Extra Topic 5.8 -- Hypertrophic Obstructive Cardiomyopathy

Question 1

Will you agree to an epidural anesthetic?

(A 22-year-old parturient with a history of hypertrophic obstructive cardiomyopathy is in labor and requesting an epidural for pain control.)

Answer 1

After ensuring euvolemia in order to maintain adequate preload,

I would agree to the placement of an epidural anesthetic.

The concern in providing neuraxial anesthesia to a patient with hypertrophic obstructive cardiomyopathy (HOCM) is that – a sympathectomy-induced reduction in systemic vascular resistance (SVR) may lead to reduced preload and the subsequent development or exacerbation of left ventricular outflow tract (LVOT) obstruction.

However, as long as euvolemia is maintained, epidural anesthesia may be safely employed to achieve levels sufficient for vaginal or surgical delivery.

Moreover, since the low thoracic levels required for adequate analgesia during vaginal delivery (T10) are unlikely to result in significant sympathectomy, I could also choose to utilize low dose spinal anesthesia for her delivery.

However, if cesarean delivery were necessary, I would AVOID spinal anesthesia due to the increased risk of reduced preload associated with the rapid onset of a high thoracic neuraxial block (hypotension is more likely to occur with a rapid sympathectomy to the level of T4).

Question 2

What is HOCM?

(A 22-year-old parturient with a history of hypertrophic obstructive cardiomyopathy is in labor and requesting an epidural for pain control.)

Answer 2

Hypertrophic obstructive cardiomyopathy (HOCM) = is a genetic condition characterized by –

• left ventricular hypertrophy,
• systolic anterior movement of the mitral valve (SAM),
• dynamic left ventricular outflow tract (LVOT) obstruction,
• decreased left ventricular size,
• diastolic dysfunction,
• myocardial ischemia (even in the absence of coronary artery disease), and
• dysrhythmias (these dysrhythmias are responsible for the sudden death that may occur in young adults with HOCM).

In patients with HOCM, hyperdynamic left ventricular contraction of the hypertrophied septum results in the rapid movement of blood through the narrowed LVOT creaing a Venturi effect on the anterior leaflet of the mitral valve.

• This Venturi effect leads to SAM, which in turn leads to dynamic LVOT obstruction and mitral regurgitation.

While many patients with HOCM are asymptomatic, others experience dyspnea, angina, fatigue, lightheadedness, syncope, tachydysrhythmias, and heart failure.

Physical examination of these patients often reveals – abnormal ECG findings, such as –

• left ventricular hypertrophy, left atrial enlargement, high QRS voltage, ST-segment and T-wave changes, and abnormal Q-waves (similar to those present following myocardial infarction).

Moreover, echocardiography may demonstrate –

• asymmetrical hypertrophy of the intraventricular septum,
• a normal ejection fraction (due to the hypercontractile condition of the heart),
• SAM,
• LVOT obstruction (a valsalva maneuver may be required to induce LVOT obstruction),
• mitral regurgitation,
• pressure gradients across the LVOT, and
• diastolic dysfunction.

A definitive diagnosis, however, is made by endomyocardial biopsy and DNA analysis (performed when unable to establish the diagnosis by other means).

Question 3

What factors lead to, or exacerbate, left ventricular outflow tract obstruction?

(A 22-year-old parturient with a history of hypertrophic obstructive cardiomyopathy is in labor and requesting an epidural for pain control.)

Answer 3

The dynamic outflow obstruction associated with HOCM is accentuated by any intervention or event that results in a reduction in left ventricular end diastolic volume.

Therefore, the obstruction is potentially exacerbated by the following conditions:

1. hypovolemia (reduced preload);
2. sympathectomy and/or vasodilation (decreased SVR/afterload, which facilitates left ventricular emptying);
3. increased myocardial contractility (increased left ventricular emptying);
4. tachycardia (reduced diastolic filling time);
5. sympathetic stimulation (tachycardia and/or increased inotropy) ;
6. dysrhythmia (inadequate ventricular filling);
7. excessive positive-pressure ventilation and/or PEEP (decreased preload); and,
8. in this case, inadequate left uterine displacement (decreased preload).

Question 4

The uterus is “boggy” following delivery. What will you do?

(A 22-year-old parturient with a history of hypertrophic obstructive cardiomyopathy is in labor and requesting an epidural for pain control.)

Answer 4

Recognizing that the systemic vasodilation and reflex tachycardia often associated with the administration of oxytocin could accentuate LVOT obstruction,

I would consider administering –

• an intramuscular injection of methylergonovine (methergine) or
• intravenous 15-methyl prostaglandin F2-alpha (Hemabate) to induce uterine contraction.

I would avoid the intravenous injection of methergine due to the increased risk of acute hypertension, seizures, cerebrovascular accident, retinal detachment, and myocardial arrest associated with this route of administration.

If I believed it was necessary to administer oxytocin, I would give it very slowly to reduce the risk of a significant reduction in SVR>

Question 5

Shortly after delivery, the patient develops dyspnea and pulmonary edema.

What is your differential?

(A 22-year-old parturient with a history of hypertrophic obstructive cardiomyopathy is in labor and requesting an epidural for pain control.)

Answer 5

The diastolic dysfunction associated with HOCM places these patients at increased risk of developing pulmonary edema with fluid overload.

• Therefore, the timing of this event suggests that her pulmonary edema may be secondary to – the abrupt autotransfusion of blood into the central circulation that occurs with post-delivery uterine contraction and involution.
• However, recognizing that patient with HOCM are at increased risk of developing myocardial ischemia, I would also consider the possibility of left heart failure secondary to myocardial ischemia or infarction.
• Another consideration would be that the “bearing down” (valsalva-induced reduction in preload) and/or pain (sympathetic-induced tachycardia and/or inotropy) occurring during delivery resulted in worsening LVOT obstruction, with subsequent left heart failure.
• Other considerations would include –
  
  • hypovolemia (excessive blood loss secondary to uterine atony or other cause),
  • a sympathectomy-induced decrease in SVR (due to excessive level of neuraxial anesthesia),
  • cardiac arrhythmia,
  • thrombotic embolism (pregnant patients are hypercoagulable), and
  • amniotic fluid embolism.

Question 6

Assuming her pulmonary edema was secondary to worsening LVOT obstruction, how would you treat her condition?

(A 22-year-old parturient with a history of hypertrophic obstructive cardiomyopathy is in labor and requesting an epidural for pain control.)

Answer 6

My treatment would be aimed at the correction or elimination of factors that could be accentuating her dynamic LVOT obstruction.

Therefore, I would ensure adequate volume replacement and treat any hypotension, tachycardia, and/or dysrhythmia.

More specifically, I would administer a B-blocker to slow her heart rate, prolong diastolic filling time, and decrease myocardial contractility.

If she were hypotensive, I would administer phenylephrine (the tachycardia assocaited with ephedrine administration would be undesirable) and ensure adequate volume replacement.

If intubation and positive pressure ventilation became necessary, I would perform a rapid sequence induction (assuming a reassuring airway) and begin positive pressure ventilation with smaller tidal volumes and an appropriately increased ventilatory rate (to avoid the decreased preload associated with excessive intrathoracic pressures).

While PEEP and diuretics are often utilized in the treatment of pulmonary edema, these interventions would potentially reduce her cardiac preload, thereby accentuating LVOT obstruction, the primary cause of her pulmonary edema.