GROWN-UP CONGENITAL HEART DISEASE & SCUBA DIVING
by Ulf ThilÚn MD (Cardiology), Lund, Sweden, Hans Írnhagen, MD (Naval medicine), Stockholm, Sweden
Background and general considerations
SCUBA diving has become an increasingly popular recreation, which also attracts the expanding population of patients with grown-up congenital heart disease. SCUBA is short for Self-Contained Underwater Breathing Apparatus and it is usually a shallow diving. The maximal depth is about 40 m.
Patients with grown-up congenital heart disease are often young and many are in a good shape. However, even so, there may be conditions or circumstances that disqualifies from SCUBA diving.
The experience of grown-up congenital heart disease and diving is low. However, considering the environmental factors of diving and the specific heart lesion a fairly good assessment of the risk of in-water incapacity can be made in most cases. In-water incapacity is a life threatening condition for both the diver him-/herself and the diving companions. They face the risk of drowning or of barotrauma. If in any doubt regarding the risk of in-water incapacity diving should be deterred. One must also understand that conditions mastered on land may have a deadly potential underwater.
As there are seldom formal medical regulations in sport diving the medical task is restricted to counseling. In this context it must be emphasized that a person unfit for diving puts not only the own life but also the lives of the buddy divers at stake when he or she dives.
And do not forget that the easiest way of abolishing the risks of diving is not to dive.
The cardiovascular stress of diving
Diving stresses the cardiovascular system in several ways. Diving is deceptively easy as the diver suddenly can be faced with requirements for vigorous exercise (swim against strong currents or rescue attempts)
Anxiety and emotional stress are common features in diving. This raises the sympathic tone, which in turn increases the heart rate and augments the blood pressure.
When diving in cold water vasoconstriction raises the blood pressure and puts a further load on the circulation.
The diving reflex induces peripheral vasoconstriction and slows the heart rate to keep the blood pressure unchanged. A sudden loss of the facemask in cold water may trigger this reflex acutely during a dive.
Immersion. In water there is a loss of gravitational pooling of the blood in the legs which cause a fluid shift into the central circulation and the distension of the right atrium gives (via atrial naturetic peptide) a reduction of the water reabsorption from primary urine and an increase of the urinary output. The increased pressure in the tissues also increases the reabsorption of interstitial fluid to the blood. In a compromised heart this may provoke pulmonary edema. Interstitial pulmonary edema after diving has also been observed in persons with no known heart disease.
Thus, the diver must have a certain exercise tolerance and must have a sufficient cardiovascular reserve. In professional diving several tests have been proposed and used. For recreational diving a normal or near normal physical working capacity as the lower limit seems reasonable.
Many grown-up congenital heart disease patients have had chest surgery. If the scar involves the pleura there is a theoretical risk of pathological air trapping if the adherence or scar restricts the movement of the lung or the gas flow in the airways, which in turn is a risk of pulmonary overpressure accidents. When the diver ascends pressure is reduced and gas expands. The lung may rupture if there are parts that are blocked off, not permitting the expanding gas to leave through the airways. When this happens gas may enter the arterial blood and embolise the central nervous system or the coronary arteries with serious symptoms. In the case of a lateral thoracotomy this risk is far greater than if it concerns a sternotomy with the surgical procedure not entering the pleural spaces (N.B. that coronary artery by-pass grafting with LIMA affects the pleura). A lateral thorocotomy is regarded as a contraindication for diving, at least without a thorough investigation by a pulmonary medicine specialist. When it comes to sternotomy sport diving is permitted provided pleural scarring is not involved.
Patent foramen ovale (PFO)
Decompression illness or bends may occur when a diver ascends too rapidly. Free gas bubbles then form in the venous blood and in the tissues. A serious form is neurological bends when the central nervous system is struck. There is a great individual variation in sensitivity and following the decompression table does not guarantee freedom from bends. Frequently, even in unprovocative dives venous bubbles are formed and flow into the pulmonary circulation and are dissipated in the lung without any symptoms. If that diver has a communication between the right and left atria these bubbles may transit to the arterial side and embolise if, for some reason, the right atrial pressure exceeds that of the left atrium.
In PFO there is a true valve function permitting exclusively a right to left shunt at the atrial level under certain circumstances. The incidence of PFO is 25-30 % in the general population but has been found to be much higher in divers who have experienced early neurological bends in spite of unprovocative dives. Although PFO is a risk factor for neurological bends - the diver must be informed - its presence does not necessarily disqualify from diving. However, if diving some precautions should be taken (from Dr. John Parker in The Sports Diving Medical):
In atrial septal defect (ASD) there is nearly always a small right to left shunt even if left to right shunting dominates; therefore ASD is considered as a contraindication for diving. In ventricular septal defect (VSD) the pressure gradient between the right and the left ventricle is small in diastole and a transient right to left shunt may occur. In a small VSD the amount of shunted blood this way, if it occurs, is little and it seems reasonable to apply the same precautions as in PFO (see above) if diving. However, there are diving medicals that consider even a small VSD incompatible with diving. In repaired ASD or VSD diving can be permitted provided there are no residual shunt and normal or near normal size of the heart chambers.
In isolated partial anomalous pulmonary venous drainage there is no risk of right to left shunting and if the lesion is of minor haemodynamic importance diving would not be restrained.
In small persistent ductus arteriousus (PDA), with minor haemodynamic importance, diving is permitted as there is no risk of right to left shunting; there is a large pressure gradient between the aorta and the pulmonary artery throughout the cardiac cycle.
From a strict cardiac point of view a surgically closed PDA would not hamper diving but often there is a lateral thoracotomy making diving dangerous. If the PDA is closed by means of a device with percutaneous transluminal approach diving is permitted provided there are no cardiac sequelae.
Left- and right-sided valvular lesions
Left side obstructive lesions carries a risk of pulmonary congestion when venous return raise or a risk of systemic hypotension if hypovolemia or vasodilation. Therefore mitral or aortic stenosis of any importance disqualifies from diving. When it comes to regurgitant lesions mild to moderate leaks are tolerated as long as the physical working performance is undisturbed. The same rules can be applied to right-sided valvular lesions, repaired or not.
A bicuspid aortic valve is a common lesion. Per se it does not affect the ability of diving. However, the risk of developing significant valvular dysfunction makes it mandatory to perform regular medical checks including an echocardiogram.
Prosthetic heart valves
There are different types of prosthetic heart valves. Mechanical heart valves carries a risk of thrombo-embolism necessitating anticoagulant treatment. As bruises and scratches are common when diving such a treatment may be hazardous. Patients with mechanical heart valves are recommended not to dive.
Xenografts and homografts do not have this drawback but carry a risk of degeneration, which makes a regular check of valve status necessary.
Tetralogy of Fallot
In repaired tetralogy of Fallot a number of conditions must be ruled out before the person can be cleared for diving. He, or she, must have a normal working capacity, must not have pleural adhesions after a lateral thoracotomy (from shunt surgery), must not have a residual VSD of any degree, must not have an outflow obstruction or regurgitation of haemodynamic importance and there must not be any haemodynamically significant arrhythmia.
Complex congenital heart lesions. Other entities.
Atrial corrected transposition of the great arteries (Senning/Mustard procedure) is a condition generally incompatible with diving because the cardiac response to exercise is often abnormal and there is a risk of bradyarrhytmia as well as tachyarrhythmia. Baffle leaks in the atria are very common and constitutes a risk of right to left shunting. Univentricular heart malformations palliated by means of a Fontan or TCPC (total cavo-pulmonary connection) procedure are incompatible with diving for several reasons. This is also true for unrepaired or palliated cyanotic congenital heart disease and hypertrophic cardiomyopathy.
Any arrhytmia associated with a risk of sudden incapacitation in-water is a cause of rejection for diving. In many cases of arrhythmia there is also an underlying structural cardiac disease which in itself disqualifies from diving. Low degrees of AV-block are of no importance in diving provided there is no structural heart disease and a normal chronotropic response to exercise. Higher degrees of AV-block make diving dangerous and it should be discouraged. In cases with atrial tachyarrhythmias diving is permitted provided they are successfully treated without any significant disturbance of normal cardiac response to exercise.
When treated with pacemaker the underlying cardiac disease is often disqualifying. However, there are exceptions, like congenital heart block. You must then consider the ability of the pacemaker case to withstand high pressure. Usually they withstand 2 to 4 atmospheres, which corresponds to a depth of 10 - 30 m (33 - 100 ft). There are variations and before diving the manufacturer's specification of that specific pacemaker must be checked. In order to get an adequate heart rate the pacemaker must be A-V sequential.
The patient with a preexcitation syndrome may give a history of arrhythmia and is then not suited for diving, unless the accessory pathway has been successfully ablated. In cases without arrhythmia many diving medicals would suggest a risk assessment and only allow the "low risk" patients to dive. If not "low risk" or if demanded by formal regulations (professional diving) ablation may make the person fit for diving.
Acquired heart disease
Also the grown-up congenital heart disease patient will become middle-aged or old and face the risk of acquired cardiovascular disease. Coronary artery disease and hypertension, wellknown causes of rejection for diving, must then be considered.