In obstructive HCM, thickening of the heart muscle, especially the wall between the two lower chambers, narrows the path blood takes out of the heart, says Milind Desai, MD, a cardiologist at Cleveland Clinic in Ohio.
Too much sodium raises blood volume and filling pressure — the pressure inside the heart’s chambers as they fill with blood between beats — and a thickened, stiff heart doesn’t adapt well to that extra pressure, he says.
“It can worsen congestion, thus increasing shortness of breath, chest pressure, exercise intolerance, and swelling,” says Dr. Desai.
Underfilling the heart is just as much a concern with obstructive HCM, and it works through a different mechanism, he says. When the heart’s chamber is underfilled, it becomes smaller, which can bring that thickened wall and the mitral valve — the valve between the heart’s left chambers — closer together and narrow the outflow path even more, says Desai. That narrowing can bring on dizziness, near fainting, chest discomfort, palpitations, and shortness of breath, he adds.
Dehydration from any cause, not just low sodium intake on its own, can trigger that same underfilling problem, says Nformbuh Asangmbeng, MD, a cardiologist at Atrium Health Floyd Harbin Clinic in Rome, Georgia. “Inadequate fluid intake, vomiting, diarrhea, heavy sweating, heat exposure, and excessive diuretic use can all reduce circulating volume enough to worsen obstruction,” he says.
That two-sided risk is also why there’s no single sodium number that works for everyone with obstructive HCM, says Desai. “Much of the guidance is based on expert consensus, and extrapolation from broader cardiovascular practice, rather than HCM-specific outcome trials.”
Obstructive HCM works differently, says Desai: Pumping ability is often normal or even high, and the problem is a stiff, small chamber rather than a weak, enlarged one. “The standard ‘restrict sodium aggressively’ message may backfire in some obstructive HCM patients,” he says.
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