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Cardiovascular Research 1998 37(1):101-107; doi:10.1016/S0008-6363(97)00236-8
© 1998 by European Society of Cardiology
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Copyright © 1998, European Society of Cardiology

Improvement of left ventricular function and cardiovascular neural control after endoventriculoplasty and myocardial revascularization

Laura Dalla Vecchiaa,*, Andrea Manginib, Pietro Di Biasib, Carmine Santolib and Alberto Malliania

aMedicina Interna II, Ospedale "L. Sacco", Università di Milano, Milano, Italy
bDivisione di Cardiochirurgia, Ospedale "L. Sacco", Milano, Italy

* Corresponding author. Tel. (+39-2) 3579 9316; Fax: (+39-2) 356 4630.

Received 28 May 1997; accepted 6 August 1997


   Abstract
Top
 Abstract
1 Introduction
 2 Methods
 3 Results
 4 Discussion
 References
 
Objective: To investigate the effects of endoventriculoplasty (EVP) and myocardial revascularization on left ventricular function and on sympathovagal balance modulating sinus node and vasomotor activity, we studied patients with left anterior, septal or anteroseptal ventricular aneurysm, before and after surgery. It has been demonstrated that, compared to the standard aneurismectomy, EVP associated with coronary grafting has a lower operative mortality and improves ventricular function, clinical status and prognosis. Methods: We collected pre- and post-operative echocardiographic and angiographic data to determine morphological and hemodynamic changes. The pre- and post-operative neural cardiovascular control was assessed by power spectrum analysis of heart rate and systolic arterial pressure (SAP) variabilities during rest and tilt. Results: As expected, post-operative ventricular function improved significantly: ejection fraction increased from 33±2 to 46±3% (p<0.01) when assessed by echocardiography and from 40±4 to 55±5% (p<0.01) when assessed by angiography; left ventricular end-diastolic pressure fell from 22±3 to 13±2 mmHg (p<0.05). Pre-operatively sympathovagal balance responsiveness was blunted: tilt test did not induce, in respect to resting values, any significant change in low frequency (LFRR) and high frequency (HFRR) components of RR variability (in normalized units, n.u.) and in LFSAP. Post-operatively, tilt induced significant changes in LFRR and HFRR (in n.u.), in LF/HF ratio and LFSAP in respect to resting values. The pre- and post-operative percent differences —delta %—, from rest to tilt, of LFRR, HFRR, LF/HF and LFSAP were also significantly different (p<0.01, p<0.05, p<0.05, p<0.05). In addition, we compared data obtained from survivors and non-survivors (6 out of 19 patients died within 4 months because of heart failure). Non-survivors were characterized by significantly lower RR variance (184±80 vs. 1193±309 ms2 at rest, 196±87 vs. 546±104 ms2 during tilt, p<0.05) and lower LFRR (15±7 vs. 61±6 at rest, 23±10 vs. 58±6 during tilt, in n.u., p<0.01). Conclusions: (1) The improvement of ventricular function induced by EVP and myocardial revascularization is accompanied by a restored capability to oscillate of cardiovascular neural regulatory mechanisms; (2) the drastic reduction of variance and LF component from RR variability seems to be associated with an ominous outcome.

KEYWORDS Endoventriculoplasty; Myocardial revascularization; Left ventricular function; Heart rate variability; Power spectrum analysis; Sympathovagal balance


   1 Introduction
Top
 Abstract
 1 Introduction
2 Methods
 3 Results
 4 Discussion
 References
 
Left ventricular (LV) remodeling after myocardial infarction is a progressive process which involves both infarcted and non-infarcted ventricular regions leading to ventricular dilatation with distortion of the geometry of the heart [1]. It has been demonstrated that treatment with ACE inhibitors and/or β blockers improves survival in the course of ischemic heart disease [2–4]; their beneficial effects have been attributed to several mechanisms, including a blunting effect on the sympathetic drive and on the renin–angiotensin–aldosterone system, that are activated after acute myocardial infarction [5, 6]. In patients with established LV dysfunction the prognosis is indeed related to the degree of neurohumoral activation [4, 6, 7].

Whenever a marked ventricular dilatation, with or without ventricular aneurysm, is present, in the setting of a severe coronary artery disease, revascularization is indicated. In particular, when a large ventricular aneurysm is present, the use of endoventriculoplasty (EVP) and coronary artery bypass graft (CABG) allows a reconstruction of a geometry close to that of the original left ventricle, providing an improved prognosis [8–10].

It has been reported that patients with regional left ventricular dysfunction, due to critical single-vessel disease, exhibit a sympathetic activation that returns to normal levels after successful angioplasty and improvement of regional wall motion [11].

Patients with severe global LV dysfunction and regional dyskinesis, due to the presence of a ventricular aneurysm, would represent a more advanced degree of ischemic disease likely to be characterized by an enhanced sympathetic activity [7, 12, 13].

Aim of the present study was to assess whether the surgically induced hemodynamic improvement was accompanied by a restoration of neural cardiovascular regulatory mechanisms.

Sympathovagal balance regulating sinus node and vasomotor activity was assessed by spectral analysis of heart rate variability (HRV) and systolic arterial pressure (SAP) variability, an approach that has been applied to physiological [14, 15]and pathophysiological studies exploring conditions such as arterial hypertension [16, 17], ischemic heart disease [5, 18]and congestive heart failure [19, 20]


   2 Methods
Top
 Abstract
 1 Introduction
 2 Methods
3 Results
 4 Discussion
 References
 
We studied 19 patients (16 men and 3 women, mean age 59±2 years, range 45 to 75 years) admitted to the Division of Thoracic and Cardiovascular Surgery for left endoventriculoplasty and revascularization. The study protocol was approved by our Institutional Committee on Human Research following Helsinki declaration [21]and all patients gave an informed consent.

In all patients careful clinical history and physical examination were obtained by the admitting physician; patients with history of diabetes or other systemic disorders, severe or moderate renal failure or chronic obstructive lung disease, were excluded from the study, as these pathophysiological conditions can alter, per se, the spectral profile of HRV [13, 22, 23].

2.1 Clinical characteristics
In the group under study indication for surgery was unstable angina in eight patients, stable angina in two, and congestive heart failure in six, while in the remaining three patients (in absence of symptoms) surgical criteria were represented by the presence of a low ejection fraction (<30%), three-vessel disease, and below 50 years of age.

All patients had normal sinus rhythm and none had sustained ventricular tachycardia or more than 3 episodes of non-sustained ventricular tachycardia on a 24 h ECG monitor performed the day before admission.

The mean interval between the acute myocardial infarction and surgery was 15±3 months (range 6 to 40 months).

Therapeutical regimen common to all patients included ACE inhibitors, aspirin and oral or transdermal nitrates. In addition, diuretics were used in seven patients, digitalis also in seven patients and calcium channel blockers in five.

The aneurysm resulted in all cases from a critical lesion of the left anterior descending (LAD) coronary artery. Five patients only had an LAD involvement, five had a two-vessel disease and nine had a three-vessel disease.

Eight patients were in the New York Heart Association (NYHA) class I, four in class II, five in class III and two in class IV.

2.2 Echocardiography and angiography
M-mode and two-dimensional echocardiography, pulsed and continuous wave Doppler and Color Doppler examinations were performed pre-operatively in all patients; thirteen patients were evaluated 6 months post-operatively.

Left ventricular chamber sizes were measured from M-mode imaging; left ventricular volumes and ejection fractions were calculated using the modified Simpson's model [24]. Mitral regurgitation (MR) was quantified by grading from 0+ to 4+; pre-operatively nine patients were characterized by slight or no MR, seven by a mild, one by a moderate and one by a severe MR.

All patients underwent cardiac catheterization with coronary and left ventricular angiography; seven patients repeated the invasive study post-operatively while six refused.

Computer-assisted evaluation of wall motion [25]provided quantitative indexes of regional and global left ventricular kinesis; end-diastolic and end-systolic silhouettes were divided into 5 segments and 20 (5x4) subsegments: the systolic percentage reduction of each area (subsegmental ejection fraction) was obtained to draw a contraction curve. A specific algorithm then computed a score for each subsegment (0=normal wall motion, 1=mild hypokinesis, 2=moderate hypokinesis, 3=severe hypokinesis, 4=akinesis, 5=dyskinesis); the global hypokinetic score (SCORE) was the sum of the score for all segments. This analysis system overestimated the ejection fraction, the normal values being 79±5% [25].

2.3 Operative technique
Combined EVP and CABG were performed during the aortic cross-clamp time (ACCT): the mean ACCT was 94±9 min, while the mean extra corporal circulation time (ECCT) was 158±15 min.

Myocardial protection was accomplished by moderate hypothermia, cold antegrade cardioplegia and topical cooling. The left ventricle was entered at the ‘dimpling’ point and the ventriculotomy was extended, taking into account the endocardial fibrosis and the thickness of the free wall; in the presence of viable muscle overlapping the area of endocardial scar, the extension of ventriculotomy was limited to permit the exclusion of the distal septum. A patch was inserted into the left ventricle at the junction between scarred and viable myocardial tissue using a running suture or separate U stitches. Care was taken not to deform the LAD in order to accomplish a successful revascularization. The patch material was autologus pericardium. The aneurysm wall was sutured over the patch with an over-and-over suture. No resection of left ventricular tissue was performed.

All diseased vessels were bypassed. The LAD was bypassed in all patients with the internal thoracic artery; mitral valvuloplasty was performed in one patient with severe MR for prolapse of both leaflets.

A second group of patients undergoing only revascularization without endoventriculoplasty could not be planned for ethical reasons.

2.4 HRV data and analysis
Each patient was evaluated 4±2 days before surgery and 8±1 months after. ACE inhibitors, calcium channel blockers and digitalis were withheld the day before the study; nitrates and diuretics were withheld only the morning of the study to minimize the effects on measurements (health status of patients was not compromised). The recording sessions were carried out in a quiet room, at a stable temperature, in the late morning (10 to 12 am); electrocardiogram (ECG by a conventional electrocardiographic amplifier), non-invasive arterial pressure (Finapres Monitor, Ohmeda Englewood, Co, USA) and respiratory signal (nasal Thermistor, Marazza, Monza, Italy) were continuously recorded during supine position (10 min) and passive head-up (90°) tilt (7 min).

The signals were recorded on a FM tape (Racal Store 7DS, Southampton, UK) and then played back and digitized at 300 Hz (MicroVAX, Digital Equipment, Corpo, Marlboro, Ma, USA). The data were analyzed off-line with a personal computer (AST 486). The principles of the software for data acquisition and spectral analysis have been described elsewhere [14, 22]. In summary, a derived/threshold algorithm provided the continuous series of RR interval (tachogram) derived from the ECG. Stationary segments (200–300 RR intervals) were analyzed with autoregressive algorithms. These algorithms provided the number, center frequency and power of the oscillatory components.

The low frequency (LF) and high frequency (HF) components of RR variability were expressed in absolute (ms squared) and normalized units (n.u.), which represent the relative power of each component in proportion to the total power minus the very low frequency component (<0.03 Hz).

Previous studies [14, 22, 23]have shown that these two major oscillatory components are usually identified in the RR variability: the HF component (~0.25 Hz) is synchronous with respiration and is considered a marker of vagal modulation of sinus node pacemaker activity, the LF component is a marker of sympathetic modulation: its center frequency is ~0.10 Hz, but can vary considerably from 0.04 to 0.15 Hz [24]. The LF/HF ratio is used to assess the state of the sympathovagal balance [14].

The signals of SAP and respiratory activity were sampled every cardiac cycle, thus providing a systogram and a respirogram synchronized with the tachogram. These time series underwent an analysis similar to that described above for the tachogram. The LF component of SAP variability was expressed in absolute units (mmHg squared) and considered a marker of sympathetic modulation of vasomotor activity [14, 15, 22].

2.5 Statistical analysis
Results were expressed as mean±SEM. Comparisons between pre-operative and post-operative data and survivor and non-survivor data were obtained with paired and unpaired Student's t test. Data were also analyzed using non-parametric tests (Wilcoxon Signed Rank test and Mann-Whitney Rank Sum test). Values of p<0.05 were considered significant.


   3 Results
Top
 Abstract
 1 Introduction
 2 Methods
 3 Results
4 Discussion
 References
 
Thirteen patients had a 1-year follow-up free of cardiac events. Post-operatively, no patient required prolonged antiarrhythmic therapy. Compared to the pre-operative period, therapy was almost unmodified except for a reduction in the use of nitrates and diuretics.

Six patients died from intractable heart failure: one died intra-operatively, one died 4 days post-operatively and four died within 4 months. Patients who died (non-survivors) were, pre-operatively, in NYHA class III or IV, while the thirteen patients treated successfully (survivors) were less symptomatic.

3.1 Echocardiographic and angiographic results
Pre- and post-operative end-diastolic and end-systolic ventricular diameters (basal level) were not significantly different (61±2 vs. 58±2 and 46±2 vs. 42±3 mm, respectively), while end-diastolic and end-systolic ventricular volume indexes decreased significantly post-operatively (from 131±9 to 101±6 ml/m2, p<0.05 and from 104±8 to 68±7 ml/m2, p<0.01, respectively). There were no significant changes in MR grading (the only patient with severe MR, who required valvuloplasty, died 2 months post-operatively).

Ejection fraction improved significantly (p<0.01) in concomitance with a reduction of left ventricular end diastolic pressure (LVEDP) (p<0.05) and of the computed SCORE (p<0.01) (Fig. 1).


Figure 1
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  		Fig. 1 Pre- and post-operative hemodynamic data obtained by echocardiography (n = 13; top panel left) and angiography (n = 7; top panel right and bottom panels); EF=ejection fraction, SCORE=global hypocontractility score (see Methods), LVEDP=left ventricular end diastolic pressure. *p<0.05 pre- vs. post-op.

 
All LAD grafts were patent; in one case the graft to the right coronary artery presented 70% stenosis, while in 3 other cases the stenosis was not critical (<60%).

Survivors (n = 13) and non-survivors (n = 6) presented no significant differences in regard to LV sizes, ejection fraction, severity of coronary disease, extension of the aneurysm, LVEDP, number of performed bypass, ACCT or ECCT; the angiographic SCORE resulted significantly higher in the group of patients who died (57±3 vs. 44±3, p<0.01).

3.2 HRV results
We compared HRV analysis obtained pre- and post-operatively (Table 1). A pre-operatively tilt test induced, in respect to resting values, no significant changes in LFRR and HFRR and in LFSAP. Post-operatively, at rest, patients were characterized by a slight, but significant (p<0.05), reduction in RR interval, while RR variance, SAP value and variance were not significantly different from pre-operative values. More importantly, LFRR (n.u.) was significantly reduced at rest (p<0.05), while HFRR (n.u.) was slightly, but not significantly, increased and LF/HF ratio decreased. No significant changes were present in the resting values of LFSAP.


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  		Table 1 Pre-operative and post-operative data

 
Post-operatively, tilt induced significant changes in LFRR (n.u.) and HFRR (n.u.), in LF/HF (p<0.01) and LFSAP (p<0.05), with respect to resting values. Comparing pre- and post-operative delta % changes of spectral variables from rest to tilt, differences of LFRR (n.u.) (p<0.01), HFRR (n.u.), LF/HF and LFSAP (p<0.05) were also significant (Fig. 2).


Figure 2
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  		Fig. 2 Left panel: {Delta}% of LFRR (n.u.)=percent differences, from rest to tilt, of LF component of RR variability pre- and post-operatively for each patient; middle panel: {Delta}% of HFRR (n.u.)=percent differences, from rest to tilt, of HF component of RR variability pre- and post-operatively for each patient; right panel: {Delta}% of LFSAP=percent differences, from rest to tilt, of LF component of SAP variability pre- and post-operatively for each patient; *p<0.05 pre- vs. post-op.

 
Table 2 reports the HRV data obtained in survivors and non-survivors: patients who died were characterized by significantly lower RR variance (p<0.05) and LFRR component (in both absolute units and n.u.) at rest, as well as during tilt (p<0.01).


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  		Table 2 HRV data in survivors and non-survivors

 
An example of power spectrum analysis of RR variability, at rest, in a patient who died one month post-operatively is compared with that of a patient with a favorable follow-up (Fig. 3). It can be seen that the surviving patient presented a prevalent LF component in both RR and SAP variability spectra, while the non-surviving patient had no LF component in the same variability spectra.


Figure 3
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  		Fig. 3 Panels, from top to bottom, show examples of RR interval variability, RR variability spectrum, SAP variability spectrum and respiratory variability spectrum in a patient dead 1 month post-operatively from heart failure (left column) and in a patient with favorable 1-year follow-up (right column). In variability spectra on the left column x10 magnified spectra are provided in inset. PSD=power spectrum density; a.u.=arbitrary units.

 

   4 Discussion
Top
 Abstract
 1 Introduction
 2 Methods
 3 Results
 4 Discussion
References
 
In this study, endoventriculoplasty and myocardial revascularization improved left ventricular function in post-MI patients with ventricular aneurysm and severe mechanical dysfunction. The favorable results of this surgical approach have been already described [8–10]and might be due to a positive interaction between the reduction of the dilated chamber and the improved coronary perfusion [9, 10].

The main aim of the present study was to investigate whether this gross change in cardiac geometry was also accompanied by modifications in cardiovascular neural regulatory mechanisms.

Power spectrum analysis of HRV is a now widely used non-invasive technique, which has been proven capable of quantifying the state of sympathovagal balance modulating sinus node pacemaker activity in several physiological and pathophysiological conditions [13, 14, 22, 23, 26]. On the other hand, the LF component of SAP variability is a widely accepted marker of sympathetic modulation of vasomotor activity [14, 22]. In addition, it was recently demonstrated that a sympathetic excitation or inhibition was tightly correlated with coherent changes of LF components (and, reciprocally, of HF components) of the variability of RR, SAP and muscle sympathetic nerve activity and that this relationship was better seen when power spectral components were normalized [27].

In normal subjects, orthostatic position, either active or induced by tilt [14, 22, 23, 26, 28], is accompanied, as a rule, by an increase in the LF (n.u.) component of RR variability and in the LF (both absolute and n.u.) component of SAP variability. In our patients, before surgery, tilt induced no significant changes in LF and HF components of RR variability and in sympathetic modulation of vasomotor activity (LFSAP). After surgery, concomitantly to a well-discernible improvement in cardiac function, the effects of sympathetic excitation and of vagal withdrawal induced by tilt were restored, as indicated by the significant increase in LF (n.u.) and decrease in HF (n.u.) components of RR variability and by the significant increase in LF component of SAP variability.

The pathophysiological mechanisms for the reduced responsiveness of sympathovagal balance preceding the surgical intervention might partly consist of an altered neural discharge from the heart to the centers. In particular, the afferent discharge of both sympathetic and vagal afferent fibers, with sensory endings in the ventricles and in other reflexogenic cardiovascular thoracic areas, might be altered by an increased LVEDP, regional and global ischemia and various mechanical abnormalities [29]. For instance, a different pattern of discharge might characterize the sensory endings located in an akinetic part of ventricular wall and the endings embedded in a nearby normally or overcontracting portion of myocardium. Such an abnormal afferent input to the centers might thus disrupt the normal rhythms present in the afferent discharge and, thereby, in the autonomic outflow.

Bonaduce et al. [11]have already reported that segmental left ventricular dysfunction is involved in determining what they defined a sympathovagal imbalance, i.e. a reduction of the absolute power of LF and HF components in the 24 h spectrum of RR variability and that successful coronary angioplasty reversed regional ventricular dysfunction and enhanced spectral power. These authors attributed to an altered afferent sympathetic discharge the reduction of the absolute power of these two spectral components of HRV. Although it is unknown whether the scarred akinetic area still possesses a sensory neural apparatus capable of generating a consistent afferent discharge, in the case of our study, the reconstruction of the distorted ventricle associated to myocardial revascularization were likely to have led to a more homogeneous contraction of the ventricular muscle. This, as a whole, might restore more normal phasic properties in the afferent nerve discharge which are likely to be important for central rhythmicity and hence for cardiovascular oscillations [22].

Non-survivors were characterized by a higher NYHA class, despite a similarity in the other clinical, morphological and functional parameters. The non-survivor group was also characterized, in both clinostatic and orthostatic conditions, by a significant reduction in RR variance; moreover LFRR component was also reduced in both absolute units and n.u.

The drastic reduction of an LF component from RR variability seems associated, also in other groups of patients, with the worsening of clinical state [13, 20, 30]. In the presence of a markedly reduced total power, the prevailing HFRR (in n.u.) is likely to be due to mechanical effects of respiration [31], while the disappearance of LFRR component might be due to an unresponsiveness of the sinus node pacemaker activity [12, 13]and/or to a primary reduction in the neural rhythmicity. In fact, from this latter point of view, van de Borne et al. [30]have recently demonstrated that, in some patients with severe heart failure, an absence of the LF component can occur in the variability of both RR and sympathetic muscle nerve activity. In a closed-loop conception [22]of cardiovascular rhythmicity both conditions can clearly coexist and reinforce each other.

In conclusion, parallel alterations seem to occur between abnormal patterns of LV function and of cardiovascular rhythmicity: this link, which deserves further studies, could be of clinical importance in terms of monitoring the course of the disease and its prognosis.

Time for primary review 21 days.


   Acknowledgements
 
We thank Dr. Massimo Pagani and Dr. Nicola Montano for the helpful discussion on the paper and Dr. Stefano Guzzetti for statistical advice.


   References
Top
 Abstract
 1 Introduction
 2 Methods
 3 Results
 4 Discussion
 References
 

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