The cardiac phenotype: when mast cell disease shows up only in the heart

Most descriptions of mast cell disease start with the skin. Flushing, hives, itching, a reaction after a meal. That picture is useful, but it quietly sets a filter: no rash, no mast cell problem.

Two papers argue that the filter is wrong. In a real subset of patients, the heart is not one symptom among many. It is the only symptom.

A phenotype with a name

A 2025 review in Frontiers in Cardiovascular Medicine, written for cardiologists rather than allergists, lists the recognised clinical variants of mast cell activation syndrome. Alongside the irritable-bowel type, the fibromyalgia type and the nervous-system type sits one called simply the cardiac phenotype.

That naming matters. It means the pattern is recognised in the literature, not just reported by patients.

The review’s headline figure: up to 80% of people with mast cell activation disease report cardiovascular symptoms. Mast cells sit between heart muscle cells, in the lining of the heart, around the coronary microvessels and next to sensory nerves, so proximity is not the puzzle. The puzzle is why this rarely reaches the cardiology clinic as a diagnosis.

The authors are blunt about the evidence: despite that 80%, no systematic studies of cardiovascular symptoms in these patients have ever been done. What exists is small series, case reports and the accumulated experience of specialists.

What the heart actually does

Earlier work by the same Bonn group put numbers on the individual symptoms:

• Palpitations and supraventricular tachycardia — 29% in systemic mastocytosis, at least 20% in MCAS
• Hypotension with lightheadedness or fainting — 22% to 55% of patients, against 5% in controls
• High blood pressure — up to 31%, sometimes in the same person who also has episodes of low pressure

The rhythm disturbances described across the literature are the ordinary ones: sinus tachycardia, extra beats from the atria and the ventricles, runs of ventricular tachycardia, and — less often — heart block that progresses in stages. Nothing exotic. That is exactly why it blends in.

The related idea is that mast cells and the heart already have a documented relationship, covered in more detail in the histamine and MCAS post.

The 23 cases where the heart was all there was

The second paper is the sharper one. Australian cardiologists reviewed every published adult case of systemic mastocytosis that presented with cardiac symptoms — syncope, unexplained hypotension, cardiac arrest, chest pain or arrhythmia. They screened 619 publications and found 23 that qualified.

What they found in those 23:

• 35% had no other identified symptom at all. No rash, no gut trouble, nothing. Only the heart.
• 26% had a rash; 26% had gastrointestinal symptoms
• Unexplained cardiac arrest was the first presentation in 26%
• Short-term mortality was 22%
• 83% were male

Their own index case shows how this goes wrong. A 72-year-old man had years of unexplained fainting. A stress echo suggested a problem, he was stented for a narrowed artery, and thirty minutes after the procedure his heart stopped. Repeat angiography showed the artery in severe spasm — Kounis syndrome, an allergic-type coronary event. Three days later he arrested again. Only then was systemic mastocytosis identified as the cause of the fainting he had been having all along. He was discharged 56 days later on appropriate treatment and recovered fully.

One important caveat about those numbers. These are 23 published case reports, which means they are the cases dramatic enough to publish. A 22% mortality rate reflects that selection, not the risk facing someone with palpitations. The 83% male figure should be treated the same way — mast cell activation syndrome overall is diagnosed more often in women, so this almost certainly reflects which cases get written up rather than who gets ill.

The finding that survives the caveat is the one about missing symptoms. If a third of published cardiac presentations had no other feature of the disease, then “but there is no rash” is not a safe reason to stop looking.

Why it gets missed

The workup comes back clean. Arteries are open, the echo is unremarkable, the monitor shows extra beats that are labelled benign. The patient is told the heart is structurally fine, which is true, and that there is nothing wrong, which is not the same thing.

Meanwhile the symptom that would point elsewhere — a rash, a food reaction — is absent in a large minority of these patients. Nobody sends the tryptase.

The 2025 review notes that a definitive diagnosis of mast cell activation disease takes more than five years on average. In a cardiac presentation there is no reason to think it is faster.

The treatment problem

This is the part with practical consequences, and also the part to be most careful with.

The standard first move for palpitations and unexplained tachycardia is a beta blocker. The review argues that in mast cell disease this should be avoided where possible, for a specific mechanistic reason: beta receptors normally act as a brake on mast cell mediator release. Blocking them releases the brake, and the authors report symptoms often worsening immediately. Ivabradine, which slows the sinus rate by a different route, is suggested instead where available.

ACE inhibitors come with a related caution. ACE breaks down bradykinin, which activates mast cells. Inhibit the enzyme, bradykinin persists, and mast cells become easier to set off.

Two things need saying about this. First, it is a genuinely useful thing to know exists, because it would explain a patient who got worse rather than better on a standard drug. Second, and more importantly: this is expert opinion, not trial evidence. The review says so directly — its recommendations come from clinical experience with a large number of patients, not from randomised trials, and there is no long-term outcome data at all. A beta blocker prescribed for an established cardiac reason may be doing something important. This is a question to raise with the doctor who prescribed it, not a reason to stop anything.

How much of this is solid

Worth separating clearly.

Reasonably solid: mast cells are present throughout the heart and vasculature; their mediators can produce tachycardia, low blood pressure and coronary spasm; systemic mastocytosis has caused cardiac arrest and Kounis syndrome in documented cases; a meaningful share of published cardiac presentations had no other symptoms.

Much weaker: the prevalence figures. They come from specialist clinics and self-report, which selects for the people already suspected of having the condition. The 80% figure is a summary of that literature, not a population measurement.

Expert opinion only: essentially all of the treatment guidance, including the beta blocker caution. It is also worth noting that the same researcher, Gerhard Molderings, is an author on both the 2025 review and the earlier symptom paper. These are not two independent groups reaching the same conclusion — they are largely one line of work, and it is the line most favourable to a broad interpretation of MCAS. That is not a reason to dismiss it, but it is a reason to read it as one position in a field that is still arguing.

What might be worth raising with a doctor

Not a checklist, and not a diagnosis. Situations where these papers suggest the question is at least reasonable:

• Recurrent fainting with no cardiac cause found after a full workup
• Cardiac arrest or coronary spasm with arteries that look normal or near-normal
• Palpitations that arrive with flushing, gut symptoms, or after specific triggers
• Blood pressure that swings high and low without explanation
• Cardiac symptoms that got clearly worse after starting a beta blocker

The test usually raised first is serum tryptase, ideally measured both at baseline and during or shortly after an episode, since the difference between the two is what carries the information. Whether that is the right test, and what else belongs alongside it, is a conversation for a doctor who knows the whole picture.

References:

• Taumann W, Molderings GJ. “Cardiovascular manifestations in mast cell activation disease: key insights for cardiologists and angiologists.” Frontiers in Cardiovascular Medicine, 2025;12. doi:10.3389/fcvm.2025.1705201
• Paratz ED, Khav N, Burns AT. “Systemic Mastocytosis, Kounis Syndrome and Coronary Intervention: Case Report and Systematic Review.” Heart, Lung and Circulation, 2017;26(8):772-778. doi:10.1016/j.hlc.2016.12.009
• Paratz ED, Khav N, Burns AT. “Cardiac Manifestations of Systemic Mastocytosis: a Systematic Review.” Heart, Lung and Circulation, 2017;26:S290-S291. doi:10.1016/j.hlc.2017.06.571
• Kolck UW, Haenisch B, Molderings GJ. “Cardiovascular symptoms in patients with systemic mast cell activation disease.” Translational Research, 2016;174:23-32.
• Kounis NG. “Kounis syndrome: an update on epidemiology, pathogenesis, diagnosis and therapeutic management.” Clinical Chemistry and Laboratory Medicine, 2016;54(10):1545-1559.
• Valent P, Akin C, Bonadonna P, et al. “Proposed diagnostic algorithm for patients with suspected mast cell activation syndrome.” Journal of Allergy and Clinical Immunology: In Practice, 2019;7(4):1125-1133.
• Afrin LB, Ackerley MB, Bluestein LS, et al. “Diagnosis of mast cell activation syndrome: a global ‘consensus-2’.” Diagnosis, 2021;8(2):137-152.