Analysis of QT interval in patients with idiopathic mitral valve prolapse

Arrhythmogenic Mitral Valve Prolapse: Can We Risk Stratify and Prevent Sudden Cardiac Death?

Ventricular arrhythmias associated with mitral valve prolapse (MVP) and the capacity to cause sudden cardiac death (SCD), referred to as 'malignant MVP', are an increasingly recognised, albeit rare, phenomenon. SCD can occur without significant mitral regurgitation, implying an interaction between mechanical derangements affecting the mitral valve apparatus and left ventricle. Risk stratification of these arrhythmias is an important clinical and public health issue to provide precise and targeted management. Evaluation requires patient and family history, physical examination and electrophysiological and imaging-based modalities. We provide a review of arrhythmogenic MVP, exploring its epidemiology, demographics, clinical presentation, mechanisms linking MVP to SCD, markers of disease severity, testing modalities and management, and discuss the importance of risk stratification. Even with recently improved understanding, it remains challenging how best to weight the prognostic importance of clinical, imaging and electrophysiological data to determine a clear high-risk arrhythmogenic profile in which an ICD should be used for the primary prevention of SCD.

Imaging for the assessment of the arrhythmogenic potential of mitral valve prolapse

Mitral valve prolapse (MVP) is the most common valve disease in the western world and recently emerged as a possible substrate for sudden cardiac death (SCD). It is estimated an annual risk of sudden cardiac death of 0.2 to 1.9% mostly caused by complex ventricular arrhythmias (VA). Several mechanisms have been recognized as potentially responsible for arrhythmia onset in MVP, resulting from the combination of morpho-functional abnormality of the mitral valve, structural substrates (regional myocardial hypertrophy, fibrosis, Purkinje fibers activity, inflammation), and mechanical stretch. Echocardiography plays a central role in MVP diagnosis and assessment of severity of regurgitation. Several abnormalities detectable by echocardiography can be prognostic for the occurrence of VA, from morphological alteration including leaflet redundancy and thickness, mitral annular dilatation, and mitral annulus disjunction (MAD), to motion abnormalities detectable with "Pickelhaube" sign. Additionally, speckle-tracking echocardiography may identify MVP patients at higher risk for VA by detection of increased mechanical dispersion. On the other hand, cardiac magnetic resonance (CMR) has the capability to provide a comprehensive risk stratification combining the identification of morphological and motion alteration with the detection of myocardial replacement and interstitial fibrosis, making CMR an ideal method for arrhythmia risk stratification in patients with MVP. Finally, recent studies have suggested a potential role in risk stratification of new techniques such as hybrid PET-MR and late contrast enhancement CT. The purpose of this review is to provide an overview of the mitral valve prolapse syndrome with a focus on the role of imaging in arrhythmic risk stratification. CLINICAL RELEVANCE STATEMENT: Mitral valve prolapse is the most frequent valve condition potentially associated with arrhythmias. Imaging has a central role in the identification of anatomical, functional, mechanical, and structural alterations potentially associated with a higher risk of developing complex ventricular arrhythmia and sudden cardiac death. KEY POINTS: • Mitral valve prolapse is a common valve disease potentially associated with complex ventricular arrhythmia and sudden cardiac death. • The mechanism of arrhythmogenesis in mitral valve prolapse is complex and multifactorial, due to the interplay among multiple conditions including valve morphological alteration, mechanical stretch, myocardial structure remodeling with fibrosis, and inflammation. • Cardiac imaging, especially echocardiography and cardiac magnetic resonance, is crucial in the identification of several features associated with the potential risk of serious cardiac events. In particular, cardiac magnetic resonance has the advantage of being able to detect myocardial fibrosis which is currently the strongest prognosticator.

What Do We Know So Far About Ventricular Arrhythmias and Sudden Cardiac Death Prediction in the Mitral Valve Prolapse Population? Could Biomarkers Help Us Predict Their Occurrence?

PURPOSE OF THE REVIEW

To summarize currently available data on the topic of mitral valve prolapse (MVP) and its correlation to the occurrence of atrial and ventricular arrhythmias. To assess the prognostic value of several diagnostic methods such as transthoracic echocardiography, transesophageal echocardiography, cardiac magnetic resonance, cardiac computed tomography, electrocardiography, and electrophysiology concerning arrhythmic episodes. To explore intra and extracellular biochemistry of the cardiovascular system and its biomarkers as diagnostic tools to predict rhythm disturbances in the MVP population.

RECENT FINDINGS

MVP is a common and mainly benign valvular disorder. It affects 2-3% of the general population. MVP is a heterogeneous and highly variable phenomenon with three structural phenotypes: myxomatous degeneration, fibroelastic deficiency, and forme fruste. Exercise intolerance, supraventricular tachycardia, and chest discomfort are the symptoms that are often paired with psychosomatic components. Though MVP is thought to be benign, the association between isolated MVP without mitral regurgitation (MR) or left ventricle dysfunction, with ventricular arrhythmia (VA) and sudden cardiac death (SCD) has been observed. The incidence of SCD in the MVP population is around 0.6% per year, which is 6 times higher than the occurrence of SCD in the general population. Often asymptomatic MVP population poses a challenge to screen for VA and prevent SCD. Therefore, it is crucial to carefully assess the risk of VA and SCD in patients with MVP with the use of various tools such as diagnostic imaging and biochemical and genetic screening.

Identifying Mitral Valve Prolapse at Risk for Arrhythmias and Fibrosis From Electrocardiograms Using Deep Learning

BACKGROUND

Mitral valve prolapse (MVP) is a common valvulopathy, with a subset developing sudden cardiac death or cardiac arrest. Complex ventricular ectopy (ComVE) is a marker of arrhythmic risk associated with myocardial fibrosis and increased mortality in MVP.

OBJECTIVES

The authors sought to evaluate whether electrocardiogram (ECG)-based machine learning can identify MVP at risk for ComVE, death and/or myocardial fibrosis on cardiac magnetic resonance (CMR) imaging.

METHODS

A deep convolutional neural network (CNN) was trained to detect ComVE using 6,916 12-lead ECGs from 569 MVP patients from the University of California-San Francisco between 2012 and 2020. A separate CNN was trained to detect late gadolinium enhancement (LGE) using 1,369 ECGs from 87 MVP patients with contrast CMR.

RESULTS

The prevalence of ComVE was 28% (160/569). The area under the receiver operating characteristic curve (AUC) of the CNN to detect ComVE was 0.80 (95% CI: 0.77-0.83) and remained high after excluding patients with moderate-severe mitral regurgitation [0.80 (95% CI: 0.77-0.83)] or bileaflet MVP [0.81 (95% CI: 0.76-0.85)]. AUC to detect all-cause mortality was 0.82 (95% CI: 0.77-0.87). ECG segments relevant to ComVE prediction were related to ventricular depolarization/repolarization (early-mid ST-segment and QRS from V1, V3, and III). LGE in the papillary muscles or basal inferolateral wall was present in 24% patients with available CMR; AUC for detection of LGE was 0.75 (95% CI: 0.68-0.82).

CONCLUSIONS

CNN-analyzed 12-lead ECGs can detect MVP at risk for ventricular arrhythmias, death and/or fibrosis and can identify novel ECG correlates of arrhythmic risk. ECG-based CNNs may help select those MVP patients requiring closer follow-up and/or a CMR.

Arrhythmogenic Mitral Valve Prolapse and Sudden Cardiac Death: An Update and Current Perspectives

Mitral valve prolapse (MVP) affects about 2% to 3% of the general population, mostly women, and is the most common cause of primary chronic mitral regurgitation (MR) in western countries. The natural history is heterogeneous and widely determined by the severity of MR. Although most patients remain asymptomatic with a near-normal life expectancy, approximately 5% to 10 % progress to severe MR. As largely recognized, left ventricular (LV) dysfunction due to chronic volume overload per se identifies a subgroup at risk of cardiac death. However, there is rising evidence of a link between MVP and life threating ventricular arrhythmias (VAs)/sudden cardiac death (SCD) in a small subset of middle-aged patients without significant MR, heart failure and remodeled hearts. The present review focuses on the underlying mechanism of electric instability and unexpected cardiac death in this subset of young patients, from the myocardial scarring of the LV infero-lateral wall due to mechanical stretch exerted by the prolapsing leaflets and mitral annular disjunction, to the inflammation's impact on fibrosis pathways along with a constitutional hyperadrenergic state. The heterogeneity of clinical course reveals a necessity of risk stratification, preferably through noninvasive multimodality imaging, that will help to identify and prevent adverse scenarios in young MVP patients.

Malignant Mitral Valve Prolapse: Risk and Prevention of Sudden Cardiac Death

Purpose of review

The purpose of this review is to explore the prevalence and risk factors for a malignant phenotype in mitral valve prolapse (MVP) characterized by life-threatening ventricular arrhythmias and sudden cardiac arrest and death (SCD), including mechanistic and pathophysiologic findings and mechanism-based potential therapies.

Recent findings

A malignant phenotype in MVP characterized by life-threatening arrhythmias has long been recognized, although MVP is often benign. Efforts to identify this malignant phenotype have revealed potential risk factors for SCD that include elongated, myxomatous leaflets, ECG changes and complex ventricular ectopy. More recently, malignant MVP has been associated with myocardial fibrosis in the papillary muscles and inferobasal left ventricular wall. This localization suggests a central role of prolapse-induced mechanical forces on the myocardium in creating an arrhythmogenic substrate and triggering life-threatening arrhythmias. This mechanism for fibrosis is also consistent with imaging evidence of prolapse-induced mechanical changes in the papillary muscles and inferobasal left ventricular wall. Currently, no therapy to prevent SCD in malignant MVP has been established and limited clinical data are available. Mechanistic information and prospective study have the potential to identify patients at risk of SCD and preventive strategies.

Summary

Malignant MVP relates to unique properties and mechanical abnormalities in the mitral valve apparatus and adjacent myocardium. Increased understanding of disease mechanisms and determinants of arrhythmias is needed to establish effective therapies.

Arrhythmic Mitral Valve Prolapse and Mitral Annular Disjunction: Clinical Features, Pathophysiology, Risk Stratification, and Management

Mitral valve prolapse (MVP) is a common cause of valvular heart disease. Although many patients with MVP have a benign course, there is increasing recognition of an arrhythmic phenotype associated with ventricular arrhythmias and sudden cardiac death (SCD). Pathophysiologic mechanisms associated with arrhythmias include cardiac fibrosis, mechanical stress induced changes in ventricular refractory periods, as well as electrophysiologic changes in Purkinje fibers. Clinically, a variety of risk factors including demographic, electrocardiographic, and imaging characteristics help to identify patients with MVP at the highest at risk of SCD and arrhythmias. Once identified, recent advances in treatment including device therapy, catheter ablation, and surgical interventions show promising outcomes. In this review, we will summarize the incidence of ventricular arrhythmias and SCD in patients with MVP, the association with mitral annular disjunction, mechanisms of arrhythmogenesis, methods for arrhythmic and SCD risk stratification including findings with multimodality imaging, and treatments for the primary and secondary prevention of SCD.

Mitral Valve Prolapse, Ventricular Arrhythmias, and Sudden Death

Despite a 2% to 3% prevalence of echocardiographically defined mitral valve prolapse (MVP) in the general population, the actual burden, risk stratification, and treatment of the so-called arrhythmic MVP are unknown. The clinical profile is characterized by a patient, usually female, with mostly bileaflet myxomatous disease, mid-systolic click, repolarization abnormalities in the inferior leads, and complex ventricular arrhythmias with polymorphic/right bundle branch block morphology, without significant regurgitation. Among the various pathophysiologic mechanisms of electrical instability, left ventricular fibrosis in the papillary muscles and inferobasal wall, mitral annulus disjunction, and systolic curling have been recently described by pathological and cardiac magnetic resonance studies in sudden death victims and patients with arrhythmic MVP. In addition, premature ventricular beats arising from the Purkinje tissue as ventricular fibrillation triggers have been documented by electrophysiologic studies in MVP patients with aborted sudden death.

The genesis of malignant ventricular arrhythmias in MVP probably recognizes the combination of the substrate (regional myocardial hypertrophy and fibrosis, Purkinje fibers) and the trigger (mechanical stretch) eliciting premature ventricular beats because of a primary morphofunctional abnormality of the mitral valve annulus.

The main clinical challenge is how to identify patients with arrhythmic MVP (which imaging technique and in which patient) and how to treat them to prevent sudden death. Thus, there is a necessity for prospective multicenter studies focusing on the prognostic role of cardiac magnetic resonance and electrophysiologic studies and on the therapeutic efficacy of targeted catheter ablation and mitral valve surgery in reducing the risk of life-threatening arrhythmias, as well as the role of implantable cardioverter defibrillators for primary prevention.

Evaluation of Prolonged QT Interval: Structural Heart Disease Mimicking Long QT Syndrome

BACKGROUND

In about 20-25% of patients with congenital long QT syndrome (LQTS) a causative pathogenic mutation is not found. The aim of this study was to explore the prevalence of alternative cardiac diagnoses among patients exhibiting prolongation of QT interval with negative genetic testing for LQTS genes.

METHODS

We conducted a retrospective analysis of 239 consecutive patients who were evaluated in the inherited arrhythmia clinic at the Toronto General Hospital between July 2013 and December 2015 for possible LQTS. A detailed review of the patients' charts, electrocardiograms, and imaging was carried out.

RESULTS

The analysis included 56 gene-negative patients and 61 gene-positive patients. Of the gene-negative group, 25% had structural heart disease compared to only 1.6% of gene-positive patients (P < 0.001). Structural heart disease was more likely if only one abnormal QTc parameter was found in the course of the evaluation (35.2% vs 9.1%, P = 0.01). The most common structural cardiac pathology was bileaflet mitral valve prolapse (8.9%). No gene-positive patient had episodes of nonsustained ventricular tachycardia, compared to seven of the gene-negative patients (0% vs 12.5%, P = 0.005).

CONCLUSIONS

Structural pathology was detected in a quarter of gene-negative patients evaluated for possible LQTS. Hence, cardiac imaging and Holter monitoring should be strongly encouraged to rule out structural heart disease in this population.

QT dispersion and ventricular arrhythmias in children with primary mitral valve prolapse

AIM

To investigate ventricular arrhythmias in children with primary mitral valve prolapse and to evaluate its relation with QT length, QT dispersion, autonomic function tests and heart rate variability measurements.

MATERIAL AND METHODS

Fourty two children with mitral valve prolapse and 32 healthy children were enrolled into the study. Twelve-lead electrocardiograms, autonomic function tests, echocardiography and 24-hour rhythm Holter tests were performed. Electrocardiograms were magnified digitally. The QT length was corrected according to heart rate. The patients were grouped according to the number of premature ventricular contractions and presence of complex ventricular arhythmia in the 24-hour rhythm Holter monitor test. Heart rate variability measurements were calculated automatically from the 24-hour rhythm Holter monitor test. Orthostatic hypotension and resting heart rate were used as autonomic function tests.

RESULTS

The mean age was 13.9±3.3 years in the patient group and 14.6±3.1 years in the control group (p>0.05). Thirty four of the patients (81%) were female and eight (19%) were male. Twenty five of the control subjects (78%) were female and seven (22%) were male. The QT dispersion and heart rate corrected QT interval were found to be significantly increased in the children with primary mitral valve prolapse when compared with the control group (56±16 ms vs. 43±11 ms, p=0.001; 426±25 ms vs. 407±26 ms, p=0.002, respectively). In 24-hour rhythm Holter monitor tests, ventricular arrhythmias were found in 21 out of 42 patients (50%) and 6 out of 32 control subjects (18.8%) (p=0.006). QT dispersion was found to be significantly increased in patients with premature ventricular contractions ≥ 10/day and/or complex ventricular arrhythmias compared to the control group without ventricular premature beats (p=0.002). There was no significant difference in autonomic function tests and heart rate variability measurements between the patient and control groups.

CONCLUSIONS

The noted increase in QT dispersion may be a useful indicator for the clinician in the evaluation of impending ventricular arrhythmias in children with primary mitral valve prolapse.

QT dispersion and diastolic functions in differential diagnosis of primary mitral valve prolapse and rheumatic mitral valve prolapse

There is no specific criteria established to guide physicians in the differential diagnosis of primary mitral valve prolapse (MVP) and rheumatic MVP. Previous studies suggested that history and pathology of mitral valve could be helpful in differential diagnosis of MVP. The aim of this study was to evaluate the value of QT interval, QT dispersion, and diastolic function in differential diagnosis of MVP. We examined electrocardiographies and echocardiographies of 24 primary MVP patients, 20 rheumatic MVP patients, and 21 healthy subjects. MVP was defined as superior displacement of the mitral leaflets more than 2 mm into the left atrium during systole. QT dispersion was significantly higher in primary MVP patients (71 +/- 13.5 ms, p < 0.01). Maximum QT dispersion value in rheumatic MVP patients was 55 ms. E and A velocity values which show ventricular early and late diastolic filling, were lower in primary MVP patients (p < 0.01). There was no difference in the heart rate corrected QT interval values between the primary MVP patients (397 +/- 28.1), rheumatic MVP patients (403 +/- 23.8) and healthy children (404 +/- 15.8; p > 0.05). Our findings may indicate that QT dispersion can be used as a parameter for differential diagnosis of primary MVP and rheumatic MVP. Further studies are needed to identify a cut-off point of QT dispersion.

Relation between QT dispersion and ventricular arrhythmias in uncomplicated isolated mitral valve prolapse

Complications of mitral valve prolapse (MVP), among which serious ventricular arrhythmia and sudden death are of major importance, affect many individuals due to the high incidence of MVP itself in the community despite the actual low incidence of these complications. The present study investigated the incidence and distribution of ventricular arrhythmias according to their severity and relationship with the QT interval and dispersion of repolarization in uncomplicated isolated MVP (IMVP) cases. Fifty-eight uncomplicated IMVP patients, 33 patients with accompanying tricuspid valve prolapse (TVP), to compare its relationship with ventricular arrhythmia, and 60 age- and sex-matched control subjects were enrolled in the study. Individuals with accompanying cardiac or systemic disease, or who were on drug therapy that could potentially affect QT characteristics, were excluded. The incidence of ventricular arrhythmia was 48% in the IMVP group and 64% in the TVP group; the difference was statistically insignificant. In addition, the differences of the QT and Q peak T values were insignificant, whereas QT dispersion (QTd) and Q peak T dispersion (QpeakTd) values were significantly higher in the patient group (60+/-14, 54+/-14 ms, respectively) compared with the control group (42+/-10, 38+/-10 ms, respectively, p<0.001). Complex ventricular arrhythmias (Lown Grade > or =III) in the IMVP group had a significant relationship with QTd and QpeakTd (p<0.001), but not with QT or QpeakT. As a result of the study, it is concluded that TVP accompanying MVP does not increase the incidence of ventricular arrhythmia, that ventricular arrhythmia is related to QT dispersion rather than QT interval in IMVP, that the QT dispersion is a fairly good marker for identifying the high-risk group for serious ventricular arrhythmia and sudden death, and that QpeakT dispersion measurement is an additional indicator that could be an alternative when QT is difficult to determine in conditions such as high heart rate or the presence of U wave.

Survivors of out-of-hospital cardiac arrest with apparently normal heart. Need for definition and standardized clinical evaluation. Consensus Statement of the Joint Steering Committees of the Unexplained Cardiac Arrest Registry of Europe and of the Idiopathic Ventricular Fibrillation Registry of the United States

BACKGROUND

A wide variety of structural abnormalities are associated with the vast majority of cardiac arrests. However, there is no evidence of structural heart disease in approximately 5% of victims of sudden death, indicating that cardiac arrest in the absence of organic heart disease is more common than previously recognized. The risk of recurrence and the acute and long-term response to therapy are important but unanswered questions. Data from the small series reported so far are of limited value because of the lack of uniform criteria to define and diagnose idiopathic ventricular fibrillation (IVF).

METHODS AND RESULTS

This report originates from a Consensus Conference convened by the Steering Committees of the European (UCARE) and North American (IVF-US) Registries on IVF under the auspices of the Working Group on Arrhythmias of the European Society of Cardiology. Its objective is to provide a unified definition of IVF and to outline the investigations necessary to make this diagnosis. Minimal diagnostic tests for the exclusion of an underlying structural heart disease include non-invasive (blood biochemistry, physical examination and clinical history, ECG, exercise stress test, 24-hour Holter recording, and echocardiogram) and invasive (coronary angiography, right and left ventricular cineangiography, and electrophysiological study) examinations. Programmed electrical stimulation, ventricular biopsy, and ergonovine test during coronary angiography are recommended but not mandatory.

CONCLUSIONS

It is recognized that despite careful evaluation, conditions such as focal cardiomyopathy, myocarditis, or fibrosis and transient electrolyte abnormalities may remain silent. Therefore, patients should undergo careful follow-up, with noninvasive tests repeated every year. The existence of a unified terminology will allow meaningful comparison of data collected by different investigators and will thus contribute to a better understanding of IVF.

Significance of QT dispersion on ventricular arrhythmias in mitral valve prolapse

The present study was designed to detect the arrhythmogenic effect of mitral valve prolapse, and the relationship between QT, QT dispersion and ventricular arrhythmias in subjects with mitral valve prolapse. Sixty-four mitral valve prolapse subjects (24 men and 40 women, mean age 27 +/- 6), and 80 healthy control subjects (32 men and 48 women, mean age 28 +/- 7) were studied. The frequency of ventricular arrhythmias by means of 24-h ambulatory electrocardiographic (ECG) monitoring was investigated. Grade > or = 3 ventricular arrhythmias according to modified Lown and Wolf classification were accepted as complex arrhythmias. The QT intervals were measured from the beginning of depolarization of the QRS complex to the end of the T wave. Using the Bazett formula, QT interval was corrected (QTc) for heart rate. QT dispersion was calculated as the difference between the maximum and minimum QT intervals on any of 12 leads. Premature ventricular complexes seemed to develop in 56 of 64 (87.5%) subjects with mitral valve prolapse. Thirty-eight of the mitral valve prolapse subjects had complex premature ventricular complexes during 24-h ECG and the prevalence of premature ventricular complexes was found to be higher than the control subjects (P < 0.001). We found QT and QTc intervals of 388 +/- 27 and 406 +/- 33 ms in mitral valve prolapse subjects, these values in control subjects were 382 +/- 18 and 402 +/- 11 ms respectively (P > 0.05). QT dispersion and QTc dispersion intervals were 71 +/- 17 and 78 +/- 19 ms in mitral valve prolapse subjects and these values were 43 +/- 16 and 52 +/- 22 ms in control subjects, respectively (P < 0.001). No correlation was found between complex premature ventricular complexes and QT, but there was a correlation between complex premature ventricular complexes and QT dispersion in the mitral valve prolapse subjects. It was concluded that QT dispersion might be a useful marker of cardiovascular morbidity and mortality due to complex ventricular arrhythmias.

QT intervals at heart rates from 50 to 120 beats per minute during 24-hour electrocardiographic recordings in 100 healthy men. Effects of atenolol

BACKGROUND

Conflicting reports about changes in QT intervals suggest that QT values should be compared at similar heart rates.

METHODS AND RESULTS

Relations between QT and RR intervals were determined after measurement of QT values by Holter recording at heart rates of 50, 60, 70, 80, 90, 100, 110, and 120 beats per minute in 100 healthy young men. Fifteen men underwent a second recording during acute treatment with the beta-blocking agent atenolol. At heart rates between 80 and 120 beats per minute, the QT interval was significantly longer (from 9 to 16 msec), and at a heart rate of 50 beats per minute significantly shorter (26 msec), than values calculated from Bazett's formula. Sleep prolonged QT values by 18 msec at a heart rate of 60 beats per minute and by 21 msec at a heart rate of 50 beats per minute compared with the waking state. Atenolol lengthened QT intervals significantly (by 11-14 msec) at heart rates between 90 and 110 beats per minute and shortened them (by 12 msec) at a heart rate of 60 beats per minute. During sleep, QT intervals were the same before and after atenolol.

CONCLUSIONS

The method of plotting QT against RR intervals after measurement of QT values at similar stable spontaneous heart rates before and after intervention allows changes in autonomic state and heart rate to be taken into account. By this method, QT values can be compared without distortion effects caused by correction formulas.

Ventricular arrhythmias and the autonomic tone in patients with mitral valve prolapse

The aim of this study was to evaluate a possible relation between the autonomic tone determined by daily urine catecholamine excretion and the incidence of ventricular arrhythmias (VA) in patients with mitral valve prolapse (MVP). The study included 53 patients (31 women and 22 men) aged 19-52 years (mean age 32.7). The diagnosis of MVP was based on medical history, physical examination, and echocardiography. Cardiac arrhythmias were detected by Holter monitoring and classified according to Lown grades. Daily heart rate and duration of corrected QT interval using Basett's formula were also analyzed. Daily urine adrenaline and noradrenaline levels were determined fluorometrically by Von Euler and Lishajko's method. The patients with Lown's grade III-V VA were evaluated with particular consideration. Student's t-test was used for statistical analysis. On Holter monitoring 26 patients showed VA, including 6 with grade I, 11 with grade II, 2 with grade III, 4 with grade IV, and 3 with grade V according to Lown's classification. The remaining 27 patients were free of cardiac arrhythmias. Mean daily heart rate ranged from 54-93 beats/min (73 +/- 8.44, mean +/- SD) and corrected QT from 336-494 ms (411 +/- 37.17). Daily adrenaline and noradrenaline excretion for the whole group of patients were 0.01-16.2 micrograms (2.1 +/- 2.38) and 1.6-31.0 micrograms (13.1 +/- 7.27), respectively, which was within normal range. However, the patients with serious ventricular arrhythmias showed significantly higher daily adrenaline excretion. Individual analysis of two-thirds of patients with ventricular arrhythmias grade III-V showed daily urine noradrenaline levels exceeding mean values for the whole group.(ABSTRACT TRUNCATED AT 250 WORDS)

Sympathetic and vagal influences on rate-dependent changes of QT interval in healthy subjects

Dependence of QT interval duration on cardiac heart rate has been well established and is considered to be an intrinsic property of ventricular myocardium. Conclusive results of autonomic influences on such phenomena are lacking. To evaluate whether rate-dependent changes of QT interval are conditioned by the autonomic nervous system, 28 normal subjects with no heart disease and a normal QT interval were electrophysiologically assessed. The QT interval was calculated at 6 paced cycle lengths (600, 540, 500, 460, 430 and 400 ms) during the basal state, and after beta blockade (propranolol 0.2 mg/kg) and autonomic blockade (propranolol plus atropine 0.04 mg/kg). Because of atrioventricular nodal conduction limits, intrapatient cross-comparisons were performed in 10 subjects (aged 42 +/- 15 years). Single regression lines, evaluated in each subject, showing correlation between pacing cycle length and QT duration at each of the 3 states were analyzed. The mean slope observed after autonomic blockade (b = 0.10 +/- 0.04) was significantly lower than that seen during the basal state (b = 0.22 +/- 0.12, p less than 0.05) and after beta blockade (b = 0.23 +/- 0.08, p less than 0.05); nonsignificant differences were found between slopes during the basal state and after beta blockade. Results showed that vagal tone increased intrinsic dependence of QT at increasing cycle length, whereas sympathetic tone did not seem to interfere significantly. Since (in each subject) beta blockade was performed--or achieved--before atropine administration, the vagal influences are likely to be directly exerted on the ventricular electrophysiologic substrate.

Exercise response in young women with mitral valve prolapse

To detect for possible evidence of autonomic nervous system dysfunction, we assessed exercise response in 198 young women with echocardiographically documented MVP. The same test was used to determine whether patients with or without physical symptoms or with various auscultatory findings responded differently. Compared with 105 age- and sex-matched healthy subjects, the MVP patients showed significantly higher mean heart rate, systolic blood pressure, pulse pressure and rate-pressure (double) product, at both rest and exercise; significantly lower mean near-maximal physical working capacity (PWC170); significantly higher incidence of both arrhythmias and nonspecific ST and T wave changes; and a significantly longer mean corrected QT interval. None of these findings was associated with the presence of physical symptoms or with specific auscultatory or echocardiographic findings. These observations strongly suggest an autonomic nervous system imbalance in some young women with MVP, irrespective of whether physical symptoms are present.

The QT and QS2 intervals in patients with mitral leaflet prolapse

The QT interval was plotted against the R-R interval in 92 patients with mitral prolapse and 92 age- and sex-matched control subjects. Ten patients (11%) lay above the upper 95% confidence limit for the control group, and analysis of variance confirmed a small group effect (p less than 0.05). Despite this, the mean QT intervals in the two groups differed by only 7 msec and a t test showed no significant difference between the groups. The prevalence of QT prolongation was exaggerated by Bazett's rate correction formula (62%) or historical control groups published by Simonson (58%) or Ashman (70%). Simultaneous QT and QS2 intervals were measured in 67 patients with mitral prolapse. Inversion of the normal QT:QS2 relationship occurred in nine patients (13%) and was more common in the presence of severe mitral regurgitation. It was not associated with an increased prevalence of absolute QT prolongation and was therefore thought to be caused by relative shortening of the QS2 interval. In conclusion, the prevalence of QT prolongation in mitral prolapse is low (11%). The QT:QS2 ratio is unlikely to be a reliable indicator of QT prolongation in these patients.

Ventricular tachyarrhythmias in the long QT syndromes

Marked prolongation of the electrocardiographic QT interval often is associated with a distinctive form of ventricular tachycardia characterized by the gradual oscillation around the baseline of the peaks of successive QRS complexes. This was named torsades de pointes, or "twisting of the points." This form of ventricular tachycardia tends to be rapid and self-terminating and often occurs in clusters, leading afflicted patients to present with recurrent dizziness and syncope. Ventricular fibrillation and sudden death are common.

Conduction system abnormalities in symptomatic mitral valve prolapse: an electrophysiologic analysis of 60 patients

This study examined the site of atrioventricular (AV) block in mitral valve prolapse (MVP). Sixty symptomatic patients with MVP underwent electrophysiologic study; 49 had documented arrhythmias and 28 had syncope. Eight patients had spontaneous second- or third-degree AV block and 10 had chronic bundle branch block. Electrophysiologic study revealed abnormal sinus node function in 8 patients, prolonged HV interval in 10, intra-Hisian delay in 9, and functional bundle branch block in 15. Dual AV nodal pathways were demonstrated in 24 patients. Comparison with 101 similarly symptomatic patients without MVP revealed a greater prevalence of dual AV nodal pathways in the MVP patients. Infranodal conduction abnormalities and dual AV nodal pathways are frequently revealed by electrophysiologic testing in symptomatic patients with MVP.

The QT interval during reflex cardiovascular adaptation

We examined the relationship between changes in heart rate and the measured QT interval of the electrocardiogram in healthy subjects after exercise and during breath holding, hyperventilation, the dive reflex, the Valsalva maneuver, and the cold-pressor test. The tachycardia of exercise was accompanied by the familiar shortening of the QT interval, but substantial heart rate changes encountered in other more "sedentary" maneuvers were accompanied by very small changes in QT. Calculating the corrected QT in the latter instances, therefore, yielded spurious results. The data suggest very little, if any, direct effect of heart rate on the QT interval. The length of the interval in healthy subjects appears to be determined largely by reflexly elicited discrete autonomic influences. Those associated with exercise result in QT shortening but, during neurally mediated cardiovascular adjustments that do not involve exercise, QT is maintained within narrow limits.