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ABSTRACT: The mechanisms underlying cardiac resynchronization therapy have consistently been studied at rest and remain ill defined. Peak stress total isovolumic time (t-IVT) is a major determinant of cardiac output (CO) in chronic heart failure. In this study, pharmacologic stress was used to assess the effects of atrioventricular (AV) delay shortening and ventricular resynchronization elements of cardiac resynchronization therapy. Thirty patients undergoing cardiac resynchronization therapy were studied <6 months after implantation. t-IVT and CO were measured during native activation (left bundle branch block), AV delay shortening (right ventricular dual-chamber pacing), and full resynchronization (atrio-biventricular pacing). Full resynchronization shortened peak stress t-IVT by 9.4 +/- 6.2 s/min (p <0.001) and increased peak stress CO by 0.9 +/- 0.4 L/min (p <0.001), with the effects in individual patients showing a large correlation (r = -0.64, p <0.001). In contrast, simple AV delay shortening did not shorten peak stress t-IVT nor increase peak stress CO, nor was CO at rest affected by full resynchronization or AV delay shortening. Of all measurements during native activation, the best predictor of gain in peak stress CO from full resynchronization was peak stress t-IVT (r = 0.75, p <0.001), with every 5 s/min increment in peak stress t-IVT during native activation predicting a 6% gain in peak stress CO. No conventional measures during native activation at rest or during stress (including QRS duration, the Tei index, tissue Doppler intraventricular delay, and t-IVT at rest) added significant additional information. In conclusion, only during stress does resynchronization consistently increase CO. Second, little of this increment in CO is achieved by AV delay shortening alone. Third, under native activation, long t-IVT during peak stress is the single best predictor of resynchronization-mediated increment in peak stress CO.
The American Journal of Cardiology 05/2006; 97(9):1358-64. · 3.37 Impact Factor
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ABSTRACT: Cardiac resynchronization fails to improve symptoms in up to one third of patients meeting criteria for this treatment, for reasons which are unclear. Indeed, the very mechanism of benefit from resynchronization is controversial. Resynchronization may work by improving ventricular filling: we tested the hypothesis that benefit from resynchronization depends on filling pattern.
We assessed symptoms (NYHA class) and LV filling of 40 patients with chronic heart failure and prolonged QRS who underwent resynchronization. Fifteen had restrictive filling pattern (E velocity>or=1.0 m/s, E/A ratio>1 and E wave deceleration time<or=140 ms) and 25 had late filling pattern (single isolated A wave or summation wave filling in late diastole). At 6 months, the patients with restrictive filling failed to show the improvements observed in those with late filling. They failed to reduce NYHA class (DeltaNYHA: 27% improved one class, 66% unchanged, 7% worsened one class, P=NS; vs. 8% improved two classes, 72% improved one class and 20% unchanged, P<0.001; difference between groups, P<0.001). They failed to reduce LV end-diastolic dimension (DeltaLVEDD -0.04 cm, P=NS; vs. -0.6, P<0.001; difference between groups, P<0.05) or end-systolic dimension (DeltaLVESD -0.01 cm, P=NS; vs. -0.6, P<0.001; difference between groups, P<0.05). They failed to improve cardiac cycle efficiency (Deltatotal isovolumic [wasted] time 2.1 s/min, P=NS; vs. -5.4 s/min; difference between groups, P<0.001).
Among patients routinely eligible for resynchronization, those with restrictive filling may show significantly less (and possibly no) improvement in symptom class and ventricular dimensions after resynchronization. Their failure to improve cardiac cycle efficiency may account for their attenuated clinical benefit.
International Journal of Cardiology 04/2005; 100(1):5-12. · 7.08 Impact Factor
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ABSTRACT: To investigate ventricular long-axis function in cardiac amyloidosis (CA) and idiopathic restrictive cardiomyopathy (IRC), 16 patients with CA and 14 with IRC were studied. Left ventricular (LV) long-axis function was depressed in all patients with CA compared with only 36% of patients with IRC. Impairment in longitudinal function was clearly evident, even if fractional shortening and LV filling were normal. Ventricular long-axis function may be used as a sensitive marker of early systolic dysfunction. CA and IRC have quite distinct pathophysiologic profiles, raising some concerns about the appropriateness of considering them as 2 subtypes of a single nosographic entity.
The American Journal of Cardiology 02/2005; 95(1):146-9. · 3.37 Impact Factor
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Philip Poole-Wilson
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ABSTRACT: Cardiovascular disease is the commonest chronic illness in both developed and developing countries, causing the most deaths and the greatest impact on morbidity. The superiority of disease prevention over treatment was appreciated at least 5,000 years ago in China. The link between the existence of disease in society and the political and social circumstances of a country was emphasised by Virchow in the nineteenth century. The scientific basis and methods for prevention of cardiovascular disease are known. What are lacking are the will and the means to implement change. The well-intentioned often have a dominant sense of entitlement in the pursuit of the common goal of disease prevention. There is a failure of many organisations to acknowledge the importance of other groups within society in achieving the common goal. Doctors, particularly cardiovascular physicians and cardiologists, must play a much greater role in linking with the public, other health workers, epidemiologists, media, industry, academia and politicians. Too many vested interests obstruct progress in the prevention of cardiovascular disease.
Clinical medicine (London, England) 5(4):379-84. · 1.15 Impact Factor
