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Time course of functional recovery after coronary artery bypass graft surgery in patients with chronic left
J L Vanoverschelde1, C Depré, B L Gerber
1Division of Cardiology, Université Catholique de Louvain, Brussels, Belgium. Vanoverschelde@card.ucl.ac.be
Insights
Recovery of heart function after bypass surgery is gradual, taking weeks to months. Improved blood flow and less structural damage predict better outcomes in patients with chronic left ventricular dysfunction.
Area of Science:
- Cardiology
- Cardiac Surgery
- Medical Imaging
Background:
- Chronic left ventricular (LV) ischemic dysfunction, or myocardial hibernation, involves myocyte ultrastructural changes like myofilament loss and glycogen accumulation.
- These structural alterations suggest that contractile function may not immediately recover after revascularization procedures.
Purpose of the Study:
- To assess the timeline of functional improvement following successful revascularization in patients with chronic LV ischemic dysfunction.
- To identify potential structural correlates that influence the rate and extent of functional recovery.
Main Methods:
- Studied 32 patients with coronary disease and chronic LV dysfunction undergoing bypass surgery.
- Utilized dynamic positron emission tomography (PET) for myocardial perfusion and glucose metabolism assessment.
- Performed serial echocardiography to measure LV function and transmural biopsies to analyze extracellular matrix and cardiomyocyte structure.
Main Results:
- Nineteen patients showed improved LV function post-revascularization, while 13 had persistent dysfunction.
- Reversibly dysfunctional segments exhibited higher myocardial blood flow and glucose uptake, with less extracellular matrix increase compared to persistently dysfunctional segments.
- Functional recovery followed a monoexponential time course (median time constant of 23 days), correlating with myocardial blood flow and cardiomyocyte structural integrity.
Conclusions:
- Regional and global LV function recovery after revascularization is a progressive, monoexponential process.
- The extent of structural changes in cardiomyocytes and extracellular matrix significantly influences the rate of functional recovery.
- Myocardial blood flow and preserved myocyte structure are key determinants for successful functional restoration in hibernating myocardium.
Abstract:
Chronic left ventricular (LV) ischemic dysfunction, a condition often referred to as myocardial hibernation, is associated in humans with ultrastructural alterations of the myocytes, including the loss of myofilaments and the accumulation of glycogen. Given the severity of these structural changes, contractile function is unlikely to resume immediately upon revascularization. Therefore, the aim of the present study was to assess the time course of functional improvement after successful revascularization as well as its potential structural correlates. We studied 32 patients with coronary disease and chronic LV ischemic dysfunction who underwent bypass surgery. Dynamic positron emission tomography with N-13 ammonia and F-18 deoxyglucose to assess myocardial perfusion and glucose metabolism was performed in 29 patients. In all patients, a transmural biopsy was harvested from the center of the dysfunctional area, to quantify the increase in extracellular matrix and the presence of structurally altered cardiomyocytes. LV function was serially measured by digitized 2-dimensional echocardiography before and at 10 days, 2 months, and 6 months after revascularization. The time course of recovery of regional function was estimated from the monoexponential decrease in dysfunctional wall motion score. At follow-up, 19 patients had improved LV function, whereas 13 patients showed persistent dysfunction. Before revascularization, reversibly dysfunctional segments had higher myocardial blood flow (82 +/- 29 vs 53 +/- 21 ml. (min. 100 g)(-1), p = 0.044), higher glucose uptake (40 +/- 16 vs 21 +/- 9 micromol. (min. 100 g)(-1), p = 0.001), and less increase in extracellular matrix (25 +/- 15% vs 46 +/- 17%, p = 0.0008) than segments with persistent dysfunction. The extent to which function recovered was positively correlated with myocardial blood flow and negatively correlated with the increase in the extracellular matrix. In patients with reversible dysfunction, the return of segmental function was progressive and followed a monoexponential time course with a median time constant of 23 days (range 6 to 78). The rate of recovery correlated best with the proportion of altered cardiomyocytes in the biopsy. The present study thus indicates that the recovery of regional and global LV function after successful revascularization is progressive and follows a monoexponential time course that is influenced by the extent of the structural changes affecting cardiomyocytes.