Heart failure module 5: surgical management

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Introduction

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

Much contemporary focus in heart failure (HF) management remains on medical and device therapy but surgeons remain an integral part of any HF team and bring four main approaches to treatment:

  • coronary revascularisation
  • surgical ventricular restoration
  • mechanical circulatory support
  • cardiac transplantation.

The first two approaches have seen their role questioned in recent years. This module therefore concentrates on the latter two approaches, which continue to provide life-saving therapy to patients with the most advanced disease.

Left ventricular assist devices

Figure 2. Contemporary indications for left ventricular assist device implantation. Panel A shows implants in the UK between 2004−2011. Panel B shows implants in 2012 recorded in the 5th Report from the Interagency Registry for Mechanically Assisted Circulatory Support, which collects data from centres in North America
Figure 1. HeartMate II® (Thoratec Corporation)

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 been developed as separate, implantable left ventricular assist devices (LVADs) used as a holding measure until an organ becomes available for cardiac transplantation (see figure 1). This so-called ‘bridge to transplantation’ (BTT) is the only indication available in the UK for NHS funding although, in practice, there are emergency cases where eligibility for transplantation cannot be fully assessed and a ‘bridge to decision’ or ‘bridge to candidacy’ is necessary. BTT is the most common LVAD indication in the UK but long-term treatment of patients ineligible for transplantation (so-called destination therapy [DT]) is overtaking it worldwide (see figure 2).1,2 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.

The standard circuit brings blood from the left ventricle to the pump with outflow to the aorta, creating a mechanical bypass of the left ventricular (LV) outflow. This can yield benefits such as those shown in figure 3.

Figure 3. Benefits of left ventricular assist devices
Figure 3. Benefits of left ventricular assist devices

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. Their clear haemodynamic benefits were offset by significant morbidity from extensive surgical dissection owing to their size, high rates of infection due to the high calibre driveline, and limited durability necessitating reoperation.

The second-generation pumps are impeller pumps providing continuous flow (e.g. HeartMate® II, Jarvik 2000) and in a direct comparison with first-generation technology, the HeartMate® II showed a survival benefit (see figure 4).3 Moreover there was less morbidity owing to their significantly smaller size.

Figure 4. Improved survival with second-generation technology
Figure 4. Improved survival with second-generation technology

Various third-generation devices are now in use or undergoing further evaluation. An example is the HeartWare® HVAD®. This provides continuous flow but using a balance between magnetic and hydrodynamic forces to levitate and rotate the impeller, avoiding wear on bearings and facilitating a smaller device size. These are promising and bring potentially large benefits, 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. A study by Slaughter et al. found that 44% of patients implanted with the second-generation HeartMate® II device still suffered death or disabling stroke within two years, despite improvement from first-generation devices. Contemporary data still document 70% of patients suffering a first episode of infection, bleeding, device malfunction, stroke or death within one year (see figure 5).2

Figure 5. 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 5. 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.

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.