Performance of an artificial intelligence algorithm to detect atrial fibrillation on a 24-hour continuous photoplethysmography recording using a smartwatch: ACURATE study

Background

In the awakening era of mobile health, wearable devices capable of detecting atrial fibrillation (AF) are on the rise. Smartwatches and wristbands are equipped with photoplethysmography (PPG) technology that enables (semi)continuous rhythm monitoring. These devices have been pioneered already in a few screening trials. However, such devices are being spread among consumers at a pace that is not paralleled by the evidence supporting their clinical performance. This imbalance reflects the urgent need for validation studies.

Purpose

To determine the diagnostic performance of an artificial intelligence algorithm to detect AF using photoplethysmography acquired by a smartwatch.

Methods

One hundred patients (≥18 years) without a pacemaker-dependent heart rhythm who were referred to a university hospital or a large tertiary hospital for elective 24-hour ECG Holter monitoring were asked to wear a continuous PPG monitoring smartwatch (i.e. Samsung GWA2 or Empatica E4) simultaneously with the Holter. All activities of daily life were allowed. The ECG trace and PPG waveform were synchronised and fragmented in one-minute fragements. The one-minute ECG fragments were labelled as AF, non-AF, or insufficient quality based on the routine clinical interpretation of the 24-hour Holter (i.e. software + physician overreading). The one-minute PPG fragments were analysed by an artificial intelligence (AI) algorithm (i.e. FibriCheck) and were given the same labels. Diagnostic metrics of the PPG AI algorithm were calculated with respect to the ECG interpretation, for all fragments with sufficient quality for both PPG and ECG.

Results

Four patients had to be excluded due to technical error (3 Holter errors, 1 smartwatch error). The mean age in the remaining study population (n=96) was 59±16 years, 51 (53%) were men and 15 (15.6%) were known with permanent AF. In this population, simultaneous ECG and PPG monitoring was recorded for 115,245 one-minute fragments. Fragments of insufficient quality for ECG (n=1,454; 1.3%), PPG (n=25,704; 22.3%) or both (n=15,362; 13.3%) were excluded. PPG fragments were more frequently of insufficient quality (p<0.001). AF was present in 10,255 (14.1%) of the resulting 72,725 high-quality one-minute fragments. The sensitivity of PPG to detect AF was 93.4% (CI 92.9% - 93.8%). The specificity of PPG to exclude AF was 98.4% (CI 98.3% - 98.5%). As a result, the overall accuracy of the PPG algorithm on one-minute fragment level was 97.7% (CI 97.6%- 97.8%).

Conclusion

Continuous out-of-hospital PPG monitoring using a smartwatch in combination with an AI algorithm can accurately discriminate between AF and non-AF rhythms in a heterogenous patient population. PPG quality is more often affected than ECG quality during daily life activities.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Research Foundation-Flanders, Strategic Basic Research Fund

Assessment of heart rate agreement on continuous photoplethysmography monitoring using a smartwatch versus beat-to-beat synchronized ECG monitoring

Background

In the awakening era of mobile health, wearables equipped with photoplethysmography (PPG) technology to monitor the heart rate (HR) and rhythm are on the rise. Smartwatches and wristbands enable HR monitoring for consumers at massive scale. Unfortunately, once consumers become patients, physicians are limited by insufficient evidence to support the clinical use of PPG based wearables. Accurate identification of heartbeats is the first step in the interpretation of PPG traces and should be validated.

Purpose

To assess the agreement between continuous PPG monitoring using a smartwatch and continuous ECG Holter monitoring in the identification of heartbeats and calculation of the HR.

Methods

One hundred patients (≥18 years) without a pacemaker-dependent heart rhythm who were referred to a university hospital and a large tertiary hospital for elective 24-hour ECG Holter monitoring were asked to wear a continuous PPG monitoring smartwatch (i.e. Samsung GWA2 or Empatica E4) simultaneously with the 24-hour Holter monitor. All activities of daily life were allowed. The ECG trace and PPG waveform were synchronised and fragmented in one-minute fragments. The one-minute ECG fragments were labelled as AF, non-AF, or insufficient quality based on the routine clinical interpretation (i.e. software + physician overreading), and the average HR during each fragment was calculated by Holter algorithm. The PPG fragments were analysed by an artificial intelligence (AI) algorithm (i.e. FibriCheck) that labelled fragments as sufficient or insufficient quality, identified the number of heartbeats and calculated the HR. The agreement between the HR on ECG and PPG in sufficient quality tracings was analysed with linear regression, Pearson's product-moment correlation and Bland-Altman analysis. A subanalysis was performed for AF rhythm and non-AF rhythms.

Results

A total of 72,725 simultaneous ECG and PPG one-minute fragments were recorded in 96 patients, after excluding 4 patients (due to 3 Holter and 1 smartwatch technical error) and 42,520 minutes (36.9%) of insufficient quality (ECG 1,454 (1.3%); PPG 25,704 (22.3%), ECG and PPG 15,362 (13.3%)). The correlation (r=0.935) between ECG and PPG HR was statistically significant (CI 0.934–0.936; P<0.001), with a mean difference between ECG and PPG of 0.8bpm. The lower and upper limit boundary (LLB and ULB; defined as ±1.96 SD) were −8.0bpm and 9.7bpm, respectively, i.e. 95% of PPG measurements identified the HR within 8bpm below or 10bpm above the ECG reference. The mean difference between ECG and PPG HR in the AF subgroup (n=10,255 (14.1%)) was 0.9bpm (LLB −8.4bpm; ULB 10.2bpm) and 0.8bpm in the non-AF subgroup (LLB −0.8bpm; ULB 9.6bpm).

Conclusion

The AI algorithm analysing continuous out-of-hospital PPG tracings can annotate heartbeats and assess HR without a clinically significant bias compared to continuous ECG monitoring, both during AF and non-AF rhythms in a heterogenous patient population.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research Foundation-Flanders, Strategic Basic Research Fund Correlation plot & Bland-Altman plot

Evaluation of the device independent nature of a photoplethysmography-deriving smartphone app

Funding Acknowledgements

Type of funding sources: None.

Background

Smartphone apps using photoplethysmography (PPG) technology enable digital heart rhythm monitoring through their built-in camera, without the need for additional, specific, or costly hardware. This may positively impact the availability and scalability of remote monitoring. However, the diversity of smartphone specifications on the consumer market may raise concerns regarding the robustness of AF detection algorithms between various devices.

Purpose

To study the device independency of AF detection performance by a PPG-based smartphone application.

Methods

Patients from the cardiology department were consecutively enrolled. Patients were handed 7 iOS models and 1 Android model and were asked to consecutively perform one PPG measurement per device. A 12-lead electrocardiogram (ECG) was collected during the same consultation and interpreted by a cardiologist as reference diagnosis. To allow an objective comparison across the devices, patients who failed to perform one successful measurement on each device were excluded. Additional exclusions were atrial flutter rhythms and insufficient quality results. Sensitivity, specificity and accuracy were calculated with respect to the reference diagnosis. McNemar’s analysis was used for the head-to-head comparison of the sensitivity and specificity of the proprietary algorithm on the different smartphone devices.

Results

A total of 150 patients participated in the study with a median CHA2DS2-VASc score of 3 (interquartile range: 1-5). The median age of the study population was 70 (interquartile range: 56-79) years. In total, 54.7% of the population was male and the AF-prevalence was 35.3%. After the exclusion of patients with atrial flutter (n = 14) and patients who did not successfully perform a PPG measurement on each device (n = 5), diagnostic-grade results of 131 patients were used to calculate the performance of the proprietary algorithm. The sensitivity and specificity of the AF detection algorithm ranged from 90.9% (95% CI 75.7-98.1) to 100.0% (95% CI 91.0-100) and 94.5% (95% CI 86.6-98.5) to 100.0% (95% CI 94.6-100), respectively. The overall accuracy across the devices ranged from 94.4% (95% CI 88.3-97.9) to 99.0% (95% CI 94.6-100). Head-to-head comparisons of the results did not reveal significant differences in sensitivity (P = 0.125-1.000) or specificity (P = 0.375-1.000) of the proprietary AF detection algorithm among the different devices.

Conclusion

This study demonstrated the device-independent nature of the PPG-deriving smartphone application with respect to 12-lead ECG diagnosis.

The accuracy of physician interpretation of PPG vs single-lead ECG vs 12-lead ECG for the detection of atrial fibrillation

Funding Acknowledgements

Type of funding sources: None.

Introduction

The increasing availability of smartphones has enabled rhythm monitoring in large populations using standalone photoplethysmography (PPG) apps or singe-lead electrocardiography (ECG) with add-on devices. Current guidelines note that when atrial fibrillation (AF) is suspected by an automated algorithm, confirmation on an ECG tracing is required. The use of PPG alone to establish the diagnosis is not generally accepted, even when overread. The performance of physicians to discriminate between sinus rhythm (SR) and AF based on PPG alone is unknown.

Purpose

To study the performance of physicians to detect AF based on PPG vs single-lead ECG vs 12-lead ECG, and to explore the incremental value of a tachogram, Poincaré plot, and algorithm output to the interpretation of the PPG waveform by physicians.

Methods

PPG, single-lead ECG and 12-lead ECG data were simultaneously recorded in 30 patients. Diagnostic reference was the 12-lead ECG, read by two cardiologists. Cardiologists, electrophysiologists and cardiology fellows were invited to analyse the data of 30 patients (10 in SR, 10 in SR with extrasystoles and 10 in AF) through online surveys and classify the readings as ‘SR’, ‘ectopic/missed beats’, ‘AF’, ‘flutter’ or ‘unreadable’. For dichotomous analysis, ‘unreadable’ was reclassified as incorrect, the other options were reclassified as AF ‘present’ or ‘absent’. In the first survey, PPG data were presented subsequently as a waveform, stepwise adding the tachogram and Poincaré plot, and algorithm information. In the next two surveys, the single-lead and 12-lead ECG traces were presented. Sensitivity and specificity for all presentations were calculated with respect to the reference diagnosis. Diagnostic performances were compared with the Obuchowski-Rockette’s ANOVA approach with Jackknife covariance estimation and Benjamini-Hochberg correction.

Results

Sixty-five physicians completed the PPG survey and analysed the PPG waveforms with 88.8% sensitivity and 86.3% specificity for AF. The diagnostic metrics significantly increased to 95.5% sensitivity (P < 0.001) and 92.5% specificity (P < 0.001) after providing the tachogram and Poincaré plot. Fifty-seven physicians completed both ECG surveys and analysed the single-lead ECG outputs with 91.2% sensitivity and 93.9% specificity, while 12-lead ECG outputs were analysed with 93.9% sensitivity and 98.6% specificity. Hence, qualitative analysis of a PPG waveform with tachogram and Poincaré plot had a similar diagnostic performance to detect AF compared to single-lead ECG analysis and a similar sensitivity (P = 0.792) but lower specificity (P = 0.035) compared to 12-lead ECG.

Conclusions

PPG rhythm recordings, analysed by physicians as a waveform in combination with the corresponding tachogram and Poincaré plot, achieve similar diagnostic accuracy as single-lead ECG to detect AF. Abstract Figure.

Endothelial Zeb2 preserves the hepatic angioarchitecture and protects against liver fibrosis

Aims

Hepatic capillaries are lined with specialized liver sinusoidal endothelial cells (LSECs) which support macromolecule passage to hepatocytes and prevent fibrosis by keeping hepatic stellate cells (HSCs) quiescent. LSEC specialization is co-determined by transcription factors. The zinc-finger E-box-binding homeobox (Zeb)2 transcription factor is enriched in LSECs. Here, we aimed to elucidate the endothelium-specific role of Zeb2 during maintenance of the liver and in liver fibrosis.

Methods and results

To study the role of Zeb2 in liver endothelium we generated EC-specific Zeb2 knock-out (EC^KO) mice. Sequencing of liver EC RNA revealed that deficiency of Zeb2 results in prominent expression changes in angiogenesis-related genes. Accordingly, the vascular area was expanded and the presence of pillars inside EC^KO liver vessels indicated that this was likely due to increased intussusceptive angiogenesis. LSEC marker expression was not profoundly affected and fenestrations were preserved upon Zeb2 deficiency. However, an increase in continuous EC markers suggested that Zeb2-deficient LSECs are more prone to dedifferentiation, a process called ‘capillarization’. Changes in the endothelial expression of ligands that may be involved in HSC quiescence together with significant changes in the expression profile of HSCs showed that Zeb2 regulates LSEC–HSC communication and HSC activation. Accordingly, upon exposure to the hepatotoxin carbon tetrachloride (CCl₄), livers of EC^KO mice showed increased capillarization, HSC activation, and fibrosis compared to livers from wild-type littermates. The vascular maintenance and anti-fibrotic role of endothelial Zeb2 was confirmed in mice with EC-specific overexpression of Zeb2, as the latter resulted in reduced vascularity and attenuated CCl₄-induced liver fibrosis.

Conclusion

Endothelial Zeb2 preserves liver angioarchitecture and protects against liver fibrosis. Zeb2 and Zeb2-dependent genes in liver ECs may be exploited to design novel therapeutic strategies to attenuate hepatic fibrosis.

P1457Preliminary results of the FLASH-AF: Validation of the device independent nature of a pulse deriving smartphone application for the detection of atrial fibrillation

Background

Smartphone applications using photoplethysmography (PPG) technology through their camera are becoming an attractive alternative for atrial fibrillation (AF) screening due to their low cost, convenience, and broad accessibility. However, some important questions concerning their diagnostic accuracy, robustness and device independent nature remain to be answered.

Purpose

This study evaluated the diagnostic accuracy of a PPG-based pulse-deriving smartphone application with respect to handheld single-lead ECG and 12-lead ECG. In addition, the device dependent nature and robustness of the performance of the application was assessed.

Methods

300 Patients who are scheduled for a regular consultation or procedure (i.e. ablation or cardioversion) will be recruited from the cardiology ward. Additionally, patients hospitalized for continuous cardiac monitoring will be recruited to enrich the database with AF measurements. After obtaining written informed consent, the patients fill in a questionnaire collecting demographic and medical information.

The pulse-deriving application will be tested on total of 14 different smartphones, 7 iOS devices and 7 Android devices. In total, each device will be measured with 150 times. The patients will additionally perform a single-lead ECG measurement with a handheld device. Subsequently, a 12-lead ECG will be recorded to obtain the reference diagnosis.

Results

A total of 164 patients already participated in the study. The mean age was 64 (±19) years, 58% was male. The AF-prevalence was 37%. On average, patients in AF had a higher CHA2DS2-VASc score; 3.93 (±1.80) compared to 2.02 (±1.63) for non-AF patients.

The amount of insufficient quality measurements recorded with the pulse-deriving smartphone application ranged from 4% (iOS) to 13% (Android). Averaged for all the smartphone devices, the pulse-deriving application scored 81.2% (±5%) sensitivity, 97.1% (±1%) specificity, 88.8% (±2%) NPV, 95.0% (±1%) PPV, and 90.9% (±2%) accuracy. The handheld single-lead ECG device had 78.2% sensitivity, 95.5% specificity, 87.6% NPV, 91.5% PPV, and 88.9% accuracy.

The same calculations were preformed after excluding regular atrial flutter measurements. On average, the pulse-deriving application scored 90.1% (±2%) sensitivity, 97.1% (±1%) specificity, 95.2% (±1%) NPV, 94.0% (±1%) PPV, and 94.8% (±1%) accuracy. The handheld single-lead ECG device had 90.2% sensitivity, 97.7% specificity, 97.7% NPV, 95.1% PPV, and 96.9% accuracy.

Conclusion

The diagnostic accuracy of the pulse-deriving smartphone application and the handheld single-lead ECG device was strongly influenced by the presence of regular atrial flutters, stressing the importance of further thorough validation. For the pulse-deriving smartphone application, there was no significant influence from device type in terms of diagnostic accuracy for the detection of AF. Insufficient quality measurements were more frequently performed on Android devices.

Elimination of a Human T-cell Region in Staphylokinase by T-cell Screening and Computer Modeling

Staphylokinase is a potent highly fibrin-selective thrombolytic agent, but it induces a humoral immune response in most treated patients. Staphylokinase-specific T-lymphocytes can be found in normal healthy individuals, from whom a large panel of staphylokinasespecific T-cells were cloned. The staphylokinase amino acid sequence 71-87 was widely recognized, as it induced proliferation of T-cell clones isolated from 90% of the donors. Computer modeling of this area, threaded as 11-mer peptides within the peptide-binding groove of the major HLA-DR alleles, indicated two putative partially overlapping binding sequences. The region-(71-87)-specific T-cell clones recognized either one or the other minimal peptide, confirming that both sequences could be functional T-cell epitopes. Furthermore, to guide the mutagenesis to eliminate T-cell reactivity, the contribution of each residue to the HLA-DR-anchoring and T-cell receptor exposure was evaluated for both binding motifs. Computer calculations combined with functional assays resulted in the design of staphylokinasevariants, including 2 to 4 amino acid substitutions in the region 71-87. These variants were no longer recognized by the region-(71-87)specific T-cell clones, and importantly no new staphylokinase-variantspecific cellular immune response could be measured.

Thrombospondin-1 Deficiency Accelerates Atherosclerotic Plaque Maturation in ApoE −/− Mice

Thrombospondin (TSP)1 is implicated in various inflammatory processes, but its role in atherosclerotic plaque formation and progression is unclear. Therefore, the development of atherosclerosis was compared in ApoE −/− and Tsp1 −/− ApoE −/− mice kept on a normocholesterolemic diet. At 6 months, morphometric analysis of the aortic root of both mouse genotypes showed comparable lesion areas. Even when plaque burden increased ≈5-fold in ApoE −/− and 10-fold in Tsp1 −/− ApoE −/− mice, during the subsequent 3 months, total plaque areas were comparable at 9 months. In contrast, plaque composition differed substantially between genotypes: smooth muscle cell areas, mostly located in the fibrous cap of ApoE −/− plaques, both at 6 and 9 months, were 3-fold smaller in Tsp1 −/− ApoE −/− plaques, which, in addition, were also more fibrotic. Moreover, inflammation by macrophages was twice as high in Tsp1 −/− ApoE −/− plaques. This correlated with a 30-fold elevated incidence of elastic lamina degradation, with matrix metalloproteinase-9 accumulation, underneath plaques and manifestation of ectasia, exclusively in Tsp1 −/− ApoE −/− mice. At 9 months, the necrotic core was 1.4-fold larger and 4-fold higher numbers of undigested disintegrated apoptotic cells were found in Tsp1 −/− ApoE −/− plaques. Phagocytosis of platelets by cultured Tsp1 −/− macrophages revealed the instrumental role of TSP1 in phagocytosis, corroborating the defective intraplaque phagocytosis of apoptotic cells. Hence, the altered smooth muscle cell phenotype in Tsp1 −/− ApoE −/− mice has limited quantitative impact on atherosclerosis, but defective TSP1-mediated phagocytosis enhanced plaque necrotic core formation, accelerating inflammation and macrophage-induced elastin degradation by metalloproteinases, speeding up plaque maturation and vessel wall degeneration.

Thrombospondin-1 Activates Medial Smooth Muscle Cells and Triggers Neointima Formation Upon Mouse Carotid Artery Ligation

OBJECTIVE

Thrombospondin-1 (TSP1) is described as a positive regulator of vascular smooth muscle growth in cell culture. However, insight into the in vivo effects of TSP1 on smooth muscle cell (SMC) function is lacking.

METHODS AND RESULTS

We analyzed wild-type (WT) and TSP1-deficient (Tsp1-/-) mice in a carotid artery ligation model, in which neointimal lesions form without overt mechanical damage to the endothelium. On ligation, the expression of TSP1 increased strongly in the matrix of neointima and adventitia. In the early phase after ligation (day 3 to 7), activation, proliferation, and migration of medial SMCs were delayed and impaired in Tsp1-/- mice, in parallel with defective upregulation of metalloproteinase (MMP)-2 activity. As a result, Tsp1-/- arteries developed smaller neointimal lesions, a thicker media but comparably attenuated patency as in WT arteries, 28 days after ligation. Furthermore, medial and neointimal SMCs in Tsp1-/- mice produced more collagen, more osteopontin, and displayed weaker smooth muscle actin staining than WT SMCs, indicative of a modified SMC phenotype in Tsp1-/- mice.

CONCLUSIONS

Arterial SMC activation in the absence of TSP1 is delayed and dysregulated, reducing neointima formation, on mild vascular injury.

Enhanced peripheral thrombogenicity after lung inflammation is mediated by platelet-leukocyte activation: role of P-selectin

BACKGROUND

Inhaled ultrafine particles trigger peripheral thrombotic complications.

METHODS

We have analyzed the systemic prothrombotic risk following lung inflammation induced by pulmonary carbon nanotubes (CNTs).

RESULTS

Intratracheal instillation in Swiss mice of 200 and 400 microg of multiwall ground CNTs triggered substantial lung neutrophil, but not macrophage influx, 24 h later. The detection of circulating platelet-leukocyte conjugates exclusively 6 h after CNT instillation pointed to early but transient activation of circulating platelets. At 24 h, elevated plasma procoagulant microvesicular tissue factor activity was found in CNT-exposed but not in saline-exposed mice. However, at 24 h, both the tail and jugular vein bleeding times were prolonged in CNT-exposed but not in saline-exposed mice, arguing against strong CNT-induced platelet activation at this point. Nevertheless, at 24 h, enhanced peripheral thrombogenicity was detected in CNT-exposed but not in saline-exposed mice, via quantitative photochemically induced carotid artery thrombosis measurements. P-selectin neutralization abrogated platelet-leukocyte conjugate formation and microvesicular tissue factor generation, and abolished the CNT-induced thrombogenicity amplification. In contrast, the weak vascular injury-triggered thrombus formation in saline-treated mice was not affected by P-selectin neutralization at 24 h.

CONCLUSIONS

The mild CNT-induced lung inflammation translates via rapid but mild and transient activation of platelets into P-selectin-mediated systemic inflammation. Leukocyte activation leads to tissue factor release, in turn eliciting inflammation-induced procoagulant activity and an associated prothrombotic risk.

Thrombospondin-1 controls vascular platelet recruitment and thrombus adherence in mice by protecting (sub)endothelial VWF from cleavage by ADAMTS13

The function of thrombospondin-1 (TSP-1) in hemostasis was investigated in wild-type (WT) and Tsp1-/- mice, via dynamic platelet interaction studies with A23187-stimulated mesenteric endothelium and with photochemically injured cecum subendothelium. Injected calcein-labeled WT platelets tethered or firmly adhered to almost all A23187-stimulated blood vessels of WT mice, but Tsp1-/- platelets tethered to 45% and adhered to 25.8% of stimulated Tsp1-/- vessels only. Stimulation generated temporary endothelium-associated ultralarge von Willebrand factor (VWF) multimers, triggering platelet string formation in 48% of WT versus 20% of Tsp1-/- vessels. Injection of human TSP-1 or thrombotic thrombocytopenic purpura (TTP) patient-derived neutralizing anti-ADAMTS13 antibodies corrected the defective platelet recruitment in Tsp1-/- mice, while having a moderate effect in WT mice. Photochemical injury of intestinal blood vessels induced thrombotic occlusions with longer occlusion times in Tsp1-/- venules (1027 +/- 377 seconds) and arterioles (858 +/- 289 seconds) than in WT vessels (559 +/- 241 seconds, P < .001; 443 +/- 413 seconds, P < .003) due to defective thrombus adherence, resulting in embolization of complete thrombi, a defect restored by both human TSP-1 and anti-ADAMTS13 antibodies. We conclude that in a shear field, soluble or local platelet-released TSP-1 can protect unfolded endothelium-bound and subendothelial VWF from degradation by plasma ADAMTS13, thus securing platelet tethering and thrombus adherence to inflamed and injured endothelium, respectively.

Assessment of LV diastolic filling using color M-mode Doppler echocardiography: validation in a new hydraulic model

The effect of LV properties on v(p) and the E/v(p) ratio remains a matter of debate. Therefore,the objective of this study is to explore - in a new hydraulic model - the individual contributions of LV relaxation, filling pressure and compliance in changes of E, v(p) and E/v(p) for different stages of diastolic function. A new hydraulic model, consisting of an open cylindrical LA connected to an ellipsoidal LV, is designed. E and v(p) are measured for varying values of tau (45-60-90 ms), LV compliance (0.45-1.35 ml/mmHg) and filling pressure (3-10-30 mmHg). The results are used for predicting the evolution of E, v(p) and E/v(p) during different stages of diastolic function. An increase in compliance decreases E, whereas it augments v(p). v(p) is less load-dependent than E. E decreases with delayed relaxation, increases for the case of pseudonormalisation, and becomes higher than the reference values during restrictive filling. The v(p) value is lower for the case of delayed relaxation than for the reference situation. During pseudonormalisation, the value of v(p) remains lower than the reference value but higher than the value for delayed relaxation. v(p) further decreases during restrictive filling. In conclusion, the effect of simultaneous changes in compliance and loading counterbalance changes in v(p). Therefore, under normal physiologic conditions where load and compliance are coupled, v(p) is apparently load-intensive and E/v(p) increases as filling pressure increases. Moreover, in the different stages of diastolic dysfunction, due to the interference of the co-varying relaxation, the increase in E/v(p) is more pronounced.

Elimination of a human T-cell region in staphylokinase by T-cell screening and computer modeling

Staphylokinase is a potent highly fibrin-selective thrombolytic agent, but it induces a humoral immune response in most treated patients. Staphylokinase-specific T-lymphocytes can be found in normal healthy individuals, from whom a large panel of staphylokinase-specific T-cells were cloned. The staphylokinase amino acid sequence 71-87 was widely recognized, as it induced proliferation of T-cell clones isolated from 90% of the donors. Computer modeling of this area, threaded as 11-mer peptides within the peptide-binding groove of the major HLA-DR alleles, indicated two putative partially overlapping binding sequences. The region-(71-87)-specific T-cell clones recognized either one or the other minimal peptide, confirming that both sequences could be functional T-cell epitopes. Furthermore, to guide the mutagenesis to eliminate T-cell reactivity, the contribution of each residue to the HLA-DR-anchoring and T-cell receptor exposure was evaluated for both binding motifs. Computer calculations combined with functional assays resulted in the design of staphylokinase-variants, including 2 to 4 amino acid substitutions in the region 71-87. These variants were no longer recognized by the region-(71-87)-specific T-cell clones, and importantly no new staphylokinase-variant-specific cellular immune response could be measured.

Staphylokinase-specific cell-mediated immunity in humans

Staphylokinase is a highly fibrin-specific clot-dissolving agent that constitutes a promising drug for clinical development. It is of bacterial origin, and the majority of patients develop neutralizing Ab after its administration. Several antigenic regions, recognized by these Ab, have been identified, but the underlying immunogenic features of staphylokinase remain unknown. In this study, we show that staphylokinase is a T cell-dependent Ag, and that an immunological memory may be acquired, even without administration of staphylokinase. Thrombolysis with staphylokinase provokes the proliferation of staphylokinase-specific T lymphocytes, which remain elevated over 10 mo posttreatment. Interestingly, analysis of a large number of staphylokinase-specific T cell clones isolated from 10 unrelated donors revealed only six distinct immunogenic regions in the molecule. Moreover, five of the six regions are recognized by T lymphocytes from several individuals, indicating that these regions are not restricted to a single HLA-DR allele. Therefore, these new insights can guide the design of variants with a lower immunogenic profile in humans.

A semiautomated objective technique for applying the proximal isovelocity surface area method to quantitate mitral regurgitation: Clinical studies with the digital flow map

BACKGROUND

Clinical application of the color Doppler proximal isovelocity surface area (PISA) method to quantify mitral regurgitation (MR) has been limited by the often inaccurate assumption that isovelocity surfaces are hemispheric. This study applied an objective method for selecting the region where the hemispheric geometry holds best on the basis of mathematic analysis of results at different distances from the orifice. We aimed to demonstrate this approach can be applied accurately in the clinical setting and can be semiautomated to promote routine use by extracting velocities from the digital Doppler output and then performing all the calculations automatically.

METHODS

In 75 patients with isolated MR, centerline velocities (V(r)) at each distance (r) from the orifice in the proximal flow field were extracted digitally. The automated analysis calculated peak MR flow rates as 2pir(2)V(r) and plotted these against their respective velocities. The optimal value for peak flow rate was obtained mathematically at the site where the slope of this curve was minimal (least inaccuracy). This value was combined with continuous wave Doppler data to provide regurgitant stroke volume (RSV) and orifice area (ROA), which were compared with quantitative Doppler in 75 patients and angiography in 42.

RESULTS

RSV and ROA by this optimized, semiautomated PISA method correlated and agreed well with values from quantitative Doppler (y = 0.9x + 1.9, r = 0.90, standard error of the estimate [SEE] = 8.1 mL, mean difference = -0.7 +/- 8.5 mL for RSV; y = 0.9x + 0.02, r = 0.90, SEE = 0.048 cm(2), mean difference = -0.005 +/- 0.1 cm(2) for ROA) and correlated well with angiography (rho = 0.90 for both RSV and ROA).

CONCLUSIONS

This objective PISA method for quantifying MR is accurate in the clinical setting and has been semiautomated by use of analysis of digital velocity data to provide a rapid and practical technique suitable to facilitate more extensive application in routine practice.

Age independence of the difference in duration of pulmonary venous atrial reversal flow and transmitral A-wave flow in normal subjects

Aging influences pulmonary venous flow and mitral inflow velocities. The duration of pulmonary venous atrial reversal flow exceeds that of the mitral inflow A wave in patients with left ventricular end-diastolic pressures greater than 15 mm Hg. The objective of this study was to investigate the effect of age on the difference between the duration of pulmonary venous atrial reversal flow and that of the mitral inflow A wave in a large number of normal individuals. Pulsed wave Doppler transthoracic echocardiograms of the pulmonary venous flow and the transmitral inflow with respiratory monitoring were made of 72 normal volunteers (40 women) ranging in age between 23 and 84 years. The differences in the durations of pulmonary venous atrial reversal flow and mitral inflow A wave were measured and their correlation with age assessed. Age was not highly correlated with the duration of pulmonary venous atrial reversal flow (r = 0.25) nor the duration of the mitral inflow A wave (r = 0.33). The duration of pulmonary venous atrial reversal flow exceeded the duration of the mitral inflow A-wave flow only in three (4%) of 72 subjects, and age was not related to the index in this group (r = -0.16; p = 0.19). The difference in durations was not significantly affected by the phase of respiration. Men had higher values on all measurements than women. The difference between the pulmonary venous atrial reversal duration and the mitral inflow A-wave duration is independent of age and thus may be used as a reliable index of left ventricular end-diastolic pressure, even in elderly patients.

Ondansetron, a 5-HT3 antagonist, improves cerebellar tremor

It has been previously shown that ondansetron, a 5-HT3 antagonist, can ameliorate vertigo in patients with acute brainstem disorders. A coincidental benefit was the improvement of cerebellar tremor in some patients with both vertigo and tremor. To further evaluate this effect, a placebo controlled, double blind, crossover study was conducted of a single dose of intravenous ondansetron in 20 patients with cerebellar tremor caused by multiple sclerosis, cerebellar degeneration, or drug toxicity. The principal outcome measures were the change in blind assessment of a writing task (spiral copying) and the timed completion of a nine hole peg test. Thirteen of 19 patients were deemed to have improved spiral copying after treatment with ondansetron when compared with baseline performance. One patient had a better response to the placebo compared with baseline performance (P = 0.00024). Patients completed the nine hole peg test in less time after ondansetron than after placebo (P = 0.08). Twelve patients thought that their tremor was functionally improved with the ondansetron treatment. None thought that the placebo gave improvement (P = 0.00098). The efficacy of orally administered ondansetron in tremor control is currently under study.

An index of early left ventricular filling that combined with pulsed Doppler peak E velocity may estimate capillary wedge pressure

OBJECTIVES

This study sought to determine the applicability of the combined information obtained from transmitral Doppler flow and color M-mode Doppler flow propagation velocities for estimating pulmonary capillary wedge pressure.

BACKGROUND

Although Doppler-derived measurements of left ventricular (LV) filling have been applied to determine left atrial pressure, their accuracy has been limited by the variable effect of ventricular relaxation in these indexes. Recently, flow propagation velocity measured by color M-mode Doppler echocardiography has been suggested as an index of ventricular relaxation.

METHODS

We studied 45 patients admitted to the intensive care unit who underwent invasive hemodynamic monitoring. We measured peak early (E) and late (A) transmitral Doppler velocities, E/A ratio and flow propagation velocity (vp) and compared them by linear regression with pulmonary capillary wedge pressure (pw).

RESULTS

We found a modest positive correlation between pw and E (r = 0.62, p < 0.001) and the E/A ratio (r = 0.52, p < 0.001) and a negative correlation between pw and vp (r = -0.34, p = 0.02). By stepwise linear regression, only E and vp were statistically significant predictors of pw. However, the E/vp ratio provided the best estimate of pw (r = 0.80, p < 0.001; pw = 5.27 x [E/vp] + 4.6, SEE 3.1 mm Hg).

CONCLUSIONS

The ratio of component velocity (E) over the color M-mode propagation velocity during early LV filling, by correcting for the effect of LV relaxation, provides a better estimate of pw than standard measurements of transmitral Doppler flow.

Bench repair of donor mitral valve before heart transplantation

Bench repair of the donor mitral valve was performed before orthotopic heart transplantation in a 57-year-old status I recepient. Mitral regurgitation in the structurally normal mitral valve was due to annular dilatation at the attachment of the posterior leaflet and was corrected with posterior annuloplasty. The patient is clinically well 18 months after transplantation.

Value of proximal regurgitant jet size in tricuspid regurgitation

Recent studies have shown good agreement between proximal regurgitant jet size obtained with transthoracic color flow mapping and regurgitant fraction in patients with mitral regurgitation. To evaluate this in patients with tricuspid regurgitation, we analyzed 40 patients in sinus rhythm, 16 with free jets and 24 with impinging jets, comparing proximal jet size (millimeters) with parameters derived from the Doppler two-dimensional echocardiographic method (regurgitant fraction) and the flow-convergence method (peak flow rate, effective regurgitant orifice area, and momentum). Good agreement was noted between peak flow rate (r = 0.80, p < 0.001), momentum (r = 0.80, p < 0.001), and effective regurgitant orifice area (r = 0.78, p < 0.001), with proximal jet size measured in the apical four-chamber view in patients with free jets. The average of jet proximal size in three planes also had good correlation with peak flow rate (r = 0.75, p < 0.001), regurgitant fraction, momentum, and effective regurgitant orifice area (r = 0.74, p < 0.001). In patients with impinging jets, agreement was fair between effective regurgitant orifice (r = 0.65, p < 0.001), peak flow rate (0.65, p < 0.001), and momentum (r = 0.62, p < 0.001) with mean jet proximal size. Jet proximal size obtained with transthoracic color flow mapping is a good semiquantitative tool for measuring tricuspid regurgitation in free jets that correlates well with established measures of the severity and with new parameters available from analysis of the proximal acceleration field. In patients with eccentrically directed wall jets, the correlation weakens but still appears clinically significant.

Pulmonary vein thrombosis and peripheral embolization

A 78-year-old-woman was admitted to the hospital with bilateral femoral arterial occlusion. Her medical history disclosed atrial fibrillation and a left thoracoplasty performed 50 years earlier for treatment of tuberculosis. A transesophageal echocardiogram demonstrated intraluminal thrombus in a left pulmonary vein. The patient recovered after thromboembolectomy. This case documents another uncommon cause of cardiac thromboembolism in which a transesophageal echocardiogram was essential to make the diagnosis.

Mechanisms of hemolysis with mitral prosthetic regurgitation. Study using transesophageal echocardiography and fluid dynamic simulation

OBJECTIVES

The aims of this study were to define the hydrodynamic mechanisms involved in the occurrence of hemolysis in prosthetic mitral valve regurgitation and to reproduce them in a numeric simulation model in order to estimate peak shear stress.

BACKGROUND

Although in vitro studies have demonstrated that shear stresses > 3,000 dynes/cm2 are associated with significant erythrocyte destruction, it is not known whether these values can occur in vivo in conditions of abnormal prosthetic regurgitant flow.

METHODS

We studied 27 patients undergoing reoperation for significant mitral prosthetic regurgitation, 16 with and 11 without hemolysis. We classified the origin and geometry of the regurgitant jets by using transesophageal echocardiography. By using the physical and morphologic characteristics defined, several hydrodynamic patterns were simulated numerically to determine shear rates.

RESULTS

Eight (50%) of the 16 patients with hemolysis had paravalvular leaks and the other 8 had a jet with central origin, in contrast to 2 (18%) and 9 (82%), respectively, of the 11 patients without hemolysis (p = 0.12, power 0.38). Patients with hemolysis had patterns of flow fragmentation (n = 2), collision (n = 11) or rapid acceleration (n = 3), whereas those without hemolysis had either free jets (n = 7) or slow deceleration (n = 4) (p < 0.001, power 0.99). Numeric simulation demonstrated peak shear rates of 6,000, 4,500, 4,500, 925 and 950 dynes/cm2 in these five models, respectively.

CONCLUSIONS

The distinct patterns of regurgitant flow seen in these patients with mitral prosthetic hemolysis were associated with rapid acceleration and deceleration or high peak shear rates, or both. The nature of the flow disturbance produced by the prosthetic regurgitant lesion and the resultant increase in shear stress are more important than the site of origin of the flow disturbance in producing clinical hemolysis.

Proximal jet size by Doppler color flow mapping predicts severity of mitral regurgitation. Clinical studies

BACKGROUND

Recent studies have shown that many instrument and physiological factors limit the ability of color Doppler total jet area within the receiving chamber to predict the severity of valvular regurgitation. In contrast, the proximal or initial dimensions of the jet as it emerges from the orifice have been shown to increase directly with orifice size and to correlate well with the severity of aortic insufficiency. Only limited data, however, are available regarding the value of proximal jet size in mitral regurgitation, and it has not been examined in short-axis or transthoracic views. The purpose of the present study, therefore, was to evaluate the relation between proximal jet size and other measures of the severity of mitral regurgitation.

METHODS AND RESULTS

In 49 patients, the anteroposterior height of the proximal jet as it emerges from the mitral valve was measured in the parasternal long-axis view; proximal jet width and area were measured in the short-axis view at the same level. Results were compared with regurgitant volume and fraction by pulsed Doppler subtraction of aortic and mitral flows in 47 patients without more than trace aortic insufficiency; with angiographic grade determined within 24 hours in 33 catheterized patients; and with angiographic regurgitant fraction in 13 patients who were in normal sinus rhythm and had no significant aortic and tricuspid insufficiency. Proximal jet height, width, and area correlated well with Doppler regurgitant volume and fraction (r = .86 to .95; SEE = 7.7 to 9.0 mL; 5.9% to 7.3%). Proximal jet size could also be used to distinguish angiographic grades of mitral regurgitation with minimal overlap (P < .0001) and correlated well with angiographic regurgitant fraction (r = .85 to .91; SEE = 4.1% to 5.1%).

CONCLUSIONS

Proximal jet size correlates well with established measures of the severity of mitral regurgitation. It is conveniently available with transthoracic clinical scanning and should be useful in the routine evaluation of patients with mitral regurgitation.

Bilateral occlusion of the internal carotid arteries. Presenting symptoms in 74 patients and a prospective study of 34 medically treated patients

The presenting characteristics of 74 patients with atherosclerotic occlusion of both internal carotid arteries are described. All had suffered either ischaemic hemisphere infarcts (80%) and/or transient ischaemic attacks (80%) involving one (78%) or both (22%) carotid territories. In addition, 10 subjects (14%) incurred recurrent vertebrobasilar or presyncopal episodes, many of which appeared secondary to haemodynamic insufficiency. The incidence of risk factors and concomitant vascular disease was high; 93% gave a history of heavy smoking. Thirty-four subjects were treated conservatively and followed prospectively for a mean of 42 months. Eighteen patients (53%) suffered further cerebrovascular events, an ischaemic event rate of 15% per patient per year. These were isolated transient ischaemic attacks (TIAs) in 7 and stroke in 11 patients. The latter suffered a total of 15 strokes during the follow-up period of 42 months; the annual stroke rate was 13% per patient year. Patients who had presented with ischaemic events involving more than one carotid territory were significantly more prone to subsequent cerebral infarction than those in whom symptoms had been confined to one territory (P less than 0.05). None of the 5 patients with haemodynamic TIAs who were managed conservatively developed a stroke during the follow-up period and their symptoms remitted spontaneously. Deaths per year amounted to 8%. Twenty-four patients (71%) survived, of whom half were either symptom-free or minimally disabled. In this group of preselected patients, which excludes those with severe deficits at presentation, bilateral occlusion of the carotid arteries may be a condition compatible with useful existence.