Journal Meeting

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Journal Meeting

• References
• 1.Slater EE, Dougenis Surgery of the thoracic
  aorta. Am Heart J 3361876-1888,1997
• 2.Pretre R. Von Segresser LK Aortic dissection.
  Lancet 3491461-1464,1997

?? ??? 92-1-4
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Aortic dissection

• Definition
• ?tear in the intima of aorta (blood through
  the tear and dissects into the media of aorta .
  The hematoma ? progress along the coarse of the
  aorta and occlude any of the arterial branches of
  the aorta) or Retrograde dissection involved
  coronary artery.

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Where is the intimal tear located?

• 70?located in ascending aorta
• 10?aortic arch
• 20?descending thoracic aorta

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Frequency and motality of aortic dissection

• In USA, new cases 2000/ year
• Incidence 520/million
• Mortality up to 90 within 3 months if untreated
  after diagnosis

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Classifications

• 1. DeBakey classification
• 2. Stanford classification

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Pathophysiologic mechanisms

• 1. Rupture and tearing of the intima of aorta,
  and development of an intramural hematoma
• 2. Spontaneous rupture of the vaso vasorum
  (occurs in lt10 patient)

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Clinical manifestation

• Manifestation
• Pain gt 90
• vasovagal symptoms
• Syncope 5
• neurologic deficit 20

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Pain

• the most common complaint (gt 90 of cases).
• tearing, ripping, different patients in
  many different ways.
• Typically ? abruptly and is most severe at onset.

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• Aortic dissection accompanied by vasovagal
  symptoms
• diaphoresis, nausea, vomiting, light-headedness,
  and severe apprehension.
• Syncope
• most associated with ascending aorta dissection
• dissection into the pericardium?pericardial
  tamponade
• Other causes of syncope secondary to aortic
  dissection are hypovolemia, excessive vagal tone,
  and cardiac conduction abnormalities.

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• In approximately 20 of patients, neurologic
  deficit is the presenting manifestation of aortic
  dissection.
• The neurologic presentations are CVA, spinal cord
  ischemia, and peripheral nerve ischemia

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PE

• Appearance very apprehensive
• Tachycardia and signs of inadequate end-organ
  perfusion may be present even in the face of an
  elevated blood pressure.
• e.g., clammy skin, altered mental status, delayed
  capillary refill
• chronic hypertension gt 75 of patients
• may be exacerbated by a catecholamine release
  related to the acute event

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• Severe hypertension refractory to medical therapy
  
• may occur if the dissection involvesthe renal
  arteries with subsequent renin release
• hypotension
• dissection has progressed back into the
  pericardium with resulting pericardial tamponade
• hypovolemia occurred from rupture along the aorta
• pseudohypotension
• the blood pressure in the arms is low or
  unobtainable and the central arterial pressure is
  normal orhigh.
• results from the interruption of blood flow to
  the subclavian arteries

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Pulse deficits and discrepancies in blood
pressure between limbs

• Pulse deficits(a unilaterally weakened or absent
  pulse) in almost 50 of patients with proximal
  dissections
• Usually in the upper extremities
• mechanisms
• An intimal flap cover the true lumen of a branch
  vessel
• dissecting hematoma compress an adjacent true
  lumen.
• Careful documentation of pulses and frequent
  reexamination are important because pulse
  deficits are commonly transient

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Lab

• Routine Laboratory Tests.
• of little value.
• Serial analysis of cardiac enzymes is usually
  negative.
• Microscopic hematuria may occur where the renal
  artery is involved

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EKG

• EKG
• Useful in excluding MI however, 10 to 40 of
  patients with aortic dissection may have EKG
  abnormalities suggesting ischemia or infarction
• Acute MI
• Proximal dissection ? coronary artery
• Heart block
• retrograde dissection ? interatrial septum with
  compression of the AV node

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CXR

• Routine chest x-ray studies will be abnormal in
  80 to 90 of cases.
• mediastinal widening gt75 of cases.
• The calcium sign uncommon but highly specific
• the calcium deposit separated from the outermost
  portion of the aorta gt 5 mm
• Double-density appearance of the aorta
• suggesting true and false channels

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CXR

• localized bulge along a normally smooth aortic
  contour
• disparity in the caliber between the descending
  and ascending aorta
• Displacement of the trachea or nasogastric tube
  to the right by the dissection
• Previous CXR very useful for comparison
• Pleural effusions are common and usually occur on
  the left side
• small effusion periaortic inflammation
• a large effusion leaking or rupture of the
  dissection into the pleural space? Thoracentesis

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TEE

• Dramatically improved the quality of
  echocardiography in the diagnosis of aortic
  dissection
• 97 to 100 sensitive and 90 to 100 specific
• difficulty in evaluating the ascending aorta and
  proximal arch because of the interposition of the
  air-filled trachea and left main bronchus, but
  this problem has been largely overcome by the use
  of the newer biplane probes.

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TEE

• TEE is excellent at detecting pericardial
  effusion and compares favorably with other
  modalities in evaluating aortic regurgitation,
  flow in the proximal coronary arteries, the
  intimal flap, and site of entry.
• For these reasons, TEE has become the primary
  diagnostic method for detecting aortic dissection
  in many institutions

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CT

• both false-positive and false-negative diagnoses
  of aortic dissection appear to be less than 5.
• Signs on the CT scan ?particularly suggestive of
  aortic dissection include dilatation of the
  aorta, identification of an intimal flap,
  differential rates of flow in true and false
  channels, and the clear demonstration of both the
  false and true lumina.

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CT

• does not provide information about the presence
  of aortic regurgitation, which is important in
  determining appropriate therapy
• Fails to provide reliable information about the
  relationship of the dissection to the major
  arterial branches of the aorta
• Some patients have serious adverse reactions to
  the administration of IV contrast material
• A CT scan is time consuming and requires the
  patient to be outside of the ED or intensive care
  unit

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Aortography

• In most institutions, aortography remains the
  standard imaging modality for detection of aortic
  dissection against which all other modalities are
  measured
• In skilled hands, this procedure can be performed
  with low morbidity and mortality and with high
  diagnostic accuracy

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The disadvantages of aortography

• invasive techniques? requires that a catheter be
  inserted into a potentially abnormal aorta.
• It is also the most expensive of the modalities
  available.
• Specialized personnel are required, and the
  patient must be removed from the ED.
• Other disadvantages are the risks of IV contrast
  material and inadequate detection of pleural leak

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advantages of aortography

• Despite these limitations, aortography remains an
  informative procedure to diagnose aortic
  dissection.
• It is a sensitive test for detecting aortic
  dissection and very accurate for determining the
  site of the intimal tear and the extent of the
  dissection
• Aortic regurgitation is easily demonstrated with
  aortography, and it is the only procedure that
  demonstrates the extent and location of
  dissection into aortic side branches

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MRI

• For the evaluation of the stable patient with
  suspected aortic dissection
• Useful in
• the evaluation of chronic aortic dissection,
• in the follow-up of postoperative patients
• for monitoring nonoperative patients for
  progression of the dissection

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TREATMENT

• careful monitoring of cardiac rhythm, blood
  pressure, and urine output
• eliminate the forces favoring progression of the
  dissection by maintaining systolic blood pressure
  between 100 and 120 mm Hg (or the lowest level
  commensurate with vital organ perfusion) and by
  reducing the force of cardiac contraction and the
  rate of rise of the arterial pulse (dP/dT).

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• Narcotics should be administered in adequate
  amounts for pain control
• Therapy should begin immediately to attain these
  goals while other diagnostic tests are performed
• The early hours are a critical period
• The mortality in the first 24 to 48 hours of
  aortic dissection is between 1 and 2 per hour.
• Those patients presenting with hypotension
  secondary to aortic rupture or pericardial
  tamponade should be resuscitated with IV fluids
  and blood transfusions
• More typically, the patient will be hypertensive

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Sodium nitroprusside

• Prompt reduction of the blood pressure can be
  accomplished with sodium nitroprusside
• 50 to 100 mg are mixed in 500 ml of D5W and
  initially infused at a rate of 0.5 to 3 mg/kg/min
• The rate is adjusted to achieve the desired blood
  pressure
• The solution is light sensitive, and the bottle
  and tubing containing the mixture should be
  wrapped in aluminum foil

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• Because sodium nitroprusside increases the heart
  rate and may also increase the dP/dT,
  administration of this drug alone may worsen the
  dissection
• A b-adrenergic blocker must be used in
  conjunction with sodium nitroprusside to lower
  the dP/dT
• Propranolol
• more selective b-blocking agent such as
  metoprolol.
• Esmolol short-acting (continuous infusion)

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• Trimethaphan camsylate
• effective in the initial treatment of acute
  aortic dissection
• It is generally used as a single agent and is the
  preferred drug in a patient who has a
  contraindication to b-blockers
• IV labetalol
• This drug has both a- and b-blockade properties
• May be used as a single agent for the management
  of aortic dissection

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Definitive Therapy

• Type A acute aortic dissections require surgical
  treatment.
• The aortic segment containing the original
  intimal tear is resected when possible, with
  graft replacement of the ascending aorta to
  redirect blood into the true lumen.
• An operative mortality rate of 7 has recently
  been reported

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• The only contraindication to immediate surgical
  repair of a type A dissection ? simultaneous
  occurrence of a progressing stroke

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Type B acute aortic dissections

• Definitive treatment is less clear
• Generally, these patients tend to be worse
  surgical risks
• The hospital mortality in patients treated
  without surgery who have acute type B dissections
  is 15 to 20, and that is comparable to or
  better than the mortality rate with surgery in
  most institutions, although the mortality rate in
  surgery for type B dissections appears to be
  decreasing

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• Control of blood pressure is the cornerstone of
  therapy
• b-Blocking agents ? the most commonly used oral
  antihypertensive drugs in the treatment of these
  patients
• other agents, such as thiazide diuretics, calcium
  channel blockers, and angiotensin-converting
  enzyme inhibitors, may need to be added.