Background The impact of varying AV delay on the acute mechanoenergetic efficiency of cardiac resynchronisation therapy (CRT) is not known; nor is known if non-invasive haemodynamic optimisation by blood pressure agrees with invasive haemodynamic measures during optimisation. We studied these invasively, in contemporary patients.

Methods Eleven patients with heart failure (EF 29±8%) and left bundle branch block (LBBB, QRS 154±26 ms) underwent measurements of left ventricular (LV) pulse pressure (systolic minus diastolic), aortic flow velocity and myocardial oxygen consumption (MVO2) at four settings: 3 AV delays during biventricular (BiV) pacing (reference BiV-AV120 ms; BiV-AV40 ms; individualised haemodynamic BiV-AVoptimum), and at intrinsic ventricular conduction (LBBB). Atrial pacing at 100 bpm ensured a fixed heart rate.

Results LV pulse pressure rose from LBBB to BiV-AV120 ms by 10±2% (p<0.001) and 2±1% more (p<0.05) at the haemodynamic BiV-AVoptimum. At BiV-AV40 ms, pressure was 10±2% worse than BiV-AV120 ms (p<0.001), no different to LBBB (Δ=0.8±0.4%, p=ns). Invasive aortic flow velocity, measured at a fixed position throughout each individual's study (ie, cardiac output index), rose by 9±2% (p<0.01) from LBBB to BiV-AV120 ms, rising a further 3±1% (p<0.01) at BiV-AVoptimum. At BiV-AV40 ms, aortic flow was, no different to LBBB (p=NS). MVO2 increased from LBBB to BiV-AV120 ms by 9±4% (p=0.035) and to BiV-AVoptimum by 12±3% (p=0.002). MVO2 at At BiV-AV40 ms and LBBB was not significantly different (Δ4±3%, p=ns), The 4 pacing states lay on a straight line: for Δpressure against Δflow, r=0.99 (p<0.01), Abstract 88 figure 1. Δexternal work (Δpressure ×Δflow) correlated with Δ MVO2, r=0.99 (p<0.01), with slope 1.61±0.17, significantly greater than 1.00 (p<0.05), Abstract 88 figure 2.

• Download figure
• Open in new tab
• Download powerpoint

Abstract 88 Figure 1

The correlation of LV pulse pressure and aortic flow velocity during acute biventricular pacing, (at three AV delays) and during LBBB, at a fixed heart rate.

• Download figure
• Open in new tab
• Download powerpoint

Abstract 88 Figure 2

The correlation of cardiac work and myocardial oxygen consumption during acute biventricular pacing, (at three AV delays) and during LBBB, at a fixed heart rate.

The correlations of optimal AV delays by non-invasive (Finometer) systolic blood pressure (SBP) vs invasive measures were as follows; aortic SBP, r²=0.96, p<0.01; aortic flow velocity, r²=0.81, p<0.01; LV dP/dtmax, r²=0.68, p<0.01.

Conclusions During acute biventricular pacing, at a fixed heart rate, changing the AV delay affects the cardiac mechanoenergetics. When an AV delay improves external cardiac work, compared to LBBB or a physiologically too short AV delay (eg, AV 40 ms), it also increases the myocardial oxygen consumption. However, only 1% more energy is consumed per 1.6% more external work (pressure×flow) done; as a result cardiac efficiency improves. Haemodynamic optimisation of AV delay can be achieved with high precision using non invasive beat-to-beat pressure measurements. This should enable routine haemodynamic optimisation (easily automated) of CRT devices in clinical practice.