T-wave alternans: desempenho clínico, limitações, metodologias de análise

Reconhecer com precisão indivíduos com maior risco imediato de morte súbita cardíaca (MSC) ainda é uma questão em aberto. A natureza fortuita dos eventos cardiovasculares agudos não parece se adequar ao conhecido modelo de indução de taquicardia/fibrilação ventricular por um gatilho em sincronia a um substrato arritmogênico estático. Quanto ao mecanismo da MSC, uma instabilidade elétrica dinâmica explicaria melhor a raridade da associação simultânea de um gatilho certo a um substrato cardíaco apropriado. Diversos estudos tentaram medir essa instabilidade elétrica cardíaca (ou um equivalente válido) em uma sequência de batimentos cardíacos no ECG. Dentre os mecanismos possíveis podemos citar o prolongamento do QT, dispersão do QT, potenciais tardios, alternância de onda T ou T-wave alternans (TWA), e turbulência da frequência cardíaca. Este artigo se atém em particular ao papel da TWA no panorama atual da estratificação de risco cardíaco. Os achados sobre TWA ainda são heterogêneos, variando de um desempenho prognóstico muito bom até um quase nulo, dependendo da população clínica observada e protocolo clínico usado. Para preencher as atuais lacunas no conhecimento sobre TWA, profissionais médicos e pesquisadores devem explorar melhor as características técnicas das diversas tecnologias disponíveis para a avaliação de TWA e atentar ao fato de que os valores de TWA respondem a diversos outros fatores, além de medicamentos. Informações sobre mecanismos celulares e subcelulares da TWA estão fora do escopo deste artigo, mas são referenciados alguns dos principais trabalhos sobre este tópico, com o intuito de auxiliar no entendimento dos conceitos e fatos cobertos neste artigo.

Comparative study of two autogenous graft techniques using piezosurgery for sinus lifting

PURPOSE: Maxillary sinus lifting is a technique, in which, a possible complication is sinus membrane perforation. The aim of this study was to compare two techniques using ultrasound surgery to perform autogenous graft for maxillary sinus lifting. METHODS: Ten rabbits were used in the study, one of them did not undergo surgery. The other nine rabbits had their maxillary sinuses filled with autogenous bone grafts collected from the external skull diploe in particulate form on the right side, and shaved on the left side, both with ultrasonic device. Data on bone density in left and right maxillary sinus, obtained by computed tomography in transverse and longitudinal sections, recorded 90 days after the grafts, were statistically compared. RESULTS: There were no statistically significant differences between the two techniques that used shaved and particulate bone collected by means of ultrasonic device from rabbit skulls. CONCLUSION: Assessment of operative procedures led to the conclusion that piezoelectric ultrasound was shown to be a safe tool in the surgical approach to the maxillary sinus of rabbits, allowing sinus membrane integrity to be maintained during surgical procedures.

Electrocardiographic study on geriatric dogs undergoing general anesthesia with isoflurane

The purpose of this study was to clarify the degree of influence of anesthetic agents commonly used during anesthesia on the heart conduction systems of geriatric dogs, with or without the presence of electrocardiographic changes in the pre-anesthetic electrocardiogram and also to determine the possible causes of ST-segment and T-wave changes during anesthesia, by monitoring ventilation and oxygenation. 36 geriatric dogs were evaluated. In addition to electrocardiographic evaluation, the pre-anesthetic study included serum levels of urea, creatinine, total protein, albumin and electrolytes. The pre-anesthetic medication consisted of acepromazine (0.05mg kg-1) in association with meperidine (3.0mg kg-1) by IM injection. Anesthesia was induced with propofol (3.0 to 5.0mg kg-1) by IV injection and maintained with isoflurane in 100% oxygen. During the anesthesia, the animals were monitored by continued computerized electrocardiogram. Systemic blood pressure, heart rate, respiratory rate, end-tidal carbon dioxide, partial pressure of carbon dioxide in arterial blood, arterial oxygen saturation, partial pressure of arterial oxygen and oxygen saturation of hemoglobin were closely monitored. During maintenance anesthesia, normal sinus rhythm was more common (78%). ST-segment and T-wave changes during the anesthetic procedure were quite common and were related to hypoventilation. The use of isoflurane did not result in arrhythmia, being therefore a good choice for this type of animal; Electrocardiographic findings of ST-segment and T-wave changes during the maintenance anesthesia were evident in animals with hypercapnia, a disorder that should be promptly corrected with assisted or controlled ventilation to prevent complicated arrhythmias.

Estudo eletrocardiográfico de equinos de salto sadios

Avaliou-se o eletrocardiograma de 100 equinos sadios praticantes de hipismo clássico modalidade salto, com idades entre 4 e 19 anos, sendo 61 machos e 39 fêmeas, com média de 516,3 kg. Observou-se frequência cardíaca média de 40,20 ±13,33 bpm, sendo o ritmo cardíaco mais freqüente o sinusal (56%). As alterações de ritmo cardíaco estiveram presentes em 38% dos animais estudados, sendo a mais presente o marcapasso migratório (22%), seguido de bloqueio atrioventricular de 2º grau (4%), bloqueio atrioventricular de 1º grau (3%), contração ventricular prematura (2%), contração atrial prematura (1%). Não se observou correlação entre as variáveis estudadas (freqüência cardíaca, ritmo e arritmias) e a capacidade atlética, a idade e o sexo. O escore cardíaco após analise estatística não diferiu entre os grupos quanto ao desempenho atlético, a faixa etária e o sexo. O escore cardíaco, nesta amostra, não se mostrou um parâmetro confiável para se predizer o futuro atlético ou o nível de treinamento do eqüino.

TRAINING ALTERS CARDIAC NEURON SIZES IN WISTAR RATS

The action of the parasympathetic nerves on the heart is made through a group of neurons located on the surface of the atria. This study evaluated the effect of a chronic training protocol on the number and sizes of the cardiac neurons of Wistar rats. Whole mount preparations of the atria of 12-month old male sedentary and trained rats (40 weeks of running on a treadmill 3 times a week, 16 m/min) were assessed for number and size (maximal cellular profile area) of the cardiac neurons. The cardiac neurons were ascertained by using the NADH-diaphorase technique that stains the cell bodies of the neurons in dark blue. The, number of cardiac neurons in the trained rats (P>0.05) did not change significantly. In the sedentary group there were small, medium sized and large neurons. However there was a notable increase in the percentage of small neurons in the rats submitted to the training compared to the sedentary group (P<0.05). Previous studies have shown that electrophysiologically, the small neurons are more easily excitable than the large neurons. It is possible that the results of the present work reflect an adaptation mechanism of the cardiac neurons presumably with the objective of increasing the excitability of the neurons for the vagal action and resulting facilitation of the sinusal bradycardia observed at rest and in the exercise. We concluded that the training affects significantly the size of the cardiac neurons in Wistar rats. (Biol.Sport 26.245-254, 2009)

Electrocardiographic Alterations During Endosseous Implant Placement Performed with Local Anesthetic Agents

Purpose: The purpose of this study was to analyze electrocardiographic alterations during dental implant surgeries when local anesthetic agents were used. Materials and Methods: Twenty implants were placed in 18 healthy patients. An electrocardiogram and Wincardio software were used to gather recordings from 12 static leads every 2 minutes, continuously record coronary artery (D2) derivations, and automatically measure the following electrocardiographic parameters: heart rate, duration and amplitude of the P wave, PR segment duration, ST segment deviation, QRS complex duration, and duration of the RR, QT, and corrected QT (QTc) intervals. Results: Analysis of variance of the values obtained at the different stages showed significant differences (P < .05) for the heart rate and for the duration of the RR and QT intervals. The heart rate increased during the anesthesia, incision, and bone drilling stages, reaching a peak during drilling. Duration of the RR and QT intervals decreased during the incision and drilling stages. Among the electrocardiographic parameters individually assessed, several altered values were found for the duration of the P wave, the QRS complex, and the QT and QTc intervals. Sinusal tachycardia and bradycardia, sinusal arrhythmia, supraventricular extrasystole, ventricular extrasystole, and T-wave inversion were detected. Conclusion: Dental implant placement surgery may induce electrocardiographic alterations. The most frequently found arrhythmias were extrasystole and sinusal tachycardia. The anesthesia, incision, and bone drilling stages exhibited the highest heart rate values and the shortest durations of the RR and QT intervals. INT J ORAL MAXILLOFAC IMPLANTS 2009;24:412-418