Patients that have valvular or some form of congenital heart disease have an excess strain situation that is particularly susceptible to the effects of increased exercise and blood shifting intoo the heart and lungs due to water immersion.
The presence of an abnormality per se is not a contraindication to diving. In the case of intracardiac shunts due to holes in the walls, and in the presence of significant valve narrowing or widening inside the heart, diving is contraindicated.

Pathophysiological Principles

In considering the pathophysiology of congenital and valvular heart disease one should be aware of the effect of the lesions on the heart muscle. Overload lesions of the heart can be classed as either pressure or volume overload types.

Pressure overload lesions include the enlargement of the left ventricle of the heart that results from blockage of the blood due to narrowing of the aortic valve (aortic stenosis), whereas volume overload of the left side of the heart (ventricle) can occur from leaking aortic and mitral valves (aortic or mitral regurgitation) or in the right side of the heart from a hole between the upper chambers (atria) or atrial septal defect. The response of the heart muscle to these overload states depends on whether the overload is a pressure or volume type. The myocardium appears to adapt specifically to handle the type of load imposed.

The endocardium is the lining of the heart and is the first area that is damaged by a reduction in blood supply (ischemia). This occurs for several reasons: first, the forces in the subendocardial layers of the myocardium are higher, thus requiring somewhat greater oxygen demand from the cells of the endocardial regions; second, the resistance vessel of the sub-endocardium are most distant from the supplying arteries which reside in the epicardium. Early enlargement and thickening, which may even be undetected by electrocardiogram, can be associated with evidence of subendocardial ischemia detected by exercise stress testing.

Fortunately, the changes induced in the endocardium by maldistribution of blood flow during exercise is often detected by the exercise stress test, which can be used to evaluate the presence or absence of ischemia in patients who have volume or pressure overloads due to acquired or congenital heart disease. Although there are specific contraindications, it is possible to allow selected patients with congenital or valvular heart disease to dive (see table below).

The basic principle of reproducing the diving exposure in the controlled environment of the exercise stress test with electrocardiographic and blood pressure monitoring should be followed. This information is then used to determine individual’s exercise capacity. By approaching the patient with valvular or congenital heart disease in this manner, it is possible to allow some candidates to dive if the lesion is small and no right to left shunts exist.

CIRCULATORY CONSIDERATIONS IN VALVULAR AND CONGENITAL DISEASE

Some circulatory abnormalities which are present in acquired valvular and congenital heart disease need special consideration when evaluating diving candidates. Patients with circulatory obstruction such as aortic stenosis, mitral stenosis, aortic coarctation, or pulmonic stenosis have limitations to exercise because of the narrowed segment of the circulation.
Fainting with Exercise
When an imbalance occurs between the bodies’ circulatory demand and cardiac output, blood pressure will fall and the patient will develop syncope (fainting). This is the probable mechanism for sudden death in patients with narrowed aortic valve (aortic stenosis). These patients should not be approved for diving. This approach to the diving candidate is similar to that taken for competitive sports.

Patients with leaky valves or shunt lesions (holes in the wall between the right and left sides of the heart) are generally less likely to develop syncope or low blood pressure (hypotension) with diving, but are more likely to develop heart failure with pulmonary congestion and associated severe shortness of breath from combined exercise and water immersion. Considerations mentioned above apply both to valvular regurgitation and to shunt lesions such as atrial and ventricular septal defect. In patients with minimal or no symptoms who have either atrial or ventricular septal defects, if pressures in the central circulation are normal, the shunt will be directed from left to right and no arterial desaturation occurs. Any patient with a right to left shunt and low arterial oxygen levels (hypoxemia) will normally have severely limited exercise capacity.

In diver candidates with atrial or ventricular septal defects, during decompression, there is a risk of venous bubbles getting into the arterial circulation without the filtering effect of the lungs, causing cerebral embolization. Since intra-atrial and intra-ventricular shunts can be bidirectional at different phases of the cardiac cycle, presence of an atrial or ventricular septal defect is generally thought to be a contraindication to diving. Persons with atrial septal defects and patent foramen ovale should have the defect repaired. However, ventricular pressures are normally higher in the left ventricle and right to left shunts are rare. The diver who is found to have a ventricular septal defect should be studied with exercise stress testing and an echocardiogram. If the shunt is small, there is no evidence of heart failure or strain and if the shunt is left to right – the person should be advised of the risks and allowed to continue diving.