Extra Topic 6.4 -- Denervated Heart

Question 1

You see two P-waves for every QRS complex on his ECG tracing. What do you think?

(A 52-year-old male is scheduled for total hip arthroplasty. His history includes severe asthma and a heart transplant 2 years ago.)

Answer 1

The non-conducted P-wave is unlikely to represent atrioventricular block, but rather,

is originating from residual native atrial tissue.

The impulse from the native sinus node is unable to traverse the anastomotic line and, therefore, does not result in ventricular contraction and the generation of a QRS complex on ECG.

Question 2

You agree to general anesthesia, based on patient preference. What monitoring would you employ?

(A 52-year-old male is scheduled for total hip arthroplasty. His history includes severe asthma and a heart transplant 2 years ago.)

Answer 2

The monitoring requirements for a heart transplant recipient undergoing noncardiac surgery are similar to those for nontransplant patients undergoing a similar procedure.

However, this is a preload dependent patient (the denervated heart primarily increases cardiac output by increasing stroke volume via the Frank-Starling mechanism, rather than heart rate),

at increased risk for accelerated coronary atherosclerosis (44% in the first 10 years following transplant) and arrhythmias,

undergoing a procedure associated with significant blood loss and hemodynamic instability (secondary to intraoperative hemorrhage, bone cement implantation* *syndrome*, and/or *thromboembolism).

Therefore, special monitoring that I would employ include:

1. a 5-lead ECG, to detect ischemia and/or dysrhythmias;
2. an arterial line, to facilitate the rapid assessment and treatment of hemodynamic instability;
3. a central line, to facilitate fluid management and maintenance of preload (**Note – is central line to be placed in certain area, however?? check this),
4. a Foley catheter, to help monitor renal function (cyclosporine is nephrotoxic) and volume status; and
5. a peripheral nerve stimulator, to carefully monitor neuromuscular blockade, recognizing that immunosuppressive drugs have varying effects on neuromuscular-blocking drugs (azathioprine may antagonize the drugs, while cyclosporine may potentiate their effects).

Moreover, indefinite immunosuppressive therapy increases the risk of infection in heart transplant patients. Therefore, I would ensure a strict aseptic technique when placing invasive monitors, and I would only employ this type of monitoring when I felt that the benefits outweighed the risk of infection.

Clinical Note:

• The Frank-Starling mechanism describes an increase in stroke volume that results from more forceful cardiac contraction in response to increased cardiac filling and ventricular wall stretching.

Question 3

The anesthesia resident working with you asks if she can try a nasal intubation. What would you say?

(A 52-year-old male is scheduled for total hip arthroplasty. His history includes severe asthma and a heart transplant 2 years ago.)

Answer 3

I would tell her that nasal intubation is associated with an increased risk of infection from nasal flora.

Therefore, since this patient is at increased risk for infection secondary to immunosuppressive drug therapy, I would avoid nasal intubation, if possible.

Clinical Note:

• Immunosuppressive therapy usually includes – cyclosporine, azathioprine, and prednisone.

Question 4

How would you induce this patient?

(A 52-year-old male is scheduled for total hip arthroplasty. His history includes severe asthma and a heart transplant 2 years ago.)

Answer 4

GIve this patient’s severe asthma and preload dependence (in the denervated heart, compensatory increases in cardiac output are achieved by increased stroke volume, rather than increased heart rate),

I would –

• optimize his asthmatic condition with a B2-agonist,
• ensure the presence of isoproterenol (a pure B-agonist), and
• perform a slow controlled induction, with the goal of avoiding a significant drop in systemic vascular resistance,
• while at the same time, achieving a depth of anesthesia sufficient to prevent bronchospasm. To achieve this, I would utilize etomidate combined with narcotics.

Clinical Note:

• Isoproterenol:
  
  • A potent B1 and B2 adrenoceptor agonist
  • Direct action on B-receptors makes it a good choice in patients with a cardiac transplant
  • B1 receptor stimulation increased cardiac output (inotropic and chronotropic effects)
  • B2 receptor stimulation leads to bronchodilation (smooth muscle relaxation)
  • No alpha adrenergic activity

Question 5

You plan to reverse muscle relaxation with neostigmine. Do you need to administer a muscarinic antagonist, like glycopyrrolate, to a patient who has received a transplanted heart?

(A 52-year-old male is scheduled for total hip arthroplasty. His history includes severe asthma and a heart transplant 2 years ago.)

Answer 5

I would administer a muscarinic antagonist, recognizing that cholinesterase inhibitors (i.e. neostigmine) have been reported to cause bradycardia (muscarinic effect) in transplanted hearts, especially after 6 months when partial cardiac reinnervation sometimes occurs.

Moreover, even in the absence of muscarinic effects on the heart, it would be desirable to block other peripheral muscarinic effects such as bronchospasm and increased salivation.

Question 6

The postop nurse asks if she can administer an NSAID for pain control.

What would you say?

(A 52-year-old male is scheduled for total hip arthroplasty. His history includes severe asthma and a heart transplant 2 years ago.)

Answer 6

These patients are at increased risk for –

• underlying renal dysfunction, secondary to nephrotoxic immunosuppressive drugs (cyclosporine), and
• gastritis, secondary to chronic steroid use.

Therefore, I would not administer an NSAID, which could further exacerbate both of these undesirable complications.