It is estimated that 20–30% of patients with heart failure (HF) have intraventricular conduction disorders resulting in a discoordinate contraction pattern and a wide QRS interval on the electrocardiogram (ECG). This abnormality appears to be associated with increased morbidity and mortality. Biventricular pacing, also known as cardiac resynchronization therapy (CRT) is a treatment for HF that uses an implantable device to improve the pumping efficiency of the heart. Biventricular pacemakers using three leads (one in the right atrium and one in each ventricle) have been investigated as a technique to coordinate the contraction of the ventricles, thus improving patients’ hemodynamic status.
Two strategies are being explored:
- Incorporating biventricular pacing into automatic implantable defibrillators, and
- The development of stand alone biventricular pacemakers.
One stand-alone biventricular pacemaker (InSync® Biventricular Pacing System, Medtronic) has received approval by the U.S. Food and Drug Administration (FDA) for the treatment of patients with NYHA Class III or IV HF, on a stable pharmacologic regimen, who also have a QRS duration of 130 msec or longer and a left-ventricular ejection fraction of 35% or less. Biventricular pacemakers have also been combined with automatic implantable cardiac defibrillators (AICDs). Both Guidant (CONTAC CD® CRT-D System) and Medtronic (InSync® ICD Model 7272) have received FDA approval for combined resynchronization therapy defibrillators for patients at high risk of sudden death due to ventricular arrhythmias and who have NYHA Class III or IV HF with left ventricular ejection fraction of 35% or less, QRS duration of 130 msec or longer (120 msec for the Guidant device) and remain symptomatic despite a stable, optimal HF drug therapy. This combined ventricular/AICD is additionally equipped to monitor intrathoracic fluid levels using bioimpedance technology, referred to as OptiVol™ Fluid Status monitoring.
In 2005, the InSync Sentry system received FDA approval through the supplemental premarket approval (PMA) process. This combined biventricular pacemaker/ICD is also equipped to monitor intrathoracic fluid levels using bioimpedance technology, referred to as OptiVol Fluid Status monitoring. Bioimpedance measures, defined as the electrical resistance of tissue to flow of current, are performed many times per day using a vector from the right ventricular coil on the lead in the right side of the heart to the implanted pacemaker devices; changes in bioimpedance reflect intrathoracic fluid status and are evaluated based on a computer algorithm. For example, changes in a patient’s daily average intrathoracic bioimpedance can be monitored. Differences in the daily average compared to a baseline are reported as the OptiVol™ Fluid Index. It has been proposed that these data may be used as an early warning system of cardiac decompensation, or provide additional feedback enabling a physician to further tailor medical therapy.
In September 2010, the FDA expanded the indications for CRT to include patients with class I and II HF. In addition to NYHA class I/II HF, indications for CRT in mild HF include a left ventricular (LV) ejection fraction of less than 30% and a QRS duration of 130 msec or greater.
The Stages of Heart Failure – NYHA Classification
Class I: no limitation is experienced in any activities; there are no symptoms from ordinary activities.
Class II: slight, mild limitation of activity; the patient is comfortable at rest or with mild exertion.
Class III: marked limitation of any activity; the patient is comfortable only at rest.
Class IV: any physical activity brings on discomfort and symptoms occur at rest.
Galectin-3 is a recently developed biomarker associated with fibrosis and inflammation, and it may play a role in cardiac remodeling in HF. Elevated galectin-3 levels identify a subset of patients with chronic heart failure who suffer from an inherently progressive form of heart failure due to galectin-3-mediated fibrosis and adverse remodeling.
Patients with elevated galectin-3 levels may have worse prognosis in terms of mortality or risk of hospitalization than comparable patients with low levels of galectin-3. It is noted that measuring galectin-3 in patients with heart failure may offer clinically useful information pertaining to risk of adverse outcomes and this information can be used in heart failure patient management
The BGM Galectin-3 blood test is the first novel cardiovascular in-vitro diagnostic to be cleared by the FDA in >5 years. It marks the first clinical application derived from the galectin-3 research and the first blood test indicating the prognosis of patients diagnosed with chronic heart failure that is due to underlying fibrosis resulting in adverse outcomes. The BGM Galectin-3 blood test is based on the common ELISA format, using the standard microtiter plate presentation.