Examining the Science Underlying Myocardial Ischemia.
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Transcript of Examining the Science Underlying Myocardial Ischemia.
Examining the Science Underlying Myocardial Ischemia
Severe obstruction (angina, no rupture) vs mild obstruction (no angina, likely to rupture)
RevascularizationAnti-anginal Rx
Exertional angina• (+) ETT
Severe fibrotic plaque• Severe obstruction• No lipid• Fibrosis, Ca2+
Pharmacologic stabilizationEarly identification of high-risk?
Plaque rupture• Acute MI• Unstable angina• Sudden death
Vulnerable plaque• Minor obstruction• Eccentric plaque• Lipid pool• Thin cap
Courtesy of PH Stone, MD.
Major cardiac events occur in non-target areas following successful PCI
Hazardrate (%)
Cutlip DE et al. Circulation. 2004;110:1226-30.
Substantial number of cardiac events could be preventedif non-obstructive, high-risk lesions were identified
Target lesion event
Non-target lesion event
0
5
10
15
20
1 2 3Year
4 5
Local determinants of the natural history of individual coronary lesionsOpportunities for identification and intervention
Courtesy of PH Stone, MD and R Gerrity, PhD.
Quiescent,stable plaque No symptoms
Fibrotic/scarred plaque Angina
Thin capFibroatheroma MI, sudden death
Quiescen
ce
Inflammation
Proliferation
Calcification
Local factorsLocal factorsShear stress
•Proliferation•Inflammation•Remodeling
Proposed classification scheme for atherosclerotic plaque
Plaque trajectory Histopathology
Progression rate
Vascular remodeling
Proclivity to rupture
Clinical manifestation
Quiescent plaque
Small lipid core
Thick fibrous cap
Minimal Compensatory expansive remodeling
Low Asymptomatic
Stenotic plaque
Small lipid core
Very thick fibrous cap
Gradual Constrictive remodeling
Low Stable angina
High-risk plaque
Large lipid core
Thin and inflamed fibrous cap
Increased Excessive expansive remodeling
High ACS
Chatzizisis YS et al. J Am Coll Cardiol. 2007;49:2379-93.
The spectrum of CAD
Chatzizisis YS et al. J Am Coll Cardiol. 2007;49:2379-93.ESS = endothelial shear stress
Substrate• Vulnerable ischemic zone• Intracoronary thrombus• Autonomic influence• Hemodynamic compromise
Ventricular arrhythmogenesis in ischemic myocardium
Adapted from Luqman N et al. Int J Cardiol. 2007;119:283-90.
VPC = ventricular premature contractionVT = ventricular tachycardia
Risk factors• Age• Heredity• Gender• Smoking• Lipids• Hypertension• Diabetes• Obesity
•Clinical or subclinical susceptibility •Structural substrate present
High risk of transient acute ischemia reperfusion
Triggers• VPC• VT• Reentry
+ Ventricular fibrillation
Causes and consequences of myocardial ischemia: New understanding
Consequences of ischemia
Electrical instabilityMyocardial dysfunctionIschemia
Heart rateBlood pressurePreloadContractility
Development of ischemia
O2 demand
O2 supply
Na+ and Ca2+ overload
Belardinelli L et al. Heart. 2006;92(suppl IV):iv6-14.
Overview of the sodium channel
out
in
out
in
Na+/Ca2+
Exchanger
Ca2+
Ca2+
Ca2+
Ca2+
Na+
Na+
Na+
Na+Na+
Na+
Na+
Restingclosed
Na+
ActivatedActivatedInactivated
Na+
Na+
Na+ Ca2+
Ca2+
[Na+]= 140 mM ~10mM
Courtesy of L Belardinelli, MD.
Ca2+
[Na+]
Origin of late INa
• During the plateau phase of the action potential, a small proportion of sodium channels either do not close, or close and then reopen
• These late channel openings permit a sustained Na+ current to enter myocytes during systole
Belardinelli L et al. Heart. 2006;92(suppl IV):iv6-14.
Sodiumcurrent
0
Late
Peak
Sodiumcurrent
0
Late
Peak
0
Late
Peak
Sodiumcurrent
Ischemia
Myocardial ischemia causes enhanced late INa
Enhanced late INa appears to be a major contributor to increased intracellular Na+ during ischemia
Belardinelli L et al. Heart. 2006;92(suppl IV):iv6-14.
Role of altered ion currents in adverse consequences of myocardial ischemia
[Na+]i = intracellular [Na+]NCX = Na+/Ca2+ exchanger APD = action potential duration Belardinelli L et al. Heart. 2006;92(suppl IV):iv6-14.
Disease(s) and pathological states linked to imbalance of O2 supply/demand
Cytosolic Ca2+
NCX
Late INa
Na+ entry ([Na+]i)
Mechanical dysfunction• Abnormal contraction and relaxation• Diastolic tension
Electrical instability• Afterpotentials• Beat-to-beat APD• Arrhythmias (VT)
Diastolic relaxation failure adversely affects myocardial O2 supply and demand
• Sustained contraction of ischemic tissue during diastole:– Increases MVO2
– Compresses intramural small vessels• Reduces myocardial blood flow
Courtesy of PH Stone, MD.
Exacerbates ischemia
MVO2 = myocardial oxygen consumption
Fraser H et al. J Mol Cell Cardiol. 2006;41:1031-8.
Late INa inhibition blunts Ca2+ accumulation
Time of perfusion (min)
ATX-II alone (n = 11)
ATX-II + ranolazine 4 μM (n = 9) or 9 μM (n = 9)
*P < 0.05 vs ATX-II aloneATX-II = sea anemone toxin (selectively late INa)
Indo fluorescence(F405/F485
ratio)
0.30
0.25
0.20
0.15
0.100 10 20 30 40 50
LV work(L/min per
mm Hg)
12
8
4
0
ATX-II
RAN
0 10 20 30 40 50
RAN
ATX-II
**
*
*
Ranolazine blunts sotalol-induced action potential prolongation in dogs
Antzelevich C et al. Circulation 2004;110:904-10.
Control
d-Sotalol
+ Ranolazine 5 uM
+ Ranolazine 10 uM
50 mV
1 sec
Transmembrane action potentials (superimposed)