Cardiovascular symptoms of MCAS

MCAS patients often have a number of cardiovascular symptoms.  In true mast cell disease fashion, these symptoms often represent both ends of the spectrum.
Heart palpitations are the most common cardiac complaint, with true rhythmic abnormalities being fairly rare.  Tachycardia is also very common, but occasionally slow heart rate (bradycardia) is reported.  In bradycardic patients, no obvious cause for this can be identified.  Both low and high blood pressure can be seen, many times in the same patient, sometimes even following one after the other in a short period of time.  These changes in blood pressure often have no clear trigger.
True syncope (fainting) is uncommon in MCAS, but presyncope (lightheadedness, weakness, dizziness or vertigo) affects the majority of patients.  These presyncope episodes can be distinct from POTS symptoms, and may not be related to position.  Some patients experience as many as several episodes a day.  When tested for POTS with tilt table, MCAS patients may or may not be positive.  However, when treated for POTS, mast cell patients in general only see mild reduction in their presyncope episodes, with little improvement in their other symptoms.
MCAS patients often complain of chest pain, which may or may not reveal ECG abnormalities.  This type of pain is generally localized specifically to the chest and does not radiate down the arm.  Chest pain must be carefully evaluated due to the potential for two rare cardiac syndromes.  Additionally, mast cell disease can indirectly cause congestive heart failure by the long term action of histamine. 
Takotsubo syndrome, or stress-induced cardiomyopathy, is caused by sudden weakening of the myocardium that causes ballooning of the left ventricle.  It can cause acute heart failure, ventricular arrhythmias, and acute heart failure.  Angiography shows that there is no coronary artery defect to explain the left ventricular abnormalities.  If the patient survives, the left ventricle typically returns to normal after about eight weeks.  This does not occur as a result of an allergic reaction, but is sometimes seen in patients with idiopathic anaphylaxis.  In 75% of patients, serum catecholamines are elevated, a finding sometimes seen in MCAS patients.  Due to severe emotional stress frequently being the trigger for the cardiac event, Takotsubo syndrome is also known as broken heart syndrome.
Kounis syndrome is also known as allergic angina or allergic myocardial infarction.  In these patients, there are no obstructive lesions in the coronary artery.  Patients suffer severe chest pain or heart attack as an extension of an allergic reaction.  Kounis syndrome is caused by mast cell activation causing vasospasm of the coronary artery.  It is not known if the mast cells effecting this pathology are normally developed mast cells or improperly developed, such as seen in mastocytosis and MCAS.  This syndrome accounts for about 0.002% of all acute heart attacks.  (An in depth post on Kounis syndrome is on the way.)
MCAS patients often experience coronary and peripheral atherosclerosis.  Some have pain due to narrowing of the vessels.  Sclerosis and poor healing is seen in many MCAS patients.  Due to the importance of mast cells in angiogenesis, long term mast cell activation can contribute to aneurysms, hemorrhoids, varicosities, hemangiomas, arteriovenous malformations and telangiectasias. 
Edema is a common finding.  Most MCAS patients who have edema have no heart abnormalities and do not have pitting edema, indicating that the edema is likely not from heart disease.  MCAS patients often have widespread edema that can shift to different parts of the body.  There is usually no detectable low albumin.  This is thought to be due to third spacing. 

Afrin, Lawrence B. Presentation, diagnosis and management of mast cell activation syndrome.  2013.  Mast cells.
Molderings GJ, Brettner S, Homann J, Afrin LB. Mast cell activation disease: a concise practical guide for diagnostic workup and therapeutic options. J. Hematol. Oncol.2011; 4:10-17.
Ribatti D, Crivellato E. Mast cells, angiogenesis, and tumour growth. Biochim. Biophys. Acta Mol. Basis Dis. 2012 Jan; 1822(1): 2-8.
Glowacki J, Mulliken JB. Mast cells in hemangioma and vascular malformations.  Pediatrics 1982; 70(1):48-51.
Ribatti D, Crivellato E. Mast cells, angiogenesis, and tumour growth. Biochim. Biophys. Acta Mol. Basis Dis. 2012 Jan; 1822(1):2-8.
Glowacki J, Mulliken JB. Mast cells in hemangioma and vascular malformations. Pediatrics 1982; 70(1):48-51.
Kolck UW, Alfter K, Homann J, von Kügelgen I, Molderings GJ. Cardiac mast cells: implications for heart failure. JACC 2007 Mar 13; 49(10):1106-1108.