More left ventricular mass does not mean bigger heart cells
In short
Deep-learning morphometry (MyoSAM) of myocardial slides from 334 patients found that myocyte size, measured as the Myocyte Maximum Inscribed Circle radius, was the strongest histological predictor of left ventricular mass index and correlated with clinical heart failure at r = 0.77. In severe coronary artery disease, however, myocyte hypertrophy was blunted despite rising mass (p = 0.001), with remodelling shifting toward interstitial stromal expansion (p = 0.025). Male myocytes were 1.08 times larger than female (p = 0.003). The same mass figure can be filled by very different tissue.
The usual reading of a left ventricular mass figure on a report is "the heart muscle got bigger". This study shows, at tissue resolution, that the equals sign does not always hold.
The team ran H&E-stained whole-slide images from 334 patients through a deep-learning framework called MyoSAM, extracting the radius of the largest circle inscribed in each myocyte (MMIC), nuclear size, perinuclear halo size, and interstitial and macrodomain stromal fractions. This is a layer clinical imaging cannot resolve.
What did myocyte size predict?
MMIC radius was the strongest histological predictor of left ventricular mass index (p < 0.001) and correlated with clinical heart failure at r = 0.77 (p < 0.001). So far, as expected: bigger cells, more mass; more mass, more heart failure.
So why was coronary disease different?
In severe coronary artery disease the mass-to-cell-size association was significantly attenuated (p = 0.001). Mass went up while myocyte hypertrophy went down. What expanded instead was the interstitial stroma (p = 0.025). The added weight was not muscle but the tissue between it.
Anyone who lifts knows the skeletal-muscle version of this distinction: a bigger circumference is not proof of bigger fibres — it can be swelling or connective tissue. The heart has the same trap, except there the distinction decides prognosis.
Each cause left a different tissue signature
- Anthracycline-treated hearts — large MMIC radii and perinuclear halos, minimal stroma
- Non-ischaemic cardiomyopathy — the greatest nuclear enlargement and stromal macrodomain expansion
- Severe coronary artery disease — blunted myocyte hypertrophy with interstitial stromal expansion
How different are men and women?
Male MMIC radii were 1.08 times larger than female (p = 0.003). The reason 'normal' thresholds for wall thickness and mass are sex-specific turns out to hold at the level of the cell. It is the same problem the Muscle Index solves for strength — an absolute number means nothing without the body it came from.
On how blood pressure thickens the wall, see blood pressure thickens the heart wall; on the molecular split between athletic and pathological growth, see an athlete's enlarged heart and a diseased one.
This is observational work on patients whose tissue was available for slides. No healthy athletes were measured, so which signature a training-enlarged heart would show is not answered here.
Frequently asked questions
Does rising left ventricular mass mean the heart muscle grew?
Not always. In 334 patients, severe coronary artery disease showed blunted myocyte hypertrophy despite increased mass (p = 0.001), with interstitial stromal expansion instead (p = 0.025). The same mass figure can reflect larger cells or more tissue between them.
How closely is myocyte size related to heart failure?
The myocyte size measure, MMIC radius, correlated with clinical heart failure at r = 0.77 (p < 0.001) and was the strongest histological predictor of left ventricular mass index (p < 0.001).
Does the underlying disease change what the tissue looks like?
Yes. Anthracycline-treated hearts showed large myocytes and perinuclear halos with minimal stroma; non-ischaemic cardiomyopathy showed the greatest nuclear enlargement and stromal macrodomain expansion; severe coronary artery disease showed blunted myocyte hypertrophy with interstitial expansion.
How much do male and female heart cells differ?
Male MMIC radii were 1.08 times larger than female (p = 0.003), a cell-level counterpart to the sex-specific normal ranges used for wall thickness and left ventricular mass.
Were athletes' hearts included?
No. The study analysed patients whose myocardial tissue slides were available, not healthy athletes, so it cannot say which tissue signature exercise-induced cardiac enlargement produces.
Source: PubMed