Splitting the anterior mitral leaflet impairs left ventricular function in an ovine model.

OBJECTIVES: During mitral valve replacement, the anterior mitral leaflet is usually resected or modified. Anterior leaflet splitting seems the least disruptive modification. Reattachment of the modified leaflet to the annulus reduces the annulopapillary distance. The goal of this study was to quantify the acute effects on left ventricular function of splitting the anterior mitral leaflet and shortening the annulopapillary distance. METHODS: In 6 adult sheep, a wire was placed around the anterior leaflet and exteriorized through the left ventricular wall to enable splitting the leaflet in the beating heart. Releasable snares to reduce annulopapillary distance were likewise positioned and exteriorized. A mechanical mitral prosthesis was inserted to prevent mitral incompetence during external manipulations of the native valve. Instantaneous changes in left ventricular function were recorded before and after shortening the annulopapillary distance, then before and after splitting the anterior leaflet. RESULTS: After splitting the anterior leaflet, preload recruitable stroke work, stroke work, stroke volume, cardiac output, left ventricular end systolic pressure and mean pressure were significantly decreased by 26%, 23%, 12%, 9%, 15% and 11%, respectively. Shortening the annulopapillary distance was associated with significant decreases in the end systolic pressure volume relationship, preload recruitable stroke work, stroke work and left ventricular end systolic pressure by 67%, 33%, 15% and 13%, respectively. Shortening the annulopapillary distance after splitting the leaflet had no significant effect. CONCLUSIONS: Splitting the anterior mitral leaflet acutely impaired left ventricular contractility and haemodynamics in an ovine model. Shortening the annulopapillary distance after leaflet splitting did not further impair left ventricular function.

Selecting the optimal treatment for left main coronary disease: The importance of identifying subgroups of patients.

Randomized trials of stenting versus surgery for patients with unprotected left main (LM) coronary stenosis have largely shown similar survival between the two interventions. However, patients with LM stenosis represent a heterogeneous group in which subgroups likely to benefit from one therapy more than another are difficult to identify. Increasing coronary disease burden is the most accepted subgrouping for identifying optimal therapy but this can be defined in more detail allowing greater discrimination. Competitive flow reduces bypass graft patency in patients with isolated LM stenosis and complex bifurcation stenoses reduce the effectiveness of coronary stenting. The evidence for LM stenosis subgroupings is presented.

Analogue Mean Systemic Filling Pressure: a New Volume Management Approach During Percutaneous Left Ventricular Assist Device Therapy.

The absence of an accepted gold standard to estimate volume status is an obstacle for optimal management of left ventricular assist devices (LVADs). The applicability of the analogue mean systemic filling pressure (Pmsa) as a surrogate of the mean circulatory pressure to estimate volume status for patients with LVADs has not been investigated. Variability of flows generated by the Impella CP, a temporary LVAD, should have no physiological impact on fluid status. This translational interventional ovine study demonstrated that Pmsa did not change with variable circulatory flows induced by a continuous flow LVAD (the average dynamic increase in Pmsa of 0.20 ± 0.95 mmHg from zero to maximal Impella flow was not significant (p = 0.68)), confirming applicability of the human Pmsa equation for an ovine LVAD model. The study opens new directions for future translational and human investigations of fluid management using Pmsa for patients with temporary LVADs.

Intracardiac Echocardiography for Point-of-Care Guided Left Ventricular Assist Device Implantation: Surgical Implications for COVID-19.

Data from animal models is now available to initiate assessment of human safety and feasibility of wide-angle three-dimensional intracardiac echocardiography (3D ICE) to guide point-of-care implantation of percutaneous left ventricular assist devices in critical care settings. Assessment of these combined new technologies could be best achieved within a surgical institution with pre-existing expertise in separate utilization of ICE and Impella.

Incorporating the anterior mitral leaflet to the annulus impairs left ventricular function in an ovine model.

Objectives: Transcatheter mitral valve prostheses are designed to capture the anterior leaflet and surgical techniques designed to fully preserve the subvalvular apparatus at prosthetic valve insertion both serve to shorten the anterior mitral leaflet height, thus effectively incorporating it into the anterior annulus. This study quantifies the acute effects of incorporating the anterior mitral leaflet into the annulus on left ventricular function. Methods: Fourteen adult sheep (weight, 48.7 ± 6.2 kg) underwent a mechanical mitral valve insertion on normothermic beating-heart cardiopulmonary bypass, with full retention of the native mitral valve but with placement of exteriorized releasable snares around the anterior mitral leaflet. Continuous measurements of left ventricular mechano-energetics were recorded throughout, alternating incorporating and releasing of the anterior mitral leaflet to the mitral annulus. Echocardiography confirmed the incorporation into the annulus and release. Results: The independent indices of left ventricular contractility (ie, end systolic pressure volume relationship and preload recruitable stroke work) were both significantly impaired when the anterior mitral leaflet was incorporated to the annulus and restored after release, as were the hemodynamic parameters: cardiac output, stroke volume, stroke work, and left ventricular pressure decreased by 15%, 17%, 23%, and 11%, respectively. Echocardiography demonstrated increased sphericity of the left ventricle during anterior mitral leaflet incorporation. Conclusions: Incorporating the anterior mitral leaflet to the anterior annulus adversely affected left ventricular contractility, caused distortion of the left ventricle in the form of increased sphericity, and impaired hemodynamic parameters in normal ovine hearts.

Bioprosthetic interstrut distance subtending the preserved anterior mitral leaflet mitigates left ventricular outflow tract obstruction.

Background: The anterior mitral leaflet (AML) contributes to left ventricular (LV) function but is normally excised at the time of a bioprosthetic valve insertion. This study aimed to investigate methods of safely retaining the AML at the time of mitral valve replacement. Methods: Five adult sheep (57 ± 3.8 kg) each underwent 3 insertions of a bioprosthetic mitral valve (asymmetric interstrut sectors) alternating the wide and narrow interstrut distance under the AML. Each insertion was performed on normothermic beating-heart cardiopulmonary bypass, with full retention of the native valve. After each valve insertion, continuous measurements of LV and aortic pressures were recorded with echocardiographic assessment of mitral valve function. If LV outflow tract obstruction (LVOTO) was not seen on the resumption of normal cardiac output, a bolus of adrenaline was given to precipitate it. Results: Thirteen of 15 valve insertions resulted in LVOTO caused by systolic anterior motion (SAM), independent of valve orientation. The wide interstrut distance subtending the AML was associated with a greater requirement for inotropic stress to precipitate an obstruction and was associated with late systolic rather than holosystolic obstruction. Conclusions: The predisposition to and nature of LVOTO due to SAM were associated with the bioprosthetic valve interstrut distance subtending the fully retained AML and may explain the survival differences in such patients. This model represents an effective method for research into prevention of LVOTO following mitral valve replacement with preservation of the native valve.

Radial Artery vs Bilateral Mammary Composite Y Coronary Artery Grafting: 15-Year Outcomes.

BACKGROUND: Total arterial coronary revascularization for three coronary territory disease can be achieved with a second arterial conduit joined to the left internal mammary artery as a Y graft, by using either a radial artery (RAY) or a second mammary artery (BIMAY). METHODS: Patients undergoing total arterial revascularization for three coronary territory disease were identified from two cardiac surgical databases (in Sydney and Melbourne, Australia) using Society of Thoracic Surgeons-based definitions. BIMAY-treated patients underwent surgery between 1994 and 2009, mostly using an age-limited protocol, whereas RAY-treated patients underwent surgery between 1996 and 2003 without age limits. All-cause mortality data were acquired from the national death registry, and survival was estimated by the Kaplan-Meier method. Propensity score matching was performed using 13 variables. Given the age imbalance between the groups, the primary comparison was performed for age 66 years or younger. RESULTS: Overall, 1896 patients underwent RAY procedures, and 720 patients underwent BIMAY operations. Older age at surgery was the strongest independent predictor of mortality, with a hazard ratio of 2.06, and a 95% confidence interval of 1.93, 2.22 (P < .001). After propensity score matching, we identified 299 pairs of patients 66 years of age or younger with no preoperative or operative differences and similar ages at surgery: RAY 56.4 ± 7.0 years of age vs BIMAY 56.4 ± 6.8 years of age (P = .96). The RAY group had 4.0 ± 0.9 grafts, and the BIMAY group had 3.9 ± 0.9 grafts (P = .814). All-cause mortality was not different, with the proportion surviving at 15 years at 74.9% for the RAY group vs 76.2% for the BIMAY group (P = .211). CONCLUSIONS: Survival was not different between the RAY and BIMAY groups for total arterial revascularization of three coronary territory bypass grafting.

Implantation of Impella CP left ventricular assist device under the guidance of three-dimensional intracardiac echocardiography.

Impella CP is a percutaneously inserted left ventricular assist device indicated for temporary mechanical cardiac support during high risk percutaneous coronary interventions and for cardiogenic shock. The potential application of Impella has become particularly relevant during the current COVID-19 pandemic, for patients with acute severe heart failure complicating viral illness. Standard implantation of the Impella CP is performed under fluoroscopic guidance. Positioning of the Impella CP can be confirmed with transthoracic or transoesophageal echocardiography. We describe an alternative approach to guide intracardiac implantation of the Impella CP using two-dimensional and three-dimensional intracardiac echocardiography. This new technique can be useful in selected groups of patients when fluoroscopy, transthoracic and transoesophageal echocardiography is deemed inapplicable or limited for epidemiological or clinical reasons. Intracardiac three-dimensional echocardiography is a feasible alternative to the traditional techniques for implantation of an Impella CP device but careful consideration must be given to the potential limitations and complications of this technique.

Comparison of dynamic changes in stressed intravascular volume, mean systemic filling pressure and cardiovascular compliance: Pilot investigation and study protocol.

The mean systemic filling pressure (MSFP) represents an interaction between intravascular volume and global cardiovascular compliance (GCC). Intravascular volume expansion using fluid resuscitation is the most frequent intervention in intensive care and emergency medicine for patients in shock and with haemodynamic compromise. The relationship between dynamic changes in MSFP, GCC and left ventricular compliance is unknown. We conducted prospective interventional pilot study following euthanasia in post cardiotomy adult sheep, investigating the relationships between changes in MSFP induced by rapid intravascular filling with fluids, global cardiovascular compliance and left ventricular compliance. This pilot investigation suggested a robust correlation between a gradual increase in the intravascular stressed volume from 0 to 40 ml/kg and the MSFP r = 0.708 95% CI 0.435 to 0.862, making feasible future prospective interventional studies. Based on the statistical modelling from the pilot results, we expect to identify a strong correlation of 0.71 ± 0.1 (95% CI) between the MSFP and the stressed intravascular volume in a future study.

Three-dimensional intracardiac echocardiography and pulmonary embolism.

BACKGROUND: Three-dimensional intracardiac echocardiography (3D ICE) with wide azimuthal elevation is a novel technique performed for assessment of cardiac anatomy and guidance of intracardiac procedures, being able to provide unique views with good spatial and temporal resolution. Complications arising from this invasive procedure and the value of 3D ICE in the detection and diagnosis of acute cardiovascular pathology are not comprehensively described. This case illustrates a previously unreported iatrogenic complication of clot displacement from the intra-vascular sheath upon insertion of a 3D ICE catheter and the value of 3D ICE in immediate diagnosis of clot in transit through the heart with pulmonary embolism. CASE PRESENTATION: We conducted a translational study of 3D ICE with wide azimuthal elevation to guide implantation of a left ventricular assist device (Impella CP®) in eight adult sheep. A large-bore 14 Fr central venous sheath was used to enable right atrial and right ventricular access for the intracardiac catheter. Insertion of the 3D ICE catheter was accompanied by a sudden severe cardiorespiratory deterioration in one animal. 3D ICE revealed a large highly mobile mass within the right heart chambers, determined to be a clot-in-transit. The diagnosis of pulmonary clot embolism resulting from the retrograde blood entry into the large-bore sheath introducer, rapid clot formation and consequent displacement into venous circulation by the ICE catheter was made. The sheep survived this life-threatening event following institution of cardiovascular support allowing completion of the primary research protocol. CONCLUSION: This report serves as a serious warning to the researchers and clinicians utilizing long large-bore sheath introducers for 3D ICE and illustrates the value of 3D ICE in detecting clot-in-transit within right heart chambers.

Composite Y Grafts From the Left Internal Mammary Artery: Current Considerations.

The use of composite coronary artery bypass grafts from the left internal mammary artery (LIMA) has increased over the last 20 years. Total arterial revascularisation can be achieved with two arterial conduits and is associated with a reduced risk of stroke. However, the traditional coronary bypass graft configurations of the in situ LIMA and aorto-coronary saphenous vein grafts remain as the mainstay of coronary bypass surgery in most centres. Concerns regarding composite Y grafts relate to (1) the adequacy of a single inflow for all coronary bypass grafts; (2) the risk of compromising the LIMA flow to the left anterior descending coronary artery; (3) the effects of competitive flow on graft patency; and (4) the use of sequential coronary anastomoses. The evidence upon which these concerns are based will be discussed along with the evidence relating to the use of the various second conduit options.

Composite Y-Grafting Using the Left Internal Thoracic Artery: Survival and Angiography in 198 Cases.

BACKGROUND: Extended left internal thoracic artery (LITA) harvesting allows maximal grafting to the anterior and lateral walls with a single ITA conduit. This study evaluates outcomes following the use of a LITA Y graft as the primary grafting strategy. METHODS: Patients who underwent LITA composite Y-grafting (n=198) between 1995 and 2009 were identified from a cardiac surgical database. Follow-up (mean 13.1 years) was obtained by cross-reference with the state death registry and local cardiology databases. RESULTS: Operative mortality was zero in the 168 patients who underwent isolated CABG and was 3.5% overall. There were no episodes of perioperative myocardial infarction. Kaplan-Meier 10-year survival was 75.9%. Independent predictors of worse late survival were age, diabetes, chronic obstructive pulmonary disease and pre-existing left ventricular dysfunction. There were 53 episodes of post-discharge angiography at an average of 5.8 years post LITA Y grafting. Twenty cases of LITA Y graft failure were identified, predominantly affecting the free limb (n=15). The ratio of symptom driven angiography to Y graft failure increased over time. Eighteen patients required revascularisation, percutaneous intervention in 15 and reoperative coronary bypass in three. CONCLUSIONS: Left Internal Thoracic Artery Y grafting is a feasible revascularisation strategy with satisfactory outcomes. These are comparable to other arterial composite graft configurations. A LITA Y allows efficient conduit use without compromising the in situ LITA graft.

Bilateral Internal Thoracic Artery Composite Y Grafts: Analysis of 464 Angiograms in 296 Patients.

BACKGROUND: The use of bilateral internal thoracic arteries (BITA) in coronary artery bypass graft surgery improves patient survival. The optimum BITA graft configuration is unknown. This study evaluates outcomes after the use of bilateral internal mammary Y grafting as the primary grafting strategy. METHODS: Patients who underwent BITA composite Y grafting (n = 1,011) between October 1994 and March 2009 were identified from a cardiac surgical database. Follow-up (mean 12 years) was obtained by cross-reference with the state death registry and local cardiology databases. RESULTS: Perioperative mortality was 1.6%. Kaplan-Meier 10-year survival was 87.2%. There were 464 episodes of postdischarge angiography in 296 patients, at an average of 5.5 years to first angiography. Graft failure occurred in 151 patients, predominately affecting the right ITA limb (n = 139). Degree of native vessel stenosis (odds ratio [OR] 0.66 per 10% increase), anatomic territory grafted (circumflex OR 2.64, right coronary OR 6.73 versus anterior), and end-to-side free wall anastomoses (OR 1.98) predicted anastomotic occlusion. The left anterior descending artery graft patency was unaffected by sequential grafting. Progression to graft failure after the first angiogram was rarely seen in the 111 patients who had serial angiography. CONCLUSIONS: Outcomes of BITA Y grafting are similar to those for other BITA configurations. The rate of presentation with arterial graft dysfunction decreases over time. Although competitive flow affects anastomotic patency, there is no threshold at which risk of occlusion substantially increases.