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Biomedical subjects

A Donato

Publications and source records attributed to A Donato.

At least 37 records · Page 2Linked to original sources
PubMed1992

Irregular ventricular tachycardia: a possible manifestation of longitudinal dissociation within the reentry pathway.

Sustained monomorphic ventricular tachycardia is usually regular; that is, it is associated with constant R-R intervals. In several cases, however, the cycles of ventricular tachycardia are more or less variable. Fifty-four cases of sustained monomorphic ventricular tachycardia were evaluated in order to assess whether tachycardia was regular. Nine cases were defined as irregular (i.e., the R-R cycles varied by more than 40 msec throughout a 1-minute recording). In five cases tachycardia was "regularly irregular," since the R-R cycles could be divided into two separate groups: the group of long cycles and that of short cycles. In these cases the variability manifested according to a defined and constant pattern: bigeminal pattern (alternation of short and long cycles), trigeminal pattern (two short cycles followed by a long cycle), and so on. The regular variability of tachycardia cycle length suggests one of the following possibilities. (1) There are two alternative circuits (a short circuit and a long circuit) that share the same exit pathway. Whenever the reciprocating impulse runs through the short circuit, the R-R cycle is short; but if a block in the short circuit occurs, the impulse runs through the long circuit, resulting in a long R-R cycle. (2) There is a longitudinal dissociation within the reentry circuit; two separate pathways with different inherent conduction velocities are present. When the impulse runs through the fast pathway, the R-R cycle is short; whereas when a block in the fast pathway occurs, the impulse traverses the slow pathway, resulting in a long R-R cycle.

Electrocardiography↗
PubMed1992

Electrocardiographic changes associated with haematocrit variations.

The electrical resistivity of intracardiac blood is less than the resistivity of the surrounding tissues. This affects the transmission of cardiac forces to the body surface: the radial forces are enhanced, whereas the transmission of tangential forces is diminished (the Brody effect). Blood resistivity is directly related to haematocrit, hence, haematocrit changes are expected to affect the transmission of cardiac forces, resulting in changes in QRS complex voltage. To assess this hypothesis, a 12-lead electrocardiogram was recorded in 40 patients affected by thalassaemia before and after a transfusion of concentrated red cells. The voltage of each QRS component was carefully measured in every lead, and the sum of all R wave amplitudes (sigma R) was calculated. The post-transfusional electrocardiogram reflected a significant decrease in the R wave amplitude in every lead. sigma R also decreased, whereas S wave amplitude in lead V6 increased. A negative correlation between the ratio of haematocrit pre/post transfusion and that of the corresponding sigma R values was also observed (r = -0.434; P less than 0.01). An increase in haematocrit is therefore associated with a decrease in R wave amplitude. These findings explain why several patients with high haematocrit manifest relatively low voltage QRS complexes.

Adolescent↗
PubMed1992

Supernormal conduction in the left bundle branch unmasked by the linking phenomenon.

This presentation reflects a case of phase-3 left bundle branch block (LBBB). Analysis reveals that relatively early QRS complexes are wide, whereas beats occurring later than a critical time are narrow. There are, however, two unexpected phenomena: (1) an overlap occurs between the range of R-R intervals resulting in normal intraventricular conduction and the range of R-R intervals resulting in LBBB pattern. Complexes that follow a wide beat are often wide although they are associated with relatively long R-R intervals, whereas complexes that follow a normal beat tend to be normal even after relatively short R-R cycles. This is due to concealed retrograde penetration of the bundle branch that is blocked in anterograde direction (the so-called linking phenomenon). (2) Some early supraventricular impulses, paradoxically, resulted in normal intraventricular conduction. The phenomenon is a manifestation of supernormal LBB conduction, and only occurs following a wide QRS complex associated with retrograde activation of the LBB. The linking phenomenon reveals or unmasks the supernormal phase of LBB conduction. Following a retrograde and delayed activation of the LBB, the refractory period of the bundle branch is postponed, in such a way that a supraventricular impulse is allowed to occur during the early phase of supernormal conduction.

Aged↗
PubMed1992

Atrial parasystole and tachycardia. Modulation and automodulation of a parasystolic focus.

This report deals with a patient reflecting atrial parasystole and episodes of atrial tachycardia. The P' waves during tachycardia were identical to the parasystolic P' waves. Atrial parasystole was at times regular, as revealed by a precise mathematical relationship between the interectopic intervals, and on other occasions irregular. Irregularity was due to modulation, namely electrotonic influence exerted by the sinus impulses upon the parasystolic focus. Atrial tachycardia occurred only during the periods when atrial parasystole was modulated. Atrial tachycardia has been interpreted as due to automodulation, a situation where the propagated parasystolic impulse exerts an electrotonic influence on the ectopic focus itself, leading to a marked unexpected acceleration of the ensuing parasystolic discharge.

Aged↗
PubMed1991

Sinus parasystole.

Sinus parasystole is the expression of a protected nondominant sinus pacemaker, which is totally independent of the dominant rhythm. Two forms of sinus parasystole are described: (1) an active form, where both the dominant and the parasystolic pacemakers are located within the sinus node and (2) a passive form, where the basic rhythm is ectopic and the sinus pacemaker is protected as a result of complete retrograde SA block. Three cases of sinus parasystole are analyzed. In the active form of the arrhythmia the parasystolic sinus P waves are identical to those of the basic sinus rhythm. The diagnosis is suggested by variably coupled premature sinus P waves occurring with mathematically related intervals. This relationship between the parasystolic intervals can not be precise whenever complicating factors such as modulation occur. The recognition of active sinus parasystole is difficult, since the parasystolic P waves do not differ from basic P waves, so that the pattern resembles that of sinus arrhythmia or sinus extrasystoles. The passive form of sinus parasystole is more easily recognized due to the clear-cut difference between the dominant ectopic atrial waves and the "parasystolic" sinus P waves, which manifest with variable coupling intervals and reflect mathematically related intervals in between.

Adult↗
PubMed1991

Pseudo pre-excitation with concertina effect in idioventricular tachycardia.

The concertina effect is a phenomenon where the QRS complexes reflect alternating phases of gradual widening and narrowing. This is most commonly due to ventricular pre-excitation, and the changes in QRS morphology are due to variability of the ventricular zone that undergoes pre-excitation. This presentation reflects a case where the concertina effect is due to an idioventricular tachycardia at a rate nearly identical to the sinus rate. Variable degrees of ventricular fusion therefore occur, and the concertina effect ensues, in relation to slight variations of the sinus cycle.

Electrocardiography↗
PubMed1991

[A-V conduction in atrial fibrillation and flutter].

The assessment of A-V conduction in the presence of atrial fibrillation is based upon analysis of the R-R intervals. This is because in atrial fibrillation it is impossible both to identify the impulse that has been conducted to the ventricles, and to measure the A-V conduction time. The first step is, therefore, to evaluate whether the QRS complexes are the expression of conducted atrial impulses, or they are A-V junctional or ventricular in origin. In other words, it is necessary to distinguish between A-V conduction and A-V dissociation. Conduction in atrial fibrillation commonly results in irregular R-R cycles, whereas in the presence of dissociation the R-R cycles are mainly regular. This differentiation can be difficult in the presence of: aberrant conduction; A-V conduction disturbances; or A-V junctional tachycardia with anterograde 2nd degree exit block. The problem occurs both with tachycardia-dependent (or phase 3), and with bradycardia-dependent (or phase 4) aberrant conduction. Distinction between aberration and ectopy is helped by: the sequence long cycle-short cycle; the pause that follows the wide QRS complex; the configuration of the wide QRS complex. Since aberrant conduction may be sustained, due to the linking phenomenon, the pattern may mimick ventricular tachycardia. In atrial flutter the atrial electrical activity is far less chaotic than in atrial fibrillation, so that assessment of A-V conduction is less difficult. Nevertheless, it is impossible to determine exactly which out of the atrial impulses has been conducted, due to the extremely fast atrial rate: the conducted impulse, indeed, is not always the one that immediately precedes the QRS complex. Furthermore, it is also difficult to measure the A-V conduction time, because the F waves follow to each other without any interruption, so that it is impossible to define exactly the beginning of atrial activation. In atrial flutter, thus, as well as in atrial fibrillation, A-V conduction may be assessed by analysis of the R-R intervals, apart from measurement of F-R intervals. In the absence of drugs, atrial flutter is usually associated with 2:1 (or, less frequently, 4:1) conduction ratio, being the odd ratios (3:1, 5:1) far more rare. Due to concealed penetration of non-conducted impulses, A-V conduction intervals are often variable, so that the R-R cycles are irregular even in the presence of a constant A-V conduction ratio. The most common mechanisms leading to irregularity are the alternation of A-V conduction times, and the alternating Wenckebach phenomenon.(ABSTRACT TRUNCATED AT 400 WORDS)

Atrial Fibrillation↗
PubMed1991

[Electrocardiographic diagnosis of ventricular tachycardia in patients with previous myocardial infarct: frequency and significance of diverse diagnostic criteria].

Electrocardiographic tracings of ventricular tachycardia were recorded from 34 patients with old myocardial infarction. The diagnostic criteria of ventricular tachycardia were carefully assessed in each tracing. The most commonly observed signs were: 1) QRS duration greater than 140 msec; 2) a prevalent negative deflection in Lead V6; 3) an interval from the beginning of the QRS complex to the S wave nadir greater than 100 msec in at least one precordial lead. The cases were subdivided into two groups on the basis of a predominant positive or negative deflection in Lead V1 (Group 1 and 2, respectively). The most common signs in Group 1 were a monophasic R wave configuration of the QRS complex in Lead V1, and a QS configuration in Lead V6. On the other hand, the most frequent criteria in Group 2 were an interval between the beginning of the QRS complex and the S wave nadir greater than 60 msec in Lead V1, and a QS configuration in Lead V6. Furthermore, none of the cases reflected a normal frontal plane QRS axis, but an axis deviation was evident in all 29 cases where axis could be calculated.

Diagnosis, Differential↗
PubMed1990

Longitudinal dissociation within the reentry pathway of ventricular tachycardia.

Two cases of nonsustained, repetitive ventricular tachycardia are analyzed. In both, the episodes of tachycardia do not contain random numbers of beats, but the complexes in each phase of tachycardia are either always in even numbers (case 1) or always in odd numbers (case 2). This indicates longitudinal dissociation within the reentry circuit: i.e., there are two functionally separate pathways in some part of the reentry circuit, and the reciprocating impulse runs alternatively through the two pathways. Tachycardia ends due to block of the impulse always in the same pathway, thus, the number of beats in each episode of tachycardia is always either in odd or even numbers.

Aged↗
PubMed1989

Modulated parasystole complicating permanent ventricular pacing: the different influence of spontaneous and paced impulses upon the parasystolic rhythm.

A case of modulated ventricular parasystole observed in a patient with a VVIM pacemaker is reported. Analysis reveals that the electronic influence (modulation) effected upon the parasystolic focus by the sinus impulses is different from that exerted by the paced impulses. Furthermore, fusion beats reflect an intermediate modulating effect according to the prevalence of the sinus or the paced wavefront.

Aged↗
PubMed1989

Atrioventricular junctional parasystole with ventricular fusion beats due to complicating Wolff-Parkinson-White syndrome.

We present a case of atrioventricular (AV) junctional parasystole manifesting with ventricular fusion beats due to the presence of an accessory AV conduction pathway. Ventricular fusion beats are usually impossible in AV junctional parasystole. In the reported case the ventricular fusion occurs because the ectopic AV junctional impulse is conducted through the His bundle, whereas the sinus impulse is conducted to the ventricles through the Kent bundle.

Adult↗
PubMed1989

[A-V conduction in atrial flutter. Electrocardiographic study].

One hundred and twenty-nine cases of atrial flutter were analyzed to assess the A-V conduction. The R-R intervals, the A-V conduction ratio, and the F-R intervals were measured in each case. Conduction in atrial flutter was defined either as constant or as variable depending on whether the A-V conduction ratio was fixed or variable. Furthermore, atrial flutter was defined as regular whenever the R-R intervals were mathematically related to each other, any interval being a multiple of the F-F cycle. On the other hand, atrial flutter was defined as irregular when the R-R cycles did not reflect a precise mathematical relationship. The R-R intervals in irregular atrial flutter were not exactly multiples of the F-F cycle. This was because the F-R intervals were variable. Sixty-five cases of atrial flutter had constant A-V conduction, whereas 64 cases were associated with variable A-V conduction. Eighty-eight per cent of cases with constant conduction were regular. On the contrary, 91% of cases with variable A-V conduction were irregular. These data reflect a relationship between the constancy of the A-V conduction ratio and the regularity of the R-R intervals. Several mechanisms were identified as being responsible for atrial flutter irregularity. Alternation of the F-R intervals was the most frequent mechanism leading to irregularity of atrial flutter with constant A-V conduction. Alternating Wenckebach periodicity was the most common cause of irregularity in atrial flutter with variable conduction ratio. Concealed conduction of blocked impulses was also frequently involved in determining atrial flutter irregularity.

Atrial Flutter↗
PubMed1988

"Irregular" ventricular parasystole: the influence of sinus rhythm on a parasystolic focus.

Fifteen cases of ventricular parasystole were analyzed to determine whether the interectopic intervals were regular, as expressed by long intervals being exact multiples of the short ones, or not. The regularity of the interectopic intervals was assessed by means of the variation index: the ratio of the maximal difference between various measurements of the parasystolic cycle length and the mean parasystolic cycle length. Three out of 15 cases had a variation index less than 5, and were classified as "regular parasystole." Twelve cases were associated with a variation index greater than 7.5, and were classified as "irregular parasystole." The cases of irregular parasystole were then analyzed to determine whether the variability of the interectopic intervals was casual or dependent on action of the sinus beats. A parasystolic resetting by critically timed sinus impulses (a form of intermittent parasystole) was evident in three cases. The irregularity in the remaining nine cases was due to modulation (viz., due to electrotonic influence exerted by the sinus beats on the parasystolic focus). In every case of modulated parasystole a phase-response curve was constructed, which enabled an analysis of all the interectopic intervals on the basis of a time-dependent effect exerted by the sinus impulses on an otherwise rhythmic parasystolic focus.

Adolescent↗
PubMed1985

Bluetongue virus infection in Costa Rican and Colombian cattle.

Bluetongue virus (BTV) group antibodies are widely distributed in Costa Rica and Northern Colombia; prevalence is highest at lowest altitudes. Clinical evidence of bluetongue (BT) infection in cattle is not seen. Evidence exists of the circulation of BTV serotypes 6 and 14 in Costa Rica and BTV serotype 12, 14 and 17 in Northern Colombia in the period 1981-1983. Culicoides insignis is implicated as a probable vector in Colombia.

Animals↗