A Left Ventricular Assist Device (LVAD) is a mechanical pump surgically implanted in patients with advanced heart failure. It assists the left ventricle in circulating blood to the body. LVADs serve as a bridge to heart transplantation for some, and provide long-term support (destination therapy) for others. Assessing LVAD function is important for patient well-being and safety.
Understanding LVAD Operation
An LVAD operates on a continuous flow principle, unlike the pulsatile action of a healthy heart. The device draws blood from the left ventricle and continuously propels it into the aorta, supplementing the heart’s natural pumping ability. This continuous flow means LVAD patients typically do not have a palpable pulse.
Traditional blood pressure measurements, which rely on detecting a pulse, are ineffective for LVAD patients. Instead, mean arterial pressure (MAP) is measured using a Doppler device. The LVAD system consists of an internal pump, an external driveline, a controller, and batteries.
The LVAD controller displays several important parameters. “Speed” indicates the revolutions per minute (RPM) at which the pump’s rotor is spinning, a setting typically adjusted by healthcare providers. “Flow” is an estimated measurement of the blood volume (in liters per minute) being pumped, derived from the pump’s speed and power. “Power,” measured in watts, reflects the energy the pump is using to move blood.
Another parameter, “Pulsatility Index” (PI), indicates the native heart’s contribution to blood flow. A higher PI suggests more support from the patient’s own heart, while a lower PI indicates greater reliance on the LVAD. Monitoring these parameters helps understand how effectively the device supports circulation.
Practical Assessment Methods
Assessing LVAD function involves device monitoring and observing the patient’s physical state. One straightforward method is listening for the characteristic hum of the pump, which indicates it is actively running. This hum can be heard over the patient’s left chest area.
The LVAD controller should be routinely checked for any alarms or error messages. The display also provides real-time readings of the pump’s speed, flow, power, and pulsatility index. These values should be consistent with the patient’s normal operating parameters and trends.
Beyond device readings, observing the patient’s overall well-being offers clues about LVAD function. Signs of adequate perfusion include warm, pink skin, a brisk capillary refill (where color returns quickly after pressing on a fingernail), clear mental alertness, and normal urine output.
Measuring mean arterial pressure (MAP) using a Doppler device is a standard assessment for LVAD patients. This involves placing a blood pressure cuff on the arm and a Doppler probe over the brachial artery to detect blood flow. The cuff is inflated until the flow sound disappears, then slowly deflated; the pressure at which the sound reappears is recorded as the MAP.
A typical target MAP range for LVAD patients is between 70 and 90 mmHg, though optimal ranges can vary based on individual patient needs. Maintaining daily logs of LVAD parameters and physical observations is valuable for tracking trends and identifying any subtle changes that might indicate a developing concern.
Understanding and Addressing Common Concerns
Changes in LVAD parameters or patient symptoms can signal various concerns. A sudden drop in flow, accompanied by low power or speed readings, may indicate hypovolemia (low blood volume) or a suction event, where the pump pulls against the heart wall due to insufficient blood in the ventricle. Administering fluids may help in cases of hypovolemia.
Conversely, an unexpected increase in pump power, sometimes with high flow readings, can be a sign of pump thrombosis, which is the formation of a blood clot within the device. This is a serious concern requiring immediate medical attention. Any significant shifts in the pulsatility index should also be noted, as they can reflect changes in the heart’s native function or volume status.
Anticoagulation therapy is a critical aspect of LVAD management to prevent blood clots. Patients are typically prescribed medications like warfarin, often combined with aspirin, to reduce the risk of pump thrombosis and stroke. Regular monitoring of the International Normalized Ratio (INR) is necessary to ensure the blood’s clotting time remains within a target range, often between 2.0 and 3.0.
Recognizing when to seek medical help is paramount for LVAD patients and their caregivers. Persistent alarms from the controller, unexplained changes in LVAD parameters, or new or worsening symptoms such as dizziness, shortness of breath, or chest pain warrant immediate contact with the LVAD coordination team or emergency services. Timely intervention can prevent more serious complications.