Low-flow, low-gradient aortic stenosis: from evaluation to treatment

Invasive assessment of aortic stenosis in contemporary practice

The authors review the current role of cardiac catheterization in the characterization of aortic stenosis, its main clinical applications, its pitfalls, and its additional value to the information provided by echocardiography. Discrepancies that may arise between these two modalities are discussed and further explained. Hemodynamic variables besides transvalvular pressure drop are described, and emphasis is given to an integrative approach to aortic stenosis assessment, that includes invasive and noninvasive evaluation.

Contemporary Imaging of Aortic Stenosis

Degenerative or fibrocalcific aortic stenosis (AS) is now the most common native valvular heart disease assessed and managed by cardiologists in developed countries. Transthoracic echocardiography remains the quintessential imaging modality for the non-invasive characterisation of AS due to its widespread availability, superior assessment of flow haemodynamics, and a wealth of prognostic data accumulated over decades of clinical utility and research applications. With expanding technologies and increasing availability of treatment options such as transcatheter aortic valve replacements, in addition to conventional surgical approaches, accurate and precise assessment of AS severity is critical to guide decisions for and timing of interventions. Despite clear guideline echocardiographic parameters demarcating severe AS, discrepancies between transvalvular velocities, gradients, and calculated valve areas are commonly encountered in clinical practice. This often results in diagnostically challenging cases with significant implications. Greater emphasis must be placed on the quality of performance of basic two dimensional (2D) and Doppler measurements (attention to detail ensuring accuracy and precision), incorporating ancillary haemodynamic surrogates, understanding study- or patient-specific confounders, and recognising the role and limitations of stress echocardiography in the subgroups of low-flow low-gradient AS. A multiparametric approach, along with the incorporation of multimodality imaging (cardiac computed tomography or magnetic resonance imaging) in certain scenarios, is now mandatory to avoid incorrect misclassification of severe AS. This is essential to ensure appropriate selection of patients who would most benefit from interventions on the aortic valve to relieve the afterload mismatch resulting from truly severe valvular stenosis.

Impact of concomitant mitral regurgitation on transvalvular gradient and flow in severe aortic stenosis: a systematic ex vivo analysis of a subentity of low-flow low-gradient aortic stenosis

AIMS

Evaluation of aortic stenosis (AS) is based on echocardiographic measurement of mean pressure gradient (MPG), flow velocity (Vmax) and aortic valve area (AVA). The objective of the present study was to analyse the impact of systemic haemodynamic variables and concomitant mitral regurgitation (MR) on aortic MPG, Vmax and AVA in severe AS.

METHODS AND RESULTS

A pulsatile circulatory model was designed to study function and interdependence of stenotic aortic (AVA: 1.0 cm², 0.8 cm² and 0.6 cm²) and insufficient mitral prosthetic valves (n=8; effective regurgitant orifice area [EROA] <0.2 cm² vs. >0.4 cm²) using Doppler ultrasound. In the absence of severe MR, a stepwise increase of stroke volume (SV) and a decrease of AVA was associated with a proportional increase of aortic MPG. When MR with EROA <0.2 cm² vs. >0.4 cm² was introduced, forward SV decreased significantly (70.9±1.1 ml vs. 60.8±1.6 ml vs. 47.4±1.1 ml; p=0.02) while MR volume increased proportionally. This was associated with a subsequent reduction of aortic MPG (57.1±9.4 mmHg vs. 48.6±13.8 mmHg vs. 33.64±9.5 mmHg; p=0.035) and Vmax (5.09±0.4 m/s vs. 4.91±0.73 m/s vs. 3.75±0.57 m/s; p=0.007). Calculated AVA remained unchanged (without MR: AVA=0.53±0.04 cm² vs. with MR: AVA=0.52±0.05 cm²; p=ns). In the setting of severe AS without MR, changes of vascular resistance (SVR) and compliance (C) did not impact on aortic MPG (low SVR and C: 66±13.8 mmHg and 61.1±20 mmHg vs. high SVR and C: 60.9±9.2 mmHg and 71.5±13.5 mmHg; p=ns) In concomitant severe MR, aortic MPG and Vmax were not significantly reduced by increased SVR (36.6±2.2 mmHg vs. 34.9±5.6 mmHg, p=0.608; 3.89±0.18 m/s vs. 3.96±0.28 m/s; p=ns).

CONCLUSIONS

Systemic haemodynamic variables and concomitant MR may potentially affect diagnostic accuracy of echocardiographic AS evaluation. As demonstrated in the present study, MPG and Vmax are flow-dependent and significantly reduced by a reduction of forward SV from concomitant severe MR, resulting in another entity of low-flow low-gradient aortic stenosis. In contrast, calculated AVA appears to be a robust parameter of AS evaluation if severe MR is present. Changes of SVR and C did not affect the diagnostic accuracy of AS evaluation.

Hemodynamic characterization of aortic stenosis states

Aortic stenosis (AS) has become an increasingly prevalent clinical condition, as a result of the "greying of the population", the widespread application of sophisticated diagnostic tools including non-invasive imaging and invasive techniques, and the advent of minimally invasive surgical and percutaneous valve therapies. The diagnosis of severe AS traditionally has relied on the assessment of the mean transvalvular gradient (ΔP_mean ) and aortic valve area (AVA) by either echocardiography or catheterization. However, other hemodynamic variables as flow, pressure recovery, and jet eccentricity also play a major role in determining the final hemodynamic state of AS. Moreover, mismatch between ΔP_mean and AVA as in low flow low gradient AS and discordance between catheterization and echocardiographic studies in grading severity of AS have increased the complexity of AS diagnosis. The present case-based treatise emphasizes a multi-modality approach to delineation of the hemodynamic pathophysiology of different AS states. KEY POINTS: Reduction in the aortic valve area, flow across the aortic valve, and direction of the aortic stenosis jet determine the pressure gradient generated across the aortic valve in patients with aortic stenosis. Discordance between echo and catheterization maximum gradients is related to the inherent temporal differences between the times of their acquisition. Discordance between echo and catheterization mean gradients is related to pressure recovery and assumptions in the application of Bernoulli equation to estimate the aortic valve gradient. Pressure recovery relates to the ratio of the aortic valve area and ascending aortic diameter as well as the jet direction. Mismatch between area and gradient criteria for aortic stenosis severity may occur with or without concordance between echocardiographic and catheterization data. Errors of measurement should be excluded prior to assuming any mismatch or discordance between the data. Area gradient mismatch occurs when the aortic valve area is in the severe range, while the gradient is in the non-severe range as in low flow low gradient aortic stenosis. Reverse area gradient mismatch occurs when the gradient is in the severe range, while the aortic valve area is in the non-severe range as in congenital aortic stenosis with an eccentric jet.

Low gradient aortic stenosis

OPINION STATEMENT

Severe low-gradient (LG) aortic stenosis (AS) [aortic valve area (AVA) ≤ 1.0 cm(2), mean pressure gradient (MG) < 40 mmHg] represents a frequently encountered and challenging clinical dilemma. A systematic approach, which often requires several imaging modalities, should be undertaken to confirm the hemodynamic findings and rule out measurement error. Low-flow conditions often account for the discrepancy and can be present whether the left ventricular ejection fraction (LVEF) is depressed or normal. In patients with classical low-flow (LF), LG AS in which LVEF is reduced (<40-50 %), dobutamine stress echocardiography (DSE) should be used to distinguish patients with true severe AS and pseudo-severe AS, as well as to evaluate for the presence of left ventricular contractile or flow reserve. Surgical or transcatheter aortic valve replacement (AVR) should likely be reserved for those patients with true severe AS. Patient outcome with medical or surgical management generally relates to patient functional capacity, stenosis severity, and left ventricular functional reserve. Patients with severe LG AS with preserved LVEF can have a stroke volume that is either normal (>35 mL/m(2)) or low (<35 mL/m(2)). New data suggest that DSE can identify pseudo-severe AS in up to 30 % of patients with severe LF-LG AS with preserved LVEF. AVR should likely be restricted to those patients with true severe AS, although there is currently little data to support this strategy. Symptomatic patients with severe LG AS with preserved LVEF, whether they have normal or low flow, should be offered AVR. Transcatheter AVR provides an alternative therapeutic option in the high-risk patient.

Echocardiographic Evaluation of Aortic Stenosis - Normal Flow and Low Flow Scenarios

The echocardiographic evaluation of the patient with aortic stenosis (AS) has evolved in recent years, beyond confirming the diagnosis and measuring the resting mean pressure gradient or valve area. New echocardiographic approaches have developed to address the clinical dilemmas related to discordant haemodynamic data, asymptomatic haemodynamically severe AS and low-flow, low-gradient AS in order to better evaluate the disease severity, enhance the risk stratification of patients and provide important prognostic information. This article reviews the echocardiographic evaluation of the AS patient and focuses on the echocardiographic assessment of the haemodynamic severity, the prediction of clinical outcome and the use of echocardiography to guide patient management in the presence of normal flow and low flow scenarios.

Preoperative management of the neonate with critical aortic valvar stenosis

Neonatal critical aortic stenosis is a rare form of CHD that often presents with cardiogenic shock. Although surgical and cardiac catheterisation-based interventions have been successful in alleviating left ventricular outflow tract obstruction, it remains associated with high morbidity and mortality. Critical aortic stenosis results in elevated left ventricular wall stress, which ultimately increases myocardial oxygen consumption and disrupts coronary artery perfusion during diastole, leading to ventricular dysfunction and cardiogenic shock. Critical care management before definitive intervention should be tailored to optimising oxygen delivery and reducing metabolic consumption of the myocardium and peripheral organ systems. This can be accomplished with prostaglandin infusion to maintain system perfusion through patency of the arterial duct, inotropic support, mechanical ventilation, and central nervous system abrogation. Management should also include a multi-specialty medical team including paediatric cardiothoracic surgeons and paediatric cardiologists with expertise in cardiac catheterisation, imaging, and transplantation.

Aortic balloon valvuloplasty prior to orthotopic liver transplantation: a novel approach to aortic stenosis and end-stage liver disease

The combination of severe aortic stenosis and end-stage liver disease increases the morbidity and mortality of surgical aortic valve replacement or orthotopic liver transplantation resulting in a prohibitive operative risk. We propose a staged approach of balloon aortic valvuloplasty prior to orthotopic liver transplantation as a bridge to definitive aortic valve replacement. Between 2010 and 2012, four patients with severe aortic stenosis and end-stage liver disease underwent staged balloon aortic valvuloplasty followed by orthotopic liver transplantation. All patients had been deemed to be inappropriate candidates for liver transplantation or aortic valve surgery due to their comorbidity. One patient died of complications from a perivalvular abscess. Three patients went on to successful graft implantation and function and surgical recovery. Two of the three patients proceeded to definitive surgical aortic valve replacement with the remainder currently undergoing evaluation. In this case series, we present a novel approach of balloon aortic valvuloplasty prior to liver transplantation as a potential bridge to definitive treatment of severe aortic stenosis in the end-stage liver patient.

Significance of aortic valve calcification in patients with low-gradient low-flow aortic stenosis

BACKGROUND

Assessment of patients with aortic stenosis (AS) and impaired left ventricular function remains challenging. Aortic valve calcium (AVC) scoring with computed tomography (CT) and fluoroscopy has been proposed as means of diagnosing and predicting outcomes in patients with severe AS.

HYPOTHESIS

Severity of aortic valve calcification correlates with the diagnosis of true severe AS and outcomes in patients with low-gradient low-flow AS.

METHODS

Echocardiography and CT database records from January 1, 2000 to September 26, 2009 were reviewed. Patients with aortic valve area (AVA)<1.0 cm2 who had ejection fraction (EF)≤25% and mean valvular gradient≤25 mmHg with concurrent noncontrast CT scans were included. AVC was evaluated using CT and fluoroscopy. Mortality and aortic valve replacement (AVR) were established using the Social Security Death Index and medical records. The role of surgery in outcomes was evaluated.

RESULTS

Fifty-one patients who met the above criteria were included. Mean age was 75.1±9.6 years, and 15 patients were female. Mean EF was 21%±4.6% with AVA of 0.7±0.1 cm2. The peak and mean gradients were 35.5±10.6 and 19.0±5.1 mmHg, respectively. Median aortic valve calcium score was 2027 Agatston units. Mean follow-up was 908 days. Patients with calcium scores above the median value were found to have increased mortality (P=0.02). The benefit of surgery on survival was more pronounced in patients with higher valvular scores (P=0.001). Fluoroscopy scoring led to similar findings, where increased AVC predicted worse outcomes (P=0.04).

CONCLUSIONS

In patients with low-gradient low-flow AS, higher valvular calcium score predicts worse long-term mortality. AVR is associated with improved survival in patients with higher valve scores.

Aortic stenosis in the elderly: challenges in diagnosis and therapy

Severe aortic valve stenosis, remains the main cause of morbidity and mortality in the elderly, reaching a prevalence of 2-7% above the age of 65 years old. Despite its frequency and the development in invasive and noninvasive approach of the disease, several of its aspects remain controversial. This review is focused on the clinical aspects, the indices for assessment severity, newly markers related to prognosis and new therapeutic modalities for the elderly population. The term low flow, low gradient severe aortic stenosis with preserved LV systolic function has revealed a new modality in the field of diagnostic evaluation and therapeutic approach. Aortic valve replacement is the choice therapy for symptomatic severe aortic stenosis. Despite the recent advances in cardiac surgery, the overall operative mortality rate for isolated aortic valve replacement surgery ranges from 2.5% to 4.0% and is higher in octogenarians and can be up to 25% in patients with comorbid conditions. The fact that surgery is not being performed for 30% or more of patients requiring it, a great attention was attracted to the percutaneous transcatheter implantation of a stent-mounted aortic valve. The up to now experience of transcatheter valve implantation in more than 25,000 patients, has shown promising results in terms of mortality and quality of life. Echocardiography still plays the central role for the evaluation of the elderly patient, as it can illustrate the pathophysiological alterations during the course of aortic valve stenosis, and guide appropriate therapy.

Cardiac resynchronization therapy for low-flow, low-gradient aortic stenosis

Low-flow, low-gradient aortic stenosis is a heterogeneous entity that encompasses truly severe aortic stenosis as well as mild-to-moderate aortic stenosis in which aortic valve orifice area is severely reduced primarily due to left ventricular (LV) contractile dysfunction. Under such circumstances the capacity of the LV to generate stroke-work is severely compromised. In this case report, we describe a patient with severe LV dysfunction and ventricular dyssynchrony due to right ventricular pacing who presented with decompensated heart failure in the setting of low-flow, low-gradient aortic stenosis. We discuss the management of this high-operative-risk patient, who ultimately underwent upgrading of his dual chamber pacemaker to a biventricular pacemaker with significant echocardiographic, haemodynamic, and clinical improvement.

Aortic stenosis

In developed countries, aortic stenosis is the most prevalent of all valvular heart diseases. A manifestation of ageing, the disorder is becoming more frequent as the average age of the population increases. Symptomatic severe disease is universally fatal if left untreated yet is consistent with a typical lifespan when mechanical relief of the stenosis is provided in a timely fashion. Management of mild disease, severe asymptomatic disease, and far advanced disease, and the effect of new percutaneous treatments, provide both controversy and exciting promise to care of patients with aortic stenosis. We discuss these issues in this Review.

Stress echocardiography expert consensus statement: European Association of Echocardiography (EAE) (a registered branch of the ESC)

Stress echocardiography is the combination of 2D echocardiography with a physical, pharmacological or electrical stress. The diagnostic end point for the detection of myocardial ischemia is the induction of a transient worsening in regional function during stress. Stress echocardiography provides similar diagnostic and prognostic accuracy as radionuclide stress perfusion imaging, but at a substantially lower cost, without environmental impact, and with no biohazards for the patient and the physician. Among different stresses of comparable diagnostic and prognostic accuracy, semisupine exercise is the most used, dobutamine the best test for viability, and dipyridamole the safest and simplest pharmacological stress and the most suitable for combined wall motion coronary flow reserve assessment. The additional clinical benefit of myocardial perfusion contrast echocardiography and myocardial velocity imaging has been inconsistent to date, whereas the potential of adding - coronary flow reserve evaluation of left anterior descending coronary artery by transthoracic Doppler echocardiography adds another potentially important dimension to stress echocardiography. New emerging fields of application taking advantage from the versatility of the technique are Doppler stress echo in valvular heart disease and in dilated cardiomyopathy. In spite of its dependence upon operator's training, stress echocardiography is today the best (most cost-effective and risk-effective) possible imaging choice to achieve the still elusive target of sustainable cardiac imaging in the field of noninvasive diagnosis of coronary artery disease.