Pleuropericardial window enhances surgery on beating heart – haemodynamic evidence

Introduction

Several randomized and observational studies have reported the superiority of coronary artery bypass grafting (CABG) procedure without the use of extracorporeal circulation (ECC) (off-pump) [1-4]. Wider use of this procedure is limited by difficulties with revascularization of the posterior wall, mainly due to haemodynamic compromise. The use of stabilizers has facilitated anastomosing within the posterior wall, but has not fully eliminated the haemodynamic disturbances that occur when the heart is exposed [5-9]. Poor late results of incomplete revascularization caused by difficulties in anastomosing within the posterior wall [10-12] prompt the search for methods providing stable haemodynamic conditions during complete off-pump revascularization.

Aim

To evaluate haemodynamic alteration during exposure of the posterior heart wall for off-pump revascularization with different methods of stabilization.

Material and methods

The study included 88 patients (66 men) aged 40–82 years (mean 61.9 yrs) who underwent elective complete off-pump revascularization including anastomoses on the posterior wall.

In all patients, a graft was made to the circumflex artery or its branches. The patients were divided into three groups according to the employed method of heart stabilization and exposure.



Intraoperative procedures

The following surgical techniques were used:

• The heart was dislocated into the right pleural cavity.

• Patient was placed in a Trendelenburg position.

• The operating table was then tilted towards the surgeon.

• Commercially available stabilizers were used.

• Dobutamine infusion was used for inotropic support.



The following haemodynamic parameters were recorded: heart rate (HR), arterial blood pressure (ABP), right atrial pressure (RAP), pulmonary artery pressure (PAP), pulmonary wedge pressure (PWP), cardiac index (CI), stroke volume index (SVI), left ventricular stroke work index (LVSWI), right ventricular stroke work index (RVSWI), systemic vascular resistance (SVR), and pulmonary vascular resistance (PVR). These haemodynamic parameters measured during posterior wall exposure with various methods of exposure and stabilization were compared with the baseline data obtained after opening the pericardium.

In Group I (25 patients), haemodynamic parameters were measured without the use of heart stabilizers as follows:

I. With open pericardium – reference position.

II. With posterior wall exposed.

III. With posterior wall exposed in the Trendelenburg position.

IV. With posterior wall exposed with the pleuropericardial window.

V. With posterior wall exposed with the pleuropericardial window, in the Trendelenburg position, and the operating table tilted towards the surgeon.



In Group II (35 patients), haemodynamic parameters were measured using three methods of heart exposure:

I. With open pericardium – reference position.

II. With posterior wall exposed with the aid of tissue stabilizer (Octopus Medtronic Inc. USA).

III. With posterior wall exposed with the aid of a Lima suture [13].

IV. With posterior wall exposed with the aid of 2 tissue stabilizers (Octopus and Starfish, Medtronic Inc. USA).

V. With posterior wall exposed with the aid of a stabilizer (Octopus Medtronic Inc. USA), pleuropericardial win-dow, and Trendelenburg position.

VI. With posterior wall exposed with the aid of a Lima suture, pleuropericardial window, and Trendelenburg position.

VII. With posterior wall exposed with the aid of stabilizers (Starfish, Octopus Medtronic Inc. USA), pleuroperi-cardial window, and Trendelenburg position.



In Group III (28 patients), the influence of dobutamine on haemodynamic parameters was studied. Measurements were taken at the following points in the operation:

I. With pericardium open – reference position.

II. With posterior wall exposed with the aid of a stabilizer (Octopus Medtronic Inc.).

III. With posterior wall exposed with the aid of a stabilizer (Octopus Medtronic Inc.), pleuropericardial window, and Trendelenburg position).

IV. With posterior wall exposed with the aid of a stabilizer (Octopus Medtronic Inc.) and dobutamine infusion of 3 µg/kg/min.

V. With posterior wall exposed with the aid of a stabilizer (Octopus Medtronic Inc.), pleuropericardial window, Trendelenburg position, and dobutamine infusion of

3 µg/kg/min.



The protocol of the study was approved by the local ethics committee and each patient gave informed consent to participate in the study.

Statistical analysis was performed using SPSS 12 soft-ware. Differences between continuous variables between groups were assessed using ANOVA analysis. Differences were considered statistically significant when P < 0.05.

Limitations of methodology

Compression and deformation of the right ventricle during exposure of the posterior cardiac wall may result in sporadic tricuspid valve incompetence. This can lead to an increase in right atrial pressure and falsify measurements obtained with the thermodilution method [14].

Results

In Group I, when the posterior wall was exposed (Position II), MAP (Fig. 1), CI (Fig. 2), SVI, LVSWI, and RVSWI decreased significantly compared to baseline.

In consecutive positions (III, IV, V), the implementation of planned manoeuvres resulted in significant improvements in haemodynamic parameters.

The best results, similar to baseline data, were observed in Position V, i.e. when the posterior wall was exposed with the aid of a pleuropericardial window, the Trendelenburg position, and tilting the operating table towards the surgeon.

In Group II, in Positions II, III, and IV, MAP (Fig. 3), CI (Fig. 4), SVI, LVSWI, and RVSWI decreased significantly. In Positions V, VI, and VII, MAP (Fig. 3), CI (Fig. 4), SVI, LVSWI, and RVSWI improved significantly and were similar to baseline. SVR decreased significantly. Other haemodynamic parameters (HR, RAP, PAP, PWP, and PVR) did not change significantly in either phase of the study.

In Group III, in Position II, MAP (Fig. 5), CI (Fig. 6), SVI, LVSWI, and RVSWI decreased significantly. In Position III, haemodynamic parameters tended to increase significantly when compared with Position II and similarly in Position IV; the most significant improvement was observed in Position V. In this position, haemodynamic parameters MAP (Fig. 5), CI (Fig. 6), SVI, LVSWI, and RVSWI were even better than in Position I. Other haemodynamic parameters, such as RAP, PAP, PWP, SVR, and PVR did not show statistically significant changes. Only in Positions IV and V, after dobutamine infusion, did HR increase significantly in comparison with the baseline value.

Discussion

Revascularization of the posterior cardiac wall requires rotation of the heart, which may lead to kinking of the great vessels and impaired outflow and inflow. This may cause adverse haemodynamic effects and ischaemia [8, 15] despite the fact that the coronary arteries are not mechanically deformed during heart exposure [5, 6]. A drop in perfusion pressure can be caused by bradycardia, arrhythmia, compression of the ventricles by stabilizers, or impaired inflow and/or outflow secondary to manipulation of the heart [16]. Numerous studies have shown that the haemodynamic instability in off-pump coronary artery bypass procedures results from right ventricle dysfunction caused by mechanical compression [5, 9, 17-19]. A similar result is observed in the case of the left ventricle [20, 21]. The most visible restrictive dysfunction appears during anastomosis of the posterior wall [5, 22]. Many different methods providing stable haemodynamic conditions during posterior wall revascularization have been proposed [5, 18, 23, 24].

The aim of the present paper was to identify a method providing optimal haemodynamic conditions during revascu-larization of the posterior cardiac wall. The hypothesis was that the use of the pleuropericardial window, which minimizes the effects of heart compression during exposure, and the Trendelenburg manoeuvre, which enhances heart filling, would create the best haemodynamic conditions.

In Group I, haemodynamic parameters (Fig. 1, Fig. 2) were most improved with the pleuropericardial window and the Trendelenburg position combined with tilting the operating table towards the surgeon. The effect of the pleuropericardial window was stronger than that of the Trendelenburg position with a tilted table; these manoeuvres used in combination had additive effects.

According to Porat et al., heart exposure distorts both right ventricle outflow and inflow. A compromised right ventricle function results in decreased left ventricular filling [18]. Mathison et al. believe that the mode of heart exposure, Trendelenburg position, and tilting the table towards the surgeon as well as the creation of a pleuropericardial window on the right side improve right ventricular inflow and systolic function. Subsequently, improved right ventricular ejection increases left ventricular filling pressure [19]. In Group II, haemodynamic parameters (Fig. 3, 4) deteriorated in all three methods of stabilization with a closed pleura when compared to the same methods of stabilization used with the pleuropericardial window, Trendelenburg position, and table tilted toward the surgeon.

The stabilizations used currently facilitate exposure of the posterior heart wall. Each of the stabilization systems studied caused haemodynamic conditions to deteriorate. The use of stabilizers presses the heart against the rigid pericardial sac, which impairs ventricular diastolic function and, consequently, decreases ejection volume. Opening the right pleura improves ventricular compliance, resulting in an increased ejection volume. The combined effect of improved stroke volume in the pleuropericardial window group, compared to that with a closed pleura, results from increased filling pressures related to the Trendelenburg position and table tilting. Posterior wall exposure and the use of stabilizers primarily affect the thin-walled and low-pressure right ventricle [19].

Watters et al. used deep pericardial sutures, the Octopus vacuum stabilizer, and the Trendelenburg manoeuvre with the table tilted towards the surgeon during posterior wall revascularization. They also observed that the minute volume and ejection volume dropped most when anastomoses were made to the circumflex artery [7].

When the effect of the pleuropericardial window and dobutamine infusion (both in combination with the Trendelenburg position and table tilted towards the surgeon) on heart functioning was analysed in Group III, the use of dobutamine infusion during posterior wall exposure proved beneficial; however, the effect of the pleuropericardial window was stronger.

In clinical studies, many patients require inotropic support when anastomoses are performed in the posterior wall – 36% reported by Resano and 23% according to Mathison [25, 19].

Conclusions

Trendelenburg positioning and tilting of the table towards the operator together with the creation of a pleuropericardial window resulted in an improvement of haemodynamic conditions when the posterior cardiac wall was exposed. These manoeuvres facilitate complete off-pump revascularization in stable haemodynamic conditions.

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