Low-flow low-gradient aortic stenosis: outcomes after aortic valve replacement

Abstract

Aortic stenosis is the commonest valve disorder in the Western World. The natural history of the disease is very well described; with a decreased survival once symptoms occur. There is currently, no medical therapy available to reduce the natural progression of the aortic stenosis, and therefore, aortic valve replacement has been recognised as the standard of care treatment for symptomatic aortic stenosis, with TAVI having merged as alternative for those cases with high/prohibitive surgical risk.

All types of aortic stenosis have in common a reduced valve area (AVA <1.0cm2), but depending on the mean gradients and the stroke volume index, there are different types: Normal-Flow High-Gradient (NFHG AS) and Low-Flow Low-Gradient (LFLG AS) aortic stenosis. The latter is further subdivided into Classical and Paradoxical forms depending on the ejection fraction value.

NFHG AS is the most common type. The left ventricle is capable of generating a normal flow through the stenotic valve, that it is translated onto high gradients. This type has been thoroughly studied and has an excellent prognostic with aortic valve replacement, with very low in-hospital mortality and long-term survival similar to the age-matched population.

LFLG AS, on the other hand, is defined by a reduced stroke volume (SVi < 35 ml/min) and a low gradient (mean gradient < 40mmHg). The Classical form (CLFLG AS) has impaired ventricular function. These patients have dilated ventricles that are not able to generate enough flow through the stenotic valve and hence the low gradient. Dobutamine stress echocardiography is key for the diagnosis of this subtype, as it differentiates it from the Pseudo-Severe aortic stenosis (in which the problem is not in the aortic valve but in the left ventricle, and therefore there is no benefit from aortic valve replacement) and it has also prognostic value by determining the contractile reserve. These patients have been reported to have the highest mortality post aortic valve replacement and a reduced long-term survival; however, those who survive achieve excellent functional class.

The other subtype of LFLG, the Paradoxical form (PLFLG AS) has a preserved ventricular function. These patients have a ventricular restrictive physiology, with reduced SVi due to a combination of mechanism such as subendocardial fibrosis, concentric remodeling, impaired diastolic filling and high afterload. It is paramount here to confirm the diagnosis by accurate echocardiography, ruling out measurement errors and other causes of reduced SVi. PLFLG AS patients have worse prognosis than NFHG AS but better prognosis than CLFLG AS patients.

The primary hypothesis of our research project was that aortic valve replacement could be performed in patients with LFLG AS with low in-hospital mortality. Therefore, with the objectives of determining operative and mid-term outcomes of surgical intervention in LFLG AS compared to NFHG AS, we conducted a retrospective analysis of all patients who underwent isolated aortic valve replacement in our centre. Primary end-points were mortality (in-hospital, at one and five years) and the secondary end-points analysed were postoperative complications and clinical status at follow-up.

Patients in the LFLG AS group were significantly older and had more cardiovascular risk factors and comorbidities than the NFHG AS group. Despite those differences, in-hospital mortality was equivalent and remarkably low in both groups. As expected, LFLG AS patients had a reduced mid-term survival but those who survived remained in an excellent functional class.

With the separate analysis of the LFLG AS subgroups, we confirmed that CLFLG AS had higher in-hospital and mid-term mortality than PLFLG AS patients. In both groups, the in-hospital mortality was remarkably low compared to previous literature reports. Aortic valve replacement provided symptomatic relief and excellent functional class during the mid-term follow-up as well as recovery of the ventricular function in most of the patients.

Based on our results, we concluded that aortic valve replacement should be recommended for symptomatic severe LFLG AS.

La estenosis aórtica es la enfermedad valvular más frecuente en el tercer mundo. La historia natural de la enfermedad es bien conocida desde hace décadas, siendo una enfermedad con mal pronóstico a medio-corto plazo que hace necesario someter a estos pacientes a recambio valvular aórtico tras la aparición de síntomas. La forma mas común de estenosis aórtica, con flujo normal y gradiente alto, tiene un pronóstico excelente tras el recambio valvular aórtico, con una supervivencia similar a la de la población normal. Sin embargo, la estenosis aórtica de bajo-flujo y bajo-gradiente, es una entidad menos conocida y de peor pronóstico. Estos pacientes tienen una mortalidad mucho mayor tras recambio valvular aórtico y menor supervivencia a largo plazo.

El diagnóstico en el bajo-flujo bajo-gradiente es vital para seleccionar correctamente los pacientes con estenosis aórtica que se beneficiarán de tratamiento quirúrgico, teniendo también valor pronóstico, dependiendo de la categoría de bajo flujo (Clásica o Paradójica) y otros determinantes como la presencia/ausencia de reserva contráctil del ventrículo izquierdo.

Nuestra hipótesis fue que la estenosis aórtica de bajo-flujo y bajo-gradiente, pueden ser tratada con recambio valvular aórtico con una mortalidad hospitalaria similar a aquellos con flujo normal y alto gradiente. Los objetivos del proyecto fueron el análisis de resultados hospitalarios y a medio plazo (mortalidad hospitalaria, a 1 y 5 años) así como la clase funcional y recuperación de la función ventricular, en pacientes con estenosis aórtica de bajo-flujo bajo-gradiente sometidos a recambio valvular aórtico comparado con flujo normal alto-gradiente.

Nuestros resultados nos llevan a la conclusión de que el recambio valvular aórtico en pacientes con estenosis aórtica de bajo-flujo bajo-gradiente se puede lograr con baja mortalidad quirúrgica, comparable con pacientes con flujo normal y alto gradiente. A pesar de que tener una mayor mortalidad a medio-plazo, los supervivientes exhiben una excelente clase funcional y desaparición de síntomas, que apoyan la indicación quirúrgica en estos pacientes.