Systolic anterior motion of the mitral valve associated with right ventricular systolic hypertension in 9 dogs

Evaluation of N-terminal prohormone of brain natriuretic peptide and cardiac troponin-I levels in cats with systolic anterior motion of the mitral valve in the absence of left ventricular hypertrophy

OBJECTIVES

To identify the prevalence of systolic anterior motion of the mitral valve (SAM) in apparently healthy cats in the absence of left ventricular hypertrophy (LVH) and examine the relationship between specific cardiac biomarker concentrations and echocardiographic parameters in these individuals.

ANIMALS

eighty client-owned cats.

MATERIALS AND METHODS

retrospective study; inclusion criteria were the presence of SAM on conscious echocardiography and concurrent measurement of plasma N-terminal prohormone of brain natriuretic peptide (NT-proBNP) and serum cardiac troponin-I (cTnI). Cats were excluded if they had LVH, left atrial enlargement or systemic disease. The percentages of cats with NT-proBNP and cTnI concentrations above the normal reference range were calculated. The correlation between each biomarker concentration and left ventricular myocardial wall thickness, left atrial size and maximum left ventricular outflow tract velocity was evaluated.

RESULTS

Thirty-four of 80 patients with SAM showed no evidence of cardiac remodelling (LVH or left atrial enlargement). Of these patients, 30 of 34 had elevated NT-proBNP, and cTnI was elevated in 13 of 27 (48.1%) cats where this biomarker was measured in association with the NT-proBNP assay. A positive correlation was observed between concentration of plasma NT-proBNP and maximum left ventricular outflow tract velocity (rs = 0.67, p<0.0001). No significant correlations were found between the concentration of biomarkers and the remaining echocardiographic parameters.

CONCLUSIONS

SAM is frequently observed in cats even in the absence of cardiac remodelling, and these individuals often demonstrate elevated plasma NT-proBNP and serum cTnI concentrations. Plasma NT-proBNP elevation is correlated with the severity of the left ventricular outflow obstruction caused by SAM.

Left ventricular outflow tract obstruction-be prepared!

The current trend to treat hypotension in critically ill patients is to place a greater emphasis on inotropic support and less on fluid resuscitation in order to limit the potential harm from fluid overload. This combination may trigger left ventricular outflow tract obstruction (LVOTO) in susceptible patients. Although LVOTO is classically described in patients with hypertrophic cardiomyopathy it has been reported in other conditions including septic shock, apical ballooning syndrome, myocardial infarction, respiratory failure, and post valvular surgery. It is more common in the elderly, females, and in patients with hypertension, diabetes, and chronic vascular disease because of predisposing anatomical conditions such as left ventricular hypertrophy, small left ventricle size, sigmoid septum and alterations in the positions of the aortic and mitral valve annular planes. The onset of LVOTO is largely unpredictable due to a complex interplay between preload, afterload, heart rhythm and rate in susceptible patients. The consequences of missing this treatable condition may lead to life-threatening hypotension refractory to, or exacerbated by, a further increase in inotropic support. Dynamic LVOTO should be considered in any hypotensive intensive care patient. Echocardiography is perhaps the best tool to assess LVOTO and its underlying pathophysiology in the critically ill. Detection of LVOTO is a relatively simple task using a combination of two-dimensional, M-mode and spectral Doppler imaging by an operator alert to the possible diagnosis.

Hypovolemia induced systolic anterior motion of the mitral valve in two dogs

Systolic anterior (septal) motion of the mitral valve (SAM) is a common secondary phenomenon in hypertrophic cardiomyopathy (HCM) in people and cats. In humans, it is increasingly recognized that SAM may be found in other cardiac and non-cardiac disease states. In small animal cardiology, SAM unassociated with HCM has been described in dogs with mitral valve dysplasia and right ventricular pressure overload. In this report, we describe two cases of dogs where transient SAM was caused by hypovolemia. When SAM was present both dogs showed pseudohypertrophy and tachycardia. Important factors in the genesis of SAM in this scenario are probably hypovolemia induced changes in left ventricular geometry affecting the orientation of the mitral valve apparatus combined with elevated catecholamine levels. SAM associated with increased wall thickness is not pathognomonic of HCM; this observation is of particular clinical importance when extrapolated to species where HCM is highly prevalent, e.g., cats. An echocardiographic diagnosis should always be evaluated together with full clinical assessment of history and physical examination.

Dynamic left ventricular outflow tract obstruction secondary to hypovolemia in a German Shepard dog with splenic hemangiosarcoma

Dynamic left ventricular outflow tract obstruction (DLVOTO) is a common condition in cats and humans. In this case report, a dog is described with DLVOTO secondary to severe intra-abdominal hemorrhage caused by a hemangiosarcoma. The dog was a 9-year-old, 35.7-kg, spayed female German Shepard dog that presented with a history of tachypnea and collapse. A Levine II/VI systolic murmur was present at the heart base. Abdominal ultrasonography revealed a splenic mass and a large amount of ascites. Echocardiography showed a reduced left ventricular diameter and an increased aortic velocity caused by systolic anterior motion (SAM) of the mitral valve apparatus. The heart murmur and the SAM were resolved after treatment including a splenectomy and a blood transfusion.