Introduction

Congestive heart failure (CHF) remains a major public health concern that is associated with markedly increased mortality. A significant proportion of patients with CHF demonstrate diastolic dysfunction with a normal systolic ejection fraction [1]. Diastolic dysfunction is defined as the inability of the ventricle to fill to a normal end-diastolic volume, both during exercise as well as at rest, without a significant increase in left atrial pressure [2]. Diastolic dysfunction has been reported in 44–75% of cardiac surgical patients prior to initiating cardio-pulmonary bypass (CPB) [3–5]. While diastolic heart failure annual mortality varies between 9–28%, which is up to four-fold that of disease-free subjects [6], it has also been linked to increased postoperative mortality or morbidity after cardiac surgery, increased difficulty in weaning from cardio-pulmonary bypass (CPB) and is a predictor of postoperative hemodynamic instability [2,3,7]. Following coronary artery bypass grafting (CABG), diastolic function frequently deteriorates at least temporarily [8], and may persist for at least the first several postoperative hours [2,9]. Thus, the diagnosis and management of perioperative diastolic dysfunction remains a topic of significant importance [1,10].

Intraaortic balloon pumping (IABP) was first described by Moulopoulos et al. in 1962 and has since become the most widely used temporary cardiac assist device, most frequently indicated for cardiogenic shock, hemodynamic support during catheterization and/or angioplasty, as well as for refractory post-myocardial infarction or unstable angina [11,12]. IABP has also been utilized prior to high-risk surgery as well as for difficulty weaning from CPB. The effects of IABP counterpulsation on systolic function have been well described and can be summarized as a favourable decrease in left ventricular (LV) end-systolic meridional wall stress mainly through afterload reduction during balloon deflation, and an increase in aortic diastolic pressure resulting in improved coronary perfusion during balloon inflation [13]. However, the effects of IABP counterpulsation on diastolic function have not been comprehensively investigated.

Transesophageal echocardiography (TEE) has become a widely available, practical and safe tool to evaluate patients with diastolic dysfunction [1,14]. Many TEE derived parameters such as transmitral inflow Doppler flow velocity profile assessment, E-wave deceleration time, tissue Doppler imaging of the mitral valve (MV) annulus and transmitral propagation velocity (Vp), have been proposed to assess LV compliance and the severity of diastolic dysfunction [1,15,16]. As the influence of IABP on perioperative diastolic dysfunction has not been thoroughly investigated, the goal of this study was to examine whether IABP counterpulsation influences TEE derived parameters of diastolic dysfunction in a population of patients undergoing CABG surgery.

Patients and Methods

Results

Transesophageal echocardiographic determinants of diastolic function

Parameters of transmitral inflow (E/A-ratio) increased significantly from 0.86 without IABP to 1.07 with IABP support (p < 0.05) (Fig. 1A). The deceleration time (Dt) decreased from 218 ms without IABP to 180 ms with IABP support (p < 0.05) (Fig. 1B). The S/D ratio (1.66 without IABP to 1.5 with IABP, p = 0.7) showed no significant difference between time points (Fig. 1C). The mitral annular tissue-Doppler ratio (e’/a’) increased significantly from 0.58 without IABP to 0.71 with IABP (p < 0.05) (Fig. 1D). In addition, the propagation velocity (Vp) increased significantly from 34 cm/s without IABP to 43 cm/s with IABP (p < 0.05) (Fig. 1E).

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Fig 1. Intraoperative transesophageal echocardiographic measures of diastolic function without and with intraaortic balloon counterpulsation (IABP).

A) Mitral valve Doppler flow velocity inflow ratio (E/A). B) Deceleration time (Dt) in milliseconds (ms). C) Pulmonary vein Doppler flow velocity systolic (S) to diastolic (D) ratio. D) Mitral annular tissue Doppler velocity ratio (e’/a’). E. Propagation velocity (Vp) in milliseconds (m/s). Values are Mean ± SD. P value < 0.05 was considered significant (*).

https://doi.org/10.1371/journal.pone.0118788.g001

Discussion

Intraaortic balloon counterpulsation (IABP) is the most commonly used form of temporary cardiac assist device, and is often used in cardiac surgical patients with acute coronary syndrome or to facilitate difficulty weaning from CPB. A significant number of critically ill patients experience clinically significant diastolic dysfunction, which increases their overall morbidity and mortality during and after cardiac surgery [2]. In this present study, we demonstrate that TEE derived determinants of LV diastolic function improved significantly with the use of IABP during CABG surgery. Thus, in addition to its known benefits on LV systolic function, IABP has the potential to improve LV diastolic dysfunction in cardiac surgery patients.

IABP related improvements in diastolic function may be related to both physiologic and mechanical factors. Kass et al. previously demonstrated that increased coronary perfusion during IABP support improves tissue elasticity, a major determinant of diastolic dysfunction [18,19]. Similarly, Gill et al. showed that the development of diastolic dysfunction was related to decreased coronary perfusion induced by recurrent coronary embolization [20]. Furthermore, metabolic disturbances and increased central blood volume both seem to be contributing factors for the development and continued prevalence of diastolic dysfunction [21]. Changes in preload and afterload are also known to significantly impact cardiac relaxation [20]. The impact of LV preload on ventricular relaxation was previously investigated by Komamura et al. who showed that increased LV preload impairs LV isovolumetric relaxation, and that baseline isovolumetric relaxation can be restored after normalizing loading conditions [22]. In addition to this important finding, Cheung at al. demonstrated a decrease in LV end-diastolic cross-sectional area during IABP support, suggesting that short-term IABP support decreases LV preload [13]. Furthermore, early experimental studies in LV failure showed that IABP acutely decreases left ventricular end-diastolic pressure [23], which is consistent with a decreased LV preload as previously suggested, or it could point towards improved diastolic filling mechanics and improved LV elasticity during IABP support. Thus, LV unloading, in addition to increased coronary perfusion pressure, could be one of the mechanisms leading to improved diastolic function under IABP support in our patient population.

The practical utility and value of echocardiography for the evaluation of diastolic function has been well established over the last two decades and has become an important focus for the development of practice guidelines [15]. The use of intraoperative TEE to diagnose perioperative diastolic dysfunction and its clinical relevance remains a topic of increasing importance [1]. However, hemodynamic volatility in the perioperative period may provide a challenging environment for the use of load-dependent echocardiographic measures of diastolic function including the transmitral E/A-ratio and pulmonary vein (S/D) Doppler flow velocity profiles [24]. Consequently, less load-dependent measures including tissue-Doppler ratio (e’/a’) and propagation velocity (Vp) may have greater value in the perioperative period [2,25–27]. Thus, we chose to include both conventional, known load-dependent and less-load dependent echocardiographic measures of diastolic function in our investigation.

While the impact of IABP on diastolic function has been reported, this concept has not been comprehensively investigated. Khir et al. studied 20 cardiac ICU patients within 36 hours post cardiac surgery, and evaluated left anterior descending (LAD) coronary artery and transmitral E-wave flow velocities, as well as LV long axis free-wall movement. Increased diastolic LAD coronary artery flow velocities and LV free-wall early diastolic lengthening velocity were consistent with improved diastolic function under IABP support when compared to control conditions without IABP [28]. While the results of this study are consistent with our data, the use of echocardiography was limited. Shimamoto et al. also investigated the effects of IABP on intraoperative TEE acquired mitral flow dynamics in 15 patients after CABG [29]. Similar to our results, IABP significantly decreased the ratio of the transmitral contraction phase (A wave) to rapid filling phase Doppler flow velocity integral (i.e., increased the E/A ratio). However, the less load-dependent echocardiographic measures of diastolic function including e’/a’ and Vp were not evaluated.

In our present study, the robust association between the use of IABP with an increase in the E/A ratio and a decrease in Dt, as well as increases in the less load-dependent e’/a’ and Vp towards more normal values, is consistent with an improvement in LV relaxation and a favourable impact of IABP on LV diastolic function perhaps by facilitating ventricular unloading. While a decrease in the S/D ratio would also have been consistent with a favourable effect, the absence of a statistically significant result may reflect the low sensitivity of this load-dependent parameter in the volatile hemodynamic environment of the operating room setting. Nonetheless, identifying high-risk patients preoperatively and monitoring their diastolic function intraoperatively may warrant the use of intra-aortic counterpulsation to facilitate separation from CPB.

Certain limitations of this presented work are worth noting including its small sample size and the absence of a control population to determine the potential clinical benefits of IABP associated improvements in perioperative diastolic function. Nonetheless, the demonstrated influence of IABP counterpulsation on the evaluated echocardiographic measurements of diastolic dysfunction appears favourable, and suggests that a larger study is warranted to elucidate a role of IABP in acute perioperative diastolic dysfunction.

In conclusion, IABP counterpulsation has a positive impact on TEE derived parameters of diastolic dysfunction in patients undergoing urgent CABG, in addition to the previously known beneficial effects on systolic dysfunction. The mechanisms seem to include a favourable direct effect on improving LV relaxation. Further investigation is warranted to determine whether IABP could become a complimentary part of multi-targeted approach towards therapeutic intervention in patients experiencing acute perioperative diastolic dysfunction.