Heart failure module 6: surgical management

Released1 November 2017     Expires: 01 November 2019      Programme:

Introduction

Medical and device therapy has provided great benefit for many millions of patients with heart failure: 15% of patients with stable heart failure with reduced ejection fraction (HeFREF) recover their left ventricular function within three years, the same proportion as those who deteriorate or die suddenly and surgical intervention is sometimes necessary.

Figure 1. HeartMate II® (Thoratec Corporation)
Figure 1. An example of a left ventricular assist device

Surgical treatment for heart failure includes:

  • mechanical circulatory support
      – left ventricular assist devices (LVAD)
  • cardiac transplantation
  • coronary revascularisation
  • surgical ventricular restoration.

Left ventricular assist devices (LVAD)

Mechanical circulatory support (MCS) was developed as a rescue therapy for patients in intractable cardiogenic shock. The first devices were conceived as a continuum for patients who were unable to wean from cardiopulmonary bypass (CPB) and have progressed to separate, implantable left ventricular assist devices (LVADs) (figure 1).

Until recently, LVADs were only indicated as a holding measure until an organ became available or until a decision was made regarding cardiac transplantation; so-called ‘bridge to transplantation’ (BTT) or ‘bridge to decision’ (BTD). However, in 2015 the National Institute for Health and Clinical Excellence (NICE) published guidelines also recommending LVADs as long-term therapy for patients ineligible for transplantation; so-called ‘destination therapy’ (DT).1 LVADs are used as DT more commonly than other indications worldwide (figure 2).2 In a minority of patients, the haemodynamic relief provided by the LVAD can facilitate recovery of myocardial function and explant of the device, though the majority will require continued support.

Heart failure learning module 6 - Figure 2. Contemporary indications for left ventricular assist device implantation
Figure 2. Contemporary indications for left ventricular assist device implantation

The standard LVAD circuit pumps blood from the left ventricular (LV) cavity through the device into the ascending aorta, creating a mechanical bypass of the LV outflow. The left ventricle is thus off-loaded (and the aortic valve may remain closed). Cardiac output is thus increased.

Beneficial effects of LVAD include:

  • increased systemic blood pressure
  • improved organ perfusion and subsequent beneficial neuro-hormonal changes
  • reduced cardiac chamber size
  • reduced left atrial and pulmonary pressures.

Development (click here to find out more about LVAD design)

The first generation of these devices (e.g. HeartMate® I) were large, pulsatile displacement pumps. The haemodynamic benefits were offset by significant morbidity from extensive surgical dissection required for a large device, high rates of infection due to the high calibre driveline, and limited durability necessitating reoperation.

The second-generation pumps (e.g. HeartMate® II, Jarvik 2000) are smaller devices with impeller pumps that provide continuous flow compared to biphasic flow of first generation devices. In head-to-head trials with first-generation technology, implantation of the HeartMate® II device was associated with increased survival rates (figure 3) and reduced complications rates, possibly due to the smaller size.3

Figure 3. Improved survival with second-generation technology
Figure 3. Improved survival with second-generation technology

Various third-generation devices are now in use or undergoing further evaluation. An example is the HeartWare® HVAD®, which has a miniaturised centrifugal pump that uses magnetic and hydrodynamic forces to levitate and rotate the impeller, theoretically avoiding wear on bearings. The smaller device size allows for quick and less invasive implantation though the adverse event rate remains stubbornly high.

Despite developments in design, the morbidity associated with LVAD therapy continues to obstruct further progress in the field: 70% of patients with either continuous or pulsatile LVAD suffer a first episode of infection, bleeding, device malfunction, stroke or death within one year4 (figure 4).

Figure 4. Graph showing time to first major event with 70% of patients suffering an adverse event* during the first year following implant for mechanical circulatory support
Figure 4. Graph showing time to first major event with 70% of patients suffering an adverse event* during the first year following implant for mechanical circulatory support

The most frequent problems encountered during LVAD therapy are:

Bleeding and thrombosis

All patients require anticoagulation, with the specific regime varying between devices. All patients develop acquired von Willebrand factor deficiency. The tiny pulse pressure with continuous flow pumps is associated with gastrointestinal bleeding due to angiodysplasia. Device thrombosis is a difficult problem manifested by increased power consumption, clinical or laboratory signs of haemolysis (e.g. elevated bilirubin, plasma haemoglobin and lactate dehydrogenase levels) or device stoppage. It can be treated with intravenous heparin, fibrinolytics or surgery (pump exchange or urgent transplant).

Infection

Infection risk remains high due to the artificial surfaces of the pump itself creating surfaces for colonisation, and due to the percutaneous driveline that delivers power. Severity of infection can vary from asymptomatic driveline site colonisation to deep abscesses or device-related endocarditis. Wound care requires specialist nursing oversight.

Right ventricular failure

This is precipitated by failure of the right ventricle (RV) to handle the volume returned to it by the assisted LV. This could be manifested by distended neck veins, liver congestion and increasing oedema accompanied by a deterioration in exercise capacity and increasing natriuretic peptides. Treatment is with diuretics, adjustment to the LVAD speed, or insertion of a right-sided VAD in extreme cases.

Stroke

Both types of stroke – ischaemic due to embolism or haemorrhagic due to bleeding – are often catastrophic if they occur, especially in the haemorrhagic setting where anticoagulation cannot be stopped due to the high likelihood of device thrombosis and failure.

Acquired aortic regurgitation

LVAD therapy creates a large pressure gradient from aorta to LV, transmitted across the aortic valve. This can lead to aortic regurgitation, which decreases the efficacy of support and longevity of the device. Up to 50% will have moderate to severe aortic insufficiency at 18 months, and the problem is difficult to treat. Options include open or transcatheter valve replacement, or cardiac transplantation.

High adverse event rates are inevitable in severely unwell and unstable patients such as those suitable for LVAD therapy. Trials of LVADs in patients with less severe disease have had mixed results. REVIVE-IT (Randomised Evaluation of VAD Interventillation before Inotropic therapy), a randomised controlled trial of LVADs in patients who were less ill than patients currently eligible for destination therapy (New York Heart Association [NYHA] class II-IV with ‘advanced heart failure’ defined by markers such as hyponatraemia or high natriuretic peptide), was discontinued because of the high adverse event rate.5

The ROADMAP (Risk Assessment and Comparative Effectiveness of Left Ventricular Assist Device and Medical Management in Ambulatory Heart Failure Patients) study (n=200, average age 64 years and median brain natriuretic peptide [BNP] 547 pg/mL in the LVAD arm), is a non-randomised trial of second-generation LVADs versus optimal medical therapy (OMT). The primary end point was survival on original therapy with >75 m improvement in six-minute walk distance at one year. More patients in the LVAD group met the primary endpoint, with the difference increasing at two years’ follow up (30% vs. 12%; P=0.012).6,7 In an as-treated analysis, LVAD implantation was associated with a better one year survival (80% vs. 63%, p=0.02), but because 30% of patients in the OMT group had LVAD implantation over two years, there was no significant difference in intention-to-treat analysis.6

The future of LVADs lies not only in developing technology to reduce the morbidity and cost of long-term therapy, but also in the appropriate deployment of these devices, avoiding their use very late in the natural history of heart failure when there is serious co-morbidity. Thus the timing of LVAD insertion remains critical. Only with this will the balance of risk be shifted in their favour and the health economic argument won.

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