 was considered significant.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Patients who required hemodynamic support with either positive inotropics or intra-aortic balloon counterpulsation were excluded from the statistical analyses. Results from 38 patients in group 1 and 33 patients in group 2 were analysed. Hemodynamic and echocardiographic data are shown in Tables 2 and 3GoGo.


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  		Table 2. Hemodynamic Results
 

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  		Table 3. Echocardiographic Data
 
There were no incidence of perioperative myocardial infarction in group 1 or group 2 patients. Differences in perioperative and postoperative changes in heart rate, PAWP, cardiac output, mean arterial blood pressure, and LVSWI between the 2 groups were negligible. Furthermore, left ventricular end-diastolic diameter and ejection fraction were minimally affected (Table 2Go).

Systolic and diastolic pulmonary venous forward peak flow velocity ratios were not significantly changed during the study. However, the E wave deceleration time was significantly increased in both groups at 2 and 6 hours postoperatively. E wave deceleration time reached preoperative levels at 24 hours in group 1 but the recovery was prolonged in group 2 patients who reached normal levels on the 10th postoperative day. Isovolumic relaxation time, a sensitive parameter for diastolic dysfunction, also showed significant changes during the study. Isovolumic relaxation time was increased significantly in both groups at 2 and 6 hours postoperatively. It returned to normal basal levels at 24 hours in group 1 but the increase persisted for longer in group 2 patients in whom it returned to normal by the 10th postoperative day (p < 0.05). Peak pulmonary venous reverse flow velocity showed similar changes to isovolumic relaxation time and E wave deceleration time (Table 3Go). Changes in A-pv were notable. A-pv also returned to the normal level in group 1 patients at the 24 hour examination but it remained slightly higher at the 10th day examinations in group 2 (p < 0.05) as shown in Table 3Go.

When comparing E/A ratio and AFF in the period immediately following CPB with data obtained at 6 hours and 24 hours postbypass, there was a significant difference in patients with diastolic dysfunction compared to those with normal function (Table 3Go). In those with normal diastolic function preoperatively, Doppler indices were found to return to baseline values within 72 hours after CPB. Interestingly, the E/A ratio and AFF in patients with preoperative diastolic dysfunction also returned to baseline values but only after 72 hours. Furthermore, the Doppler-derived indices increased to normal control values after 10 days (p < 0.05). This suggests that recovery of diastolic function occurred with as much as a 90.3% improvement (Figures 1 and 2GoGo).



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  		Figure 1. Mean mitral flow peak velocity ratios (E/A) before and after coronary artery bypass graft surgery.

 


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  		Figure 2. Mean atrial filling fractions (AFF) before and after coronary artery bypass graft surgery.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
This study was undertaken to characterize the potential effects of myocardial revascularization in patients with diastolic dysfunction. We found that varying degrees of diastolic dysfunction occurred in all patients in the early period after coronary artery bypass graft surgery. Pulsed (254) wave Doppler mitral flow patterns have previously been used to evaluate left ventricular diastolic function after coronary artery bypass graft surgery.13,14 However, mitral flow velocity parameters obtained by a single ultrasound examination lack predictive accuracy when assessing left ventricular filling in individual patients. This lack of predictive accuracy may be explained mainly by the considerable overlap of Doppler measurements of mitral flow velocity patterns in normal and diseased hearts. The overlap is largely due to interindividual variations in the physiologic and pathologic factors that significantly affect the mitral flow pattern.11,15 Another important reason for the overlap is that the characteristic abnormal mitral flow velocity pattern that is observed in the presence of relaxation abnormalities, may be pseudonormalized as a result of elevated left atrial pressure in association with congestive heart failure.16 Recent clinical studies have implied that analysis of the pulmonary venous velocity pattern provides a better understanding of pseudonormalization of the mitral flow pattern.17 Mitral flow velocity patterns that were confirmed by pulmonary venous velocity as manifesting a recovery of left ventricular diastolic function, were used in this study. Thus, patients with E/A ratios greater than 1 and S/D ratios less than 1 were excluded from the analyses.

There is significant dependence of E and A wave variables on hemodynamic loading, ischemia, and other factors all of which vary widely in the perioperative period. In patients with preoperative normal diastolic function, the effects of cardiopulmonary bypass and cardioplegia on diastolic function persisted for 4 hours postoperatively and returned to baseline values by 24 hours after the coronary artery bypass procedure. This was demonstrated by mitral inflow Doppler measurements.12 The E wave deceleration time is a measure of how rapidly the early diastolic filling stops. It is influenced by myocardial relaxation, passive filling, left atrial and left ventricular pressures. The isovolumic relaxation period reflects the rate of myocardial relaxation but it is also dependent on the magnitude of the decrease in the left ventricular pressure as well as the height and contour of the left atrial pressure.18 Heart rate may influence the relative amplitude of the E and A waves, although it has little effect on the deceleration time. With an increased heart rate, the A velocity will increase with respect to the E velocity.19

The mitral inflow velocity data used in this study can be influenced by variables other than the predominant diastolic components of left ventricular relaxation or compliance. These include left atrial pressure, heart rate, left atrial contractility, or the location of pulsed Doppler sample volume.13 All of these variables will be influenced by changes in the filling pressure. A low filling pressure will increase the degree of any abnormalities. If left atrial pressure is increased in a patient with abnormal myocardial relaxation, the mitral valve will open earlier and the driving pressure across the mitral valve will be higher. The result will be a decrease in the isovolumic relaxation period and an increase in the height of the E wave. An increase in early filling may lead to a more rapid increase in left ventricular diastolic pressure and a resulting decrease in deceleration time. Thus, the mitral flow velocity curve may undergo pseudonormalization.4 Left atrial pressure is known to have a significant effect on mitral E wave. Higher left atrial pressure causes pseudonormalization of mitral flow pattern. In this study, to eliminate the effects of left atrial pressure, PAWP was monitored continuously. Volume infusions were given and the reverse Trendelenburg position was used to keep PAWP within 10 ± 2 mm Hg limits during the assessment of mitral inflow.

Some parameters of mitral inflow are influenced by the age of the subject, presumably because of changing diastolic properties of the myocardium with aging.20

With increasing age, the isovolumic relaxation period is prolonged, the E velocity is decreased, and the A velocity is increased. The Doppler variables also dependon the loading conditions, heart rate, and the contractile state of the heart.15

In this prospective study, we compared 2 groups on the basis of E/A ratio, AFF, S/D ratio, isovolumic relaxation time, and E wave deceleration time. In patients who had normal diastolic function in the preoperative period, the deleterious effects of hypothermia, cardioplegia, and extracorporeal circulation resolved in the first 72 hours and diastolic function returned to normal levels. In patients with diastolic dysfunction in the preoperative period, diastolic dysfunction persisted for up to 10 days postoperatively. AFF, S/D ratio, isovolumetric relaxationtime, E wave deceleration time, and A-pv parameters showed similar changes to E/A ratio in each group.These findings indicate that recovery of left ventricular diastolic function is prolonged in patients with preoperative dysfunction, which may reflect the time required for reversal of the effects of chronic myocardial ischemia.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Labovitz AJ, Pearson AC. Evaluation of left ventricular diastolic dysfunction: clinical relevance and recent Doppler echocardiographic insights. Am Heart J 1987;114:836–51.[Medline]

  2. Bonow RO, Bacharach SL, Green MV. Impaired left ventricular diastolic filling in patients with coronary artery disease: assessment with radionuclide angiography. Circulation 1981;64:315–23.[Abstract/Free Full Text]

  3. Nishimura RA, Abel MD, Hatle LK, Tajik AJ. Assessment of diastolic function of the heart: background and current applications of Doppler echocardiography. Part II. Clinical studies. Mayo Clin Proc 1989;64:181–204.[Medline]

  4. Shoa-Lin L, Tak T, Kawanishi D, McKay C, Rahimtoola S, Chandraratna A. Comparison of Doppler echocardiographic and hemodynamic indexes of left ventricular diastolic properties in coronary artery disease. Am J Cardiol 1988; 62:882–8.[Medline]

  5. Snow FR, Gorcsan J, Lewis SA, Cowley MJ, Vetrovec GW, Nixon JV. Doppler echocardiographic evaluation of left ventricular diastolic function after percutaneous transluminal coronary angioplasty for unstable angina pectoris or acute myocardial infarction. Am J Cardiol 1990;65:840–4.[Medline]

  6. Spirito P, Maron BJ, Bonow RO. Non-invasive assessment of left ventricular diastolic function: comparative analysis of Doppler echocardiography and radio-nuclide angio-graphic techniques.J Am Coll Cardiol 1986;7:518–26.[Abstract]

  7. Carroll JD, Hess OM, Hirzel HO, Turina M, Krayenbühl HP. Left ventricular systolic and diastolic function in coronary artery disease: effects of revascularization on exercise-induced ischemia. Circulation 1985;72:119–29.[Abstract/Free Full Text]

  8. Rahimtoola SH. Postoperative exercise response in the evaluation of the physiologic status after coronary bypass surgery.Circulation 1982;65(Suppl II):II–106.

  9. Bonow RO, Vitale DF, Bacharach SL, Frederick TM, Kent KM, Green MV. Asynchronous left ventricular regional function and impaired global diastolic filling in patients with coronary artery disease: reversal after coronary angioplasty. Circulation 1985;71:297–307.[Abstract/Free Full Text]

  10. Lewis JF, Verani MS, Poliner LR, Raizner AE. Effects of transluminal angioplasty on left ventricular systolic and diastolic function at rest and during exercise. Am Heart J 1985;109:792–8.[Medline]

  11. Masuyama T, Kodama K, Nakatani S, Nato S, Kitabatake A, Kadama T. Effect of changes in coronary stenosis on left ventricular diastolic filling assessed with pulse Doppler echocardiography. J Am Coll Cardiol 1988;11:744–51.[Abstract]

  12. Gorcsan J, Diana P, Lee J, Katz WE, Hattler BG. Reversible diastolic dysfunction after successful coronary artery bypass surgery: assessment by transesophageal Doppler echocardiography. Chest 1994;106:1364–9.[Abstract/Free Full Text]

  13. Stoddard MF, Pearson AC, Kern MJ, Ratcliff J, Morasek DG, Labowitz AJ. Influence of alternation in preload on the pattern of left ventricular diastolic filling as assessed by Doppler echocardiography in humans. Circulation 1989;79:1226–36.[Abstract/Free Full Text]

  14. Ishida Y, Meisner JS, Tsuknoka K, Gallo JI, Yoran C, Frauer WM. Left ventricular filling dynamics: influence of left ventricular relaxation and left atrial pressure. Circulation 1986;74:187–96.[Abstract/Free Full Text]

  15. Kuo LC, Quiñones NA, Rokey R. Quantification of atrial contribution to left ventricular filling by pulsed Doppler echocardiography and the effect of age in normal and diseased hearts. Am J Cardiol 1987;59:1174–8.[Medline]

  16. Masuyama T, Yamamoto K, Uematsu M, Tanouchi J, Kitabatake A, St. Goar FG, et al. Contributors to characteristic mitral flow velocity pattern in congestive heart failure: from clinical observations back to experimental validations.Jpn Circ J 1992;56:740–9.[Medline]

  17. Nagano R, Masuyama T, Lee JM. Transthoracic Doppler assessment of pattern of left ventricular dysfunction in hypertensive patients: combined analysis of mitral and pulmonary venous flow velocity patters. J Am Soc Echo 1994;7:493–505.[Medline]

  18. Brutseart DL. Non-uniformity: a physiologic modulator of contraction and relaxation of the normal heart. J Am Coll Cardiol 1987;9:348–55.

  19. Herzog CA, Elsperger KJ, Manoles M, Murakami M, Asinger R. Effect of atrial pacing on left ventricular diastolic filling measured by pulsed Doppler echocardio-graphy [abstract].J Am Coll Cardiol 1987;9(Suppl A):197.[Abstract]

  20. Bryg RJ, Williams GA, Labovitz AJ. Effect of aging on left ventricular diastolic filling in normal subjects. Am J Cardiol 1987;59:971–4.[Medline]





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