[Acquired long QT syndrome]

The long QT syndrome may be acquired or genetically determined. The syndrome is characterized by a prolonged QT interval and is associated with an increased risk of cardiac arrhythmia such as a torsade de pointe and death. Electrolytes disorders such as hypomagnesemia and hypokaliemia and several drugs may increase the risk to develop a long QT syndrome. The epidemiology, the aetiology, the diagnostic approach as well as the management options of an acquired QT prolongation is discussed and reviewed herein.

Predictive models of syncope causes in an outpatient clinic

The investigation of unexplained syncope remains a challenging clinical problem. In the present study we sought to evaluate the diagnostic value of a standardized work-up focusing on non invasive tests in patients with unexplained syncope referred to a syncope clinic, and whether certain combinations of clinical parameters are characteristic of rhythmic and reflex causes of syncope.

METHODS AND RESULTS

317 consecutive patients underwent a standardized work-up including a 12-lead ECG, physical examination, detailed history with screening for syncope-related symptoms using a structured questionnaire followed by carotid sinus massage (CSM), and head-up tilt test. Invasive testings including an electrophysiological study and implantation of a loop recorder were only performed in those with structural heart disease or traumatic syncope. Our work-up identified an etiology in 81% of the patients. Importantly, three quarters of the causes were established non invasively combining head-up tilt test, CSM and hyperventilation testing. Invasive tests yielded an additional 7% of diagnoses. Logistic analysis identified age and number of significant prodromes as the only predictive factors of rhythmic syncope. The same two factors, in addition to the duration of the ECG P-wave, were also predictive of vasovagal and psychogenic syncope. These factors, optimally combined in predictive models, showed a high negative and a modest positive predictive value.

CONCLUSION

A standardized work-up focusing on non invasive tests allows to establish more than three quarters of syncope causes. Predictive models based on simple clinical parameters may help to distinguish between rhythmic and other causes of syncope.

Evaluation of ablation patterns using a biophysical model of atrial fibrillation

Atrial fibrillation (AF) is the most common form of cardiac arrhythmia. Surgical/Radiofrequency (RF) ablation is a therapeutic procedure that consists of creating lines of conduction block to interrupt AF. The present study evaluated 13 different ablation patterns by means of a biophysical model of the human atria. In this model, ablation lines were abruptly applied transmurally during simulated sustained AF, and success rate, time to AF termination and average beat-to-beat interval were documented. The gold standard Cox's Maze III procedure was taken as reference. The effectiveness of twelve less invasive patterns was compared to it. In some of these incomplete lines (entailing a gap) were simulated. Finally, the computer simulations were compared to clinical data. The results show that the model reproduces observations made in vivo: (1) the Maze III is the most efficient ablation procedure; (2) less invasive patterns should include lines in both right and left atrium; (3) incomplete ablation lines between the pulmonary veins and the mitral valve annulus lead to uncommon flutter; (4) computer simulations of incomplete lines are consistent with clinical results of non-transumural RF ablation. Biophysical modeling may therefore be considered as a useful tool for understanding the mechanisms underlying AF therapies.

Morphological, clinical and genetic aspects in a family with a novel LAMP-2 gene mutation (Danon disease)

A family with several cases of severe cardiomyopathy and moderate myopathy is described, affecting two brothers and their cousin as well as their mothers. One boy died of sudden cardiac arrest at 17 years of age. The two brothers were treated with an implantable defibrillator and their mother died suddenly at 40 years of age. Muscle biopsy in males showed vacuolar myopathy in two cases, and no abnormality on standard staining in the third case. Cardiac biopsies showed hypertrophic and vacuolated fibres. Complete absence of LAMP-2 was demonstrated by immunohistochemistry on the vacuolated skeletal and cardiac muscle, but also on the morphologically normal skeletal muscle. Sequencing of LAMP-2 gene showed a novel S157X mutation in exon 4. Danon disease is a rare and potentially lethal cause of hypertrophic cardiomyopathy. Diagnosis can be made by immunohistochemistry performed on cardiac or muscle biopsy, and confirmed by genetic analysis, which also allows for easy family screening and counselling.

Sequence variation in the bovine and ovine PRNP genes

A resequencing approach was adopted to identify sequence variants in the PRNP gene that may affect susceptibility or resistance to bovine spongiform encephalopathy. The entire PRNP gene (>21 kb) was sequenced from 26 chromosomes from a group of Holstein-Friesian cows, as well as exon 3 of PRNP (>4 kb) from a further 24 chromosomes from six diverse breeds. We identified 51 variant sequences of which 42 were single nucleotide polymorphisms and nine were insertion/deletion (indel) events. The study was extended to exon 3 of the sheep PRNP gene where 23 sequence variants were observed, four of which were indels. The level of nucleotide diversity in the complete bovine PRNP gene was pi = 0.00079, which is similar to that found at the bovine T-cell receptor alpha delta joining region (pi = 0.00077), but somewhat less than that observed for the bovine leptin (pi = 0.00265). Sequence variation within exon 3 of PRNP in both cattle (pi = 0.00102) and sheep (pi = 0.00171) was greater than that for the complete PRNP gene, with sheep showing greater sequence variation in exon 3 than cattle. The level of sequence variation reported here is greater than previously thought for the bovine PRNP gene in cattle. This study highlights the contribution that recombination plays in increasing allelic diversity in this species.

Left atrial radiofrequency compartmentalization for chronic atrial fibrillation during heart surgery

BACKGROUND

The excellent results of the Maze III operation have demonstrated that a surgical cure of atrial fibrillation (AF) is possible. A simplified Maze procedure with radiofrequency (RF)ablation of the atrial tissue added to open heart surgery may help to cure chronic AF with low risk.

METHODS

From May 1998 to March 2001, an RF left atrial compartmentalization concomitant to a cardiac surgical intervention was performed on 40 of 1,258 patients (3.2 %). Thirty-seven patients had mitral valve disease, two had aortic valve disease and one had coronary artery disease. All patients presented with chronic refractory AF for a mean time of 40.4 months ranging from 4 months to 18 years.

RESULTS

Mitral valve replacement (MVR) was performed in 19 patients, mitral valve repair in 12, combined aortic and mitral valve procedures were performed in 6, aortic valve replacement(AVR) in 2 and CABG in 1 patient. Cardiopulmonary bypass time for the complete procedure was 138 +/- 32 minutes with an ablation time of 19 +/- 5 minutes. No complication related to RF application was noted. Sinus rhythm was present in 68% after 12.5 +/- 8.5 months.

CONCLUSIONS

RF left atrial compartmentalization combined with cardiac surgical interventions proved to be easy and safe to perform. The long-term results still have to be confirmed with further regular patient follow-up examinations.

Incessant atrioventricular dissociation due to far-field QRS oversensing and recurrent mode switch in a dual chamber pacemaker

We report the case of a repetitive and incessant activation of mode switch in a dual chamber pacemaker because of the inappropriate sensing by the atrial lead of far-fields signals from the ventricular evoked response. The incidence, consequences and prevention of the oversensing of far-field QRS complexes are discussed.

[New perspectives on the surgical treatment of atrial fibrillation. From extracorporeal circulation surgery to minimally invasive heart surgery]

Atrial fibrillation remains the most common sustained tachyarrhythmia, with recurrent symptoms and thromboembolic risks. In the last few years it has become the recent focus of intense clinical and experimental interest which confirm that this arrhythmia is due to atrial re-entry mechanisms. With better understanding of its physiopathology, an efficient surgical treatment has been developed. Surgical interventions of supraventricular tachycardias is targeted to neutralize the arrhythmogenic disorder using exclusion or ablation. Several methods can be used like surgical incisions, cryoablation, radiofrequency ablation or laser energy. Surgery being a transparietal approach requiring cardiopulmonary bypass, atriotomy and myocardial preservation, associated morbidity is due to the high technicalities of this treatment and not necessarily the therapy itself. New developments in the surgical approach tend to avoid cardiopulmonary bypass to reduce morbidity. The aim of this review is to describe and report our own experiences in this evolving domain of atrial fibrillation surgery.

Evidence rather than costs must guide use of the implantable cardioverter defibrillator

Randomized controlled trials have shown superior survival rates with implantable cardioverter defibrillators (ICDs) compared with antiarrhythmic drugs in survivors of cardiac arrest and life-threatening ventricular tachyarrhythmias, as well as in high-risk patients with ischemic heart disease and inducible ventricular tachycardia (VT). Current defibrillators are small and implanted with techniques similar to standard pacemakers. They provide high-energy shocks for ventricular fibrillation (VF) and rapid VT, antitachycardia pacing for monomorphic VT, and antibradycardia pacing. Limited evidence suggests that ICD therapy is cost-effective when compared with other widely accepted treatments. The use of ICDs is likely to continue to expand in the future. Ongoing clinical trials will define further prophylactic indications of the ICD and clarify its cost-effectiveness ratio in different clinical settings.

Developing clinical indication for multisite pacing

The artificial activation of the heart modifies the mechanics of contraction and relaxation. While only little basic research has been addressed to this question, clinical observations showed that for hypertrophic as well as dilated cardiomyopathies appropriate pacing techniques can be useful. Pacing can influence the activation sequence. The spread out from a single site is slow, and so hypercontractility deminshed. With the use of multiple electrodes, two atrial and/or two ventricular, conduction delays in the atria or ventricles can be eliminated. Synchronisation of the cardiac activation has an anti-arrhythmic and positiv inotropic effect. This may lead to new indications for pacemakers or better to be named cardiac synchronisers.

[Sudden death in hypertrophic obstructive and non-obstructive cardiomyopathy: can it be prevented?]

Sudden cardiac death constitutes the most devastating aspect of obstructive and non-obstructive hypertrophic cardiomyopathy. Loss of consciousness and family history of sudden cardiac death should alert the physician to the risk of sudden death. ECG, morphological and hemodynamic assessment, and exploration of central nervous activity are of little use in stratifying the risk of sudden cardiac death. Loss of consciousness associated with nonsustained ventricular tachycardia and inducible sustained ventricular arrhythmia identify patients at very high risk of sudden cardiac death. Nevertheless, many variable factors are involved in the pathophysiology of sudden cardiac death, and hence risk stratification of sudden cardiac death in patients with hypertrophic cardiomyopathy remains a very difficult clinical challenge.

[Cardiac pacemaker dysfunction secondary to outside interference: a review]

Electromagnetic signals from various sources may cause interference with pacemakers. The safety systems developed by manufacturers are generally effective. Nevertheless, some electromagnetic sources, particularly those found in the medical environment, can induce transitory or permanent pacemaker dysfunction. This paper presents the various sources of electromagnetic signals to which a pacemaker may be exposed. Taking into account the available literature, it attempts to clarify those which are really deleterious for the pacemaker and how to avoid them.

Autonomic imbalance assessed by heart rate variability analysis in vasovagal syncope

In this prospective study, the autonomic modulation of the sinus node of 12 patients (mean age 28 +/- 7 years) suffering from vasovagal syncope (VVS) was compared to that of 11 sex and age matched control patients (mean age 32 +/- 4 years) by analysis of heart rate variability. Spectral indices (low frequency power [Plf], high frequency power [Phf], total power [Pt], sympathovagal balance [LF/HF]) and temporal indices, the mean of all coupling intervals between normal beats (mRR), the standard deviation about the mean (sdRR), the percentage of adjacent R to R intervals differing by more than 50 msec (pNN50), and the root mean square of variations in successive R to R intervals (rMSSD) were compared at baseline and during head-up tilt between and within groups. Baseline results were similar in both groups. During tilt testing, comparison of results between groups revealed only significantly higher sdRR and rMSSD and lower LF/HF ratio in VVS patients. Within VVS patients, comparison of temporal and spectral analysis between baseline and tilt showed a significant increase of most indices (Plf, Phf, Pt, sdRR, and rMSSD) but a comparable LF/HF ratio; in contrast, control patients exhibited only a significant increase of LF/HF ratio. In conclusion, VVS patients who developed vasovagal syncope during head-up tilt demonstrated a nonreciprocal modulation of the sinus node by the autonomic nervous system indicative of a pronounced physiological sympathetic surge along with a paradoxical vagal input to the cardiovascular system.

Relation between cycle length, volume, and pressure in type I atrial flutter

Assuming that type I atrial flutter is a macroreentrant circuit, its cycle length should vary with the atrial dimensions. In order to test this hypothesis, flutter cycle length was measured while inducing atrial volume and pressure changes by postural and pharmacological means in seven patients undergoing a therapeutic programmed stimulation for type I atrial flutter conversion. Right atrial volume was estimated from B-mode echocardiography data. Basal values were compared with those obtained during inspiration, expiration, Valsalva maneuver, negative tilt (head down), and positive tilt (head up) with 0.8-1.6 mg p.o. nitroglycerin. The right atrial size increased slightly from 17.8 to 18.3 cm2 (P = 0.04) during the pressure load induced by negative tilt (+3 mmHg), with a corresponding lengthening of the flutter cycle length from 228 to 233 msec (P = 0.02). Similarly, pressure unloading of -2 mmHg by positive tilting and nitrates was accompanied by a decrease in right atrial size to 16.6 cm2 (P = 0.04), with a corresponding decrease in cycle length from 228 to 219 msec (P = 0.03). Respiratory maneuver yielded similar results with an inspiratory cycle lengthening, expiratory shortening, and further shortening during Valsalva maneuver. These experiments demonstrate a direct relation between cycle length and atrial volume in human type I atrial flutter. They underline the importance of the right heart preload and atrial size for the electrophysiological characteristics of type I atrial flutter. Beside its fundamental interest, this finding is important for the understanding of the mechanism of maintenance and therapeutic responses of this common arrhythmia.

Acute and long-term ventricular stimulation thresholds with a new, iridium oxide-coated electrode

Efforts have been made to design electrodes that significantly reduce not only the acute and chronic stimulation thresholds, but also attenuate the early peaking phenomenon and polarization. At two voltage levels (2.7 V and 5.4 V, respectively), we evaluated the right ventricular stimulation thresholds obtained with a new, iridium oxide-coated electrode in ten patients who received a VVI pacemaker. Measurements were made at implant and at multiple intervals for 1 year. Pulse width stimulation thresholds at implant were as follow: 0.04 +/- 0.008 msec at 2.7 V, 0.03 +/- 0.004 msec at 5.4 V; values at 2 weeks were 0.14 +/- 0.06 msec at 2.7 V, 0.07 +/- 0.025 msec at 5.4 V; values at 3 months were 0.09 +/- 0.03 msec at 2.7 V, 0.05 +/- 0.01 msec at 5.4 V; values at 1 year were 0.08 +/- 0.02 msec at 2.7 V, 0.04 +/- 0.01 msec at 5.4 V. The maximal increase of 0.11 +/- 0.05 msec occurred at 2.7 V, 2 weeks after implant. Our results indicate that this new electrode provides low acute and long-term stimulation thresholds, as well as an attenuated early peaking phenomenon, being able to stimulate safely at 2.7 V even early after implant.

Clinical efficacy of radiofrequency current in the treatment of patients with atrioventricular node reentrant tachycardia

Eight women (mean age 41 years, range 24 to 62) with drug-resistant atrioventricular (AV) node reentrant tachycardia underwent radiofrequency catheter ablation. Radiofrequency energy was delivered in a unipolar mode with use of a back paddle as the anode placed between the two scapulae. The total applied energy was 2,233 +/- 1,919 J. The AH interval increased from 87 +/- 13 to 113 +/- 17 ms (p less than 0.05) and the PQ interval increased from 141 +/- 15 to 169 +/- 34 ms (p less than 0.05). The anterograde Wenckebach cycle length increased from 300 +/- 41 to 320 +/- 42 ms (p less than 0.05). Retrograde conduction was abolished in five patients. Atrioventricular node tachycardia was still inducible in three patients. During a follow-up period of 9 +/- 3 months, four patients remained clinically asymptomatic without drug therapy and four patients had recurrent symptoms. Three of the latter responded to previously unsuccessful antiarrhythmic drugs and the fourth patient underwent surgical cure for persistence of tachycardia. Right bundle branch block occurred in five patients; it was permanent in four and transient in one. In conclusion, radiofrequency catheter ablation represents a valuable but still investigational therapy in patients with drug-refractory AV node reentrant tachycardia.

Is there an isolated arrhythmogenic right atrial myocarditis?

Two cases with drug refractory ectopic atrial tachycardia are described. A map-guided partial resection of the right atrium (RA) was done after preoperative endocardial catheter mapping had shown well-defined areas of fractionated RA potentials. Intraoperatively, there were no aneurysmal formations present as described by other authors. Histopathologic examination of the resected tissue showed atrial myocarditis in both patients. Postoperative right ventricular myocardial biopsies revealed no inflammatory tissue. A minor elevation of antibodies against echoviruses was found in one case. Postoperative electrophysiologic studies were negative. We conclude: focal RA myocarditis without concomitant ventricular myocarditis may represent one cause of drug-resistant ectopic atrial tachycardia. Map-guided surgical intervention may cure the disease.

[Sustained ventricular tachycardia: inducibility during invasive electrophysiologic studies]

Electrophysiologic studies are used for diagnosis and treatment in patients with sustained ventricular tachycardia. This method can only be employed if high inducibility of the spontaneous tachycardia can be demonstrated. We therefore investigated prospectively the induction yield in 35 patients with a history of documented sustained ventricular tachycardia. The patients' mean age was 58 years. Coronary artery disease was present in 24 patients, cardiomyopathy in 4, other organic heart diseases in 4, and no heart disease in 3. The ventricular tachycardia induction protocol consisted of three extrastimuli delivered during sinus rhythm and at two pacing cycle lengths, followed by intravenous isoproterenol if no tachycardia was induced before. With the method sustained ventricular tachycardia was induced in 100% of patients with coronary artery disease and cardiomyopathy, in 75% of patients with other heart diseases and in 33% of patients without detectable heart disease. We conclude that electrophysiologic studies have a high yield of sustained ventricular tachycardia induction in patients with underlying organic heart disease. The rational basis for use of electropharmacologic testing therefore exists in these patients. However, in patients without heart disease, the low sensitivity of electrophysiologic studies precludes its use for drug efficacy testing.