Obstruction and other pathophysiological abnormalities
How the heart works
The heart is a mechanical pump that is used to collect blood poor in oxygen from the whole body and to push it towards the lungs (right heart) where it is oxygenated; from here it reaches the left heart where it is pumped to all organs. It consists of two upper chambers (atria) that serve to receive blood (from the whole body - right atrium; and from the lungs - left atrium) and two lower chambers (ventricles) that serve to pump blood (to the lungs - right ventricle; to the whole body - left ventricle). Inside the heart there are valves (on the right: tricuspid and pulmonary; on the left: mitral and aortic) that serve to direct the blood and prevent it from flowing back. The contraction of the heart is called "systole", the release "diastole".
In order to coordinate the mechanical activity (pump) and synchronize the various chambers, the heart is equipped with electrical activity. The electrical impulse spreads from the atria to the ventricles through an electrical conduction system.
The Heart in Hypertrophic Cardiomyopathy
The heart in hypertrophic cardiomyopathy is variably thickened, (from a few mm above normal, up to 2-3 times the normal). The vessels that carry blood to the heart are often also thickened and the blood supply may be insufficient, especially during effort (where more blood is required). Within the normal heart there is a certain degree of fibrosis (= scar tissue) which serves as an architectural and structural implant; in patients with hypertrophic cardiomyopathy, fibrosis can be increased and the fibers of the heart muscle can be oriented in a disorderly manner between them (so-called "disarrray" or misalignment). Valves can also be altered.
Left ventricular outflow tract obstruction
The left ventricular outflow tract is the portion of the left ventricle from which blood flows from the heart to the aorta (our body's main vessel) during cardiac contraction. In some patients (about 30% at rest and up to 60% under effort) there is an obstruction to the blood flow (=gradient) caused by the interposition of the mitral valve that during the cardiac contraction comes close to the outflow tract where there is the thickened interventricular septum (wall of the heart muscle that separates the left heart from the right heart) +. This particular movement of the mitral valve is called SAM (systolic anterior motion). This movement is often associated with a mitral valve insufficiency (= some blood goes back from the ventricle to the atria during cardiac contraction) which can be mild, moderate or severe. This obstruction increases the pressure inside the heart, which has to pump the blood against an obstacle; the degree of obstruction can vary from a few millimetres of mercury (30 mmHg) up to 100 mmHg or more. The obstruction is dynamic and can vary depending on the position (it increases standing up quickly), it increases with increasing contractility and heart rate (typically during exercise - in some patients the obstruction does not occur at rest, but only during effort), with heat and humidity and dehydration, after heavy meals and after ingestion of large amounts of alcohol; in addition, some drugs (often used to decrease blood pressure) may increase the gradient (ask your doctor).
Obstruction increases the cardiac workload and this can cause breathlessness (dyspnoea) (also linked to the fact that in patients with mitral insufficiency part of the blood flows back into the lungs), chest pain (angina), and reduction of blood supply to various organs, including the brain, causing dizziness and fainting (syncope).
Abnormalities of the cardiac release (diastolic dysfunction)
The heart muscle in patients with hypertrophic cardiomyopathy can be rigid, i.e. it has difficulty not so much in contracting but in relaxing itself (the diastole is the part of the heart cycle in which the heart relaxes), and therefore has problems in receiving circulating blood that accumulates upstream of the left ventricle and thus increases the filling pressures in the heart. The result of systolic dysfunction is therefore breathlessness or dyspnoea. In some forms (restrictive hypertrophic cardiomyopathy) diastolic dysfunction is the main abnormality.
Reduction in contraction capacity (systolic dysfunction)
A small proportion (around 5%) of patients with hypertrophic cardiomyopathy undergoes a so-called hypokinetic phase of the disease, a phase in which the heart has difficulty contracting, a clinical scenario similar to those observed in patients with dilated cardiomyopathy. There may be episodes of heart failure and often heart failure medications have to be taken, including beta-blockers, ACE-inhibitors, potassium sparing drugs and diuretics. These patients should be followed by Centers with expertise in the management of advanced heart failure.
Heart rhythm abnormalities (arrhythmias)
Arrhythmias are irregularities in the heart rhythm. They are classified as bradyarrhythmias, in which the heart goes too low (and which sometimes require a pacemaker implantation), and tachyarrhythmias, in which the heart goes too fast. Tachyarrhythmias may originate from the upper portion of the heart, or atria (atrial tachyarrhythmias) or from the lower portion of the heart, or ventricles (ventricular tachyarrhythmias). The most common atrial tachyarrhythmia is atrial fibrillation, where the electrical activity of the atria becomes very chaotic and irregular and the atria cannot contract in a coordinated manner. This results in an accelerated and irregular heartbeat, which patients often experience as arrhythmic palpitations, so anti-arrhythmic drugs are often recommended (the most used is amiodarone), or drugs to slow the heart beats (beta-blockers or calcium channel blockers). Atrial fibrillation favors the stagnation of blood within the atria, with the risk of clots forming, so it is recommended to use an oral anticoagulant, the most common is the Warfarin (trade name Coumadin), which serves to make the blood more fluid; the fluidity of the blood is monitored by a blood sample through the determination of the time of prothrombin, expressed as an International Normalized Ratio (INR), which should be maintained between 2 and 3.
Ventricular tachyarrhythmias can be either extrasystoles (extra beats from the ventricles), or more complex arrhythmias such as non-sustained ventricular tachycardia (few consecutive ventricular extrasystoles, but lasting less than 30 seconds) or sustained ventricular tachycardia (if lasting more than 30 seconds). Sustained ventricular tachycardia is the most dangerous and can cause fainting (syncope). There is a stratification of arrhythmic risk to identify patients prone to dangerous arrhythmias, some of whom may benefit from the implantation of an automatic defibrillator (ICD).
