Hypertrophic Nonobstructive Cardiomyopathy as a Cause of Severe Restrictive Physiology

A 66-year-old woman with a family history of hypertrophic cardiomyopathy (HCM) presented with severeprogressive exertional dyspnoea. She had recently complained of palpitations corresponding to atrial fibrillation on the ECG. A transthoracic echocardiogram (TTE) showed nonobstructive, slightly asymmetrical left ventricular hypertrophy (septum and posterior wall thickness respectively measured at 20 and 15 mm). Left ventricular (LV) cavity and ejection fraction (70%) were normal, but both atria were enlarged (Figure 1A). Diastolic function assessment was suggestive of restrictive physiology (Figure 1B). The patient did not improve despite successful cardioversion and intensive medical therapy with maximally-tolerated doses of beta-blockers and verapamil. She was then referred to the catheterisation laboratory to undergo left and right heart catheterisation and coronary angiography after proach) and left heart catheterisations were performed and revealed signs of restrictive physiology without intraventricular dynamic obstruction (Figure 2,

Table 1. Haemodynamic criteria for restrictive cardiomyopathy and constrictive pericarditis [4].

). However, the PA pressure was only mildly elevated and the ventricular diastolic pressure showed a subtle dipplateau pattern (square root sign).

Aggressive treatment with diuretics typically decreases filling pressures (preload) acutely, as confirmed by the low absolute LV and RV end-diastolic pressures, and affects recognition of the typical restrictive pressure tracings. We therefore performed an intravenous fluid challenge with 500 ml of NaCl 0.9% over approximately 10 minutes. The fluid challenge provoked an increase in systolic RV pressure from 36 mm Hg to 57 mm Hg (Figure 3), confirming a significant preload increase (probably more representative of this patient’s usual clinical condition). The typical “M or W” pattern of restriction became more obvious on the RA pressure tracing (prominent x and y descent) (Figure 4), as did the ventricular dip-plateau pattern (square root sign). These findings were interpreted as suggestive of a severe restrictive physiology (in addition to the concomitant PA pressure value >50 mm Hg, elevated LV enddiastolic pressure and ventricular diastolic pressuresdifferential >5 mm Hg). This patient did not undergo endomyocardial biopsy or MRI in view of the documented familial history of HCM, absence of clinical findings suggestive of other diagnoses, and typical echocardiographic findings. We did however perform genetic testing for HCM.

HCM is typically classified in the subgroup of noninfiltrative restrictive cardiomyopathy [1]. Most patients with HCM exhibit significant abnormalities of diastolic function at rest and under stress, even in the absence of an intraventricular pressure gradient [2]. These abnormalities of global diastolic filling are largely independent of the extent and distribution of myocardial hypertrophy [3]. HCM may cause abnormal distensibility of the ventricle due to fibrosis or cellular disorganisation. Nonobstructive HCM often presents with the clinical manifestation of restrictive cardiomyopathy, and is also associated with atrial fibrillation.

Finally, we believe it is crucial to determine whether the baseline filling pressures are artificially low, as is often the case following aggressive diuresis, since this situation may mask the typical haemodynamic patterns of restriction. This case, with demonstrative haemodynamic tracings for restrictive cardiomyopathy, clearly shows the effect of fluid challenge, which is often underused in catheterisation laboratories, in a physiology of this kind.