January 8, 2016 - Mechanical Complications of MI

Question 1

Complications of Infarction

Answer 1

Coronary - recurrent ischemia / infarction

Heart Failure - pump dysfunction, RV infarction

Arrhythmia - tachyarrhythmia, bradyarrhythmia

Pericardial - pericarditis, pericardial effusion

Intracavitary Thrombi - apical thrombus

Valvular - functional mitral regurgitation

Mechanical - freewall rupture, septal rupture, papillary muscle rupture, aneurysm, false anuerysm

Question 2

Mechanical Complications of MI

Answer 2

Freewall rupture

Septal rupture

Papillary muscle rupture

True aneurysm

False aneurysm

Question 3

Ventricular Freewall Rupture

Answer 3

Occlusion of any of the three major coronary arteries supplying the freewall of either ventricle.

Left anterior descending artery (LAD)

Left circumflex (LCx)

Right coronary artery (RCA)

Transmural necrosis weakening the tissue, with sufficient force still being gneerated by the remainder of the ventricle to disrupt/rupture the necrotic muscle. Blood then rushes out into the pericardial space, you tamponade, and you die.

Question 4

How Does a Freewall Rupture Happen?

Answer 4

Consequence of a transmural infarction (STEMI)

There is stress at a point between the normal myocardium and the dense, necrotic infarct (hinge point). Sometimes there may be a precipitant that surges the blood pressure such as a cough or straining.

Risk factors are age, female, first MI, use of NSAIDs, and late reperfusion.

This happens when tissue is necrotic (2-7 days post infarct).

Question 5

What Happens in a Freewall Rupture?

Answer 5

Sudden transmission of LV cavitary blood (and pressure) into the pericardial space. The patient experiences abrupt hypotension often resulting in cardiogenic shock or cardiac arrest as this leads to a tamponade.

This can be preceded by a vagal reaction (nausea, bradycardia, cold diaphoresis)

Question 6

Making the Diagnosis of Freewall Rupture

Answer 6

Be suspicious

Get a STAT echocardiogram

If you see one, get them to the operating room immediately

Question 7

Freewall Rupture - Treatment

Answer 7

Emergent surgical repair with patch closure

A minority survive. Patients with smaller tears and less severe compression of the heart are potentially salvageable, but the majority with large tears result in immediate death.

Question 8

Septal Rupture

Answer 8

Caused by an occlusion of an artery supplying the ventricular septum.

Left anterior descending artery (LAD) (twice as often)

Right coronary artery (RCA)

Transmural necrosis weakening the tissue, while sufficient force is generated by the remainder of the ventricle to rupture the necrosed myocardium and result in shunting of blood from the LV into the RV.

Question 9

What Happens in a Septal Rupture?

Answer 9

Left to right heart shunting of blood.

Usually more than half of the LV stroke volume is lost into the right heart, and forward output from the LV falls severely. Systemic hypoperfusion or shock develops. Increased flow in the lungs and left atrium increases pulmonary pressures, congesting the lungs.

Question 10

Making the Diagnosis of a Septal Rupture

Answer 10

Be suspicious

New pansystolic murmur

Bedside echocardiogram or cardiac catheterization

Question 11

Septal Rupture - Treatment

Answer 11

Emergent surgical repair

About 50% salvage if operated

Rare survival without an operation

Unfortunately, this is a crummy situation. If you don’t operate, the patient will die. But if you do operate, the patient will most likely die too. Particularly, the earlier you operate, the harder the operation is and the higher the complications because the tissue is necrotic.

Question 12

Papillary Muscle Rupture

Answer 12

Occlusion of an artery supplying a papillary muscle.

Results in necrosis of the papillary muscle

Sufficient forces generated by the remainder of the LV to rupture partially or completely, a papillary muscle.

Question 13

What Happens in Papillary Muscle Rupture?

Answer 13

Severe regurgitation of blood into the left atrium, raising left atrial and pulmonary venous pressure and causing immediate pulmonary edema.

Loss of stroke volume into the left atrium occurs at the expense of forward flow, and the systemic output of the heart falls which can lead to cardiogenic shock.

Question 14

Making the Diagnosis of a Papillary Muscle Rupture

Answer 14

Clinical suspicion (murmur, low BP)

Diagnosed via echocardiography

Question 15

Papilalry Muscle Rupture - Treatment

Answer 15

Surgical mitral valve replacement within 6 hours of occurrence (before the low output state results in irrepairable kidney failure)

Supportive care is not to delay surgery, merely to attempt to stabilize or improve before surgery.

Majority survive with good quality of life if operated on. The mortality rate if left un-operated is 85% within 48 hours.

Question 16

Aneurysm - Definition

Answer 16

A localized widening (dilatation) of an artery, vein, or the heart. At the area of an aneurysm, there is typically a bulge and the wall is weakened and may ruptured.

Question 17

Left Ventricular Aneurysm

Answer 17

Cause is from an occlusion of an artery resulting in transmural necrosis of the wall. Sufficient forces is generated by the remainder of the LV to distend/dilate the infarct territory.

If it dilates in diastole it is an aneurysm

If it further dilates in systole, it is a “dyskinesis”

Question 18

What Happens in LV Aneurysm

Answer 18

Loss of contractile function by the transmural infarction reduces forward ejection fraction.

Systolic dilation of the infarct territory wastes/consumes potential stroke volume, further reducing forward ejection.

Stagnation of flow in the non-contractile infarct segment promotes local thrombosis, which has the potential of systemic embolization.

Question 19

Making the Diagnosis of LV Aneurysm

Answer 19

Imaging such as echocardiogram.

Cardiac catheterization.

Question 20

Left Ventricular Aneurysm - Treatment

Answer 20

Medical therapy is the standard treatment. Particulary ACE inhibitors to prevent further remodelling of the heart.

Surgical aneurysmectomy may be performed as a secondary indication for open heart surgery. Doing surgery in and of itself for LV aneurysm has not been shown to have a mortality benefit.

Prognosis is a higher risk of heart failure.

Question 21

False Aneurysm

Answer 21

“Contained” freewall rupture

Prior adhesive pericarditis which has caused fibrosis and tougher tissue.

Occlusion of a coronary artery resulting in transmural necrosis of the myocardium (STEMI). Sufficient forces generated by the remainder of the LV to result in rupture of the infarct territory.

The rupture through the myocardium is contained locally within the pericardial space.

Question 22

What Happens in False Aneurysm?

Answer 22

Loss of systolic function by ejection into the body of the false aneurysm.

Stagnation of flow within the false aneurysm is conducive for thrombus formation, which can result in systemic embolization.

Eventually, local containment of the rupture can be lost, resulting in tamponade and death.

Question 23

True vs. False Aneurysm

Answer 23

In a true aneurysm, all layers of the endocardium are out-pouched together.

In a false aneurysm, just the pericardium is out-pouched.

Question 24

False Aneurysm

Answer 24

Sugical treatment repair with a patch.

Good prognosis.