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Global Left Ventricular Systolic Function: Ejection Fraction Versus Strain
The assessment of global left ventricular (LV) systolic function is a cornerstone of risk evaluation and management in most cardiac diseases. The simplest and most widely used parameter for this purpose has been ejection fraction (EF) and regional wall motion analysis, but over the past decade, new parameters such as global longitudinal strain (GLS) have become available.
Indications for Systolic Function Evaluation
Echocardiography is appropriately indicated when cardiac related symptoms or conditions are suspected, most commonly in the setting of suspected heart failure (HF). Despite the value of LV dysfunction as an important component of risk evaluation for decision making, the methodologies and cut-offs used in studies that have defined these EF criteria for the guidance of management are highly variable, with few studies using core laboratories ( Table 24.1 ). The EF criteria for implantable defibrillators or cardiac resynchronization therapy (CRT) , or for intervention in regurgitant valve lesions have not been gathered with a high degree of accuracy, and it seems irrational to use them as exact thresholds.
TABLE 24.1
Multicenter Studies That Have Defined Ejection Fraction Criteria for the Guidance of Management in Heart Failure
| Study, Year | Intervention | Patients ( n ) | Technique | Core Lab | Entry Criteria |
|---|---|---|---|---|---|
| SOLVD, 1991 | Enalapril | 2569 | Echo, RNV, LVgram | Yes | EF ≤35% |
| Hydralazine–nitrate, 1991 | Enalapril vs hydralazine–nitrate | 804 | Echo, RNV | Yes | EF <45%, LVEDD >27 mm/m 2 BSA |
| CIBIS, 1994 | Bisoprolol | 641 | RNV, LVgram | No | EF <40% |
| US Carvedilol, 1996 | Carvedilol | 1094 | Echo | Yes | EF ≤35% |
| MERIT-HF, 1999, 2000 | Metoprolol XL | 3991 | Unspecified | No | EF ≤40% |
| CIBIS II, 1999 | Bisoprolol | 2647 | Echo, RNV, LVgram | No | EF ≤35% |
| Capricorn, 2001 | Carvedilol | 1959 | Echo, RNV, LVgram | No | EF ≤40%, WMSI ≤1.3 |
| Carvedilol, 2001 | Carvedilol | 2289 | Unspecified | No | EF <25% |
| BEST, 2001 | Bucindolol | 2708 | RNV | No | EF <35% |
| MIRACLE-ICD, 2003 | CRT/ICD | 369 | Echo | Yes | EF ≤35% |
| COMET, 2003 | Carvedilol vs metoprolol | 1511 | Echo, RNV | No | EF <35% |
| CHARM, 2003 | Candesartan | 2548 | Unspecified | No | EF ≤40% |
| SCD-HeFT, 2005 | ICD | 3521 | Unspecified | No | EF<35% |
| CARE-HF, 2005 | CRT | 813 | Echo | Yes | EF ≤35%, LVEDD >30 mm/m height |
BSA, Body surface area; CRT, cardiac resynchronization therapy; echo, echocardiography; EF, ejection fraction; ICD, implantable cardioverter-defibrillator; LVEDD, left ventricular end-diastolic dimension; LVgram, contrast ventriculography; RNV, radionuclide ventriculography; WMSI, wall motion score index. Studies, in order of appearance: SOLVD, Studies of Left Ventricular Dysfunction; CIBIS, The Cardiac Insufficiency Bisoprolol Study; MERIT-HF, Metoprolol CR/XL Randomized Intervention Trial in Chronic Heart Failure; BEST, Beta-Blocker Evaluation in Survival Trial; MIRACLE-ICD - Multicenter InSync ICD Randomized Clinical Evaluation; COMET, Carvedilol Or Metoprolol European Trial; CHARM, Candesartan in Heart failure—Assessment of moRtality and Morbidity; SCDHeFT, Sudden Cardiac Death in Heart Failure Trial; CARE-HF, Cardiac Resynchronization—Heart Failure.
In asymptomatic subjects at risk for HF, the use of echocardiography to detect reduced EF or subtle structural heart disease reclassifies the patient from stage A to stage B of HF, with resulting management implications. These patients with a subclinical phase to their cardiomyopathy include those treated with cardiotoxic chemotherapy and those with gene-positive cardiomyopathies, amyloidosis, or other infiltrative conditions. The detection of subclinical disease not only includes global but also regional dysfunction (in ischemic heart disease, sarcoidosis, and myocarditis).
Finally, although the temporal analysis of LV contraction carries prognostic information, the clinical application of this remains uncertain. There are very strong prognostic reasons to undertake CRT in patients with HF symptoms, systolic dysfunction, and left bundle branch block, irrespective of the measurement of mechanical synchrony, and there are reasonable grounds to doubt the reliability of some of the literature on prediction of response. Paradoxically, measurement of synchrony may come into clinical use in the selection of patients for implantable defibrillators rather than CRT because measurements of dispersion of mechanical activation may be of value in understanding the risk of arrhythmia.
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