GLS in Difficult CPB Weaning

Background and Rationale

Difficult separation from cardiopulmonary bypass (CPB) is a serious intraoperative complication associated with increased perioperative morbidity and mortality. Myocardial contractility is the key determinant of successful CPB separation, and perioperative echocardiography is an established method for evaluating ventricular function. Conventionally, left ventricular ejection fraction (LVEF) measured by Simpson's biplane method is used to assess myocardial performance. However, LVEF has notable limitations, including high inter-operator variability, preload/afterload dependence, and poor sensitivity in detecting early myocardial dysfunction.

Global longitudinal strain (GLS), measured by two-dimensional speckle-tracking echocardiography, has emerged as a sensitive, reproducible, and geometry-independent parameter of myocardial function. GLS can detect subtle ventricular dysfunction earlier than conventional LVEF and has demonstrated prognostic value in a variety of clinical settings. Despite this, its use in the perioperative cardiac surgery population remains limited, partly due to uncertainty about the optimal timing of assessment. Anesthesia induction, CPB, and myocardial protection strategies may alter myocardial performance, and therefore both absolute GLS values and dynamic perioperative changes may carry prognostic significance.

Study Objectives

The primary objective of this prospective, multicenter, observational study is to evaluate the predictive value of GLS measurements for difficult separation from CPB. Specifically, the study will assess whether GLS measured by preoperative transthoracic echocardiography (TTE) can independently predict the need for multiple inotropic/vasoactive agents during CPB weaning.

Secondary objectives include exploring the associations between GLS parameters and postoperative outcomes such as intensive care unit (ICU) and hospital length of stay, postoperative changes in cardiac biomarkers, and all-cause 30-day mortality.

Methods

Eligible patients are adults (>18 years) scheduled for elective cardiac surgery requiring CPB, including isolated valve replacement or repair, coronary artery bypass grafting (CABG), combined procedures, and ascending aortic/arch surgery. Patients undergoing emergency or redo surgery, those with contraindications to TEE, or in critical preoperative states (mechanical circulatory support, inotrope dependence, atrial fibrillation, or mechanical ventilation) are excluded.

Echocardiographic assessments are performed at standardized time points: preoperative TTE (T1), intraoperative TEE after induction (T2, if performed), before CPB initiation (T3), immediately after CPB weaning (T4), and following sternal closure (T5). Intraoperative TEE is not mandated by the protocol but may be performed according to institutional practice or operator discretion. GLS analysis follows American Society of Echocardiography (ASE) guidelines, averaging strain from 18 myocardial segments.

Anesthetic and surgical protocols follow institutional standards, with cardioplegia delivered via Buckberg's or del Nido solutions. Clinical, intraoperative, and postoperative data-including operative times, need for pharmacologic support, and recovery variables-are collected systematically by trained staff.

Outcomes

* Primary Endpoint: Ability of GLS value to predict difficult CPB separation, defined as the need for at least two vasoactive or inotropic agents.
* Secondary Endpoints: Association of GLS with ICU/hospital length of stay, postoperative biomarker trends, hospital readmission, and all-cause mortality within 30 days.

Significance

This study addresses a clinically important knowledge gap by evaluating the GLS as a novel predictor of intraoperative difficulty and adverse outcomes in cardiac surgery. If validated, GLS assessment could enhance perioperative risk stratification, guide intraoperative decision-making, and ultimately improve patient outcomes.

• Myocardial strain imaging (Diagnostic test): Two-dimensional strain analysis was performed using frame-by-frame tracking of unique patterns of bright and dark pixels in grayscale (B-mode) sector images to assess myocardial deformation. The frame rate was maintained between 40 and 90 Hz. The myocardium in each image was divided into six myocardial segments, which were individually assessed for tracking quality. GLS was calculated as the average strain value of 18 myocardial segments obtained from the three echocardiographic views. Patients were included in the final analysis if at least 15 out of 18 segments were considered acceptable for strain measurement by the investigator.

Primary outcomes

• To evaluate the predictive value of GLS measurements for difficult separation from cardiopulmonary bypass. [perioperative]: Separating from CPB was categorized as easy and difficult separation from CPB. Easy separation from CPB was defined as no pharmacologic support or use of a single agent (either vasoactive or inotropic). Difficult CPB separation can be defined as the need of at least 2 inotropes or vasopressors to successfully accomplish the separation from CPB

Secondary outcomes

• To assess the associations between strain imaging and ICU/hospital length of stay, postoperative trajectories of cardiac biomarkers, and all-cause mortality. [Post operative 30 days]

Sex: All, ages: 18 Years to any

Inclusion Criteria

* Age > 18 years.
* Scheduled for elective cardiac surgery requiring cardiopulmonary bypass (CPB).
* Provided written informed consent to participate.
* Eligible surgical procedures include:

  * Isolated mitral valve replacement or repair.
  * Isolated aortic valve replacement or repair.
  * Isolated coronary artery bypass grafting (CABG).
  * Combined valve and CABG surgery.
  * Multiple valve replacement or repair.
  * Surgery involving the ascending aorta or aortic arch.

Exclusion Criteria

* Emergency cardiac surgery.
* Redo cardiac surgery.
* Contraindications to transesophageal echocardiography (TEE).
* Critical preoperative conditions, including:

  * Ongoing inotropic drug therapy.
  * Preoperative mechanical circulatory support (e.g., IABP, ECMO, VAD).
  * Requirement for mechanical ventilation.
  * Preoperative atrial fibrillation.

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