Clinical presentation of inappropriate sinus tachycardia and differential diagnosis.

Inappropriate sinus tachycardia (IST) is a syndrome characterized by a sinus tachycardia not related to a medical condition, to a physiological response, or to medication or drugs and associated with symptoms, often invalidating and altering the quality of life of affected patients. It occurs predominantly in adolescents and young adults, and in the female sex. The diagnosis requires a complete work-up in order to exclude other causes of sinus tachycardia and one or several additional tests: 24-h ECG ambulatory recordings, echocardiogram, exercise testing, and autonomous nervous system assessment. It should be differentiated from the postural orthostatic tachycardia syndrome, with which it shares a number of symptoms, and other supraventricular tachycardias originating in the high right atrium. An electrophysiological study should be considered in selected cases in order to differentiate IST from other supraventricular tachycardias. The mechanism is still unclear, and possible etiologies may include intrinsic abnormality of the sinus node, autonomic dysfunction, hypersensitivity of the sinus node to catecholamines, blunted vagal system, or a combination of the above. The authors emphasize the wide spectrum of clinical presentations and the need to better define the IST and the criteria required to ascertain its diagnosis.

Epidemiology and definition of inappropriate sinus tachycardia.

Inappropriate sinus tachycardia (IST) is a clinical syndrome lacking formal diagnostic criteria. It is generally defined as an elevated resting heart rate (HR; >90-100 bpm) with an exaggerated response to physical or emotional stress and a clearly sinus mechanism. Clinical manifestations are broad from a complete lack of symptoms to incapacitating incessant tachycardia. Now understood to be relatively prevalent, it is observed to have a generally benign prognosis, though symptoms may persist for years. Whether IST is a single discrete entity or a heterogeneous condition with overlap to other syndromes such as postural orthostatic tachycardia syndrome remains a matter of debate.

The sinus tachycardias.

Sinus tachycardia, in the forms of four distinct rhythm disturbances, is frequently encountered in clinical practice but is often overlooked. The most common rhythm, normal sinus tachycardia, whether physiologic, pathologic or iatrogenic, is predominantly catecholamine driven, is virtually asymptomatic and is managed by identifying and treating the underlying cause. The other so-called primary sinus tachycardias, which include inappropriate sinus tachycardia, postural orthostatic tachycardia syndrome and sinus node re-entry tachycardia, have fundamentally different clinical features, basic underlying etiologic mechanisms and treatment strategies. Differentiation of these types from normal sinus tachycardia and from other atrial arrhythmias is crucial for successful management. Accurate diagnosis and appropriate therapy of the sinus tachycardias not only prevents multiple consultations but might also have important long-term prognostic implications.

First postpacing interval variability during right ventricular stimulation: a single algorithm for the differential diagnosis of regular tachycardias.

BACKGROUND: Failure to differentiate supraventricular from ventricular arrhythmias is the most frequent cause of inappropriate implantable cardioverter-defibrillator therapies. Although a sudden-onset criterion is available to differentiate sustained monomorphic ventricular tachycardias (SMVTs) and sinus tachycardias (STs), SMVTs arising during ST and SMVTs gradually accelerating above the cutoff rate can remain undetected. Regular paroxysmal atrial tachycardias (ATs) also can be undetected by onset and stability algorithms. We hypothesized that the first postpacing interval (FPPI) variability after overdrive right ventricular pacing may differentiate SMVTs from STs and ATs. METHODS AND RESULTS: FPPI variability was measured in 23 SMVTs (cycle length [CL] 366+/-50 ms [VT group]), 27 supraventricular tachycardias, 15 episodes of induced or simulated ATs (CL 376+/-29 ms [AT group]), and 12 exercise-related STs (CL 381+/-24 [ST group]). Sequences of trains of 5, 10, and 15 beats were delivered with a CL 40 ms shorter than the tachycardia CL. An FPPI absolute mean difference between consecutive trains of 5 and 10 beats (deltaFPPI) < or =25 ms identified all VTs (mean difference 5+/-7 ms). In the AT group, the deltaFPPI was >25 ms in all sequences (mean difference 129+/-60 ms, P<0.01). In the ST group, the deltaFPPI was >50 ms in all STs (mean difference 118+/-47 ms, P<0.01). CONCLUSIONS: FPPI variability may differentiate SMVT from AT and ST. This criterion is potentially useful in implantable devices that use a single ventricular lead.

To fumble flutter or tackle "tach"? Toward updated classifiers for atrial tachyarrhythmias.

Aristotle proposed in his short work, The Categories, that a definition is a statement of a thing's essential nature, and the essence of a thing are those of its properties that cannot change without losing its identity. But Aristotle was not faced with the flux of new information that confronts modern medicine. Nowadays, the argot of a discipline arises organically at the intersection of a given state of empiric knowledge and the exigencies of present scientific discourse. Thus, when the only treatment for a regular, narrow QRS complex tachycardia was digitalis glycosides or vasopressor infusion, the term "PAT" ("paroxysmal atrial tachycardia") seemed adequate, at least to distinguish it from ventricular tachycardia. We now prefer the term "PSVT" (paroxysmal supraventricular tachycardia) because we understand that most such tachycardias are not in truth "atrial" but involve the AV node and/or an accessory AV connection, and because we wish to report on the results of treatment specific to each of the subcategories of "PSVT." Similarly, as our knowledge of atrial arrhythmias has grown and especially as we need to describe the outcome of new interventional approaches to therapy, it may be prudent to use a nomenclature for atrial tachyarrhythmias that is based on the geometry of the tachycardia substrate, the relationship of that substrate to atrial anatomy, and the type of atrial lesions required to abolish that substrate.