B P5 C36 Coronary Blood Flow and Myocardial Ischemia

Question 1

Myocardial oxygen extraction is near-maximal at rest, averaging _________ of arterial oxygen content.

Answer 1

70% to 80%

Because of the high resting oxygen extraction, increases in myocardial oxygen consumption are primarily met by proportional increases in coronary flow and oxygen delivery

Question 2

_____________________= product of hemoglobin concentration and arterial oxygen saturation plus a small amount of oxygen dissolved in plasma that is directly related to arterial oxygen tension (Pao2 )

Answer 2

Arterial oxygen content (Cao2 )

In addition to coronary flow, oxygen delivery is directly determined by arterial oxygen content (Cao2 )

Question 3

Coronary venous oxygen tension (PvO2) can only decrease from 25 mm Hg to approximately ___ mm Hg

Answer 3

15 mm Hg

Question 4

For any given flow level, anemia results in _____reductions in oxygen delivery, whereas hypoxia, resulting from the nonlinear oxygen dissociation curve, results in relatively small reductions in oxygen content until PaO2 falls to the steep portion of the oxygen dissociation curve (below 50 mm Hg)

Answer 4

Anemia: proportional

Hypoxia: small

Question 5

Identify the major determinants of myocardial oxygen consumption

Answer 5

Heart rate
Systolic pressure (or myocardial wall stress)
Left ventricular (LV) contractility

**There are five main determinants of ventricular mechanical performance: preload (or Frank-Starling mechanism), afterload, contractility, lusitropy (diastolic function), and HR.

A twofold increase in any of these individual determinants of oxygen consumption requires an approximately 50% increase in coronary flow.

Question 6

Resting coronary blood flow under normal hemodynamic conditions averages _____ mL/min/g and can increase fourfold to fivefold during vasodilation

Answer 6

0.7 to 1.0 mL/min/g

Question 7

Identify the phenomenon in coronary blood flow

Regional coronary blood flow remains constant as coronary artery pressure is reduced below aortic pressure over a wide range when the determinants of myocardial oxygen consumption are kept constant

Answer 7

Coronary Autoregulation

When pressure falls to the lower limit of autoregulation,coronary resistance arteries are maximally vasodilated to intrinsic stimuli, and flow becomes pressuredependent, resulting in the onset of subendocardial ischemia

Question 8

The ability to increase flow above resting values in response to pharmacologic vasodilation is termed ________________________

Answer 8

Coronary flow reserve

Question 9

Factors that decreases Maximum perfusion and coronary flow reserve

Answer 9

Decreased maximum flow
↑ LV mass
↓ Microvascular function
↑ HR
↑ Preload

Question 10

Coronary reserve also is diminished by anything that increases resting flow.

Factors that increases resting flow__

Answer 10

↑ HR
↑ SBP
↑ Contractility
↓ Hb

Question 11

Coronary reserve also is diminished by anything that increases resting flow.

Factors that increases resting flow__

Answer 11

↑ HR
↑ SBP
↑ Contractility
↓ Hb

Question 12

Coronary reserve also is diminished by anything that increases resting flow

Factors that increases resting flow

Answer 12

↑ HR
↑ SBP
↑ Contractility
↓ Hb

Question 13

Although initial studies suggested that the lower pressure limit of autoregulation is _____ mm Hg, it was later shown that coronary flow can be autoregulated to mean coronary pressures as low as _____ mm Hg (diastolic pressures of 30 mm Hg) in conscious dogs in the basal state

Answer 13

70 mm Hg

40 mm Hg

Question 14

Subendocardial flow occurs primarily in diastole and begins to decrease below a mean coronary pressure of ___ mm Hg.

In contrast, subepicardial flow occurs throughout the cardiac cycle and is maintained until coronary pressure falls below ___ mm Hg

Answer 14

40 mm Hg

25 mm Hg

Question 15

With the development of hemodynamically significant epicardial artery narrowing (>____% diameter reduction), the fixed conduit artery resistance begins to contribute an increasing component to total coronary resistance and, when severely narrowed (>_____%), may reduce resting flow.

Answer 15

> 50%

90%

Question 16

The resistance to coronary blood flow can be divided into three major components

Answer 16

R1 - no measurable pressure drop in the epicardial arteries, indicating negligible conduit resistance

R2 - dynamic and arises primarily from microcirculatory resistance arteries and arterioles

R3 - extravascular compressive resistance (R3 ), varies with time throughout the cardiac cycle and is related to cardiac contraction and systolic pressure development within the left ventricle

Question 17

With the development of hemodynamically significant epicardial artery (R1) narrowing (>_____% diameter reduction), the fixed conduit artery resistance begins to contribute an increasing component to total coronary resistance and, when severely narrowed (>____%), may reduce resting flow.

Answer 17

> 50%

> 90%

Question 18

The second component of coronary resistance (R2) is dynamic and arises primarily from _____.

Answer 18

Microcirculatory resistance arteries and arterioles

Even in the maximally vasodilated heart, capillary resistance accounts for no more than 20% of the microvascular resistance. Thus a twofold increase in capillary density would increase maximal myocardial perfusion by only approximately 10%.

Question 19

The third component, _____ (R3), varies with time throughout the cardiac cycle and is related to cardiac contraction and systolic pressure development within the left ventricle

Answer 19

Extravascular compressive resistance

Question 20

__________________ do not contribute significantly to coronary vascular resistance, yet arterial diameter is modulated by a wide variety of paracrine factors

Answer 20

Epicardial conduit arteries

Question 21

State the effects of the ffg substances both “normal response” and in patients with “atherosclerosis” in the conduit (C) and resistance vessels (R)

Acetylcholine
Thrombin
Serotonin
ADP
Thromboxane 2

Cholinergic stimulation
Sympathetic stimulation

Answer 21

Normal response/response in CAD

Acetylcholine
Conduit: dilate/constrict
Resistance: dilate/less dilation

Thrombin
C/R: dilate/constrict

Serotonin
C: constrict/constrict
R: dilate/constrict

ADP
C/R: dilate/less dilate

TX2
C/R: constrict/constrict

Cholinergic
Same with ACH

Sympathetic
Alpha: constrict/constrict
Beta 1 and 2: dilate/less dilate on C, dilate on R

Question 22

Nitric oxide is produced in endothelial cells by the enzymatic conversion of L-arginine to. _____ via type III or endothelial nitric oxide synthase (eNOS

Answer 22

Citrulline

Question 23

NO-mediated vasodilation is impaired in many disease states and in patients with one or more risk factors for coronary artery disease (CAD). This occurs via inactivation of NO by _____ generated in response to oxidative stress. Such inactivation is the hallmark of impaired NO- mediated vasodilation in atherosclerosis, hypertension, and diabetes.

Answer 23

Superoxide anion

Question 24

The endothelins—ET-1, ET-2, and ET-3—are peptide endothelium- dependent constricting factors. _____ is a potent constrictor derived from the enzymatic cleavage of a larger precursor molecule (pre- pro–endothelin) via endothelin-converting enzyme. In contrast with the rapid vascular smooth muscle relaxation and recovery

Answer 24

ET-1

Question 25

During sympathetic activation, coronary tone is modulated by norepinephrine released from myocardial sympathetic nerves, as well as by circulating norepinephrine and epinephrine.

In conduit arteries, sympathetic stimulation leads to alpha1 constriction as well as beta-mediated vasodilation. The net effect is to _____ epicardial coronary arteries. This dilation is potentiated by concomitant flow-mediated vasodilation from metabolic vasodilation of coronary resistance vessels.

When NO-mediated vasodilation is impaired, _____ predominates and can dynamically increase stenosis severity in asymmetric lesions where the stenosis is compliant.

Answer 25

Dilate

Alpha1 constriction

Question 26

The effects of sympathetic activation on myocardial perfusion and coronary resistance vessel tone are complex and depend on the net actions of _____.

Answer 26

(1) Beta1-mediated increases in myocardial oxygen consumption (resulting from increases in the determinants of myocardial oxygen consumption)

(2) Direct beta2-mediated coronary vasodilation

(3) Alpha1-mediated coronary constriction

Question 27

Under normal conditions, exercise-induced _____ “feed-forward” dilation predominates, resulting in a higher flow relative to the level of myocardial oxygen consumption.

This neural control mechanism produces transient vasodilation before the buildup of local metabolites during exercise and prevents the development of subendocardial ischemia during abrupt changes in demand

Answer 27

Beta2-adrenergic

Question 28

After nonselective beta blockade, sympathetic activation unmasks _____-mediated coronary artery constriction.

Although flow is mildly decreased, oxygen delivery is maintained by increased oxygen extraction and a reduction in coronary venous PO2 at similar levels of cardiac workload

Answer 28

Alpha1

Question 29

_____ results in transient functional occlusion of a coronary artery that is reversible with nitrate vasodilation. It most frequently occurs in the setting of a coronary stenosis, leading to dynamic stenosis behavior that can dissociate the effects on perfusion from anatomic stenosis severity

Answer 29

Coronary spasm

Question 30

In CAD, endothelial disruption probably plays a role in focal vasospasm; the normal vasodilation from autacoids and sympathetic stimulation is converted into a vasoconstrictor response because of the lack of competing _____. Nevertheless, although impaired endothelium-dependent vasodilation is a permissive factor for vasospasm, it is not causal, and a trigger is required (e.g.,thrombus formation, sympathetic activation).

Answer 30

Endothelium-dependent vasodilation

Question 31

Nitroglycerin dilates epicardial conduit arteries and small coronary resistance arteries but does not increase coronary blood flow in the ___________ heart

Answer 31

Normal

Transient arteriolar vasodilation is overcome by autoregulatory escape, which returns coronary resistance to control levels

It can produce vasodilation of larger coronary resistance arteries that improves the distribution of perfusion to the subendocardium when flow-mediated NO-dependent vasodilation is impaired. It also can improve subendocardial perfusion by reducing LV end-diastolic pressure through systemic venodilation in HF.

Question 32

All calcium channel blockers induce vascular smooth muscle relaxation and are, to various degrees, pharmacologic coronary vasodilators.

In ______________ the vasodilator response is similar to that of nitroglycerin

Answer 32

Epicardial arteries

Question 33

Calcium channel blockers also submaximally vasodilate coronary resistance vessels can sometimes precipitate subendocardial ischemia in the presence of a critical stenosis.

This arises from a transmural redistribution of blood flow, which is called ______________, as well as the tachycardia and hypotension

Answer 33

Coronary steal

Question 34

_________________ dilates coroary arteries through activation of A2 receptors on vascular smooth muscle and is _____________ of the endothelium

Answer 34

Adenosine

Independent

Question 35

_________________ dilates coroary arteries through activation of A2 receptors on vascular smooth muscle and is _____________ of the endothelium (restricted to vessels smaller than 100um)

Larger upstream resistance arteries dilate through a _________________ mechanism from the increase in shear stress

Answer 35

Adenosine

Independent

NO-dependent

Question 36

______________ produces vasodilation by inhibiting the myocyte reuptake of adenosine

Answer 36

Dipyridamole

Reversed by aminophylline

Question 37

______________ is a short-acting coronary vasodilator that was the first agent used for intracoronary vasodilation. It causes vascular smooth muscle relaxation by inhibiting phosphodiesterase and increasing (cAMP).

After bolus injection, it has a rapid onset of action, but the vasodilation is somewhat more prolonged than after adenosine. Its actions are independent of the endothelium.

Answer 37

Papaverine

Question 38

Structure of the coronary microcirculaiton and their regulators

Epicardial arteries
Small arteries
Arterioles

Answer 38

Epicardial arteries - conduit artery function, regulated by shear stress, and contribute minimal pressure drop (<5%)

Small arteries - response to local shear stress and luminal pressure changes (myogenic response)

Arterioles - changes in local tissue m olism and directly control perfusion of the low-resistance coronary capillary bed

Question 39

Structure of the coronary microcirculaiton and their regulators

Epicardial arteries
Small arteries
Arterioles

Answer 39

Epicardial arteries - conduit artery function, regulated by shear stress, and contribute minimal pressure drop (<5%)

Small arteries - response to local shear stress and luminal pressure changes (myogenic response)

Arterioles - changes in local tissue m olism and directly control perfusion of the low-resistance coronary capillary bed

Question 40

________________ refers to the ability of vascular smooth muscle to oppose changes in coronary arterial diameter

Answer 40

Myogenic response

Vessels relax when distending pressure is decreased and constrict when distending pressure is elevated

Question 41

Effect of the following in coronary resistance

Adenosine
Hypoxemia
Anemia
Hypercapnia
Acidosis

Answer 41

All vasodilate

Question 42

In terms of coronary flow reserve, arterial pressure supplying the RCA substantially exceeds ________________, minimizing the compressive determinants of coronary reserve.

RV oxygen consumption is ___________ than LV consumption, and coronary venous oxygen saturations are h_____ than in the left coronary circulation.

Answer 42

RV pressure

Lower

Higher

Question 43

Effect of CAD in the epicardial coronary artery disease

Answer 43

Dominant epicardial resistance in CAD

The angiographically visible epicardial coronary arteries are normally able to accommodate large increases in coronary flow without producing any significant pressure drop and thus serve a conduit function to the coronary resistance vasculature.

This changes dramatically in CAD, in which the epicardial artery resistance becomes dominant.This fixed component of resistance increases with stenosis severity and limits maximal myocardial perfusion.

Question 44

The most important determinant of stenosis resistance for any given level of flow is the ____________________________

Answer 44

Minimum lesional crosssectional area within the stenosis

Resistance is inversely proportional to the square of the crosssectional area,

Question 45

Difference of outward vs inward remodelling

Answer 45

Inward remodelling reduces minimal lesion ares along the length of the vessel

Diffuse abluminal outward remodeling with thickening of the arterial wall is common in coronary atherosclerosis but does not alter the pressure-flow characteristics of the stenosis for a given intraluminal geometry.

By contrast, diffuse inward remodeling effectively reduces minimal lesion areaalong the length of the vessel and can lead to underestimation of stenosis severity using relative diameter or area measurements (see Chapter 21) and at the same time can contribute to a significant longitudinal pressure drop that also reduces maximum perfusion.1

Question 46

Stenosis pressure drop and resistance increase exponentially as minimum lesional cross-sectional area ______________

This reflects that the pressure drop becomes ___________________ and varies with the square of the flow or flow velocity. As a result, the instantaneous stenosis resistance progressively increases during vasodilation.

Answer 46

Decreases
Flow dependent

As illustrated in Fig. 36.11A, there is no significant pressure drop across a stenosis (ΔP) or stenosis-related alteration in maximal myocardial perfusion until stenosis severity exceeds a 50% diameter reduction (cross-sectional area reduction of 75%). As stenosis severity exceeds 50%, the pressure flow relation becomes curvilinear (Fig. 36.11B) and increases in stenosis resistance are accompanied by concomitant increases in ΔP across the stenosis that reduce distal coronary pressure.

Question 47

There is no significant pressure drop across a stenosis (AP) or stenosis-related alteration in maximal myocardial perfusion until stenosis severity exceeds a ____% diameter reduction (cross-sectional area reduction of 75%).

Answer 47

50% (CSA reduction of 75%)

Question 48

A critical stenosis, one in which subendocardial flow reserve is completely exhausted at rest, usually develops when stenosis severity exceeds ________

Under these circumstances, pharmacologic vasodilation of subepicardial resistance vessels results in a reduction in distal coronary pressure that actually redistributes flow away from the subendocardium, leading to a _______________ phenomenon

Answer 48

90%
Transmural steal

Question 49

It is expressed as the ratio of maximally vasodilated flow to the corresponding resting flow value in a specific region of the heart and quantifies the ability of flow to increase above the resting value

Answer 49

Absolute Flow Reserve

Absolute flow reserve is not only altered by factors that affect maximal coronary flow (e.g., stenosis severity, impaired microcirculatory control, arterial pressure, heart rate) but also by the corresponding resting flow value. As noted previously, resting flow can vary with hemoglobin content, baseline hemodynamics, and the resting oxygen extraction. Reductions in absolute flow reserve, therefore, can arise from inappropriate elevations in resting coronary flow as well as from reductions in maximal perfusion.

Question 50

In this approach, relative differences in regional perfusion (per gram of tisssue) are assessed during maximal pharmacologic vasodilation or exercise stress and expressed as a fraction of flow to normal regions of the heart.

Answer 50

Relative coronary flow reserve

This approach compares relative perfusion states under the same hemodynamic conditions and is fairly insensitive to variations in mean arterial pressure, heart rate, and preload.

Question 51

______________ is an indirect index determined by measuring the driving pressure for microcirculatory flow distal to the stenosis (distal coronary pressure minus coronary venous pressure) relative to the coronary driving pressure available in the absence of a stenosis (mean aortic pressure minus coronary venous pressure)

Answer 51

Fractional Flow Reserve

simplified clinical FFR index of mean distal coronary pressure/mean aortic pressure (Pd/Pao).

Question 52

___________reflects the ratio of distal coronary pressure to aortic pressure averaged throughout mid-diastole (i.e., the “wave-free period”).

Answer 52

Instantaneous wave-Free Ratio (iFR)

Resting pressure gradient does not develop until stenosis severity reaches a level that significantly affects maximal perfusion during vasodilation

During mid-diastole, distal coronary resistance is free of the compressive effects of systole and phasic coronary flow and the stenosis diastolic pressure gradient are maximal

iFR will overestimate the functional significance of a stenosis versus FFR in circumstances in which resting flow is abnormally elevated

Question 53

________________ defined as starting 25% into cardiac diastole and ending 5 ms before the end of diastole

Answer 53

Wafe Free Period

Question 54

The increase in LV mass in the absence of vascular proliferation reduces the maximum perfusion per gram of myocardium. The net effect of LV hypertrophy is that coronary flow reserve at any given coronary arterial pressure is ___________ in a manner that is inversely related to the change in LV mass.

Answer 54

Reduced

Question 55

CMVD

As with hypertrophy, flow per gram of myocardium will be normal at rest and reduced during pharmacologic vasodilation.

In contrast to hypertrophy, absolute flow remains ______________ at rest in microvascular disease, and the absolute vasodilated flow is reduced.

Answer 55

Normal

Question 56

Microvascular dysfunction in the presence of normal coronary arteries (0% stenosis) attenuates coronary flow reserve.

Conversely, for any given stenosis, the FFR measured in the presence of microvascular disease will be _______________ than when vasodilator responses are normal.

Answer 56

Higher

Question 57

Describe the CFR and FFR values for

Normal
Flow limiting stenosis
Non flow limiting stenosis
Diffuse/small vessel disease

Answer 57

Normal - normal CFR ans FFR
Flow limiting stenosis - abnormal CFR and FFR
Non flow limiitng stenosis - normal CFR, abnormal FFR
Diffuse/small vessel disease - abnormal CFR, normal FFR

Microvascular d function in the presence of normal coronary arteries (0% stenosis) attenuates coronary flow reserve. Conversely, for any given stenosis, the FFR measured in the presence of microvascular disease will be higher than when vasodilator responses are normal. Thus, when maximum vasodilation is not achieved, FFR will underestimate the physiologic severity of the stenosis.

Question 58

Resting distal coronary pressure consistently falls as stenosis severity exceeds ____% diameter reduction, and the resultant interarterial pressure gradient increases endothelial shear stress in pre- existing collaterals smaller than 200 μm in diameter.

Answer 58

70%

Question 59

Proliferation of coronary collaterals occurs in response to repetitive stress-induced ischemia and the development of transient interarterial pressure gradients between the source and recipient vessel through a process termed ____________________

Answer 59

Arteriogenesis

Question 60

Collateral perfusion also can originate from de novo vessel growth, or ____________________, which refers to the sprouting of smaller, capillary-like structures from preexisting blood vessels

Answer 60

Angiogensis

Question 61

Although many interventions have been demonstrated to cause favorable angiogenesis of capillaries and improve myocardial function, few interventions have increased arteriogenesis in mature collaterals, and randomized human clinical trials have been disappointing. Part of this limitation may arise from the fact that no intervention has resulted in _____, the sine qua non of functional collateral formation.

Answer 61

Measurable increases in maximum vasodilated myocardial perfusion or coronary flow reserve indices

Question 62

The control of blood flow to collateral-dependent myocardium is governed by a series resistance arising from interarterial collateral anastomoses, largely epicardial, as well as the native downstream microcirculation.

___________________ is therefore the major determinant of perfusion, and coronary pressure distal to a chronic occlusion is already near the lower autoregulatory pressure limit.

Answer 62

Collateral resistance

Question 63

Irreversible myocardial injury begins after ________________ of coronary occlusion in the absence of significant collaterals

Answer 63

20 minutes

Question 64

Total coronary artery occlusions shorter than ___ minutes do not cause irreversible injury but can cause myocardial stunning and also precondition the heart and protect it against recurrent ischemic injury.

Answer 64

20 mins

Question 65

Irreversible injury begins _____ minutes and progresses as a wavefront from endocardium to epicardium.

After _____ minutes, the inner third of the left ventricle (LV) wall is irreversibly injured.

Answer 65

After 20 mins

After 60 mins

Question 66

After _____ hours, only a subepicardial rim of tissue remains, with the transmural extent of infarction completed between 3 and 6 hours after occlusion.

Answer 66

After 3 hours

Question 67

The most important factor delaying the progression of irreversible injury is the magnitude of _____, which is directed primarily to the outer layers of the heart.

Answer 67

Collateral flow

Question 68

Reperfusion after prolonged ischemia is accompanied by the development of _____ within the infarct area

Answer 68

No-reflow

Question 69

Repetitive reversible ischemia or angina occurring before an occlusion can reduce irreversible injury through __________________

Answer 69

Preconditioning

Question 70

The _________________________ is the most important determinant of the actual time course of irreversible injury in patients with chronic CAD.

Answer 70

Magnitude of residual coronary flow through collaterals or through a subtotal coronary occlusion

The relation between infarct size and the area at risk of ischemia during a total occlusion is inversely related to collateral flow

Question 71

Brief reversible ischemia preceding a prolonged coronary occlusion reduced infarct size, a phenomenon termed ____________________

Answer 71

Acute preconditioning

Question 72

Preconditioning also develops on a chronic basis (__________________) and, once induced, persists for up to 4 days. It reduces MI size and also protects the heart from ischemia-induced stunning.

Answer 72

Delayed preconditioning

Question 73

____________________ ability to engage cardiac protection by producing intermittent ischemia or administering pharmacologic agonists at reperfusion.

It has the greatest clinical potential to affect irreversible injury because it can be induced after myocardial ischemia is established rather than requiring pretreatment

Answer 73

Myocardial postconditioning

Question 74

A number of experimental studies have demonstrated that ischemia in an extremity remote from the infarct can reduce infarct size. _____ is particularly attractive because it can be easily implemented using a blood pressure cuff and has been shown to experimentally reduce infarct size when administered before and after the onset of ischemia as well as at the time of reperfusion.

Answer 74

Remote conditioning

Question 75

____________ transient coronary occlusion resulting from coronary vasospasm or transient thrombosis in a critically stenosed coronary artery, producing transmural ischemia

Answer 75

Supply induced ischemia

Question 76

__________________ inability to increase flow in response to increases in myocardial oxygen consumption in which ischemia predominantly affects the subendocardium

Answer 76

Demand induced ischemia

Question 77

Coronary occlusion results in an immediate fall in coronary venous oxygen saturation, with a reduction in ATP production. This causes a decline in regional contraction within several beats, reaching dyskinesis within _____ minute.

Answer 77

1 minute

Question 78

As regional contraction ceases, concomitant changes include a reduction in global LV contractility (dP/dt), a progressive rise in LV end-diastolic pressure, and a fall in systolic pressure.The magnitude of the systemic hemodynamic changes varies with the severity of ischemia and the amount of the left ventricle subjected to ischemia. Significant electrocardiographic ST-segment changes develop within ____ minutes as efflux of potassium into the extracellular space reaches a critical level

Answer 78

2 minutes

Question 79

_____ are variable and usually are the last event in the evolution of ischemia

Answer 79

Symptoms of chest pain

Question 80

On restoring perfusion, the sequence is reversed, with resolution of chest pain occurring before hemodynamic changes resolve, but regional contraction can remain depressed, reflecting the development of _____.

Answer 80

Stunned myocardium

Question 81

Physiologic changes after coronary occlusion

Coronary occlusion results in an immediate fall in __________________, with a reduction in ATP production.
This causes a decline in _________________ within several beats, reaching dyskinesis within 1 minute.
As regional contraction ceases, concomitant changes include a reduction in _____________________, a progressive rise in LV end-diastolic pressure, and a _______ in systolic pressure.
Significant electrocardiographic __________________ develop within 2 minutes as efflux of potassium into the extracellular space reaches a critical level.
Symptoms of ______________ are variable and usually are the last event

Answer 81

1. Coronary venous oxygen saturation
2. Regional contraction
3. Global LV contractility (dP/dt)
4. Fall
5. ST-segment changes
6. Chest pain

Upon restoring perfusion, the sequence is reversed, with r lution of chest pain occurring before hemodynamic changes resolve, but regional contraction can remain depressed, reflecting the development of stunned myocardium

Question 82

When coronary pressure distal to a stenosis falls below the lower limit of autoregulation, __________________ is exhausted, resulting in the onset of subendocardial ischemia

Answer 82

Flow reserve

Question 83

In steady-state ischemia, the close matching between perfusion and contraction leads to a reduced regional oxygen consumption and energy utilization, a phenomenon termed ____________________. This reestablishes a balance between supply and demand,

Answer 83

Short-term hibernation

Question 84

Chronic contractile dysfunction and regional cellular mechanisms that downregulate contractile and metabolic function of the heart so as to protect it from irreversible injury

Answer 84

Hibernating myocardium

Question 85

Myocardial function normalizes rapidly after single episodes of ischemia lasting less than _____ minutes.

Answer 85

<2 minutes

Question 86

Myocardial function remains depressed for up to 6 hours after resolution of ischemia following a 15-minute occlusion in the absence of tissue necrosis, a phenomenon called ______________

Answer 86

Myocardial stunning

Question 87

Prolonged sublethal ischemia, as seen in short-term hibernation, leads to stunning on restoration of perfusion that may take up to _____ week to resolve in the absence of necrosis

Answer 87

1 week

Question 88

_____ is also responsible for postoperative pump dysfunction after cardiopulmonary bypass.

Answer 88

Stunned myocardium

Question 89

_______________ any myocardial region in which contractile function improves after coronary revascularization

Answer 89

Viable dysfunctional myocardium

Question 90

When resting flow relative to a remote region is normal in dysfunctional myocardium distal to a stenosis, the region is _________________.

In contrast, when relative resting flow is reduced in the absence of symptoms or signs of ischemia ____________________

Answer 90

Chronically stunned

Hibernating myocardium

Question 91

The progression from chronically stunned myocardium (with normal resting flow) to hibernating myocardium (with reduced resting flow) is related to the functional significance of the chronic stenosis supplying the LAD region and is probably a reflection of its propensity to produce repetitive supply- or demand-induced ischemia.This progression can be seen as soon as ___ week after placement of a critical stenosis that exhausts coronary flow reserve

Answer 91

1 week