Distinct Hemodynamic Responses That Culminate With Postural Orthostatic Tachycardia Syndrome.

It is of paramount importance to characterize the individual hemodynamic response of patients with postural orthostatic tachycardia syndrome (POTS) to select the best therapeutic intervention. Our aim in this study was to describe the hemodynamic changes in 40 patients with POTS during the head-up tilt test and compare them with 48 healthy patients. Hemodynamic parameters were obtained by cardiac bioimpedance. Patients were compared in supine position and after 5, 10, 15, and 20 minutes of orthostatic position. Patients with POTS demonstrated higher heart rate (74 beats per minute [64 to 80] vs 67 [62 to 72], p <0.001) and lower stroke volume (SV) (83.0 ml [72 to 94] vs 90 [79 to 112], p <0.001) at supine position. The response to orthostatic challenge was characterized by a decrease in SV index (SVI) in both groups (ΔSVI in ml/m2: -16 [-25 to -7.] vs -11 [-17 to -6.1], p = NS). Peripheral vascular resistance (PVR) was reduced only in POTS (ΔPVR in dyne.seg/cm5:-52 [-279 to 163] vs 326 [58 to 535], p <0.001). According to the best cut-off points obtained using the receiver operating characteristic analysis for the variation of SVI (-15.5%) and PVR index (PVRI) (-5.5%), we observed 4 distinct groups of POTS: 10% presented an increase in both SVI and PVRI after the orthostatic challenge, 35% presented a PVRI decrease with SVI maintenance or increase, 37.5% presented an SVI decrease with PVRI maintenance or elevation, and 17.5% presented a reduction in both variables. Body mass index, ΔSVI, and ΔPVRI were strongly correlated with POTS (area under the curve = 0.86 [95% confidence interval 0.77 to 0.92], p <0.0001). In conclusion, the use of appropriate cut-off points for hemodynamic parameters using bioimpedance cardiography during the head-up tilt test could be a useful strategy to identify the main mechanism involved and to select the best individual therapeutic strategy in POTS.

Reduced Systolic Volume: Main Pathophysiological Mechanism in Patients with Orthostatic Intolerance?

BACKGROUND: Orthostatic intolerance patients' pathophysiological mechanism is still obscure, contributing to the difficulty in their clinical management. OBJECTIVE: To investigate hemodynamic changes during tilt test in individuals with orthostatic intolerance symptoms, including syncope or near syncope. METHODS: Sixty-one patients who underwent tilt test at - 70° in the phase without vasodilators were divided into two groups. For data analysis, only the first 20 minutes of tilting were considered. Group I was made up of 33 patients who had an increase of total peripheral vascular resistance (TPVR) during orthostatic position; and Group II was made up of 28 patients with a decrease in TPVR (characterizing insufficient peripheral vascular resistance). The control group consisted of 24 healthy asymptomatic individuals. Hemodynamic parameters were obtained by a non-invasive hemodynamic monitor in three different moments (supine position, tilt 10' and tilt 20') adjusted for age. RESULTS: In the supine position, systolic volume (SV) was significantly reduced in both Group II and I in comparison to the control group, respectively (66.4 ±14.9 ml vs. 81.8±14.8 ml vs. 101.5±24.2 ml; p<0.05). TPVR, however, was higher in Group II in comparison to Group I and controls, respectively (1750.5± 442 dyne.s/cm5 vs.1424±404 dyne.s/cm5 vs. 974.4±230 dyne.s/cm5; p<0.05). In the orthostatic position, at 10', there was repetition of findings, with lower absolute values of SV compared to controls (64.1±14.0 ml vs 65.5±11.3 ml vs 82.8±15.6 ml; p<0.05). TPVR, on the other hand, showed a relative drop in Group II, in comparison to Group I. CONCLUSION: Reduced SV was consistently observed in the groups of patients with orthostatic intolerance in comparison to the control group. Two different responses to tilt test were observed: one group with elevated TPVR and another with a relative drop in TPVR, possibly suggesting a more severe failure of compensation mechanisms.

Reduced Systolic Volume: Main Pathophysiological Mechanism in Patients with Orthostatic Intolerance? / Volume Sistólico Reduzido: Mecanismo Fisiopatológico Principal em Pacientes com Intolerância Ortostática?

Abstract Background: Orthostatic intolerance patients' pathophysiological mechanism is still obscure, contributing to the difficulty in their clinical management. Objective: To investigate hemodynamic changes during tilt test in individuals with orthostatic intolerance symptoms, including syncope or near syncope. Methods: Sixty-one patients who underwent tilt test at - 70° in the phase without vasodilators were divided into two groups. For data analysis, only the first 20 minutes of tilting were considered. Group I was made up of 33 patients who had an increase of total peripheral vascular resistance (TPVR) during orthostatic position; and Group II was made up of 28 patients with a decrease in TPVR (characterizing insufficient peripheral vascular resistance). The control group consisted of 24 healthy asymptomatic individuals. Hemodynamic parameters were obtained by a non-invasive hemodynamic monitor in three different moments (supine position, tilt 10' and tilt 20') adjusted for age. Results: In the supine position, systolic volume (SV) was significantly reduced in both Group II and I in comparison to the control group, respectively (66.4 ±14.9 ml vs. 81.8±14.8 ml vs. 101.5±24.2 ml; p<0.05). TPVR, however, was higher in Group II in comparison to Group I and controls, respectively (1750.5± 442 dyne.s/cm5 vs.1424±404 dyne.s/cm5 vs. 974.4±230 dyne.s/cm5; p<0.05). In the orthostatic position, at 10', there was repetition of findings, with lower absolute values of SV compared to controls (64.1±14.0 ml vs 65.5±11.3 ml vs 82.8±15.6 ml; p<0.05). TPVR, on the other hand, showed a relative drop in Group II, in comparison to Group I. Conclusion: Reduced SV was consistently observed in the groups of patients with orthostatic intolerance in comparison to the control group. Two different responses to tilt test were observed: one group with elevated TPVR and another with a relative drop in TPVR, possibly suggesting a more severe failure of compensation mechanisms.

Resumo Fundamento: O mecanismo fisiopatológico de pacientes com intolerância ortostática ainda é obscuro, contribuindo para a dificuldade no manejo clínicos desses pacientes. Objetivo: Investigar as alterações hemodinâmicas durante teste de inclinação (tilt teste) em indivíduos com sintomas de intolerância ortostática, incluindo síncope ou pré-síncope. Métodos: Sessenta e um pacientes, com tilt teste a 70º negativo na fase livre de vasodilatador, foram divididos em dois grupos. Para análise dos dados foram considerados apenas os primeiros 20 minutos de inclinação. Grupo I (33 pacientes) que tiveram elevação da resistência vascular periférica total (RVPT) durante posição ortostática e Grupo II (28 pacientes) com queda da RVPT (caracterizando insuficiência de resistência vascular periférica). O grupo controle consistia de indivíduos saudáveis e assintomáticos (24 indivíduos). Os parâmetros hemodinâmicos foram obtidos por um monitor hemodinâmico não invasivo em 3 momentos distintos (posição supina, tilt 10' e tilt 20'), ajustados para idade. Resultados: Na posição supina, o volume sistólico (VS) foi significantemente reduzido tanto no Grupo II quanto no I, quando comparado ao do Grupo controle, respectivamente (66,4 ±14,9 ml vs. 81,8±14,8 ml vs. 101,5±24,2 ml; p<0,05.) A RVPT, no entanto, foi mais elevada no Grupo II, quando comparada a do Grupo I e controles, respectivamente (1750,5± 442 dyne.s/cm5 vs.1424±404 dyne.s/cm5 vs. 974,4±230 dyne.s/cm5; p<0,05). Na posição ortostática, aos 10', houve repetição dos achados, com valores absolutos inferiores de VS Comparado aos controles (64,1±14,0 ml vs 65,5±11,3 ml vs 82,8±15,6 ml; p<0,05). A RVPT, todavia, apresentou queda relativa no Grupo II comparado ao I. Conclusão: Volume sistólico reduzido foi consistentemente observado nos grupos de pacientes com intolerância ortostática, quando comparado ao grupo controle. Foram observadas duas respostas distintas ao teste de inclinação: um grupo com elevação de RVPT e outro com queda relativa desta, indicando, possivelmente, falência mais acentuada dos mecanismos de compensação.