Temporal relationship between haemodynamic changes and activation of closed-loop stimulation during a tilt-induced vasovagal syncope

Figures

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  Figure 1. CLS pacing activated during a tilt test, followed by syncope. The top panel shows the trends of BP (grey lines: systolic, mean, and diastolic) and HR (red line) during the tilt test. After a stable phase, BP began to fall and HR began to rise from the 24th minute. Atrial-paced ventricular-sensed CLS pacing onset occurred after 26 min (blue vertical line A and bottom panel A). At that time, SBP and HR were 125 mmHg and 90 b.p.m.. Thereafter, SBP and HR briefly increased to 145 mmHg and 102 b.p.m. At 1.43 min after the onset of CLS pacing, the SBP rapidly fell to 58 mmHg, and the patient lost consciousness during sequential atrial and ventricular CLS pacing at 95 b.p.m. (blue vertical line B and bottom panel B). After tilting down, there was an immediate BP overshoot and a progressive decrease in HR. BP, blood pressure; CLS, closed-loop stimulation; HR, heart rate; SBP, systolic BP.

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  Figure 2. An impending symptomatic tilt-induced VVS, which was aborted during CLS pacing activation. The top panel shows the trend of BP (grey lines: systolic, mean, and diastolic) and HR (red line) during a tilt test. After a stabilization phase, BP began to fall from the 29th minute. Atrial-paced ventricular-sensed CLS pacing onset occurred after 30 min (blue vertical line A and bottom panel A). At that time, SBP and HR were 82 mmHg and 88 b.p.m. The atrial CLS pacing rate increased to 95 b.p.m. (blue vertical line B and bottom panel B) and remained stable until the 44th minute, when the test was stopped, and the patient was tilted down. The SBP varied slightly between 80 and 90 mmHg until the 34th minute, when the SBP exceeded 100 mmHg until the end of the test. BP, blood pressure; CLS, closed-loop stimulation; HR, heart rate; SBP, systolic blood pressure; VVS, vasovagal syncope.

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  Figure 3. Haemodynamic changes during tilt tests in 14 patients with CLS pacing activation. Data are summarized as mean (red squares) and 95% confidence interval (whiskers). The circles indicate individual values. Stage 1 is the baseline period before tilting up. Stage 2 is the time of CLS pacing onset. Stage 3 is the period of the maximum CLS pacing rate. Stage 4 is the time of syncope or of the lowest SBP in patients without syncope. For each parameter, the result was calculated as the mean value for 10 consecutive beats. P-values refer to the comparison of two consecutive stages. CLS, closed-loop stimulation; DBP, diastolic blood pressure; HR, heart rate; PP, pulse pressure; SBP, systolic blood pressure.

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  Figure 4. The individual duration of CLS pacing in 14 patients (1 bar per patient). The duration of CLS pacing from the CLS onset to syncope or the lowest SBP (left panel) and the total duration of CLS pacing from the CLS onset to the recovery of intrinsic sinus rhythm (right panel). Light blue bars represent 4 patients who did not experience syncope; dark blue bars represent 10 patients with syncope. The solid red line indicates median duration, and the dotted red lines indicate the inter-quartile range. The patients with syncope also had a longer CLS pacing, suggesting a longer duration of the vasovagal reflex. CLS, closed-loop stimulation; HR, heart rate; SBP, systolic blood pressure.

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  Figure 5. The mechanism of CLS. The CLS algorithm measures intra-cardiac impedance (Z) curves of the right ventricle during the systolic phase of each cardiac cycle by injecting sub-threshold high-frequency unipolar current pulses from the ventricular lead tip. Given that the density of electric field lines is greatest around the electrode tip, most of the induced voltage drop at each sub-threshold pulse and, in turn, the main contribution to impedance, occurs in an ∼5 cm3 volume (≍1 cm radius) surrounding the tip electrode. The local changes in the amount of blood and myocardial tissue in the small volume surrounding the tip electrode are the main drivers of measured impedance variations, rather than the changes in the entire intra-ventricular volume. During contraction, blood ejection causes tighter contact of the electrode with myocardial tissue (involving a larger proportion of tissue relative to blood volume), leading to a progressive impedance increase towards late systole. The more the speed of contraction increases, the more the slope of the impedance curve becomes steep (red curve) in comparison with a reference impedance curve obtained during patient resting periods (blue curve).…

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  Figure 6. Factors triggering CLS and pacing rate adaptation. When reading the scheme from right to left, the pacing rate is increased by CLS, which is triggered by a detected variation of the shape of rising impedance curves during systole. Changes in RV impedance are strictly correlated to RV dP/dt max, which is a surrogate of RV contraction speed. Contraction speed in turn is influenced by two factors: elevated heart rate and myocardial contractility. Reprinted with permission from Tomaino et al.10 CLS, closed-loop stimulation; FFR, force–frequency relationship; RV, right ventricular.