Coronary heart disease is the most common form of heart disease. It occurs when an accumulation of fatty substances in one of the coronary arteries reduces or interrupts the blood flow to the heart.
Over time, fatty material can build up inside the coronary arteries, forming deposits called atheroma — a process known as atherosclerosis. When this condition progresses, the diameter of the arteries may become insufficient to meet the heart’s oxygen needs. If a piece of atheroma breaks off, it can obstruct the coronary artery, cutting off blood and oxygen supply to the heart muscle. When the resulting blood supply is insufficient and a section of the heart muscle dies, this is known as a myocardial infarction.
People with heart disease should exercise for at least 150 minutes a week at a moderate intensity. This means that the heart rate and respiratory rate should be increased while being able to hold a conversation at the same time.
Understanding Coronary Artery Bypass Grafts (CABG)
Coronary artery bypass grafting (CABG), commonly referred to as “cabbage,” is a procedure performed to improve blood flow to the heart muscle by creating a detour around blocked coronary arteries. This surgical correction involves opening the chest and grafting a piece of vein or artery from elsewhere in the body onto the damaged vessel. The graft, typically from the internal mammary artery, is connected to the coronary artery, bypassing the blocked segment.
Angioplasty is a minimally invasive procedure used as an alternative treatment for coronary artery disease caused by atherosclerosis. It is typically considered when medications or lifestyle modifications are insufficient, or in cases of acute myocardial infarction, worsening angina, or other related symptoms. The procedure involves inserting a catheter with a small balloon into the narrowed artery and inflating it to restore blood flow. A stent, a tubular mesh device, is often placed to help keep the artery open and reduce the risk of future blockages. Unlike CABG, angioplasty does not require opening the chest and is often performed on an outpatient basis.
Precautions for Individuals with CABG
Scuba diving places a greater demand on the heart. In a study by Denoble, P. and colleagues examining divers over 60 years of age, 26% of the disabling injuries during diving corresponded to cardiac events. Be mindful that entering the water generates peripheral vasoconstriction and a greater amount of blood reaching the thorax, which increases cardiac preload and consequent arterial hypertension.
The maximum oxygen consumption (VO2max) is used to evaluate a person’s aerobic capacity. A recreational diver who achieves VO2max levels of 20 ml/kg/min, 6-7 METs (metabolic equivalents), will be able to handle most diving situations without cardiovascular complications. To achieve this maximum oxygen consumption, it is essential to have optimal cardiac muscle mass and coronary arteries.
Many divers have resumed diving after coronary artery bypass grafting or coronary artery stenting. Returning to diving depends on the ability to exercise without experiencing ischemia after revascularization, and the fact that diving does not place excessive stress on the cardiovascular system.
Diving Safety Measures for Individuals with CABG
Individuals who have undergone open chest surgery require proper medical evaluation before diving. After a period of rehabilitation and healing (6 to 12 months is usually recommended), the person should undergo a comprehensive cardiovascular assessment before receiving clearance to dive. Candidates must be free of chest pain and demonstrate normal exercise tolerance.
Many divers have returned to diving after coronary bypass surgery, albeit with reduced cardiovascular capacity. In controlled environments — warmer water with minimal wind or current, avoiding night diving and enclosed spaces — individuals with coronary artery disease and good left ventricular function may dive with an energy expenditure not exceeding 4 METs (i.e., 8 METs of maximum capacity). A person who has suffered a myocardial infarction with extensive necrosis (death) of cardiac muscle tissue should not return to diving because of the inability to meet cardiac pumping demand due to increased exertion during the dive.
Implications in Diving
The practice of scuba diving carries significant implications for individuals who have undergone coronary artery bypass surgery. Following this surgery, there are important medical considerations that may affect a diver’s ability to safely participate in diving activities.
For the Diver
- After coronary artery bypass surgery, as a diver, you should be aware that there are potential risks associated with scuba diving. The underlying coronary artery disease that led to the need for bypass surgery may still be present, increasing the risk of cardiac complications during diving.
- In addition, the presence of vascular grafts and scarring of cardiac tissue may affect the heart’s response to the unique physiologic demands imposed by scuba diving.
For the Dive Operator
- Divers with a history of CABG may be at higher risk for cardiac events and represent a liability for you as a dive operator. CABG itself does not preclude diving if the patient has recovered successfully, but the underlying coronary artery disease remains a concern.
- Key considerations for dive operators include:
- Medical clearance: Documentation of cardiac function post-CABG and specialist clearance for diving is essential.
- Fitness to dive: Comorbidities, medications, functional capacity, and time elapsed since CABG should be evaluated when reviewing medical fitness.
- Environmental factors: Cold temperatures, strenuous dives, and high stress environments could exacerbate underlying heart disease.
- Remoteness: Consider the risk of a cardiac event in remote environments such as liveaboards, where arranging and carrying out a timely rescue and transfer to advanced medical care may take an unacceptably long time.
- Emergency response: Operators must be prepared to handle potential cardiac events and have emergency oxygen, an AED, and evacuation procedures in place.
- Insurance coverage: Disclosing dive candidates with CABG history is prudent, as it may preclude coverage or affect policy premiums.
For the Physician
- As the cardiologist, you would conduct a thorough assessment of the patient’s current cardiovascular status including functional capacity, left ventricular function, arrhythmia risk, and coronary artery disease progression. While CABG might not necessarily be an absolute contraindication to dive, the underlying coronary disease remains a concern.
- Key considerations for physicians include:
- Time since CABG: Recovery of heart function and grafts takes time. A minimum of 6 months post-CABG is recommended before considering diving.
- Functional capacity: Exercise stress testing can assess exercise tolerance, ECG changes, arrhythmias, and myocardial perfusion. Adequate exercise capacity is required.
- Cardiac imaging: Echocardiography, nuclear imaging, or cardiac MRI to evaluate ventricular function, wall motion abnormalities, and patency of grafts.
- Cardiac rhythm: Monitoring can identify arrhythmias which could be triggered underwater.
- Coronary artery status: Further progression of coronary disease could impair exercise capacity.
- Comorbidities: Other risks like diabetes, hypertension, and obesity must be optimized.
- Specialist clearance: If fitness to dive is demonstrated, provide a detailed clearance letter.
- Medications: Anti-platelet, beta blockers, ACE inhibitors and statins may be required to manage the ongoing disease. It is important to bear in mind that once the causes of the coronary obstruction have been overcome, patients very often receive adjuvant medication both for the treatment of the sequelae left by the obstruction of one of the coronary arteries and preventively to minimize the possibility of a new arterial obstruction.
- Anti-platelets: When a diver is taking anticoagulants or anti-platelet agents, internal bleeding will be difficult to control. This is why ordinary ENT barotrauma can quickly evolve into a real medical emergency, particularly in remote settings.
- Beta-blockers: These medications may pose risks during diving. By limiting the heart’s ability to increase its output in response to sudden demands, they can reduce cardiac performance to the point of inadequate circulation, potentially leading to loss of consciousness underwater.
References
- Buzzacott, P., et al. “Exercise intensity inferred from air consumption during recreational scuba diving.” Diving and Hyperbaric Medicine, vol. 44, no. 2, June 2014, pp. 74-78.
- Begin, R., et al. “Effects of water immersion to the neck on pulmonary circulation and tissue volume in man.” Journal of Applied Physiology, vol. 40, no. 3, March 1976, pp. 293-299.
- Pollock, Neal. “Measuring aerobic fitness in divers.” Diving and Hyperbaric Medicine, 2014.
- Borjesson, M., et al. “Cardiovascular evaluation of middle-aged/senior individuals engaged in leisure-time sport activities: Position stand from the Sections of Exercise Physiology and Sports Cardiology of the European Association of Cardiovascular Prevention and Rehabilitation.” European Journal of Cardiovascular Prevention & Rehabilitation, vol. 18, no. 3, June 2011, pp. 446-458.