The Intra-aortic Balloon Pump in High-risk PCI
The Intra-aortic Balloon Pump in High-risk PCI
Somewhat surprisingly, there is no universally accepted definition of what constitutes high-risk PCI. Akin to the controversy generated by the attempt to compare rates of stent thrombosis (ST) and/or bleeding in trials of therapeutic strategies for acute coronary syndromes/PCI, prior to general acceptance of the Academic Research Consortium definition of ST and the recent Bleeding Academic Research Consortium (BARC) categorization of bleeding events, respectively, it is difficult to gauge how robust the outcomes are between trials of high-risk PCI when the patient cohort is significantly heterogeneous and lacks standardization. Box 1 lists several putative clinical, anatomical and hemodynamic criteria that have been used by various investigators to denote 'high risk'.
One way of assessing or assigning risk is to use a 'myocardium at risk' score. These scores help to systematically calculate the severity of CAD based on angiographic findings and also give an indication of the relative importance of each of the three major epicardial coronary arteries on an individual patient basis. This is clearly a preferred method of ascertaining risk over that of simply demonstrating the number of diseased major vessels. Moreover, they also provide prognostic information.
One of the most commonly adopted is the Jeopardy Score from Duke University (NC, USA), which divides the coronary tree into six segments (left anterior descending, diagonal branch, circumflex, obtuse marginal, right coronary and posterior descending arteries) with all segments distal to a ≥70% stenosis considered as being at risk. Each segment receives two points if affected, plus two further points if the lesion affects two of the six downstream myocardial territories, giving rise to a maximum score of 12. The Alberta Provincial Project for Outcome Assessment in Coronary Heart (APPROACH) disease investigators assessed and validated the prognostic value of their own Lesion Score with that of the Duke Jeopardy Score and the Bypass Angioplasty Revascularization Investigation (BARI) Myocardial Jeopardy Index in >20,000 patients undergoing coronary catheterization for ischemic heart disease and found all three scores to be predictive of 1-year mortality (see Figure 2).
(Enlarge Image)
Figure 2.
1-year mortality according to specific myocardium at-risk scores.
(A) Duke Jeopardy Score, (B) BARI Jeopardy Score, (C) APPROACH Lesion Score. The ability of three myocardial Jeopardy Scores to predict 1-year mortality were tested against a cohort of 20,067 patients with ischemic heart disease who underwent cardiac catheterization between 1995 and 1998 in the province of Alberta, Canada (9922 patients treated medically, 6334 patients treated with percutaneous coronary intervention and 3811 patients treated with coronary artery bypass graft surgery). The investigators excluded those patients with valvular heart disease and a previous history of bypass surgery. A preintervention Duke Jeopardy Score >8 is widely accepted as 'high risk' for those patients due to undergo percutaneous coronary intervention.
BARI: Bypass Angioplasty Revascularization Investigation.
Reproduced with permission from [5].
The common thread connecting these multiple variables is the relative inability of the high-risk patient to withstand the hemodynamic sequelae of arrhythmias and even transient periods of ischemia-reperfusion, for instance, during balloon inflation and stent deployment or from the distal embolization of atherogenic material (i.e., the no-reflow phenomenon). These individuals have significantly attenuated hemodynamic reserve and may develop postischemic stunning, leading to a deleterious cascade of decreased diastolic compliance, depressed systolic function leading to a fall in cardiac output and worsening ischemia culminating in cardiogenic shock (CS) or ventricular arrhythmias. Furthermore, high-risk patients with subnormal left ventricular function tend to be older and have more pre-existing comorbidities, both of which are independently associated with poorer outcome post-PCI.
As there is a heightened propensity to suffer catastrophic hemodynamic collapse, either as a direct consequence of the procedure or as a result of the pre-existing proischemic milieu, it seems intuitively attractive to use an adjunctive device that can augment the coronary circulation and reduce the workload of the endangered myocardium during high-risk PCI. One such device is the intra-aortic balloon pump (IABP; MAQUET Cardiovascular, NJ, USA) and the physiological benefits of mechanical counterpulsation it provides (Box 2, Figure 3).
(Enlarge Image)
Figure 3.
Effect of counterpulsation on myocardial oxygen supply and demand.
Diastolic augmentation through counterpulsation increases the pressure difference between the aorta and left ventricle – this is referred to as the DPTI. It is a measure of myocardial oxygen supply. Myocardial oxygen demand is directly related to the area under the left ventricle systolic pressure curve – this is referred to as the TTI. The DPTI:TTI ratio reflects the balance between myocardial oxygen supply and demand and is termed the endocardial viability ratio. Intra-aortic balloon counterpulsation results in an increase in endocardial viability ratio.
DPTI: Diastolic Pressure Time Index; TTI: Tension Time Index; VP: Ventricular pressure.
Reproduced with permission from [9].
How Do We Define High-risk PCI?
Somewhat surprisingly, there is no universally accepted definition of what constitutes high-risk PCI. Akin to the controversy generated by the attempt to compare rates of stent thrombosis (ST) and/or bleeding in trials of therapeutic strategies for acute coronary syndromes/PCI, prior to general acceptance of the Academic Research Consortium definition of ST and the recent Bleeding Academic Research Consortium (BARC) categorization of bleeding events, respectively, it is difficult to gauge how robust the outcomes are between trials of high-risk PCI when the patient cohort is significantly heterogeneous and lacks standardization. Box 1 lists several putative clinical, anatomical and hemodynamic criteria that have been used by various investigators to denote 'high risk'.
One way of assessing or assigning risk is to use a 'myocardium at risk' score. These scores help to systematically calculate the severity of CAD based on angiographic findings and also give an indication of the relative importance of each of the three major epicardial coronary arteries on an individual patient basis. This is clearly a preferred method of ascertaining risk over that of simply demonstrating the number of diseased major vessels. Moreover, they also provide prognostic information.
One of the most commonly adopted is the Jeopardy Score from Duke University (NC, USA), which divides the coronary tree into six segments (left anterior descending, diagonal branch, circumflex, obtuse marginal, right coronary and posterior descending arteries) with all segments distal to a ≥70% stenosis considered as being at risk. Each segment receives two points if affected, plus two further points if the lesion affects two of the six downstream myocardial territories, giving rise to a maximum score of 12. The Alberta Provincial Project for Outcome Assessment in Coronary Heart (APPROACH) disease investigators assessed and validated the prognostic value of their own Lesion Score with that of the Duke Jeopardy Score and the Bypass Angioplasty Revascularization Investigation (BARI) Myocardial Jeopardy Index in >20,000 patients undergoing coronary catheterization for ischemic heart disease and found all three scores to be predictive of 1-year mortality (see Figure 2).
(Enlarge Image)
Figure 2.
1-year mortality according to specific myocardium at-risk scores.
(A) Duke Jeopardy Score, (B) BARI Jeopardy Score, (C) APPROACH Lesion Score. The ability of three myocardial Jeopardy Scores to predict 1-year mortality were tested against a cohort of 20,067 patients with ischemic heart disease who underwent cardiac catheterization between 1995 and 1998 in the province of Alberta, Canada (9922 patients treated medically, 6334 patients treated with percutaneous coronary intervention and 3811 patients treated with coronary artery bypass graft surgery). The investigators excluded those patients with valvular heart disease and a previous history of bypass surgery. A preintervention Duke Jeopardy Score >8 is widely accepted as 'high risk' for those patients due to undergo percutaneous coronary intervention.
BARI: Bypass Angioplasty Revascularization Investigation.
Reproduced with permission from [5].
The common thread connecting these multiple variables is the relative inability of the high-risk patient to withstand the hemodynamic sequelae of arrhythmias and even transient periods of ischemia-reperfusion, for instance, during balloon inflation and stent deployment or from the distal embolization of atherogenic material (i.e., the no-reflow phenomenon). These individuals have significantly attenuated hemodynamic reserve and may develop postischemic stunning, leading to a deleterious cascade of decreased diastolic compliance, depressed systolic function leading to a fall in cardiac output and worsening ischemia culminating in cardiogenic shock (CS) or ventricular arrhythmias. Furthermore, high-risk patients with subnormal left ventricular function tend to be older and have more pre-existing comorbidities, both of which are independently associated with poorer outcome post-PCI.
As there is a heightened propensity to suffer catastrophic hemodynamic collapse, either as a direct consequence of the procedure or as a result of the pre-existing proischemic milieu, it seems intuitively attractive to use an adjunctive device that can augment the coronary circulation and reduce the workload of the endangered myocardium during high-risk PCI. One such device is the intra-aortic balloon pump (IABP; MAQUET Cardiovascular, NJ, USA) and the physiological benefits of mechanical counterpulsation it provides (Box 2, Figure 3).
(Enlarge Image)
Figure 3.
Effect of counterpulsation on myocardial oxygen supply and demand.
Diastolic augmentation through counterpulsation increases the pressure difference between the aorta and left ventricle – this is referred to as the DPTI. It is a measure of myocardial oxygen supply. Myocardial oxygen demand is directly related to the area under the left ventricle systolic pressure curve – this is referred to as the TTI. The DPTI:TTI ratio reflects the balance between myocardial oxygen supply and demand and is termed the endocardial viability ratio. Intra-aortic balloon counterpulsation results in an increase in endocardial viability ratio.
DPTI: Diastolic Pressure Time Index; TTI: Tension Time Index; VP: Ventricular pressure.
Reproduced with permission from [9].
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