Extra Topic 4.2 -- Mitral Valve Prolapse

Question 1

Does she need further cardiac evaluation prior to surgery?

(A 34-year-old female with a history of mitral valve prolapse (MVP) is scheduled for shoulder arthroscopy in the sitting position. She is otherwise healthy and taking no medications.)

Answer 1

The presence of asymptomatic mitral valve prolapse uncomplicated by other medical conditions is not a sufficient reason for further cardiac testing.

However, if her MVP were associated with significant mitral regurgitation, syncope, chest pain, or symptoms of congestive heart failure, further testing may be warranted.

Therefore, I would begin by performing a focused history and physical exam to illicit signs and symptoms of congestive heart failure or myocardial ischemia such as angina, orthopnea, dyspnea on exertion, exercise tolerance, peripheral edema, pulmonary rales, S3 gallop, systolic ejection click, or murmur.

If she reported significant symptomatology that was insufficiently evaluated by previous cardiac workup, I would consider pre-operative echocardiographic evaluation.

Cardiac echocardiography would be helpful in identifying any mitral regurgitation and the presence or absence of a patent foramen ovale, with the latter being important due to the increased risk of air embolism when undergoing surgery in the sitting position (in the presence of a patent foramen ovale, an air embolism may pass into the coronary or cerebral circulations).

Question 2

After induction the patient is placed in the sitting position.

Her blood pressure drops to 63/38 and heart rate is 90.

What do you think is the cause?

(A 72-year-old female undergoing CABG is about to go on bypass. The patient was given a standard heparin dose, but the ACT is still low.)

Answer 2

Since normal autonomic responses may be impaired under general anesthesia, her hypotension may simply represent an uncompensated decrease in blood pressure with movement into the head-up position.

However, I would also consider potential contributing factors, such as –

• hypovolemia;
• the systemic vasodilation and myocardial depression associated with excessive anesthesia;
• dysrhythmias (often associated with MVP); and
• the development of acute mitral regurgitation and decreased cardiac output.

The latter may occur because patients with MVP often experience worsening prolapsed and/or mitral regurgitation with increased emptying of the left ventricle.

Therefore, factors such as –

• tachycardia (decreased filling time),
• increased myocardial contractility (sympathetic stimulation and inotrope administration),
• decreased systemic vascular resistance (decreased afterload),
• hypovolemia (reduced filling), and
• assumption of the upright posture (decreased filling)
  
  • may result in –
    
    • acute mitral regurgitation,
    • decreased cardiac output, and
    • hypotension.

Finally, I would consider less likely causes, such as –

• myocardial ischemia,
• tension pneumothorax, and
• pulmonary embolism.

Question 3

How would you treat this patient?

(A 72-year-old female undergoing CABG is about to go on bypass. The patient was given a standard heparin dose, but the ACT is still low.)

Answer 3

I would –

• inform the surgeon,
• return the patient to the supine position,
• evaluate the EKG,
• auscultate the chest for cardiac murmurs and bilateral ventilation,
• ventilate with 100% oxygen,
• give a fluid bolus,
• administer a pure alpha-1-agonist such as phenylephrine (the tachycardia associated with the administration of an indirect vasoconstrictor, such as ephedrine, may worsen mitral valve prolapse and mitral regurgitation), and
• consider reducing my anesthetic.

During treatment, I would avoid agents that would increase cardiac contractility and accentuate mitral regurgitaiton.

If she remained unstable despite these interventions, I would utilize TEE to further evaluate her cardiac condition.