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A 50 year old woman presented with severe exertional dyspnoea. On physical examination, she had a 3/6 systolic ejection murmur that virtually disappeared with inspiration. Transthoracic echocardiography demonstrated findings typical of hypertrophic cardiomyopathy with a pronounced increase in ventricular septal thickness and an outflow gradient of 100 mm Hg. The patient underwent cardiac catheterisation (panel below: Ao, aortic pressure, LA, left atrial pressure, LV, left ventricular pressure, PA, pulmonary artery pressure). In the resting state, there was a significant outflow tract gradient between the left ventricular and aortic pressure. However, with each inspiration, there was a large decrease in the left ventricular outflow tract gradient. The “spike and dome” morphology of the aortic pressure curve virtually disappeared during peak inspiration, indicating a notable resolution of the outflow obstruction.
The pronounced decrease in the intensity of the systolic murmur with inspiration is unique to hypertrophic cardiomyopathy, secondary to the dynamic nature of the obstruction. The left ventricular outflow tract obstruction in patients with hypertrophic cardiomyopathy is highly dependent upon preload, afterload, and contractility. With inspiration, the intrathoracic and intrapericardial pressures decrease to a greater extent than the intracardiac pressures. As a result, the left ventricular transmural pressure increases, increasing the afterload on the left ventricle, thus decreasing the obstruction and the left ventricular outflow tract gradient.
The dynamic changes of the murmur intensity with respiration may help in the differential diagnosis of a systolic murmur. In patients with hypertrophic cardiomyopathy, there may be a notable decrease in the intensity of the murmur during peak inspiration. Since the outflow tract obstruction is also decreased, there may even be an increase in arterial pressure, which has been called “reverse pulsus paradoxus”. In contrast, patients with right sided murmurs will have an increase in the intensity of the murmur with inspiration. In patients with murmurs of fixed outflow tract obstruction or mitral regurgitation, there may be a slight decrease in the intensity of the murmur with inspiration from a slight decrease in preload but the aortic pressure will also decrease.